Clustering Rt Saturation-eval k Facies Predictions

7/27/2019 Clustering Rt Saturation-eval k Facies Predictions

1/14

S P W L A 4 4 th A n n u a l L o g g i n g S y m p o s i u m , J u n e 2 2 - 2 5 , 2 0 0 3

C L U S T E R I N G R E S I S T I V I T Y R A T I O S F O R S A T U R A T I O NE V A L U A T I O N A N D I M P R O V E D P E R M E A B I L I T Y A N D F A C IE S

P R E D I C T I O N SPh ilippe Rab iller, Consultant,Hu gues Th evoux-Chabu el, Paradigm

A B S T R A C TSo f a r, wh a t e v e r t h e i n c r e a s i n g i m p o r t a n c e o f th e NM Rr o l e , t h e r e s e r v e e v a l u a t i o n p r o c e s s i s m o s t l y b a s e dupon the in te rpre ta t ion of Rt and Rxo va lues der ivedf r o m r e s i s t i v i t y l o g s . Fo r m a n y g e o s c i e n t i s t s l a c k i n gs t rong pe t rophys ica l exper ience , th i s t ask of t en appearsd a u n t i n g a n d t e d i o u s , d e s p i t e m o s t o f t h e m i n t u i t i v e l yin te rpre t the separa t ion of the res i s t iv i ty curves tod e l i n e a t e Hc i m p r e g n a t e d z o n e s a n d q u a l i t a t i v e l yc h a r a c t e ri z e t h e i r p o r o u s n e t w o r k .I n t h e m e t h o d we d e s c r i b e h e r e , t h e r a ti o s o f Re s i s t i v i tym e a s u r e m e n t s ( c o n v e n t i o n a l a n d / o r a r r a y ) o f d i f f er e n td e p t h o f i n v e s t i g a t i o n a r e c l u s t e r e d a n d o r d e r e d u s i n gM RG C t o o b t a in wh a t we t e r m " i n v a s i o n p r o f i le s " . As i m p l e c r o s s - p l o t s r e c o n n a i s s a n c e t e c h n i q u e ,ext rapola ted f rom the fami l i a r " tornado char t " , i sp r o p o s e d t o i n t e r p r e t t h e " i n v a s i o n p r o f i l e l o g " a n dre la te i t t o sa tura t ion and permeabi l i ty . In bes t case ,Ca p i l l a r y P r e s s u r e m a y a l s o b e a d d r e s s e d b y t h em e t h o d .Th e " i n v a s i o n p r o f i l e l o g " c a n e a s i l y b e c o m b i n e d wi t hn u c l e a r , s o n i c a n d NM R l o g s t o c h a r a c t e r i z e r e s e r v o i ri n a s y n t h e t ic w a y a s s o c i a t i n g m i n e r a l o g y a n d t e x t u r e tof lu id f low proper t i es an d sa tura t ion . Thus i t p rovide st h e g e o s c i e n t i s t w i t h a d i r e c t d e t e c t io n o f h y d r o c a r b o na n d a r a n k i n g o f t h e r e s e rv o i r b y p o r o s i t y , p e r m e a b i l i t ya n d c a p i l l a r y p r e ss u r e . D e l i n e a t i o n o f z o n e s f o r p a ys u m m a r y c o m p u t a t i o n i s m a d e e a s i l y a n d wi t h o u t a n yopera tor b ias because a l l the informat ion ava i l ab le top e t r o p h y s i c i s ts i s a lg o r i t h m i c a l l y p r o c e s s e d w i t h o u t a n ya pr ior i parameter .Pe r m e a b i l i t y p r e d i c t i o n a n d g e o l o g i c f a c i e sc h a r a c t e r i z a t i o n b y c l u s t e r i n g t e c h n i q u e b e n e f i t f r o mt h is n e w m e t h o d . I n d e e d : the use of the invas ion prof il e log as an

i n t e r p o l a t o r n o t o n l y e l i m i n a t e s t h e n e e d t o b u i l dd i f f e r e n t m o d e l s f o r wa t e r a n d h y d r o c a r b o ni m p r e g n a t e d z o n e s b u t a l s o i n c o r p o r a te i n f o r m a t i o nd i r e c t l y d o c u m e n t i n g t h e i n v a s i o n p r o c e s s a n dh e n c e t h e f l o w d y n a m i c .

I n v a s i o n p r o f i l e s a r e r e l a t e d t o p e r m e a b i l i t y wh i c hi s cont ro l l ed by gra in s i ze and rock t ex ture and thusr e f l e c t d e p o s i ti o n a l e n e r g y : a n i m p o r t a n t p a r a m e t e rfor the sedimentologi s t s .

Th e m e t h o d i s i ll u s t ra t e d u s i n g f i e ld e x a m p l e s .1. I N T R O D U C T I O NTh e r e s u l t s p r e s e n t e d h e r e s t e m f r o m o u r i n v e s t i g a t i o no n h o w t o u s e Re s i s t i v i t y l o g s f o r r e s e r v o i rc h a r a c t e r i z a ti o n i n t e r m o f s e d i m e n t a r y b o d i e s a n d f l o wuni t s . I t i s a cont r ibut ion to the e f for t s meant a tp r o v i d i n g r e s e r v o i r g e o l o g i s t s wi t h a n o b j e c t i v e a n da c c u r a t e d e s c r i p t io n o f g e o l o g i c f o r m a t io n s , b a s e d o nl o g d a t a a n d p e r t i n e n t i n t e r m o f r o c k m i n e r a l o g y ,p o r o u s n e t wo r k a n d f l u i d c o n t e n t . Ou r i n v e s t i g a t i o nh e a v i l y r e l ie s o n t h e u s e o f p a r ti t io n i n g m e t h o d s a n dpat t e rn recogni t ion t echniques to process a l l ava i l ab lelog or core da ta whatever the i r type : cont inuousvar iables (curves , a r ray or images) or d i scre te (usua l lyordina l ) var i ables . We use the t e rms of "e lec t rofac ies"(Ser ra & Abbot , 1981) or " log types" to re fe r to thee l e m e n t s o f s u c h p a r t i t io n s .Sh o u l d o u r o b j e c t i v e b e m e t , t h e m e t h o d o l o g y wo u l dn o t o n l y i m p r o v e e l e c t r o f a c i e s d e s c r i p t i o n b u t t o o wi l la l l o w a b e t t e r p e r m e a b i l i t y p r e d i c t i o n . Th i s b yprovid ing unbiased c r i t e r i a and a cons i s t ent de l inea t ionm e t h o d t o d e f i n e p a y s u m m a r y , s e d i m e n t a r y b o d i e s a n df low uni t sThe in te rpre ta t ion m etho d o f res i s t iv i ty ra t io c lus te r inge x p o s e d b e l o w i s b a s e d o n t h e c o n s i s t e n c y o f p a t te r n so b s e r v e d o n a l a r g e n u m b e r o f e x a m p l e s f r o m a l l t y p eo f l i t h o l o g y a n d d e p o s i t i o n a l e n v i r o n m e n t . I t h a s b e e nt e s t e d o n s e v e r a l f i e l d s u r v e y s , a n d p r o v i d e d wi t hg e o l o g i c a l l y m e a n i n g f u l i n f o r m a t i o n . Ho we v e r wea d m i t t h a t i t c a n b e i m p r o v e d . I n t h is v i e w, w e p r o p o s ei t to o ther geosc ient i s t s as an invi t a t ion to fur therexplore th i s f i e ld of work .Pe t r o p h y s i c i s t s a r e p r i m a r i l y c o n c e r n e d b y p o r o s i t y a n dsa tura t ion es t imate , to th i s purpose they des igneda d v a n c e d p r o b a b i l i s t i c m e t h o d s r e q u i r i n g c o m p u t a t i o n o fm i n e r a l p r o p o r t i o n s i n o r d e r t o c o r r e c t m i n e r a l o g i c s i d e


2/14

S P W L A 4 4 th A n n u a l L o g g i n g S y m p o s i u m , J u n e 2 2 - 2 5, 2 0 0 3

e f f e c t s o n p o r o s i t y l o g s . Ho we v e r t h e m i n e r a l o g i cc o m p o s i t i o n i s u s u a l l y g i v e n i n t e r m s o f we i g h tp e r c e n t a g e o f a f e w " p s e u d o - m i n e r a l s " . M o r e t h a n o f te n ,not only i t f a i l s to capture the essence of ac tua l l i thologyb u t t o o i t s p r a c t i c a l r e l e v a n c e f o r s e d i m e n t a r y b o d i e s 'charac te r i za t ion i s somewhat l imi ted . As fa r as geologiccharac te r i za t ion i s concerned, the i r main l imi ta t ions canb e s u m m a r i z e d a s f o l lo ws : M i n e r a l o g i c c o m p o s i t i o n i s i n s u f f i c i e n t t o

charac te r i ze a sediment . Re s u l t s d i s p l a y d o e s n o t fi t s e d i m e n t o l o g i s t ' s

needs . Bed s a re not de l inea ted Sa t u r a t io n c o m p u t a t i o n is b a s e d s o l e l y o n t h e

Rt /Ro ra t io and the geolog ic inform at ion p oss ib lyconta ined in the pa t t e rns of res i s t iv i ty curvessepara t ion , i s l e f t unexplored .

Th e p a r a m e t e r s r e q u i r e d b e i n g s et a n d t h e s e v e r a ll o g r e s p o n s e s e q u a t i o n s a n d s a t u r a t i o n e q u a t i o n t oc h o o s e f r o m a p p e a r a l m o s t u n r e l a t e d t os e d i m e n t o l o g i s t ' s s c o p e o f wo r k .

As a c o n s e q u e n c e t h e i r u s e i s n o t r e a l l y a p p e a l i n g t og e o l o g i s t s a n d s o m e h o w r e s t r i c t e d t o p e t r o p h y s i c i s t s a tt h e e x p e n s e o f t h e s o m u c h n e e d e d s y n e r g y b e t we e n t h etwo profess ions .Geologi s t s use logs for s t ra t igraphic cor re la t ions andf a c ie s m a p p i n g . Th e y p r i m a r i l y f o c u s t h e i r a t te n t i o n o nc u r v e s s h a p e t o d i a g n o s e e v o l u t i o n s o f s e d i m e n t a r ye n v i r o n m e n t . M o s t u s u a l l y , b e c a u s e f l u i d e f f e c t s o nlogs a re cons idered as a nui sance , r es i s t iv i ty logs a ren o t u s e d f o r f a c i e s c h a r a c t e r i z a t i o n . Am o n g t h e m a n ye x c u s e s i n v o k e d b y g e o l o g i s t s , t h e f o l l o wi n g a r e t h em o s t c o m m o n l y o f f e r e d : Res i s t iv i ty logs a re chie f ly sens i t ive to e lec t ro ly te

c o n t e n t a n d c o m p l e x i n v a s i o n p h e n o m e n a w h i c ha r e a l s o c o n t r o l l e d b y m u d p r o p e r t i e s , t i m e , a n dh y d r o s t a t i c e q u i l i b r i u m b e t we e n m u d c o l u m n a n dformat ion f lu ids .

Pe r m e a b i l i ty o r c a p i l l a r y p r e s s u r e c u r v e s a r e n o tt h e s e d i m e n t o l o g i s t s ' p r e f e r r e d i n f o r m a t i o n t ocharac te r i ze fac ies .

By d i s regarding logs mos t subjec t to f lu id e f fec t s ,g e o l o g i s ts t e n d t o p r o d u c e " s u b d i v i s i o n s o f fo r m a t i o n sbased upon so le ly l i thos t ra t igraphic c r i t e r i a [which]f requent ly fa i l to capture the pe t rophys ica l var i abi l i ty oft h e r o c k a d e q u a t e l y " ( B . P . M OSS 1 9 9 7 ) . Ho we v e r , i t i swo r t h n o t i n g t h a t a p e t r o p h y s i c i s t , u s i n g p e r m e a b i l i t ym e a s u r e m e n t s t o c o n t r o l s a t u r a t i o n c o m p u t a t i o n s ( i ns i l i c i -c las t i c format ions) , impl ic i t ly acknowledges tha ts a t u r a t i o n i s p r i m a r i l y c o n t r o l l e d b y s e d i m e n t a r y

processes through gra in s i ze and pore s i ze d i s t r ibut ion(par t ly re f l ec ted by "Vsh") . Therefore , va lue ofres i s t iv i ty logs for geologi s t s i s exempl i f i ed .As t h e r e l e v a n c e a n d e f f i c i e n c y o f a n y r e s e r v o i r m o d e li s c o n t i n g e n t u p o n c o n s i s t e n c y b e t we e n g e o l o g y a n dpet rophys ic , the need for a fac ies descr ip t ionm e t h o d o l o g y i n t e g r a t i n g r e s i s t i v i t y l o g s m u s t b efu l f i l l ed . Def in ing fac ies bear ing informat ion on porousn e t wo r k r e q u i r e s p e r m e a b i l i t y t o b e t a k e n i n t o a c c o u n t .Fu r t h e r , f i n d i n g a m e a n t o a t t a c h Ca p i l l a r y P r e s s u r einformat ion to each e lec t rofac ies i s mos t des i red . Inc o n v e n t i o n a l m e t h o d s , p e r m e a b i l i t y i s d e r i v e d f r o ml o g s b y m e a n s o f d e t e r m i n i st i c m o d e l s i n v o l v i n gs u c c e s s i v e c o m p u t a t i o n o f s h a l i n e s s , p o r o s i t y a n dsa tura t ion; r e l evance of resul t s obta ined a t each s t ep isc o n d i t i o n e d b y t h e c h o i c e s m a d e o n e q u a t i o n s a n dp a r a m e t e r s u s e d i n t h e p r e v i o u s s t e p . Pe r m e a b i l i t yc o m p u t e d t h i s wa y c a n b e c l u s t e r e d wi t h o t h e r l o g s t oobta in e lec t rofac ies tha t can be l abe led in t e rm ofp o r o u s n e t wo r k p r o p e r t i e s .He r e , we p r o p o s e t o d i r e c t l y c o m b i n e , w i t h o t h e r l o g s ,t h e i n f o r m a t i o n o n p e r m e a b i l i t y b o r n b y r e s i s t iv i t y l o g s.Su c h a p p r o a c h d r a s t i c a l l y r e d u c e s t i m e a n d e x p e r t i s ed e v o t e d t o a n e l e c t r o f a c i e s s u r v e y . Th e m e t h o d i sp r e s e n t e d i n t h e l i g h t o f c u r r e n t l y a v a i l a b l e m e t h o d s f o rres i s t iv i ty log in te rpre ta t ion . Both i t s benef i t s and whatmakes i t f a i l to provide so lu t ion a re reviewed.2 . I N V A S I O N P R O F I L E S2 . 1 . I n v a s i o n P r o f i l e s a n d r e s i s t i v i t y o v e r l a y m e t h o dI n t hi s p a p e r we wi l l u s e t he t e r m o f " p r o x i m a l " t o r e fe rt o t h e r e s i s t i v i t y c u r v e wh i c h r e a d i n g i s m o s trepresenta t ive of the format io n c loses t to the boreholewa l l , y e t n o t t o o a f f e c t e d b y m u d c a k e ; i n m o s t c a s e s" p r o x i m a l " i s th e c u r v e p r o v i d i n g wi t h " Rx o " i nr e s e r v o i r f o r m a t i o n s . Th e t e r m " m e d i u m " r e f e r s t o ares i s t iv i ty curve wi th a depth of inves t iga t ioni n t e r m e d i a t e b e t we e n t h e d e e p a n d p r o x i m a l c u r v e s ,t y p i c a l l y t h e La t e ro l o g " s h a l l o w" . W h e n e v e r wo r k i n gon a f i e ld- sca le mul t i -wel l ana lys i s , curves mos ta p p r o p r i a t e t o r e p r e s e n t " p r o x i m a l " a n d " m e d i u m "m u s t b e c h o s e n o n t h e b a s i s o f t h e s i m i l a r i ty o f t h e irrespec t ive geomet r i c fac tors .Be f o r e c o m p u t a t i o n a l p o we r b e c a m e e a s i l y a v a i l a b l e ,t h e q u i c k l o o k " r e s i s t i v i t y o v e r l a y " a s a wi d e s p r e a dm e t h o d , e x e m p l i f y i n g t h e e f f e c t iv e n e s s o f p a tt e r nrecogni t ion t echnique for res i s t iv i ty curvesin te rpre ta t ion . Indeed, the graphic separa t ion be tween" d e e p " a n d " p r o x i m a l " r e s i s t i v i t y c u r v e s , p r i n t e d o nl o g a r i t h m i c s c a l e , p r o v i d e s wi t h i m m e d i a t e c l u e o n t h ei m p o r t a n c e o f th e i n v a s i o n p h e n o m e n o n , h e n c e o n t h ec a p a b i l i ty o f a p o r o u s n e t w o r k t o l e t f l ui d s f l o w t h r o u g h


3/14


4/14


r e q u i r e d s o m e h o w o r o t h e r . Ho we v e r t h e a p p a r e n tc o m p l e x i t y m u s t b e s i m p l i f i e d wh i l e r e t a i n i n g a l lposs ib le c lues for fur ther unders tanding. [0]The Mul t iR e s o l u t i o n G r a p h C l u s t e r i n g m e t h o d o r M R G C ( Y e &Ra b i l le r , 2 0 0 0 ) w a s p r o p o s e d t o p e r f o r m t h a t t as k .B e c a u s e M R G C i s n o n p a r a m e t r i c a n d d e v o i d o fr a n d o m o r o p e r a t o r c o n t r o l l e d i n i t i a l i z a t i o n p r o c e s s e s ,t h e p a r t i t i o n o b t a i n e d i s o n l y c o n s t r a i n e d b y d a t as t ruc ture . As a resul t , t he image of da ta s t ruc ture y ie ldb y M RGC s h a r p l y r e f l e c t s t h e n a t u r a l o r d e r i n g o fgeologica l sys tem a t i t s or ig in and fac i l i t a t es i t si d e n t i f i c a t i o n b y m e a n s o f s t r a t i g r a p h i c c o n c e p t sd e v e l o p e d b y g e o l o g i s t s .3 . D E F I N I N G I N V A S I O N P R O F I L E S A N DC L U S T E R I N G I N V A S IO N P R O F I L E S W I T HO T H E R L O G SCo m p u t i n g t h e r e s i s t i v i t y r a t i o , " d e e p / p r o x i m a l " ," d e e p / s h a l l o w" a n d " s h a l l o w / p r o x i m a l " , i s t h e f i r s tprocess ing s t ep of the metho d. I t i s usefu l to d i sp laythese ra t ios wi th respec t to depth .The second s t ep cons i s t s in c lus te r ing the res i s t iv i tyr a t io s u s i n g M R GC . Ea c h c l u s te r i s a s s i g n e d a ni n d i c i a l n u m b e r a u t o m a t i c a l l y o r d e r e d ( Ye & Ra b i l l e r ,s u b m i t t e d t o " Pe t r o p h y s i c s " ) a c c o r d i n g t o t h e c l u s t e rp o s i t i o n wi t h i n t h e 3 d i m e n s i o n s l o g s p a c e d e f i n e d b yres i s t iv i ty ra t ios . Due to th i s order ing , when p lo t t ed as ad i scre te ord ina l curves wi th depth (Fig 3 , t r ack 7) , thei n d i ce s d i s p l a y p a t t e m s a s m u c h c o m p e l l i n g t o s e a r c hf o r u n d e r s t a n d i n g a s t h o s e e v i d e n c e d b y t h e r e s i s t i v i t yo v e r l a y m e t h o d . F o r t h e s a k e o f b r e v i t y , we w i l l u s e t h e" R R - C I L " a c r o n y m ( Re s i s t i v i t y Ra t i o C l u s t e r I n d e xLog) to re fe r to th i s su i t e o f indices .Exper ience indica tes tha t in te rpre ta t ion i s made eas ie r i fa t l eas t 2 c lus te r ing model s a re ava i l ab le : a lowr e s o l u t io n m o d e l wi t h a m i n i m u m o f 1 0 p a rt i ti o n s a n d ah i g h e r r e s o lu t i o n m o d e l w i t h a m i n i m u m o f 2 0par t i t ions . The low resolu t ion model i s used as s t a r t ingpoin t in the in te rpre ta t ive s t ep . The h igher resolu t ionmo del i s in te rpre ted in the l ight of the lowe r resolu t ionm o d e l a n d u s e d i n t h e t h i r d p r o c e s s i n g s t e p . La b e l i n ge a c h c l u s t e r o f i n v a s i o n p r o f i l e s i s p e r f o r m e d b yi t e r a t i v e v i s u a l e x a m i n a t i o n o f d e p t h d i s p l a y a n din te rpre ta t ion of i t s pos i t ion on mul t ivar i a te c ross -p lo t sc o l o r c o d e d f o r RR- CI L , i n c l u d i n g t h o s e i n v o l v i n g c o r edata.The th i rd s t ep of da ta process ing cons i s t s in c lus te r ingt h e RR- CI L t o g e t h e r wi t h l o g s s u c h a s GR, Ne u t r o nDe n s i t y Se p a r a t i o n , De n s i t y o r So n i c " Dt " , t o n a m eo n l y t h e m o s t c o m m o n a n d s i m p l e l o g c o m b i n a t i o n .W h e n e v e r s u c h l o g s a r e a v a i l a b l e , i t i s a l s o wo r t hc l u s t e r i n g NM R T2 dis t r ibut ion (Ye & Rabi l l e r , 2000)

or spec t ra l GR (U, K, Th logs) , and incorpora te thecor respo nding c lus te r in dex logs to th i s 3 rd s t ep o fprocess ing . In so doing a l l logs a re par t i t ioneds i m u l t a n e o u s l y wi t h o u t a n y o p e r a t o r b i a s o r c o n s t r a i nother than the da ta s t ruc ture i t se l f ; hencefor th the f ina lpar t i t ion i s cons i s t ent in t e rm of a l l logs responses (Fig3 , t r ack 8 and 9) . Eventua l ly each c lus te r i s ass igned ag r o u p o f p e t r o p h y s i c c h a r a c t e ri s t ic s d e d u c e d f r o m i t spos i t ion on c ross p lo t s or poss ib ly ca l ibra ted onavai l able core da ta . Thi s group of charac te r i s t i cs can bes u m m a r i z e d b y a g e o l o g i c a l l a b e l s u c h a s " c l e a nm e d i u m p o r o s i t y , l o w p e r m e a b i l i t y , t h i n l y l a m i n a t e ds a n d s t o n e " . A m o r e d e t a i l e d l a b e l i n g i n t e r m o fs e d i m e n t o l o g y c a n b e m a d e i f t h e c l u s t e r is f o u n d t o b esys temat ica l ly assoc ia ted to a g iven pos i t ion in thes t ra t igraphic su i t e of fac ies ; as an exam ple , i f thein te rpre te r not i ces tha t a "anker i t i c compact sands tone"i s a lwa y s f o u n d o n t o p o f a r a p i d v a r i a t io n f r o m h i g h t ol o w G R v a l u e s o c c u r r i n g a t t h e b a s e o f a GR i n c r e a si n gupw ard su i t e of va lues , then he m ight re fe r to it as a" c h a n n e l l a g " .An e x a m p l e o f s u c h a 3 s te p s p r o c e s s i n g o f lo g d a t ar e c o r d e d i n No r t h Se a M i d J u r a s s i c f o r m a t io n s ,presented in f ig 3 (depth d i sp lay) and f ig 4 (Crossplo t s ) , i s used to present the method and demons t ra te i t sr e l e v a n c e b y c o m p a r i n g t h e o b t a i n e d r e s u l t s wi t h c o r ep o r o s i t y a n d p e r m e a b i l i t y m e a s u r e m e n t s . T r a c k h e a d e r sof Fig . 3 a re de ta i l ed in t ab le 1 . Refe r to t a b l e 2 forfac ies descr ip t ion cor responding to color codingd i s p l a y e d o n b o t t o m o f F i g 3 .W h e n e v e r d i s p l a y e d o n Cr o s s p l o t s d e f i n e d b y a x i sb e i n g a c o m b i n a t i o n o f a n y 2 o f t h e 3 r e s i s t iv i t y r at io s ,a n d c o l o r c o d e d f o r RR- CI L , d a t a p o i n t s wi l l a p p e a r t oform c olor c louds wi th c lea r f ront i e r s . I f r es i s t iv i ty ra t ioc l u s t e r s a r e p l o t t e d , f o r e x a m p l e o n a n Np h i - Rh o bcrossplo t the i r f ront i e r wi l l appear d i f fuse .Di f fus iveness i s cont ingent on a t l eas t two fac tors . F i r s tfac tor i s the apt i tude o f the c lus te r ing m etho d to revea lda ta s t ruc ture . Second fac tor i s the re la t ionship be tweent h e i n f o r m a t i o n b o r n b y t h e c l u s t e r e d l o g s a n d t h e l o g sd e f i n in g t h e p r o j e c t i o n p l a n e . I f o n e o r m o r e o f th ec l u s t e r e d l o g s i n f o r m o n r o c k p r o p e r t i e s s u p p o s e d l yunre la ted to the logs def in ing the pro jec t ion p lane thencolor c louds may appear d i f fuse . Note a l so tha t da tapoin t s forming d i f fuse color c louds on a g iven c rossplo t s may appear d i s t r ibuted wi th a s imple s t ra t igraphiclogic on a depth d i sp lay . In any case the cons i s t ency o ft h e p a t t e m s o b s e r v e d o n c r o s s p l o t s a n d d e p t h d i s p l a y ssubs tant i a t e both the e f f i c i ency of a c lus te r ing meth odto account for da ta s t ruc ture and the s t ren gth of thei n t e r r e l a t i o n s h i p e v i d e n c e d b e t we e n i n f o r m a t i o n b o r nby d i f fe rent logs . On f igure 4 , 6 c ross p lo t s a red i s p l a y e d i n v o l v i n g 1 0 d i m e n s i o n s ( 8 l o g s a n d 2 c o r e sm e a s u r e m e n t s ) wi t h a c o l o r c o d i n g f o r c l u s t e r s d e f i n e d


5/14


f r o m 7 l o g s. Pa t t e r n c o n s i s t e n c y b e t we e n a l l c r o s s p l o t sand depth d i sp lay of f ig 3 and 4 i s l e f t to thea p p r e c i a t i o n o f t h e r e a d e r .4 . I N T E R P R E T A T I O N O F T H E I N V A S I O NP R O F I L E S4 . 1. T h e " m o d i f ie d t o r n a d o c h a r t " o r " M T p l o t "To he lp in te rpre t ing Res i s t iv i ty Rat io c lus te r s , wei n t r o d u c e h e r e a n e w Cr o s s - p l o t f o r m e d b y p l o t t i n g o nl o g a r i t h m i c s c a l e t h e r a t i o s " d e e p / p r o x i m a l " a n d" d e e p / s h a l l o w" o n X a n d Y a x i s r e s p e c t i v e l y , e a c hp o i n t b e i n g c o l o r c o d e d f o r RR- CI L ( Se e f i g : l a ) .Ge o s c i e n t i s t s p r o f i c i e n t wi t h t h e e n v i r o n m e n t a lcor rec t ion of res i s t iv i ty a re l ike ly to f ind th i s c ross p lo tfami l i a r . Indeed i t s Y axi s i s the inverse of (La tero log)tornado char t X axi s and i t s X axi s i s comparable to theinverse of tomad o ch ar t Y axi s , the so le d i f fe renceb e i n g t h a t " d e e p / p r o x i m a l " r a t i o i s u s e d i n s t e a d o fRt / Rx o . Th e " t o m a d o " p r o p e r , s u b j e c t e d t o a 9 0 c l o c k wi s e r o t a t i o n a n d s y m m e t r y a r o u n d a h o r i z o n t a la x i s , m a y b e t r a n s f e r r e d o n t h e n e w c r o s s - p l o t . Du e t ot h e r e s e m b l a n c e wi t h To m a d o Ch a r t we wi l l re f e r to t h en e w c r o s s p l o t a s t h e " m o d i f i e d To r n a d o c h a r t " o r " M TPl o t " . E r g o n o m i c s s u g g e s t e d t h a t t h e g r a p h i cr e p r e s e n t a t i o n o f i n v a s i o n p r o f i l e c o n f o r m s t o t h ec o n v e n t i o n u s e d f o r p s e u d o 3 D d e p t h d i s p l a y o fres i s t iv i ty a r ray , NMR or o ther h i s togram, as i l lus t ra tedin f ig .2a . (R abi l l e r & a l ., 2001) .Th e c h a n g e o f a x is d o e s n o t a f f e c t t h e i n t e rp r e t a t io n o f" M T p l o t " b y m e a n s o f r u le s d e v e l o p e d f o r t h ec o n v e n t i o n a l t o r n a d o c h a r t. M T p l o t p r o v e d i t s e l f t o b ethe mos t inform at ive o f the 3 c ross p lo t s tha t can bef o r m e d wi t h t h e 3 r e s i s t i v i t y r a t i o s t a k e n 2 b y 2 . Th ei n t e r p r e t a t i v e r u l e s p r o p o s e d b e l o w f o r M T p l o t a p p l yt o d a t a r e c o r d e d i n we l l s d r i l l e d p e r p e n d i c u l a r l y t o t h eb e d d i n g . So f a r we h a v e n o t i n v e s t i g a t e d o n h o w t h e yc o u l d b e a p p l i e d a n d f u r t h e r d e v e l o p e d f o r d a t ar e c o r d e d i n h i g h l y d e v i a t e d we l l s .4 . 1 . 1 . R e s i s t i v i t y r a t i o s r e c o r d e d i n W B MW h e n t h e r e s i s t i v i t y r a t i o s r e c o r d e d i n a we l l d r i l l e dwi t h wa t e r b a s e d m u d a r e p l o t t e d o n t h e M T p l o t , ( s e eF ig lb , and re fe r to f ig 3 and t ab le 1 and 2 for fac iescolor coding and descr ip t ion; f ig 3 i s a depth d i sp lay ofsame da ta se t ) , i t i s poss ib le to ident i fy c lus te r srepresenta t ive of :

W a t e r p r o d u c t i v e c l e a n z o n e s (Elec t rofac ies 30) .P r o v i d e d t h e y a r e t h i c k e n o u g h t o b e r e s o l v e d b yl o g s , wa t e r p r o d u c t i v e c l e a n z o n e a p p e a r a s t i g h tc l u s t e r ( s ) h a v i n g l o w a n d i d e n t i c a l " De e p / M e d "a n d " De e p / P r o x " r a t i o . W h e r e v e r t h e y d o e x i s t i n a

we l l , i te r a t iv e e x a m i n a t i o n o f b o t h c o l o r c o d e dd e p t h d i s p l a y a n d c r o s s - p l o t s m a k e s t h e i rident i f i ca t ion a quick and easy t ask . . Aqui fe r s wi thdi spara te sa l in i ty would form di f fe rent c lus te r s .Rw/Rmf va lue for such aqui fe r ( s ) i s indica ted by" De e p / P r o x " r a t io v a l u e o f t h e ( it ) c l u s t er ( s) . M Tp l o t i n t e r p r e t at i o n i s m a d e e a s i e r i f b y a s i m p l eg r a p h i c o v e r l a y t h e " t o m a d o " a p e x i s l o c a t e d o nt h e c l u s t e r ' s k e r n e l r e p r e s e n t a t i v e o f a p r o d u c t i v eaqui fe r . Thi s cance l s e f fec t of d i spara te sa l in i tyb e t we e n m u d f i l t r a t e a n d f o r m a t i o n wa t e r .Al t h o u g h t h e c o m p l e t e i n t e r p r e t a t i o n p r o c e s sd e s c r i b e d h e r e c a n b e p e r f o r m e d o n r e s i s t i v i t yra t ios proper , i t i s sugges ted to reca l ibra teres i s t iv i ty ra t io so tha t r a t ios read in the waterbear ing reservoi r a re a l l se t to 1 . For mul t i -wel lappl i ca t ion th i s i s mandatory , see chapter 6 .T i g h t b e d s (Elec t rofac ies 3) , c o m p a c t b e d s( E l ec t ro f a c ie s 2 1 - " c h a n n e l l a g ") a n d s h a l e(Elec t rofac ies 4 to 13 and 17 to 20) . Th ey appearas c lus te r s wi th the three ra t ios "Deep/Med" and" De e p / P r o x " a n d " M e d / P r o x " r a t i o e q u a l t o o rs l ight ly sca t t e red a round 1 . Sha ly fac ies may p lo ti n d i f fe r e n t a r e a o f M T p l o t a c c o r d i n g t o s h a l eh y d r o c a r b o n c o n t e n t . I n d e e d wh e r e v e r s h a l e i su n d e r g o i n g a b n o r m a l p r e s s u r e , h y d r a u l i c m i c r o -f r a c t u r e s m a y d e v e l o p a n d b e i m p r e g n a t e d b yh y d r o c a r b o n s d i s m i g r a t i n g f r o m t h e e n c a s e dh y d r o c a r b o n s r e s e r v o ir s . Su c h a p h e n o m e n o n i sexempl i f i ed here . MT plo t i s ab le to separa te twogroups of sha ly fac ies , the f i r s t group (4 to 13) i so n l y f o u n d b e l o w t h e h y d r o c a r b o n r e s e r v o i r a ti r r e d u c i b l e s a t u r a t i o n , m e a n wh i l e t h e s e c o n d g r o u p(17 to 20) i s found in te r -bedded wi th o i l bear ingreservo i r wi th res i s t iv i ty ra t ios indica t ive o f Hc .i m p r e g n a t i o n . Th i s o b s e r v a t i o n i s c o n s i s t e n t wi t ht h o s e m a d e t h r o u g h t h e c o m m o n p r a c t i c e o fm o n i t o r i n g h y d r o c a r b o n s h o ws i n c a p r o c k a b o v eh y d r o c a r b o n r e s e r v o i r . Th u s M T p l o t i s a v a l u a b l etool to charac te r i ze was te zone .I n t e r v a ls m a d e o f l a m i n a t i o n s wi t h s t r o n gp e r m e a b i l i t y c o n t r a s t s a n d t h i n n e r t h a n t h e d e p t hr e s o l u t io n o f m e d i u m a n d d e e p r e s i s ti v it y . W e u s et h e t e r m o f " u n r e s o l v e d b e d s " t o r e f e r t o s u c hf o r m a t i o n wh i c h a p p e a r a s c l u s t e r s m o r e o r l e s swi d e l y s c a t t e r e d a r o u n d o n e . Th e i r r a t i o sDe e p / p r o x a n d M e d / p r o x a r e u s u a l l y s i m i l a r a n dv e r y d i f f e r e n t f r o m 1 . Th e r a t io D e e p / P r o x r e f le c t sb o t h t h e c o n t r a s t o f p e r m e a b i l i t y a n d t h e p r o p o r t io no f t ig h t b e d s w i t h i n t h e v o l u m e i n v e s t ig a t e d b y t h ed e e p r e a d i n g . W h e r e v e r t h e l a m i n a t i o n sth icknesses or the permeabi l i ty cont ras t of the l a t t e rdecrease , a l l 3 ra t ios t end towards 1 . In suchs i tua t ion poros i ty logs wi l l he lp d i f fe rent i a t e themf r o m s h a l e o r c o m p a c t b e d s . An e x a m p l e o f s u c h


6/14


u n r e s o l v e d b e d s i s s h o wn o n fig l a a n d o n f i g 2 b( fac ies 2 and 3 exhib i t ing l a rge d i spers ion ofM S F L r e a d i n g ) . U n r e s o l v e d b e d s m a y s i g n a l p o o rv e r t i c a l c o n n e c t i v i t y b e t we e n l a y e r s . I n t h e s el a m i n a t e d f o r m a t i o n s , c l o s e e x a m i n a t i o n o f h o wp o r o s i t y e v o l v e s wi t h r e s p e c t t o r e s i s t i v i ty p r o v i d e st h e s e q u e n c e s t r a t i g r a p h e r wi t h v a l u a b l ei n fo r m a ti o n . W h e r e v e r n e it h e r N M R n o r B o r e h o l eimaging da ta a re ava i l ab le , Res i s t iv i ty Rat ioc l u s t e r i n g m a y b e t h e s o l e i n d i c a t i o n t h a t o v e rs o m e d e p t h i n t e r v a l s , f o r m a t i o n l a y e r i n g i s n o tr e s o l v e d b y n u c l e a r a n d s o n i c l o g s wh i c hc o n s e q u e n t l y c o m p r i s e b i a s e d r e a d i n g s . Th e nf a c i e s " c a l i b r a t i o n o n c o r e " , p o r o s i t y p e r m e a b i l i t yr e l a t i o n s h i p s u r v e y s a n d d a t a m o d e l i n g o rc a l i b r a ti o n b y c o r e s d a t a , s h o u l d o n l y b e p e r f o r m e daf te r the core da ta se t has been par t i t ioned in twos u b s e t s c o r r e s p o n d i n g t o r e s o l v e d o r u n r e s o l v e dbeds .Sh o u l d t h e d a t a s e t b e p a r t i t i o n e d i n t o a n u m b e r o fc lus te r s l a rge enough, b e d s h o u l d e r wil l formsepara te c lus te r or be a t t r ibuted to unresolved beds .C l u s t e r i n g i s n o t t h e m o s t a p p r o p r i a t e wa y t ocharac te r i ze shoulder e f fec t s ince i t i s per formed inlog space and depth i s not t aken in to account .C a v e s . (Elec t rofac ies 14 to 16) Caves and rugos i tym a y s t r o n g l y a f f e c t t o o l c o n t a c t wi t h b o r e h o l e a n dp r o x i m a l r e s i s ti v i t y m a y r e a d m u d r e s i s t iv i t y Rm. Ar u g o s e b o r e h o l e wi l l b e i d e n t i f i e d b y r e s i s t i v i t yra t io c lus te r s p lo t t ing on the p lane def ined by theDe e p / P r o x a n d M e d / P r o x a x i s . W h e r e v e r t h e c a v e sare l a rge enough the res i s t iv i ty ra t io c lus te r wi l lp l o t i n s a m e a r e a t h a n Hy d r o c a r b o n r e s e r v o i r . Th el a r g e r t h e r e s i s ti v i t y c o n t r a s ts b e t we e n Rm a n dformat ion res i s t iv i ty the grea te r the ra t iosD e e p / P r o x a n d M e d / P r ox .T r a n s i t i o n z o n e s . ( E l e c t r o f a c i e s 2 9 ) Th e y a p p e a ras c lus te r s in the upp er l e f t par t of MT p lo t in thec lose v ic in i ty of the tornado char t apex i f the l a t t e ri s a p p r o p r i a t e l y l o c a t e d o n f a c i e s k e m e lr e p r e s e n t a ti v e o f wa t e r p r o d u c t i v e z o n e s .H y d r o c a r b o n p r o d u c t i v e r e s o l v e d b e d s .(Elec t rofac ies 24 to 28) They appear as c lus te r ss p r e a d o n t h e u p p e r l e f t q u a r t e r o f t h e M T p l o t. W eu r g e t h e r e a d e r t o k e e p i n m i n d t h a t t h e p r i m a r yobjec t ive of our inves t iga t ion i s to in tegra ter e s i s t i v i t y l o g s i n f o r m a t i o n f o r i m p r o v e d r e s e r v o i rc h a r a c t e r i z a t i o n a n d p e r m e a b i l i t y m o d e l i n g . By n om e a n s h a v e we i n t e n d e d t o p r o p o s e a s u b s t i t u t e t os a t u r a t i o n c o m p u t a t i o n m e t h o d s . Ho we v e r we d oin tend to benef i t f rom and re ly on exi s t ing ru les forres i s t iv i ty in te rpre ta t ion .Ac c o r d i n g t o t h e " f l u s h e d Zo n e M e t h o d " a n d" I n v a d e d Zo n e M e t h o d " , t h e p r o j e c t i o n o f t h e s e

c l u s t e r s o n t o t h e M T p l o t c a n b e r a n k e d i n t e r m sof."o Sa tura t ion (Sw) , accord ing to the i r pos i t ions

wi t h r e s p e c t t o t h e a p e x o f t h e t o r n a d o c h a r ta long the deep/prox axi s . A "c lus te reda v e r a g e d " e s t i m a t e o f t h e i r s a t u r a ti o n c a n b eread on the M T plo t i f i ts Rt /Rxo axi s i sr e s c a l e d u s i n g a p p r o p r i a t e m a n d n v a l u e s ,d e r i v e d f r o m P i c k e t t P l o t.

o Di a m e t e r o f i n v a s i o n , a c c o rd i n g t o t h e i rp o s i t i o n o n t o r n a d o c u r v e s f a n n i n g o u t f r o mt o m a d o a p e x a n d t o wa r d s i n c r e a s i n g d e e p / m e dv a l u e s . On e c a n i n t u i t i v e ly u n d e r s t a n d t h a t f o ra g i v e n s a t u r a t io n o r De e p / P r o x r a t i o v a l u e t h ef lushing e f f i c i ency wi l l increase wi thi n c r e a s in g i n v a s i o n d i a m e t e r.

4 . 1 . 2 . R e s i s t i v i t y r a t i o s r e c o r d e d i n O B MI n c a s e t h e r e s i s t i v i t y we r e r e c o r d e d wi t h i n d u c t i o ntool s in a wel l dr i l l ed wi th o i l based mud, the sameinte rpre ta t ion ru les apply , provided the appropr ia tet o m a d o c h a r t i s u s e d a n d c r o s s p l o t s a x i s a r e c h a n g e da c c o r d i n g l y . Ho we v e r , b e c a u s e i t r e l i e s o n t h e i n v a s i o nof the format ion b y a f i l tr a t e who se res i s t iv i ty cont ras t swi th tha t of the format ion , th i s metho d does no t br inga n y s u b s t a n t i a l i m p r o v e m e n t o v e r e x i s t i n g m e t h o d s f o rin te rpre ta t ion of res i s t iv i ty .4 . 2 . P i c k e t t P l o t a n d M T p l o tPlot t ing the res i s t iv i ty ra t io c lus te r s on Picke t t p lo t s( P I C KE TT G. R . ; 1 9 7 3 ) wi t h RR - CI L c o l o r c o d i n g i sa n o t h e r wa y t o g a i n i n s i g h t s o n h o w t h e 3 D d a t as t ruc ture o f res i s t iv i ty ra t io i s imaged b y the su i t e of 1Dv a l u e s f o r m i n g th e RR- CI L . F i g . 4 c d i sp l a y s a P i c k e t tp lo t co lor coded for fac ies def ined in the th i rd s t ep ofp r o c e s s in g . Fo r s a k e o f c l a ri t y s h a l y f a c ie s h a v e b e e nf i l t e red out . P icke t t p lo t and MT plo t ( f ig . 4d) d i sp layp a t t e r n s o f f a c i e s i n d e x t h a t c a n b e u n d e r s t o o d i n v e r ym u c h t h e s a m e w a y . I d e n t i f i c a ti o n o f c lu s t e rr e p r e s e n t a t i v e o f wa t e r b e a r i n g r e s e r v o i r i ss t ra ight forward . Fur ther , da ta be longing to t ight zones ,s h a l y i n t e r v a l s a n d m o r e p a r t i c u l a r l y u n r e s o l v e d b e d sbe ing f i l t e red out by means of the i r f ac ies index,uncer ta in t i es on Sw, Rw, a , m and n can be reduced.Indeed, the es t im ate o f the 100% Sw l ine s lope i ss t r o n g l y i n f l u e n c e d b y m e a s u r e m e n t s r e c o r d e d i n l e s sp o r o u s b e d s , wh i c h a r e o f t e n f o u n d t o b e a s t a c k o fu n r e s o l v e d a l t e m a t i n g c o m p a c t a n d p o r o u s b e d s , w i t hbiased poros i ty log readings . Thus def in ing a s ingle100% Sw l ine t rough po in t s be lon ging to two d i spara tep o p u l a t i o n s , u n r e s o l v e d a n d r e s o l v e d b e d s , i sinappropr ia te to y ie ld Rw, a , m and n va lues appl i cableto the l a t t e r popula t ion . Converse ly , in " resolved" beds ,


7/14


i t i s poss ib le in a f i r s t s t ep to sor t out groups of fac iescor resp ondin g to c lasses of pore s i ze d i s t r ibut ion and ina second s t ep to accura te ly es t imate or ca l ibra te on coreda ta the i r r espec t ive a , m and n va lues . I t i s a l so wor thnot ing tha t ident i f i ca t ion of c lus te r s represent ingdi f fe rent aqui fe r s i s made eas ie r s ince they woulddef in i t e ly p lo t separa te ly on the Picke t t p lo t .5 . P E R M E A B I L I T Y , C A P I L L A R Y P R E S S U R EC U R V E S A N D E L E C T R O F A C I E S W I T H R R - C I LSe v e r a l a u t h o r s h a v e p r o p o s e d m e t h o d s t o d e r i v ep e r m e a b i l i ty f r o m p o r o s i t y a n d s a t u r a ti o n o r i r r e d u c ib l esa tura t ion (Tix ie r , 1949; Wyl l i e & Rose , 1950; Timur ,1968; Coates & Dumanoi r , 1974) in te r re la t ionship .Be c a u s e s a t u r a t i o n a n d r e s i d u a l s a t u r a t i o n a r ei n f o r m a t i o n b o r n b y t h e t h r e e r e s i s t i v i ty c u r v e s t h e y a r ecompr i sed by the i r r a t ios and qui t e expec tedly , the i ro r d e r e d c l u s t e r s r e f l e c t t h e p o r o s i t y p e r m e a b i l i t yr e l a t i o n s h i p o b s e r v e d o n c o r e . F i g . 4 e d i s p l a y s c o r ep o r o s i t y p l o t t e d v e r s u s De e p / P r o x r a t i o i n d i c a t i v e o fSw, color coding i s for e l ec t rofac ies . Note tha t f ac ies22-23 (deep purp le ) exhib i t a l a rge sca t t e r of corep o r o s i t y m e a s u r e m e n t s n o t r e f l e c t e d b y l o gm e a s u r e m e n t s ( s e e P i c k e t t p l o t o n f i g . 4 c ) . A t r e n d c a nb e v i s u a l l y d e f i n e d t h r o u g h t h e h y d r o c a r b o n s r e s e r v o i rbear ing poin t s . As expec ted , f ac ies 29 ( trans i t ion zone)a n d 3 0 ( wa t e r b e a r i n g r e s e r v o i r ) d e p a r t f r o m t h i s t r e n dI t i s wor th not ing tha t f ac ies 26 , 27 and 28 sca t t e ra round th i s t r end, th i s denotes they a re d i f fe rent rockt y p e s . F i g 4 f d i s p l a y s c o r e p e r m e a b i l i t y p l o t t e d a g a i n s tcore poro s i ty and color coded for e l ec t rofac ies . F i t t inga s ingle t r end through a l l these da ta to def ine ap o r o s i t y - p e r m e a b i l i t y l a w a p p e a r s a s a t i s f y i n g s o l u ti o n ;however i t i s conf l i c t ing wi th the in te rpre ta t ion of f ig4 e . A d e t a i l e d e x a m i n a t i o n o f f ig 4 f c o u l d h e l p d e f i n e at rend spec i f i c to each fac ies . Our favor i t e so lu t ion top e r m e a b i l i ty p r e d i c t i o n r e l y o n m o d e l i n g c o r ep e r m e a b i l i ty b y m e a n s o f KN N t e c h n i q u e a n d l o g s ( a lllogs , inc luding RRC-CIL) as ex t rapola tors ; to th i sp u r p o s e f o r m i n g RR- CI L b y p a r t i t i o n i n g r e s i s t i v i t yra t ios in a l a rge number of c lus te r s i s preferable .C l u s t e r i n g RR- CI L wi t h o t h e r l o g s n o t o n l y i m p r o v e sp r e d i c t i o n i n Hy d r o c a r b o n z o n e s , i t a l s o s e p a r a t e s c o r ed a t a c o r r e s p o n d i n g t o wa t e r a n d o i l b e a r i n g z o n e s , t h u si t i s no longer needed to def ine a spec i f i c model fore a c h z o n e i n o r d e r t o c o m p e n s a t e f o r h y d r o c a r b o nef fec t s on neut ron and dens i ty logs .T r a c k 1 0 o f f i g 3 d i s p l a y s p e r m e a b i l i t y m o d e l e d u s i n gGR, NDS, Dt , Rh o b a n d RR- CI L a s e x t r a p o l a t o r s o fcore measurements , co lor coding i s for e l ec t rofac ies ;c o r e m e a s u r e m e n t s a r e d i s p l a y e d a s d o t s . P r e d i c t i o na c c o u n t s f o r c o r e r e p r e s e n t a t i v i t y , u s i n g STM m e t h o d(Thevoux-Chabuel & a l . , 1997) , sha ly fac ies a re f i l t e redo u t . F i g . 4 d d i s p l a y s p r e d i c t e d p e r m e a b i l i ty v e r s u s

Deep/Prox, co lor coding i s for fac ies , the c lears e p a r a t io n b e t w e e n f a c i e s d e m o n s t r a t e t h e s t r en g t h o fr e l a t i o n s h i p b e t we e n f a c i e s , p e r m e a b i l i t y a n dDeep/Prox ra t io indica t ive of sa tura t ion . Thus i t showst h e c o n s i s t e n c y b e t we e n e l e c t r o f a c i e s a n d p r o p e r t i e s o fin te res t to convent iona l pe t rophys ic .Ou r o b s e r v a t i o n s , r e s u l t s a n d m e t h o d a r e c o n s i st e n t wi t ht h e c o n c l u s i o n s o f f e r e d b y Ch e n g & a l . , wh o p r o p o s e dt h e m e t h o d o f " No r m a l i z e d Re s i s t i v i t y Ra t i o " ( Rn = l o g{(Rt/Rw)/(Rxo/Rmf)} to character ize reservoir f luidm o b i l i t y , a n d p r e d i c t we l l p r o d u c t i v i t y i n d i c e s ( P I s ) .Bo t h m e t h o d s a r e " a n a t u r a l e x t e n s i o n o f th ec o n v e n t i o n a l m o v e d - o i l p l o t m e t h o d i n l o g a n a l y s i s t h a ti s u s e d t o i n f e r z o n e s o f m a x i m u m p e r m e a b i l i t y a n dm o v a b l e h y d r o c a r b o n " ( Ch e n g . & a l . ) . Ou r m e t h o dm a k e s t h e u s e o f t h e c o n c e p t s d e v e l o p e d b y Ch e n ge a s i e r . Ho we v e r i t s m a i n a d v a n t a g e s t e m s f r o m t h e f a c ttha t because a l l the informat ion conta ined in the" d e e p / p r o x i m a l " , " d e e p / s h a l l o w" a n d " s h a l l o w/proximal" ra t ios be ing kept separa te , the ra t io can bein te rpre ted both jo in t ly and severa l ly , thus i t p rovidesm o r e d e t a i l s o n h o w t h e f l u i d s m o v e i n t o t h e p o r o u sne twork . Indeed a l l our observa t ions suppor t the idea tha tthe 3 res i s t iv i ty ra t ios , by which f lushing e f f i c i ency andsa tura t ion a re def ined , can be empi r i ca l ly re la ted to theshape of pore- throa t s i ze d i s t ribut ion . Fur ther , a grea te rf lushing e f f i c i ency s igna l s a pore s i ze d i s t r ibut ioncompr i s ing a t l eas t 2 modes , a t the sca le inves t iga ted bythe tool wi th the shor te r spac ing; indeed in such casemud- f i l t r a t e propagate fa r ther in to the format ion throughlarges t pores whi le smal le r pores a re l e f t uninvaded.Ob v i o u s l y a b o v e s t a t e m e n t s a s s u m e t h a t f o r m a t i o n wa sn o t d a m a g e d b y " s o l i d b l o c k i n g " ( FERTL, 1 9 8 1 ) .W h e r e v e r p o r e s i z e d i s t r i b u t i o n i s n o t t o o c o m p l e x ,i d e n t i c a l RR- CI L v a l u e s c h a r a c t e r i z e d e p t h i n t e r v a l swh e r e RR- CI L c a n b e c a l i b r a t e d o n l a b m e a s u r e m e n t sand cor re la ted wi th d i s t inc t se t s of coef f i c i ent s andp a r a m e t e r s o f t h e r e l a t io n s h i p P~= A ( k / ~ ) -B ,( L E V E R E T T , 1 9 4 1 ; K w o n & P I C K E T T , 1 9 7 5 ) o rW i n l a n d R35 v a l u es ( K O L O D Z I E , 1 9 80 ; P I T T M A N ,1 9 9 2 ; AGUI LERA, 2 0 0 2 ) . W h e r e v e r t h e p o r e s i z ed i s t r i b u t i o n i s m o r e c o m p l e x , RR- CI L c a n h e l p s o r t o u tobserva t ions for a be t t e r unders tanding of sca t t e r in thePc - Sw - k / ~ c o r r e l a t i o n s e x a m i n e d a t t h e s ca l ei n v e s t i g a te d b y l o g s . Sa i d i n o t h e r wo r d s , RR- C I L v a l u e sc a n b e u s e d t o s i g n a l c o m p a r a b l e d e p t h i n t er v a l s wh e r e i nthe pore s i ze d i s t r ibut ions a t sca le inves t iga ted by logsare s imi la r and complex enough to cause d i f f i cu l t i es inident i fy ing m os t ap propr ia te Pc vs . Sw vs .k / ~ c o r r e l a t i o n s .Fur ther work i s r equi red to fu l ly explore th i s subjec t ,a n d p a r t i c u l a r ly t o c o n f i r m t h a t a s h a r p e r i m a g e o f p o r es i ze d i s t r i b u t io n c a n b e o b t a i n e d b y m e a n s o f c l u s te r i n g


8/14


t h e m o r e f i n e l y d e t a i l e d i n v a s i o n p r o f i l e s p r o v i d e d b yar ray res i s t iv i ty tool s .6. P R O C E S S I N G M U L T I W E L LLog typing (e lec t rofac ies ana lys i s ) i s of t en used in a" m u l t i - we l l " m o d e t o p r o v i d e wi t h a c o n s i s t e n t i m a g eof fac ies d i s t r ibut ion a t f i e ld sca le . Such appl i ca t ionc a l ls f o r a p r e l im i n a r y p h a s e o f d a t a h o m o g e n i z a t i o n . I nc a s e t h e r e s is t i v i ty o f t h e w a t e r f o r m a t i o n d o e s n o tchange s igni f i cant ly over the f i e ld or a t l eas t var i es inan ident i f i ab le pa t t em over the f i e ld , th i s t ask can bee a s i l y p e r f o r m e d p r o v i d e d a c l e a n wa t e r b e a r i n greservoi r i s ident i f i ed in each wel l to se rve as ar e f e re n c e . F i r s t s t e p o f h o m o g e n i z a t i o n r e q u i r e s t h a t,for each wel l , t he three res i s t iv i ty ra t ios curves a rec lus te red in order to se lec t for each one , the mos tr e p r e s e n t a t i v e r e a d i n g i n t h e wa t e r b e a r i n g r e s e r v o i r ,should the l a t t e r ex i s t s in the wel l . Then the va lues ofe a c h r e s i s t i v i t y r a t i o c u r v e a r e d i v i d e d r e s p e c t i v e l y b yv a l u e m o s t r e p r e s e n t a t i v e o f wa t e r b e a r i n g r e s e r v o i r . I nso doing , the ra t ios Rw/Rmf , wh ich m os t l ike ly d i f fe rf rom one wel l to another , a re a l l se t to 1 , and mos t ofthe envi ron men ta l e f fec t s a re of f se t. Thu s , i f thea s s u m p t i o n m a d e o n Rw h o l d s t r u e , t h e c h a n g e i n t h e" h o m o g e n i z e d " r e s i s t i v i t y r e a d i n g o n l y r e f l e c t t h er e s i s t i v i t y c h a n g e s d u e t o d i s p l a c e d h y d r o c a r b o n . Th en o r m a l i z a t i o n w e p r o p o s e h e r e i s a g e n e r a l iz a t i o n o f t h em e t h o d p r o p o s e d b y Ch e n g & a l . , t o n o r m a l i z eres i s t iv i ty ra t io .7 . A P P L I C A T I O N T O P O R O S I T Y - S A T U R A T I O NA N D PA Y S U M M A R YSo f a r , t wo a p p l i c a t i o n s h a v e b e e n s u c c e s s f u l l yinves t iga ted . Fi r s t appl i ca t ion cons i s t s in us ing thee lec t rofac ies to cons t ra in probabi l i s t i c methods forporos i ty and sa tura t ion es t imate . To th i s purpose , f ac iesa r e r e g r o u p e d a c c o r d i n g t o t h e i r m i n e r a l o g y , s h a l e t y p e ,a n d p o r o u s n e t wo r k b e h a v i o r . De f i n i n g a s p e c i f i cp r o b a b i l i s t i c m o d e l f o r e a c h g r o u p h a s p r o v e d f a s t e rand eas ie r than f i t t ing a s ingle model to the wholes u r v e y e d i n t e r v a l o r s e v e ra l m o d e l s t o z o n e s d e f i n e d b yt r i a l and e r ror .Se c o n d a p p l i c a t i o n c o n s i s t s i n d e f i n i n g t h e " Pa ySu m m a r y " l a y e r i n g b y c l u s t e r i n g a l l a v a i l a b l e l o g si n c l u d in g RR - CI L , i n d e p e n d e n t l y a n d a h e a d o f th ep o r o s i t y s a t u r a t i o n c o m p u t a t i o n . Th u s t h e p a y s u m m a r yi s c o n s t r a i n e d b y d a t a s t r u c t u r e wh i c h h a s b e e n s h o wnt o r e v e a l p o r o u s n e t wo r k c h a r a c t e r i s t i c n o t d i r e c t l yava i l able through poros i ty sa tura t ion methods . I t i sd e v o i d o f o p e r a to r b i a s , v e r t ic a l c o n n e c t i o n b e t w e e nl a y e r s a n d d e f i n i ti o n o f b e d t h i c k n e s s t h r e s h o l d b e i n gthe only except ion .

8 . S U M M A R Y A N D C O N C L U S I O N SOu r i n v e s t i g a t i o n o n r e s i s t i v i t y r a t i o a d d r e s s e s o n e o ft h e m a n y a s p e c t s o f f o r m a t i o n c h a r a c t e ri z a t io n , a t f ie l do r b a s i n s c a le , b y m e a n s o f l o g d a t a , in t e r m o fm i n e r a l o g y , t e x t u r e a n d p o r o u s n e t wo r k c h a r a c t e r i s t i c s .I t wa s c a r r i e d o u t b y m e a n s o f M R GC c l u s t er i n g wh i c hma de poss ib le the explo ra t ion of the da ta s t ruc ture ofres i s t iv i ty ra t io wi thout any opera tor b ias .Resul t s obta ined so fa r suppor t the idea tha t Invas ionp r o f i l e d e f i n e d f r o m r e s i s t i v i t y c u r v e s c a n b ep a r t i t i o n e d t o d e r i v e RR- CI L wh i c h i n m m i sp a r t i t i o n e d wi t h o t h e r a v a i l a b l e l o g s . Be c a u s e t h e yc o m p r i s e t h e p e r m e a b i l i t y , a n d p o s s i b l y c a p i l l a r yp r e s s u r e i n f o r m a t i o n b o r n b y r e s i s t i v i t y l o g s , t h ee lec t rofac ies obta ined a re cons i s t ent in t e rm ofl i th o l o g y a n d p e t r o p h y s i c .Th e i n t e r p r e t a t i o n t e c h n i q u e e n c o m p a s s e s we l l p r o v e nconcept s : namely the " tornado char t " , the res i s t iv i tyover lay , the " ra t io methods" and the Picke t t p lo t . Thec o n c e p t o f i n v a s i o n p r o f i l e h a s b e e n m a d e f a m i l i a r t op e t r o p h y s i c i s t s a n d g e o l o g i s t s t h r o u g h t h e u s e o fres i s t iv i ty over lay method. Clus te r ing the 3 res i s t iv i tyr a t io s c a n b e v i e we d a s a g e n e r a l i z a ti o n o f th er e s i s t i v i t y o v e r l a y m e t h o d . Th e " M T p l o t " p r e s e n t s t h et o m a d o c h a r t c o n c e p t i n a wa y c o n s i s t e n t wi t hr e s i s t i v i t y o v e r l a y m e t h o d a n d d i s p l a y o f a r r a y l o g ssuch as NMR, Gra in Size d i s t r ibut ion , or logs resul t ingf r o m t h e " h i s t o g r a m u p - s c a l i n g " m e t h o d .Th e m e t h o d a l l o ws s o r t i n g o u t r e s e r v o i r b y t h e i rc o n t e n t : wa t e r , " t r a n s i t i o n " a n d h y d r o c a r b o n a ti r r e d u c ib l e sa t u ra t io n . I n h y d r o c a r b o n r e s e r v o ir a ti r reduc ib le sa tura t ion , c lus te r s pos i t ion on the MT plo ti s in te rpre ted in t e rm of sa tura t ion and invas iond i a m e t e r. Ca l i b r a t i o n o n c o r e m e a s u r e m e n t s c a n b eu s e d t o m a t c h RR- CI L wi t h a p p r o p r i a t e l y d e p t hm a t c h e d p o r e s i ze d i s t r i b u t io n r e p r e s e n t a t i v e o f th er o c k v o l u m e i n v e s t i g a te d b y r e s i s ti v i t y l o g s.Th e m e t h o d s a l l o ws i d e n t i f i c a ti o n o f u n r e s o l v e d b e d ss i g n a l i n g p o s s i b l e p o o r v e r t i c a l c o n n e c t i v i t y b e t we e nl a y e r s a n d p o i n t i n g o u t b i a s e d n u c l e a r a n d s o n i c l o g sreadings inappropr ia te for format ion charac te r i za t ion .W h e r e v e r d i a g e n e s i s i s n o t th e m a i n c o n t r o l o f p o r o u sn e t wo r k , s t r a ti g r a p h ic e v o l u t i o n o f p e r m e a b i l i ty a n dcap pressure revea led in the obta ined e lec t rofac iesc o l u m n c a n b e i n t e r p r e t e d i n t e r m o f g r a i n s i z e a n ds o r ti n g a n d r e l a te d t o s e d i m e n t a r y p r o c e s s e s .Th e p r o p o s e d m e t h o d i s r o b u s t wi t h r e s p e c t t oe n v i r o n m e n t c o r r e c t i o n s a n d n o t c o n t i n g e n t o nkno wle dge of Rw, Sw or even Rmf and Rm. I t does notrequi re any ca l ibra t ion on core mater i a l . A s impleh o m o g e n i z a t i o n t e c h n i q u e i s p r o p o s e d f o r a p p l i c a t i o nto mul t i -wel l pro jec t s .


9/14


Appl ica t ions o f th is m e tho d to com puta t ion o f poros i tysa tu ra t ion and pay sum m ary and to pe rm eabi l i tym ode l ing a re p roposed .R E F E R E N C E S C I T ED

Aguilera , R. , Incorporat ing capi l lary pressure , porethroat aperture radi i , height above free water table ,and Winland r35 values on Picket t plots , A A P GBu lletin , pp. 605 624, V 86, N4 apr il 2002,Brei tmeier , J .M. , Tosch W.C. , Adewumi M.A. , Mil ler ,M. N, 1989 , Inves t iga t ion o f Radia l Invas ion of M udFil t ra te in Porous Media" paper S , SPWLA 30 hA n n u a l S y m p o s i u m ,Cheng, M. L. , Leal , M.A. , McNaughton, D. , 1999,P roduc t iv i ty P red ic t ion f rom Wel l Logs in Var iab leGrain Size Reservoirs Cretaceaous , Qishn Formation,Republ ic o f Yem en. The Lo g Analyst , V. 40 N 41Coates , G.R. & Dumanoir , J .L . A New Approach toIm proved Log Der ived P e rm eabi l i ty , The LogAnalyst (Jan.-Feb. 1974) 15, NI.F e r t l , W . H . , O p e n h o l e C r o s s p l o t C o n d e p t s - AP owerfu l Technique in Wel l Log Ana lys i s , Journa lof Petroleum Technology, Marc h 1981 pp. 535-549.Kolod zie J r , S ., 1980, Analy s is of pore throat s ize andthe use o f the Wax m ans -S m i t s equa t ion to de te rm ineOOIP in the Spindle F ie ld, Colorado, SPE 55 hAnn ual Technology C onference, SPE paper 9382,Kwon. B.S . & Picket t , G.R. , A New Pore StructureModel and Pore S tructure interre la t ionships , 1975,pape r P , SP WLA 16 h Annua l Logg ing Symposium.

Leveret t , M.C. , Capil lary Behavior in Porous Sol ids , p p152-169 V 142, Transact ions of the AIME, 1941Moss, B.P . , 1997, The Part i t ioning of PetrophysicalData: a Review, in "D evelopments in Petroph ysics"Geological Society Special Publ icat ion N122, pp.

181-252Picket t G.R. ; 1973, Pat te m Recognit ion as a Me an ofF orm at ion Eva lua tion : paper A , SPWLA 14 h Annua lLogg ing Sympos ium.Pit tman, E. , 1992, Relat ionship o f Poros i ty andP erm eabi l i ty to Var ious P a ram ete rs Der ived f romMercury Inject ion-Capil lary Pressure Curves forSandstone. AA PG B ulletin, pp. 191-198, V 76, N2February 1992,Rabiller, Ph. , Leduc, J.P. , Ye, S.J. , 2001, The IterativeUse of C lus te r ing and Mode l ing to Im proveP erm eabi l i ty P red ic t ion pap er E, SPWL A 42 ndAnnua l Lo gg i ng Sympos ium.Serra , O. & Abbot , H. , 1981, The Contribut ion ofLogging Da ta to S ed im ento logy and S t ra t ig raphy .SPE of AIME, Transact ions 55 h Annu al F al lTechnology Conference, paper SPE 9270Thevoux-Chabuel , H. , Rabil ler , Ph. , Vei l lere t te , A. ,1997, Mult iwell log data coherence characterizat ion

using s imilari ty threshold method, SPWLA 3 8 thAnnua l Logg ing Sympos ium.Timur, A. , An Inv es t igat ion o f Permeabil i ty, Poros i ty,and Residual Water Saturat ion Relat ionships , 1968,pap er J, SPW LA 9 th Ann ual Lo gging Sym posium.

Tixier , M.P., 1949, Evaluat ion o f Permea bil i ty fromElectr ic Log res is t ivi ty Gradients , Oil and GasJournal. (June 16, 1949)Wyllie , M.R.J . & Rose, W.D . , 1950, Some Theoret icalConsiderat ions Related to the Quanti ta t ive Evaluat ionof the Physical Characteris t ics of Reservoir Rocksfrom Electr ical Log Data , Journa l o f PetroleumTechnology (April 195), 189.Ye, S .J . & Rabil ler , Ph. , 2000, A New Tool for Electro-facies Analys is : Mult i -Resolut ion Graph-BasedClus tering, pap er PP, SPW LA 41 th Ann ual Logg ingSymposium.Ye, S .J . & Rabil ler , Ph., 2002, A utom ated ElectrofaciesOrdering, submi t ted to "Petrophysics"

A C K N O W L E D G E M E N T SThe authors are great ly indebted to Paradigm forsupport received in preparing this paper.In addi t ion the authors grateful ly acknowledge LoicRicha rd and O bren Djord jev ic f rom P arad igm for the iradvices .A B O U T T H E A U T H O R SP hi l ippe Rabi l l e r g radua ted f rom ENS P M (Ins t i tu tFrangais du P6trole) . He joined Elf in 1976, spent 13years on ass ignments abroad and led R/D projects onBasin/Prospect evaluat ion and Shale Seal ing Effic iency.In 1992 he received the responsibi l i ty of the team incharge of geological and geophysical log appl icat ionsand deve loped new m ethodolog ies fo r boreho leimagery and facies characterizat ion. S ince 2001, hisearly re t i rement pos i t ion a l lows him to enjoy the thri l lof freelance consul t ing on teaching and R/D. Hisresearch interes ts and act ivi t ies focus o n the appl icat ionof pat tern recognit ion and s ignal process ing techniquesto log data for reservoir characterizat ion and sequences tra t igraphy.H u g u e s T h e v o u x - C h a b u e l i s c u r r e n t l y P r o j e c tManager fo r LWD deve lopm ent fo r P a rad igm inHouston. H e is in charge o f projects concerning theelectrofacies characterizat ion and real- t ime loginterpreta t ion. From 1993 to 1998 he worked for ElfExplorat ion Product ion as research scient is t on loginterpreta t ion methods . From 1998 to 2001 he wasLWD Technica l Advisor fo r Baker Hughes In teq . Hereceived a Ph.D. in Geosciences from the Univers i ty ofParis VI.


10/14


TABLE 1T R A C K C O N T E N T

1 Cal ipe r and bi t s ize2 GR, normal i zed .3 N p h i , R h o b , D t , P H I X - D N4 E l e c tr o f a ci e s d e f in e d b y M R G C - C F S O M u s in g : D t , G R , N D S , R h o b5 De pth (m. )6 Res i s t iv ity : LLd, LLs , M SF L7 RR-C IL: Res i s t iv i ty r a t io c lus te r s index log8

10

E l e c t ro f a c ie s d e f in e d b y M R G C - C F S O M u s i n g D t , G R , N D S , R h o b ,a n d R R - C I LIdem t r ack 8 ; f ac ies 1 and 2 o f tr ack 8 a re r e - indexed as f ac ies 29 and30.B lack curves i s fo r s t a t is t i ca lly model l ed p ermea bi l i ty , a base l ine ( r ed)is set at 100 mD; dots are for core permeabi l i ty; colour coding is forfacies displayed in t racks 8 and 9.

TABLE 2F A C I E S D E S C R I P T I O N

Clean quar t z s ands tone , water bea t ing , good poros i ty and permeabi l i ty( h o m o g e n e o u s )C lean quar t z s ands tone , t r ans i tion zone , good poros i ty , med iump e r m e a b i l i t y ( s c a t t e r e d )Fac ies 1 and 2 o f T rack 8 a re r e - indexed as f ac ies 29 and 30 in t r ack 9 ;co lor cod ing i s unchanged .

3 T igh t do lom i t i c4 - 13 Si l ts (4) grading to s i l ty shale (13) in w ater zon e

14 - 16 Sha ly f ac ies wi th impor tan t cav ings .17 - 20 Sha le (17) g rad ing to s i lty sha le (20) in o i l bea t ing zone .

21 Com pact f ine s ands tone and s il ts , ca rbonate cem ented , channel l ag.22 - 23 Com pact f ine s ands tone and s i lt ca rbonate cem ented (d iagene t i c )2 4 - 2 8 Clean sands tone , medium poros i ty and permeabi l i ty (24) g rad ing to

good poros i ty and permeab i l i ty . O i l bea t ing

10


11/14

SPW LA 44 h Annua l Logging Sympos ium, Ju ne 22-25, 2003

11


12/14

S P W L A 4 4 th A n n u a l L o g g i n g S y m p o s i u m , J u n e 22-25, 2003

12


13/14


13


14/14


14

Documents

Clustering Rt Saturation-eval k Facies Predictions