sumatera basin.pdf

Embed Size (px)

Citation preview

  • 8/16/2019 sumatera basin.pdf

    1/20

     101

    IPA05-G-156

    PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION

    Thirtieth Annual Convention & Exhibition, August 2005

    TELISA SHALLOW MARINE SANDSTONE AS AN EMERGING EXPLORATION TARGET IN

    PALEMBANG HIGH, SOUTH SUMATRA BASIN

    R.M. Iman Argakoesoemah*

    Maria Raharja*

    Sonny Winardhi **

    Rudhy Tarigan*

    Tino Febriwan Maksum*

    Amritzar Aimar*

    ABSTRACT

    The main productive reservoirs in the PalembangHigh, South Sumatra Basin, are sandstones of the

    Talang Akar Formation  and carbonates of the

    Baturaja Formation. The largest oil field in the region

    is the Kaji-Semoga Giant Oil Field discovered in

    1996. To maintain the production rate, exploration

    efforts continue with new ideas and concepts. It is

     believed that one of the potential exploration

    candidates is the Telisa Sandstone reservoir.

    The Telisa Sandstone, which includes the sandstones

    in the lower part of the Telisa Formation, consists of

    very fine- to fine-grained sandstones with minor

    shales, deposited in a shallow marine shoreface

    setting during both sea level lowstand and

    transgression. The acoustic impedance contrast

     between the sandstones and the overlying and

    underlying Telisa shales is very small because of

    highly argillaceous content of the sandstone.

    Consequently, the sandstone reservoir prediction

     becomes very difficult. In addition, the geophysical

    data available comprise only 2-D seismic in various

    vintages and qualities.

    The most crucial objective in this exploration effort is

    to predict the sandstone distribution, its quality and

    fluid content. This is required to generate a drillable

     prospect, add a development well, a work-over, and

    enhance field reserves calculation. The test-line work

    results of the Extended Elastic Impedance (EEI)

    Inversion technique have been applied and the

    delineation of sandstone distribution, determination of

    * Medco E&P Indonesia

    ** Institute Technology Bandung

    sandstone quality, and fluid content potential have

     been defined. The objective of this paper is to share

    the Telisa Sandstone geological interpretation and theuse of the EEI inversion in exploration of low

    acoustic impedance contrast of clastic reservoir in the

    Palembang High region, South Sumatra Basin. 

    The hydrocarbon potential in this Telisa Sandstone

     play remains unknown, but the results are

    encouraging. Several successful tests have been

    conducted through the hydraulic fracturing efforts.

    Although most of the sandstones are relatively tight,

    the reservoir flows oil. The petroleum system of this

    Early Miocene play remains uncertain, but it is

     believed that the source rocks are mature shales of the

    Lemat and Talang Akar Formations in the Jemakur

    Graben and Tamiang Lows immediately to the north.

    It is possible that the oil has been migrating from the

    fetch areas through the sandstones of the Talang Akar

    Formation  and porous limestones of the Baturaja

    Formation. In the Kaji-Semoga Field, the Telisa

    Sandstone onlaps onto the Baturaja Formation. Fault

    conduits could also be an important role in oil

    migration process as indicated in the Langkap Field.

    The top and up-dip lateral seals are the thick, basin-

    scale Telisa shales.

    INTRODUCTION

    The Telisa Sandstone exploration has been

    intensively conducted very recently since the year

    2004 though the hydraulic fracturing jobs have begun

    since late 2002. Pre-2002 period and prior to the

    success of the hydraulic fracturing work results, the

    Telisa Sandstone reservoir potential was not viewed

    attractive as a primary drilling objective. This despite

    http://gobackdoc/http://gobackdoc/http://gobackdoc/

  • 8/16/2019 sumatera basin.pdf

    2/20

     102

    the fact, that oil shows were observed in the wells and

    the hydrocarbon gas readings during drilling were

    significantly high, and in some wells, the gas readings

    are even higher than the targeted reservoir objectives.

    The sandstones were considered thin, shaly, and tight.

    At the time, the primary reservoir objectives were the

    Talang Akar and Baturaja Formations. Consequently,a lack of geological and geophysical data has been

    acquired for this Telisa Formation. Most of the logswere not properly run to cover the whole section and

    a lack of conventional cores was available to evaluate

    the reservoir deliverability. To maintain hydrocarbon

     production of the existing oil and gas fields,

    exploration efforts are obviously needed to searchother exploration plays. The Telisa Sandstone is one

    of the potential candidates. Further geological data is

    now beginning to be acquired, including conventional

    cores and modern wireline logs.

    One of the detailed exploration efforts being

    undertaken is the study of EEI inversion using

    reprocessed pre-stack time migration of 2-D seismic

    lines of various vintages, mainly to cover the Kaji-

    Semoga Oil Field. Some of the seismic lines included

    in the study are those extending over the Old Rimau

    Fields such as Langkap and Kerang Fields. The EEI

    test-line project, involving several selected 2-D

    seismic lines, was conducted to test the method in

     predicting the presence and distribution of the Telisa

    reservoir sandstone in the Palembang High region.

    The main objective of this paper is to share the results

    of the Telisa Sandstone interpretation in this region.

    The Telisa Sandstone as defined in this paper includes

    the sandstones in the lower part of the Telisa

    Formation. The thick argillaceous sediments

    overlying and underlying the Telisa Sandstone will

    not be discussed in detail. The discussion will focus

    only on the sandstone interval.

    TELISA SANDSTONE

    The Palembang High is located in the eastern part of

    the South Sumatra Basin. Geographically, it is about

    70 km to the northwest of Palembang City, Figure 1.

    The Palembang High is one of the local paleo- basement highs formed as part of the easternmost

    margin of the South Sumatra Basin. This margin is

    obviously the westernmost end of the Sunda

    Landmass and sediment source for most of the

    Tertiary sediments. On this high, syn-rift deposits of

    the Late Oligocene to Early Miocene Lemat and

    Talang Akar Formations are very thin, except for

    those deposited in the Jemakur Graben, partially

    forming a low-angle angular unconformity and later

    overlain by carbonate rocks of the Baturaja

    Formation. These carbonates have been a major

     producing reservoir for the Kaji-Semoga oil field. Inthis paleo-basement high region, the Telisa Formation

    was deposited immediately above the Baturaja

    Formation. Toward the basinal areas to the west, the

    formation is also stratigraphically inter-fingering with

    the Baturaja Formation, Figure 2.

    The Telisa Formation is lithostratigraphically defined

    as shallow-to-deep open marine, dark grey shales.

    The shallow marine shales have been observed in the

    Palembang High area. In this region, the lower part of

    the formation usually contains thin reservoir

    sandstones called “Telisa Sandstone” and hasthicknesses ranging from 20 to 80 feet. Immediately

    to the northeast of the Iliran Fault, the sandstone

    thicknesses could be in the range of 300-foot gross

    with net sand thickness of up to 200 feet. Figure 3

    shows the isochron of the Telisa Sandstone and the

    shales below it across the Palembang High. Two

    major paleo-lows, oriented northwest-southeast, are

    the areas where the shaly sediments beneath the

    Telisa Sandstone are well developed. The low

     between Kaji-Semoga High and Iliran High is mainly

    filled-in by shales and siltstones with minor

    sandstones in the uppermost part of the sequence. Incontrast, the low immediately to the north of the Iliran

    Fault consists of fine-grained sandstones with minor

    shales. It is believed that various degrees of syn-

    depositional normal faulting is responsible for the

    varying thickness development of the argillaceous

    sequence underlying the Telisa Sandstone in both

    half-grabens.

    Wireline log motifs of the Telisa Sandstone sequence

    varies significantly from well to well. The sequence

    in the Kaji-Semoga wells generally shows a blocky

    motif, occasionally coarsening upward in the lower portion and fining upward in the upper part, with an

    erosional surface in between, Figure 4. Based on this

    log shape and core descriptions, the sandstones can be

    subdivided into several more detailed facies lobes. Ingeneral, the sandstones are light olive gray, all fine

    and very fine grained, calcareous, angular to sub-

    rounded, very well sorted lithic arenites with feldspar

    and substantial numbers of globigerinids, small benthic

    foraminifers, small echinoid spines, and splinters of

  • 8/16/2019 sumatera basin.pdf

    3/20

     103

    vertebrate bone. It is a mix of sediment particles,

    created in a fully marine environment (pelagic skeletal

    materials) with detrital particles (fine sand and some

    clay mud) wafted in from the nearby coast. Wavy

    lamination and ripple bedding, and bioturbated to

    various degrees, suggest deposition below the fair-

    weather wave base but it could be close to the stormwave base.

    The Telisa Sandstone in KS-138 well has a total

    thickness of about 80 feet, consisting of three stacked

    facies, Figure 4. In the lower lobe, the facies has the

    highest gamma ray and lower resistivity values.

    Shales with many green peloids and minor scatteredsilts and fine quartz sands possibly cause this high

    gamma ray reading. Glauconite is present in the

    whole sequence, but becomes a significant component

    in this lower facies. This glauconite could be formed

    in marine waters, still quite shallow, in the shelfdepths with continuous reworking and a slow rate of

    clastic input. In contrast, the presence of glauconite in

    the higher sandstone beds suggests the activity of

    intensive erosion of the sediments below it. The

    glauconite in this sandstone could therefore be

    allochthonous rather than autochthonous origins.

    In KS-138, the middle facies is represented by a

     blocky log motif with a sharp basal contact to the

    sandstone, suggesting a possible local erosional

    surface. The sandstone consists of abundant very

    angular fine quartz sands and foraminifers. The uppersandstone lobe occasionally shows a fining upward

    log motif with a sharp basal contact. The sandstone is

    separated from the middle lobe by less than 5-foot of

    shale. The top of the sandstone sequence has a sharp

    top contact and is immediately overlain by the deeper,

    transgressive outer-neritic-to-bathyal marine shales.

    These erosional surfaces are interpreted as the product

    of the submarine incision during a transgression

     period.

    The conventional cores collected in KS-106 well

    suggest that the sandstones were deposited in amarine middle-outer sublittoral environment.

    Planktonic foraminifers are abundant indicating an

    offshore environment strongly influenced by open-sea

    currents. Hummocky cross-stratification is present onlyrarely suggesting possible minor storm influence.

    Locally derived detritus is also abundant, mainly from

    the granitic basement rocks interpreted to be derived

    from the nearby Kaji-Semoga High. Less common

     planktonic foraminifers in the lowermost part of the

    section may be indicative of shallower water

    conditions.

    In Kerang-1, the sandstone interval has several

    erosional surfaces that are difficult to directly

    interpret from the logs, Figure 5, with the upper

    sandstone bed was heavily burrowed. The sandstonesare very fine to fine grained and calcareous with

     planar sedimentary structures. The shales

    immediately below the sandstones consist of

    abundant foraminifers, are calcareous, and glauconitic

    with a streak of conglomeratic glauconitic sandstone

    (2-foot thick).

    AGE AND DEPOSITIONAL ENVIRONMENT

    Faunal content in the shales immediately overlying

    the Telisa Sandstone is abundant and has a high

    diversity of deep marine faunas. The benthic faunasinclude Uvigerina sparsicostata, Uvigerina

     peregrina, Uvigerina schwageri, Cibicides foxi,

     Haplophragmoides compressa, and Bolivina sp 

    suggesting an outer neritic marine environment.

    Several deeper marine fossils are also present:

    Cassidulina, Gyroidina, and  Buliminella,  suggesting

    an outer neritic to upper bathyal environment.

    Globigerinoides diminutus, Globorotalia birnageae,

    and Globorotalia peripheroronda  are present

    indicating that the sequence is N7 in age. The base of

    Globorotalia birnageae  in the shales just above the

    Telisa Sandstone is used as the basal boundary of N7.The presence of Catapsydrax cf dissimilis  and

    Globigerinoides trilobus  group suggests that the

    Telisa Sandstone and shales between this sandstone

    and the top of the Baturaja limestone is N5-N6 zones,

    Early Miocene. This interpretation is supported by the

    occurrence of nannofossils Sphenolithus belemnos 

    and  Helicosphaera ampliaperta indicating NN2-NN3

    zones.

    The overall Telisa Sandstone sequence in the

    Palembang High region was deposited during N5-N6

    (middle Early Miocene). The water depth isincreasing from the top Baturaja to the shales

    overlying the Telisa Sandstone: middle neritic to

    upper bathyal. This is consistent with the major

    transgression period during deposition of the TelisaFormation. Following this transgression, a series of

    regional regressions occurred when the Palembang

    Group (Lower, Middle, and Upper Palembang

    Formations) was deposited across the South Sumatra

    Basin.

  • 8/16/2019 sumatera basin.pdf

    4/20

     104

    The Telisa Sandstone was deposited immediately

    above the Baturaja Formation. Thin shales of about

    100-foot thick usually separate the Telisa Sandstone

    from the Baturaja limestones. When the Baturaja is

    absent, the Telisa Sandstone directly overlies the

    Talang Akar Formation or Basement. The Baturaja

    Formation consists of mainly carbonate rocks withoccasional stringers of calcareous shales. Deposition

    of these carbonates range from reefal build-up tocarbonate bank. The carbonates are usually found on

    the paleo-basement highs either on top or the gentle

    flank of the highs. They were deposited in shallow

    marine, clear water, inner neritic environment. The

    limestones of the Baturaja Formation were exposed tothe atmosphere (Kalan et al, 1984). The extent of the

    subaerial exposure remains unknown, but it is

     possible that the upper part of the section is the

     product of the highstand carbonate deposition.

    Another indication is that the fine clasticsimmediately overlying the Baturaja limestone tend to

    consistently show coarsening upward sequences,

    Figure 4. Although it is difficult to recognize, the

    depositional model for the Telisa Formation seems to

     be in line with the possibility of a Baturaja highstand

    model.

    The preliminary regional interpretation results of the

    Telisa Formation indicate that there is a lack of

    evidence for the presence of lowstand deepwater

    sediments in the Palembang High during deposition

    of the Telisa Sandstone. However, the sedimentsshould be present in the basinal settings away from

    the paleo-highs. In contrast, throughout most of the

    Tertiary, the sediments in the paleo-high region tend

    to be non-marine to shallow marine. Further detailed

    interpretation of depositional environment of Telisa

    Sandstone in the Palembang High is difficult to define

    due to limited supporting data being available.

    The regional parasequence chronostratigraphic

    correlation, biostratigraphic analysis results,

    conventional core, thin section, wireline log shape

    analysis, and regional geological modeling, are

    integrated together with the seismic interpretation to predict the depositional environment. It appears that

    the sandstones were possibly deposited in a shallow

    marine shoreface setting though this could still be

    controversial, as is usual in defining the origin of theisolated shallow marine sandstone bodies.

    DEPOSITIONAL MODEL

    The biostratigraphic analysis results are insufficient to

    describe the details of the depositional environment of

    the Telisa Sandstone. The 2-D seismic interpretation

    also failed to support the presence of the sandstone

    reservoir due to limited seismic quality and low

    impedance contrast between the sandstones and the

    overlying and underlying shales. Regional geological

    log correlation is very useful in verifying some of the

    regional markers and parasequences. Figure 6 showssouthwest-northeast parasequence chronostratigraphic

    correlation across the Kaji-Semoga, Langkap, andKerang areas. Several progradational parasequences

    of 4th and/or 5th order occurred in the lower section of

    the Telisa Formation. Datum of the correlation is

    hung to the maximum flooding surface (MFS)

    immediately above the Telisa Sandstone. Position ofthis MFS is defined by using wireline log responses

     particularly gamma ray and deep resistivity curves

    and roughly controlled by local biostratigraphy. This

    chronostratigraphic correlation suggests that the

    Telisa Sandstone comprises isolated shallow marinesandstone bodies encased in the Telisa marine shales.

    The wireline log shape analysis utilized in this

    correlation indicates that deposition of the Telisa

    Sandstone is not simple. The log responses in each

    well show inconsistent wireline log shape.

    A geological model of the Telisa Sandstone

    deposition is shown in Figure 7. In this model the

    sandstones are deposited at a time when the shoreline

    rapidly prograded basinward below fair-weather wave

     base during a lowstand period, producing progradinglowstand shorefaces overlying the fine clastics of the

    open-marine highstand shelf sequence

    (Figure 7, stage 2). When relative sea level rises, the

    lowstand shoreface sediments will be truncated by a

    higher erosion surface as transgression continues. The

    transgressively incised shoreface sandstones, lie on

    the transgressive surface of erosion (ravinement) and

    are related to the initial transgression across large

    shelf areas. It is possible that, as shown in this model,

    each transgressive shoreface is underlain by an

    erosion surface of the initial transgression. This is

    interpreted to be the back-stepping shoreface orerosion shoreface retreat. The ravinement surface is

    not simple, but it could be amalgamated to be a

    widespread erosional surface (Figure 7, stage 3). It is

    an amalgamation of the ravinement surface and

    lowstand sequence boundary surface. If this is the

    case, the sandstones internally in “sand-to-sand”

    contact are genetically discrete due to widespread

    cannibalization or intense reworking of the earlier

     prograding lowstand sandstones. The end product is

  • 8/16/2019 sumatera basin.pdf

    5/20

     105

    that the amalgamated sandstones of different origins

     become an isolated shallow marine sandstone body,

    Figure 6. Hence, the transgressive sequence sandstone

    has the highest preservation potential.

    This geological model of deposition is apparently

    consistent with the preliminary interpretation of theregional high-resolution sequence stratigraphy. Using

    the geological model discussed above, the mainsandstone reservoir encountered in the Kaji-Semoga

    and Langkap wells is believed to be a product of the

    depositional remnant of various lowstand shorefaces.

    This remnant is thin with individual sandstone

    thickness ranging from 20 to 50 feet but could bedeposited over widespread areas. In the case of the

    Kaji-Semoga and Langkap, the remnant of the

    shoreface facies sandstone could extend

    approximately 15 kilometers. The overall interval of

    the Telisa Sandstone deposition and erosion duringlowstand and transgression periods in the Kaji-

    Semoga, Langkap, and Kerang areas is only about

    200 feet, Figure 6. This evidence suggests that the

    shelf dip and morphology during the Telisa Sandstone

    deposition is likely to be very gentle. Small relative

    sea level change could have direct and large impact to

    the overall sedimentation on the Palembang shelf.

    Hence, the 4th  or 5th  order of parasequences may be

    sufficient to produce significant sandstone

    development. The thin transgressively incised

    shorefaces encountered in the wells are possibly

    caused by rapid relative sea level rise.

    The individual sandstone thickness of each

    transgressively incised shoreface is usually very thin,

    ranging from less than 5 feet to about 20 feet. The

    lateral distribution of each transgressive shoreface

    sandstone body seems to be independent and may not

     be connected laterally and vertically. Each of the

    sandstone units seems to have a different age of

    deposition. The sandstone becomes younger toward

    the west from Kerang to Langkap and Kaji-Semoga

    as shown in Figure 6. Possible stacked transgressive

    shoreface sandstones are likely not to occur due tolimited lateral extent of each sandstone body.

    Several isolated shallow marine sandstone bodies in

    other basins have been discussed by Burton andWalker (1999), George (2000), Hart and Plint (1993),

    Leckie and Walker (1982), Leggitt et al (1990),

    MacEachern et al (1998 and 1999), McBride et al

    (2002), Martinsen (2003b), Pattison and Walker

    (1992), Posamentier (2002), Posamentier and

    Chamberlain (1993), Snedden and Bergman (1999),

    Snedden and Dalrymple (1999), Tesson et al (2000),

    and Walker and Eyles (1988). The origin of isolated

    shallow marine sand bodies remains controversial

    (Sutter and Clifton, 1999; Snedden and Bergman,

    1999). It is undoubtedly true that estuarine parts of

    incised valley fills, erosional remnants, lowstanddeltas, and other systems may form isolated marine

    sand bodies (Nummedal, 2002).

    SEDIMENT PROVENANCES 

    It is difficult to define the provenance for the Telisa

    Sandstone and further study is still required.However, speculation is that the sediment supply is

    likely sourced from more than one location. Dipmeter

    and image logs are not available, and the preliminary

    seismic stratigraphic interpretation in this paleo-

     basement high region does not sufficiently show thedepositional direction. The test-line results of the EEI

    inversion work carried out suggest that the nature of

    the sandstones is different in each region. For

    example, the sandstones in the Kaji-Semoga area

    have different wireline log responses compared to

    those in the Kerang and Langkap wells due to

     possible differences in the mineralogic composition.

    In the Kerang wells, the deep resistivity readings have

    low contrast compared to those in the shales

    overlying and underlying the sandstones, but flow oil.

    The sandstone resistivity value is less than 1.5 times

    the resistivity of the shale base line. Hence, a low-resistivity low-contrast pay (LRLC) is present. In the

    Kaji-Semoga wells, LRLC seems not to develop

    (Figure 4).

    It is possible that at least two speculative sediment

     provenances for the Telisa Sandstone sequence can be

     predicted, Figure 3. The main sediment supply is

    most likely from the Sunda Landmass further to the

    east. Although the Kaji-Semoga High is only

    considered to be a local high, the sediments supplied

    are very significant to reservoir development in the

    region. Thin sections of the sandstones in the Kaji-Semoga wells shows very angular to sub-rounded

    quartz grains suggesting a short distance to the

    sediment supply, Figure 4. The regional parasequence

    chronostratigraphic correlation (Figure 6) and seismicinterpretation (Figure 8) are also consistent with the

    interpretation of the Kaji-Semoga High as a local

    high. The Iliran High might be the source of the

    sediments, but the shallow wells drilled in this paleo-

    high indicate that the Telisa Formation is present

  • 8/16/2019 sumatera basin.pdf

    6/20

     106

    directly on top of the basement suggesting that the

    Iliran High might be valid for the lowermost part

    only.

    EXPLORATION OBJECTIVES

    The primary objective of the Telisa Sandstone studyand EEI inversion work is to predict the distribution

    of the sandstone reservoir. The present day timestructure map of the Upper Telisa Marker shows that

    the structure is continuously and consistently

    shallowing towards the Sunda Landmass to the east.

    Figure 9 shows a west-east oriented seismic line

    showing this continuous shallowing of structuretowards the east. On the other hand, hydrocarbons

    have been encountered in the Kaji-Semoga, Langkap,

    and Kerang Fields. The most acceptable explanation

    for this geological trap is that the hydrocarbons are

    trapped in a stratigraphic play, however, a possibleup-dip small fault seal could also occur. Location of

    the up-dip lateral permeability barrier either as a

    shale-out play of the transgressively incised

    shorefaces or lowstand depositional remnant is

    important to define. It should also be noted here that

    remnants range in size from small to very large

    (basin-scale), and the larger remnants commonly

    contain several smaller remnants (Martinsen, 2003a

    and 2003b). If this permeability barrier can be defined

    and identified, perhaps some of the geological

    uncertainties can be minimized in (1) refining existing

    field reserves calculation, (2) designing work-over jobs, (3) better planning for production and in-fill

    wells, and (4) the most critical to search for additional

    new drillable exploration prospects.

    Another critical objective is to identify and map the

     presence of better quality within the sandstone

    reservoir. It is possible that the location of better

    reservoir quality should be in the areas close to the

    sediment provenances. Given the parasequence

    chronostratigraphic correlation in Figure 6 and the

    geological model in Figure 7 are both valid, it appears

    that the search for lowstand depositional remnants iscrucial. The lowstand sand body might not be in

    communication with other lowstand sand bodies. The

    sedimentary reservoir compartmentalization caused

     by the sandstone body geometry, built from differentsediment provenances, could result in separate

    stratigraphic traps. The orientation of the shoreface

    deposition might still be in agreement to the related

    shoreline orientation of the sediment provenance.

    Similarly, as shown in Figure 6, each of the

    transgressively incised shoreface sandstones is likely

    not connected to other sandstones of the same genetic

    depositional process.

    Since the thick, basin-scale shales of the Telisa

    Formation encase the sandstones, seal should not be

     problem, except in the area where the sandstones arein direct contact with the Baturaja limestones and/or

     basement. Source rocks are the mature shales of the

    Lemat and Talang Akar Formations in the Jemakur

    Graben and Tamiang Lows to the north. Hydrocarbon

    migration is interpreted to occur mainly through the

    normal faults present in the Jemakur and Langkap-

    Kerang region. The importance of lateral carrier beds

    of the Baturaja limestones and Talang Akar

    sandstones for hydrocarbon migration may not be

    crucial, because the sandstones are usually thin and

    tight, Figures 8 and 9. The Plio-Pleistocene orogeny

    resulted in the Palembang High re-orientation andtilting. Therefore, the migration pathways during the

     post Plio-Pleistocene could be substantially different

    and oil re-migration should be considered as one of

    the important geological risk components.

    EXPLORATION METHOD

    An integrated approach of geophysical and geological

    analyses is required to identify and examine the

    Telisa Sandstone geometry and potential hydrocarbon

    content in this complex. The work involves Extended

    Elastic Impedance (EEI), Lambda(λ )-Mu(µ)-Rho(ρ)(LMR) inversions and S-wave prediction based on

    other logs using generalized linear regression method.

    The EEI approach is based on Whitcombe et al (2002)

    who had modified the definition of Elastic Impedance

    (EI) beyond the range of physically meaningful angle

     by substituting tan χ  for sin2 θ. The primary variable

    now becomes χ  rather than θ, and it is allowed to vary

     between -900  and +900. This practically allows us to

    define a single function, which is proportional to a

    number of different elastic parameters, depending on

    the value of χ  used.

    In the Telisa Sandstone, the EEI (χ = -410) ≈ µρ, EEI

    (χ = 70) ≈ λρ, and EEI (χ = 50) ≈ ρ. The λ /µ parameter

    can then be obtained by dividing µρ  from λρ. λ , µ,

    and ρ  are Lamé’s parameters. µ which is related torock’s rigidity, gives information on lithology. µρ 

    can be used to distinguish between sandstones,

    calcareous sandstones, and shales. Calcareous

    sandstone has higher rigidity and incompressibility

    than sandstone, while sandstone has higher rigidity

  • 8/16/2019 sumatera basin.pdf

    7/20

     107

    than shale and coal so it has a higher value of µρ. On

    the other hand, λ   represents the rock’s

    incompressibility, which is sensitive to pore fluid

    type. Therefore, λρ  and λ /µ can be utilized to detect

    the presence of fluid. Sandstones containing gas are

    more compressive than wet sandstones so they have

    low incompressibility values. Sandstones containinggas are also less dense than sandstones containing

    water.

    Extended Elastic Impedance Method

    Connolly (1999) introduced Elastic Impedance (EI) as

    a generalization of Acoustic Impedance (AI) for non-normal incidence angle, enabling the benefits of the

    inversion approach to be applied for pre-stack/ AVO

    data.

    Reflection amplitude, as a function of angles based onthree-term Zoeppritz linearization’s (Aki and

    Richards, 1980), can be expressed as:

    θ θ θ  222 tansinsin)( C  B A R   ++=   (1)

    where θ   is the average of the incidence and

    transmission angles at a plane-reflecting interface.Connolly (1999) further showed that EI could be

    expressed as a simple function of Vp,Vs , and density

    (α,β, and ρ) :

    cba EI    ρ  β α θ    =)(   (2)

    where:

    a = (1 + sin2 θ ),

     b = -8K sin2 θ , (3)

    c = (1-4K sin2 θ ),

    and where  K is a constant, usually set to the average

    value of (β/α)2 over the log interval of interest.

    The EI function [equation (2)] was then modified(Whitcombe et al, 2002) by introducing reference

    constants α0, β0  and ρ0,, which remove the variabledimensionality of equation (2) and provide an EI

    function which returns normalized impedance values

    for all angles θ :

    ⎥⎥⎦

    ⎢⎢⎣

    ⎡⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ ⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ ⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ =

    cba

     EI 000

    00)( ρ 

     ρ 

     β 

     β 

    α 

    α  ρ α θ    (4)

    However, there are two difficulties in using the

    current EI definition. There is a requirement for |sin2θ |

    to exceed unity, and reflectivity values may exceed

    unity as sin2θ   increases; clearly, no impedance

    contrast can give rise to a reflectivity value greater

    than unity (unless negative impedance is allowed). In

     practice, this will mean that as |sin2θ | approaches and passes unity, the EI log, by its current definition, will

     become increasingly inaccurate. To compensate forthese difficulties, Whitcombe et al (2002) make two

    changes to the current definition of EI. First, by

    replacing sin2θ   with tan χ   such that the equation is

    defined between ± ∞  rather than the 0–1 limit

    imposed by sin2θ . The scaled version of reflectivity,

    which corresponds to a specific elastic parameter

    contrast, can then be defined as

     χ tan B A R   +=   (5)

    from which they derive

     χ 

     χ  χ 

    cos

    sincos  B A R

      +=   (6)

     Now introducing RS , or scaled reflectivity,

     χ cos R RS  =   (7)

    results in

     χ  χ  sincos  B A RS    +=   (8)

    The EI equivalent of equation (8) is then

    ⎥⎥⎦

    ⎢⎢⎣

    ⎡⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ ⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ ⎟⎟ ⎠

     ⎞⎜⎜⎝ 

    ⎛ =

    r q p

     EEI 000

    00)( ρ 

     ρ 

     β 

     β 

    α 

    α  ρ α  χ    (9)

    where:

     p = (cos χ  + sin χ ) 

    q =-8 K sin  χ   (10)

    r = (cos  χ - 4 K sin  χ ):

    Whitcomb et al (2002) called this Extended Elastic

    Impedance, or EEI.

  • 8/16/2019 sumatera basin.pdf

    8/20

     108

    Data preparation and Extended Elastic Impedance

    Inversion

    Data used for the test-line work to predict the

    sandstone distribution using the EEI technique,

    consists of 15 selected 2-D seismic lines and

     petrophysical analyses of 10 wells. Seven additionalwells have been utilized for validation of the test

    results. The seismic balancing work for amplitude and phase is carried out first, since the seismic lines are of

    various vintages.  The maximum angle of 230 is used

    to get the optimal results in using stacking data. The

    seismic lines are selected to cross several exploration

    wells and oil and gas fields: Kaji-Semoga, Langkap,west Iliran, Rumbi, Rimbabat, and Kerang. The Telisa

    Sandstone penetrated in these wells displays various

    wireline log responses caused by variations in

    mineralogy and hydrocarbon content.

    a. Cross-plots between well log properties

    Logs of P-wave velocity, S-wave velocity, density,

    and gamma ray are needed. Cross-plot of these log

     properties is required to know whether the properties

    are usable for distinguishing lithology and fluid

    contents. Using the predicted S-wave sonic, KS-01,

    KS-26, Langkap-1A, Langkap-4, and Kerang-10

    wells will have the required logs for performing

    cross-plot analysis. Cross-plots between density

    versus gamma ray and P-impedance versus gamma

    ray apparently cannot be used to distinguishsandstone from shale since both have almost similar

    density value. However, cross-plot between P-

    impedance and density shows that sandstone and

    shale plot at somewhat different linear trends. Cross-

     plot between λ /µ and density also shows a different

    cluster trend between sandstone and shale. It is

    observed that shale tends to cluster together with high

    water-saturated sandstones, while hydrocarbon-

     bearing sandstones tend to have low λ /µ values.

    Based on the above cross-plot analysis, wet or shale

    trend can then be used as a reference in calculating P-

    impedance and λ /µ anomalies.

    b. S-wave prediction

    To generate S-wave velocities for wells, relationships between multi log data at KS-28 well and the S-wave

    velocity derived from Castagna’s equation needs to be

    established. To estimate the S-wave velocity, various

    wireline logs such as the gamma ray, neutron

     porosity, and density logs, were used. The P-wave

    velocity log was not used to predict the S-wave

    velocity log because the P-wave velocity is sensitive

    to the changes in both pore fluids and rocks. The

    introduction of small amount of gas into the pore

    spaces of a rock can reduce the P-wave velocity. On

    the other hand, the S-wave velocity is sensitive only

    to the rocks and weakly dependent on pore fluidcontents (Mavko et al, 1988).

    c. Extended Elastic Impedance Inversion

    As mentioned above, µρ, λρ, and λ /µ can be

    approached by EEI with specific χ   value. Figure 10 

    illustrates the correlation between EEI for varyingangles (-900 to 900) with well log data at several wells

    involved in the study. It shows that the best

    correlation to predict lithology is to use µρ  with the

    angle of EEI at -410; to predict fluid, one should use a

    combination of λρ  and µρ  to form λ /µ. Figure 11 shows the location map of the selected 2-D seismic

    lines and wells with cross-plot between λ /µ and P-

    impedance anomalies in various regions, and Figure

    12 shows a seismic display across KS-01, KS-26, and

    KS-28 wells. Results of the EEI inversion are shown

    in Figure 13.

    Mu-rho can be used to distinguish between shale and

    Telisa Sandstone. A high value of mu-rho (greater

    than 6 Gpa * g/cc) will mostly be comprised of

    sandstone and calcareous sandstone while shale will

     be mostly having a low value (less than 6 Gpa * g/cc).After separating sandstone from shale, the remaining

    task is to separate good sandstone from the calcareous

    sandstone. The latter is done using density. The lower

    density value will be mostly comprised of good

    sandstone while the higher value of density is an

    indication of calcareous sandstone. The calcareous

    sandstone will mostly have a higher value of P-wave

    velocity than sandstone and shale. Cross-plots

     between P-impedance and density can also be used to

    exaggerate the separation between good sandstone

    and calcareous sandstone. In order to detect the

     presence of fluid, cross-plots between λ /µ and P-impedance anomalies are used to help in

    distinguishing between the two, sandstone and shale,

    as well as in distinguishing between hydrocarbon

     bearing sandstone and shale or wet sandstone. Figure14 is a map of λ /µ anomaly that shows distribution of

    the predicted sandstones. Good sandstones are

     predicted to exist in the area surrounding Langkap,

    Rimbabat, and Rumbi. The calcareous sandstones are

     present around Kaji-Semoga area while sandstones

  • 8/16/2019 sumatera basin.pdf

    9/20

     109

    that are rather shaly in nature, are predicted to cluster

    around Kerang area.

    Hydraulic Fracturing

    The Telisa Sandstone is present at shallow depths between 1700’ and 2500’. The sandstone generally

    has low permeability causing low production. Toimprove the production performance, the stimulation

    technique called “hydraulic fracturing” has been

    employed. This technique uses hydraulic power to

    create crack or opening at the reservoir, followed by

     pumping sand to fill the crack to avoid closing.

    Efforts to optimize the fracturing results have been

    made using six sigma (statistical approach) and

    analytical approaches. The goal is to focus on

    increasing oil gain from the fracturing job. The firststep is to identify all factors that could impact oil

    gain. The candidate selection criteria include area

    (field), resistivity, and hydrocarbon pore thickness

    (HPT). Fracturing design includes fracturing length,

    fracturing conductivity, propant size, and propant

    loads. Each of these factors is evaluated using

    statistical analysis.

    The second step is to evaluate data using a statistical

    approach: hypothesis test, such as t-test and F-test.

    The t-test is to compare the mean of the two data sets

    while the F-test is to compare the standard deviationof the two data sets. By using these hypothesis tests

    the impact of the factors to the fracturing results can

     be predicted. The evaluation continues for all of the

    factors and is combined with the analytical approach

    using a fracturing simulator to determine the

    candidate selection criteria and fracturing design.

    The third step is the execution plan and field trials in

    the Kaji-Semoga wells to confirm the work results.

    The TSO fracturing design was applied in the Kaji

    Field wells and the long hydraulic fracturing design

    was applied in the Semoga wells.

    The fourth step is monitoring work. Initially the oil

     production, after the fracturing job, from the selected

    Kaji-Semoga wells is high. There was significant oilgain improvement after the work. The mean oil gain

    after the work was 220 BOPD (35 m3/day) compared

    to the mean oil gain before the work of 168 BOPD

    (26.7 m3/day). Standard deviation also decreased from

    186 BOPD (26.9 m3/day) to 130 BOPD (20.7

    m3/day). The performance of the wells will have to be

    closely monitored.

    There are some challenges in optimizing fracturing

     job results such as sand flow back to the well bore,

     production drop after production for 3-5 months, and

    high water cut. Sand flow back to the well bore willnot only cause problems for the facilities such as pipe

    line and pumps, but will also result in productivityreduction. Both the causes of the problems and how

    to control them needs to be addressed. The

    application of resin-coated sand may be one suitable

    means of preventing this happening in the future. The

     production drop after initially good productionappears to happen in those wells that have extremely

    low permeability, as indicated by the low resistivity

    values. To develop the wells that have resistivity less

    than 5 ohm-m, will need further economic study will

     be required.

    CONCLUSIONS AND DISCUSSIONS

    1. The existing 2-D seismic lines of various vintages

    could not successfully define the reservoir

    geometry and distribution. Hence, 3-D seismic

    acquisition is recommended to better explore the

    hydrocarbon potential in the Telisa Sandstone

    stratigraphic play.

    2. The Telisa Sandstone comprises isolated shallow

    marine sandstone bodies encased in the Telisamarine shales. The origin remains uncertain, but

    an integrated interpretation of the regional

     parasequence chronostratigraphic correlation,

    conventional core and thin section description,

    and wireline log shape analysis suggests that the

    sequence was possibly deposited in the lowstand

    shoreface and transgressively incised shoreface

    environments.

    3. The lowstand shoreface sediments were truncated

     by higher erosion surface as the transgression

    continued resulting in depositional remnants. Thetransgressively incised shorefaces were deposited

    on the ravinement surface and/or amalgamated

    surface associated with the lowstand sequence

     boundary. Consequently, the sandstones of theTelisa Sandstone, internally in “sand-to-sand”

    contact, are genetically discrete.

    4. The lowstand shoreface remnant is thin with

    individual sandstone thickness up to about 50

  • 8/16/2019 sumatera basin.pdf

    10/20

     110

    feet, but it could extend laterally as much as 15

    kilometers. The overall interval of the Telisa

    Sandstone deposition and erosion during

    lowstand and transgression periods is only about

    200 feet suggesting that the shelf dip and

    morphology is likely to be very gentle. Small

    relative sea level change could have a direct andlarge impact on the overall sedimentation on the

    Palembang shelf.

    5. The EEI inversion work results have defined the

     presence of the reservoir sandstone and

    hydrocarbon. Lambda-per-Mu and P-impedance

    anomalies have been used to distinguishsandstone from shale as well as to predict

    distribution of the good sandstone which

     potentially have low water-saturation values.

    6. The hydraulic fracturing technique has beensuccessfully applied to flow oil and has

    significantly improved in oil gain from the thin,

    highly shaly, and tight reservoir sandstones of the

    Telisa Sandstone.

    ACKNOWLEDGEMENT

    The authors wish to thank the Management of P.T.

    Medco E&P Indonesia and BP Migas for their

     permission to publish this paper. The authors wish to

    thank Asril Kamal and Ukat Sukanta for their input,

    review, and discussion. Anang Ismail prepared thefigures and presentation slides.

    REFERENCES 

    Aki, K.I. and P.G. Richards, 1980. Quantitative

    seismology: theory and methods, v. 1, W.H. Freeman

    & Co.

    Burton, J. and R.G. Walker, 1999. Linear

    transgressive shoreface sandbodies controlled by

    fluctuations of relative sea level: LowerCretaceous Viking Formation in the Joffre-

    Mikwan-Fenn area, Alberta, Canada, SEPM Special

    Publication No. 64, Isolated Shallow Marine Sand

    Bodies: Sequence Stratigraphic Analysis and

    Sedimentologic Interpretation, p.255-272.

    Connolly, P., 1999. Elastic impedance, The Leading

    Edge, v. 18, n. 4, p. 438-452.

    George, G.T., 2000. Characterisation and high

    resolution sequence stratigraphy of storm-dominated

     braid delta and shoreface sequences from the Basal

    Grit Group (Namurian) of the South Wales Variscan

     peripheral foreland basin, Marine and Petroleum

    Geology, v. 17, p. 445-475.

    Goodway, B., T. Chen, and J. Downton, 1997.

    Improved AVO fluid detection and lithology

    discrimination using Lame petrophysical parameters;

    “Lambda-Rho”, “Mu-Rho”, and “Lambda/Mu fluid

    stack”, from P and S inversions, SEG Technical

    Program Expanded Abstracts, v.16, p.183-186.

    Hart, B.S. and A.G. Plint, 1993. Tectonic influence on

    deposition and erosion in a ramp setting: Upper

    Creataceous Cardium Formation, Alberta Foreland

    Basin, v. 77, n. 12, p.2092-2107.

    Kalan, T., R.J. Maxwell, and J.H. Calvert, 1984.

    Ramba and Tanjung Laban oil discoveries, Corridor

    Block, South Sumatra, Proceedings of the 13 th 

    Indonesian Petroleum Association Annual

    Convention, p. 365-384.

    Leckie, D.A. and R.G. Walker, 1982. Storm- and tide-

    dominated shorelines in Cretaceous Moosebar-Lower

    Gates Interval – Outcrop equivalents of deep basin

    gas trap in western Canada, AAPG Bulletin, v. 66,

    n. 2, p.138-157.

    Leggitt, S.M., R.G. Walker, and C.H. Eyles, 1990.

    Control of reservoir geometry and stratigraphic

    trapping by erosion surface E5 in the Pembina-Carrot

    Creek area, Upper Cretaceous Cardium Formation,

    Alberta, Canada, AAPG, v. 74, n. 8, p. 1165-1182.

    MacEachern, J.A., B.A. Zaitlin, and S.G. Pemberton,

    1998. High-resolution sequence stratigraphy of early

    transgressive deposits, Viking Formation, Joffre

    Field, Alberta, Canada, AAPG Bulletin, v. 82, n.5A,

     p.729-756.

    MacEachern, J.A., B.A. Zaitlin, and S.G. Pemberton, 

    1999. Coarse-grained, shoreline-attached, marginal

    marine parasequences of the Viking Formation, Joffre

    Field, Alberta Canada, SEPM Special Publication No.

    64, Isolated Shallow Marine Sand Bodies: Sequence

    Stratigraphic Analysis and Sedimentologic

    Interpretation, p. 273-296.

  • 8/16/2019 sumatera basin.pdf

    11/20

     111

    Martinsen, R.S., 2003a. Depositional remnants, part

    1: Common components of the stratigraphic record

    with important implications for hydrocarbon

    exploration and production, AAPG Bulletin, v. 87,

    n.12, p.1869-1882.

    Martinsen, R.S., 2003b. Depositional remnants, part2: Examples from the Western Interior Cretaceous

     basin of North America, AAPG Bulletin, v. 87, n. 12, p. 1883-1909. 

    Mavko, G., T. Mukerji, and J. Dvorkin, 1988. The

    rock physics handbook – tools for seismic analysis in

     porous media, Cambridge University Press.

    McBride, R.A., H.H. Roberts, T.F. Moslow, and R.

    Diecchio, 2002. Sedimentology and depositional

    history of a major shelf sand sheet in the northeast

    Gulf of Mexico: modern analog for ancient shallow-marine sandstones, AAPG Annual Meeting Abstract,

    March 10-13, 2002, Houston, Texas.

     Nummedal, D., 2002. Sequence stratigraphic

    significance of continental shelf sand ridges (Gulf of

    Mexico, East China Sea, North Sea), Abstract, 22nd

    Annual GCSSEPM Foundation Bob F. Perkins

    Research Conference, Sequence Stratigraphic Models

    for Exploration and Production, 8-11 December,

    2002, Houston, Texas.

    Pattison, S.A.J. and R.G. Walker, 1992. Depositionaland interpretation of long, narrow sandbodies

    underlain by a basinwide erosion surface: Cardium

    Formation, Cretaceous Western Interior Seaway,

    Alberta, Canada, Journal of Sedimentary Petrology,

    v. 62, n. 2, p. 292-309.

    Posamentier, H.W., 2002. Ancient shelf ridges – a

     potentially significant component of the transgressive

    systems tract: case study from offshore northwest

    Java, AAPG Bulletin, v.86, n. 1, p. 75-106.

    Posamentier, H.W. and C.J. Chamberlain, 1993.Sequence-stratigraphic analysis of Viking Formation

    lowstand beach deposits at Joarcam Field, Alberta,

    Canada, in  H.W. Posamentier, C.P. Summerhayes,

    B.U. Haq, and G.P. Allen (eds), Sequence

    stratigraphy and facies associations: International

    Association of Sedimentologists Special Publication

    18, p. 469-485.

    Snedden, J.W. and K.M. Bergman, 1999. Isolatedshallow marine sand bodies: deposits for all

    interpretations, SEPM Special Publication No. 64,

    Isolated Shallow Marine Sand Bodies: Sequence

    Stratigraphic Analysis and Sedimentologic

    Interpretation, p. 1-11.

    Snedden, J.W. and R.,W. Dalrymple, 1999. Modern

    shelf sand ridges: from historical perspective to a

    unified hydrodynamic and evolutionary model, SEPM

    Special Publication No. 64, Isolated Shallow Marine

    Sand Bodies: Sequence Stratigraphic Analysis and

    Sedimentologic Interpretation, p.13-28.

    Sutter, J.R. and H.E. Clifton, 1999. The Shannon

    sandstone and isolated linear sand bodies:

    interpretations and realizations, SEPM Special

    Publication No. 64, Isolated Shallow Marine Sand

    Bodies: Sequence Stratigraphic Analysis and

    Sedimentologic Interpretation, p. 321-356.

    Tesson, M., H.W. Posamentier, and B. Gensous,

    2000. Stratigraphic organization of Late Pleistocene

    deposits of the western part of the Golfe du LionShelf (Languedoc Shelf), Western Mediterranean Sea,

    using high-resolution seismic and core data, AAPG

    Bulletin, v. 84, n. 1, p. 119-150.

    Walker, R.G. and C.H. Eyles, 1988. Geometry and

    facies of stacked shallow-marine sandier upward

    sequences dissected by erosion surface, Cardium

    Formation, Willesden Green, Alberta, AAPG

    Bulletin, v. 72, n. 12, p. 1469-1494.

    Whitcombe, D.N., P.A. Connolly, R.L. Reagan, and

    T.C. Redshaw, 2002. Extended elastic impedance forfluid and lithology prediction, Geophysics, v.67, n.1,

     p. 63-67.

  • 8/16/2019 sumatera basin.pdf

    12/20

     112

     

       F   i  g  u  r  e   1

      -

       I  n   d  e  x

      m  a  p  o   f   t   h  e  s   t  u   d  y  a  r  e  a  a  p  p  r  o  x   i  m  a   t

      e   l  y  a   b  o  u   t   7   0   k  m    t  o   t   h  e  n  o  r   t   h  w  e  s   t

      o   f   P  a   l  e  m   b  a  n  g   C   i   t  y .   N  o   t  e   t   h  a   t   t   h  e

       K  a   j   i  -   S  e  m  o  g  a

       O   i   l   F   i  e   l   d  a  n   d  s  e  v  e  r  a   l  o   t   h  e  r  s  m  a   l   l  e  r  o   i   l  a  n   d  g  a  s   f   i  e   l   d  s   h  a  v  e   b  e  e  n   d   i  s  c  o  v  e  r  e   d   i

      n   t   h  e   P  a   l  e  m   b  a  n  g   H   i  g   h  r  e  g   i  o  n .

  • 8/16/2019 sumatera basin.pdf

    13/20

     113

     

    Figure 2 - Generalized stratigraphic column of the South Sumatra Basin. In the Palembang High region, the

    Telisa Sandstone developed immediately above the Baturaja Formation.

  • 8/16/2019 sumatera basin.pdf

    14/20

     114

     

       F   i  g  u  r  e   3

      -

       I  s  o  c   h  r  o  n

      m  a  p  o   f   t   h  e   T  e   l   i  s  a   S  a  n   d  s   t  o  n  e  s  e  q  u

      e  n  c  e  s   h  o  w   i  n  g   t  w  o  p  a   l  e  o  -   l  o  w  s   b  e   t  w

      e  e  n   t   h  e   K  a   j   i  -   S  e  m  o  g  a   H   i  g   h  a  n   d   I   l   i  r  a  n   H   i  g   h ,  a  n   d

       b  e   t  w  e  e  n

       I   l   i  r  a  n   H   i  g   h  a  n   d   S  u  n   d  a   L  a  n   d  m  a  s  s .   T   h  e  s  e   t  w  o  p  a   l  e  o  -   l  o  w  s  a  r  e   b  e   l   i  e  v  e

       d   t  o  o  c  c  u  r   d  u  e   t  o  s  y  n  -   d  e  p  o  s   i   t   i  o  n  a   l

      n  o  r  m  a   l   f  a  u   l   t  s

      r  e  s  u   l   t   i  n  g

       i  n   h  a   l   f  -  g  r  a   b  e  n   f  e  a   t  u  r  e  s .

  • 8/16/2019 sumatera basin.pdf

    15/20

     115

     

    Figure 4 - Typical Telisa Sandstone sequence in the Kaji-Semoga area in KS-138 well with thin sections of

    conventional core from (a) 2859.4 feet (middle facies lobe) showing dominant, angular to sub-

    rounded quartz grains of the blocky log motif section, and from (b) 2874.8 feet (lower facies lobe)

    showing partially coarsening upward pattern with well development of the green peloids and pore-

    filling ferroan calcite cement.

    Figure 5 - Part of the conventional cores cut in Kerang-1 showing strong bioturbation with erosional surface

     present in the Telisa Sandstone sequence.

  • 8/16/2019 sumatera basin.pdf

    16/20

     116

     

    Figure 6 - Southwest-northeast biostratigraphic controlled stratigraphic cross-section across the Kaji-Semoga,

    Langkap, and Kerang with a datum along the highest gamma ray values. Note that the

    transgressively incised shoreface sandstones may rest on the amalgamation surface of the

    ravinement surface and lowstand sequence boundary. Part of the lowstand shoreface sediments has

     been eroded resulting in lowstand depositional remnants. Line of cross-section is approximately 20

    km long, and wells are not proportionally spaced.

    Figure 7 - Geological model of the Telisa Sandstone deposition is apparently consistent to the preliminary

    interpretation of the regional high-resolution sequence stratigraphy. The isolated shallow marine

    sandstone bodies could be a mix of the lowstand shoreface remnants and transgressively incised

    shoreface sediments.

  • 8/16/2019 sumatera basin.pdf

    17/20

     117

     

    Figure 8 - A southwest-northeast interpreted seismic line across the Kaji-Semoga High region. The seismic

    line is flattened at the Upper Telisa Marker showing the possibility of the Kaji-Semoga High as a

    local sediment provenance. The Telisa Sandstone is in direct contact to the limestones of the

    Baturaja Formation and/or basement as hydrocarbon conduits.

    Figure 9 - West-east section of the interpreted regional 2-D seismic line across the Palembang High region.

    The structure is continuously and consistently shallowing towards the Sunda Landmass to the east.

    The hydrocarbons are trapped in the Telisa Sandstone in stratigraphic play.

  • 8/16/2019 sumatera basin.pdf

    18/20

     118

     

    Figure 10 - Correlation between EEI for varying angle (-900 to 900) with well log data at KS-26.

    Figure 11 - Location map of the selected 2-D seismic lines and wells with cross-plot between λ /µ (Lambda/Mu)

    and P-impedance anomalies in various regions.

  • 8/16/2019 sumatera basin.pdf

    19/20

     119

     

    Figure 12 - Traditional seismic display across KS-01, KS-26, and KS-28 wells.

    Figure 13 - EEI inversion display of µρ (Mu-Rho) across KS-01, KS-26, and KS-28 wells. 

  • 8/16/2019 sumatera basin.pdf

    20/20

     

    Figure 14 - EEI inversion map of λ /µ  (Lambda/Mu) anomaly at the top Telisa Sandstone (20 ms window)across Kaji, Semoga, Langkap, and Kerang Fields. The map shows distribution of the predicted

    sandstones.