Gelling Agent

SPE 117366 Hydrochloric Acid Fracturing Combined with Water Shut-Off L.A.Magadova, M.A.Silin, V.B.Gubanov, V.N.Marinenko, V.R.Magadov (Russian State University of Oil and Gas named after I.M. Gubkin, N.A.Demianenko (BelNIPIneft, RUE Production Association Belorusneft) Copyright 2008, Society of Petroleum Engineers This paper was prepared for presentation at the 2008 SPE Russian Oil & Gas Technical Conference and Exhibition held in Moscow, Russia, 2830 October 2008. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Institute of oilfield chemistry under Russian State University of oil and gas named after I.M. Gubkin in cooperation with BelNIPIneft, RUE Production Association Belorusneft have developed the technology of formation hydrochloric acid hydraulic fracturing combined with water shut-off in producing wells, exposing carbonate reservoirs. It is known that during interaction of hydrochloric acid solutions and oil, containing big quantity of tars and asphaltenes sludging and formation of emulsions colmataging porous space of reservoir take place. In our work we have used the ability of generating such compounds when hydrochloric acid contacts hydrocarbon gel, composed using gelling complex Khimeco-H based on ferric salts of organic orthophosphoric ethers and stock (commercial) oil. Hydrocarbon gels based on ferric salts of organic orthophosphoric ethers are obtained by dissoluting in hydrocarbon fluids gelling agent (mixture of alkylphosphoric ethers, mainly diakylphosphoric ethers) and activator based on ferrous compounds. As a result of interaction between gelling agent and activator we ontain ferric salts of organic orthophosphoric ethers which in their turn create associated complexes of molecular weight in hydrocarbons. Associated complexes explain formation of hydrocarbon gel used in hydraulic fracturing. Below you see the mechanism of hydrocarbon gel formation: 1. Gelling agent +activator = ferric salts of organic orthophosphoric ethers: O || [R1O - P - O]b(OH)a , where: a= 0-2; | b= 1-3; R2O a+b=3; where R1, R2 different hydrocarbon radicals, in the capacity of one of them could be hydrogen; ferrum atom. 2. Formation of associated complex while dissoluting the salts obtained (figure 1):

2 SPE 117366

Fig.1 Formation of associated complex while dissoluting the salts of organic orthophosphoric ethers

As a result of interaction of hydrocarbon gel and hydrochloric acid and generation of controlled quantity of asphaltene and tar sediments/sludges we form the layer, having selective shutting-off impact on watersaturated interlayers. For checking planned result we carried out filtration experiments on high-pressure and temperature plant HP-CFS in the formation process simulation laboratory of the Institute of oilfield chemistry under Russian State University of oil and gas named after I.M. Gubkin. Schematic diagram of experimental plant HP-CFS is shown on figure 2. Plant HP-CFS makes possible carrying out filtrarion experiments on sand packed tubes of porous mediums and core samples under temperatures up to 150C and pressure up to 20,0 MPa. If necessary back pressure system, which provides maximum level of pressure 7,0 MPa can be used. While working with core samples squeezing pressure can reach 50,0 MPa.

Main functional parts of the plant are thermostatically controlled filling formation model and core holder for experimenting with core samples. Thereby depending on type of study its possible to use core holder for composite cores 30 sm long (study of hydrodynamic parameters of porous medium), or core holder for one core sample (study of compositions for acid treatment, drilling muds, kill fluids).

Supply of operating fluids into porous medium is performed through press tubes with separating pistons by fluid presses ISCO. From fluid presses ISCO oil is supplied into under piston volume of press tubes. Thereby its possible to perform separate-simultaneous supply of oil into each of press tubes, or just in one press tube with planned supply rate.

Filling the press tubes with operating fluids is carried out under vacuum after the separating piston is in its lowermost position by gas pressure from the tank.

For injection of high-viscosity compositions, polymer or disperse systems into formation model high pressure vessel is used. From the vessel reagent is supplied under gas pressure from the tank or under immissible with reagent fluid from the press tube. During filtration process pressure drops are being controlled by Gould differential manometer. Fluid filtration can be performed under fixed flow rates up to 600 sm3/h.

Thermostating of filling model and preliminary heating of input line are performed by heat tape winded around filling model body and input line. Heat tape is fed from the net 200V

SPE 117366 3

through autotransformer. The rate of temperature rise is provided by voltage control, maintenance and control of temperature is provided by temperature sensor-controller -1, connected to thermocouple, located on the model body. Heating of the core sample inside the core holder to the temperature of the experiment is provided by liquid thermostat. During carried out filtration experiments we used hydrocarbon gel based on stock oil (20 oil = 825 kg/m3), composition 1, also 12% and 24% inhibited hydrochloric acid with addition of 4% of volume of multifunctional surface-active substance Neftenol (mark NK-FD), formation water model of calcium chloride type, carbon oil and light gas oil. Neftenol (mark NK-FD) is multifunctional surface-active substance based on multicomponent mixture of anion and cation surface-active substances of different chemical structure with modified polymer additives hydrochloric acid thickening agent, which is used as an additive to hydrochloric acid while formation acid hydraulic fracturing. Description of the experiments is given below (figures 3-4).

4 SPE 117366

Figure 2.

SPE 117366 5

Figure 2. Schematic diagram of experimental plant HP-CFS 1,2 press tubes with separating pistons for reagent supply 3 fluid thermostate 4 formation model 5 back pressure system 6 heating element 7,8,9 high pressure press (IS) 10, 19 vessels with oil for filling presses 11,12 gas tanks 13 core sampler 14 core holder 15 rubber collar 16 core sample 17 press for generation of squeezing pressure

6 SPE 117366

Experiment 1 Objective: Estimation of acid treatment impact on gel cementing properties Sample: filling waters aturated model filling silica sand fraction diameter 3,09 sm cross-section area 7,50 sm2 viscosity of formation water under temperature 20 1,301 MPas Initial model parameters: model length 62,4 sm initial water permeability 18,11 mkm2 porous volume 163 sm3 porosity 34,8 % Reagents under study: 1) gelling complex Khimeco-H-based hydrocarbon gel, composed on base of stock oil (20 oil = 825 kg/m3) Volume of reagents, l/m3: Gelling agent Khimeco-H 16,0 activator Khimeco-H18,0; gel viscosity under temperature 20 = 68,83 MP.s under shear rate 656 s-1; 2) Carbon oil, viscosity under temperature 20 = 1,16 MP.s 3) Inhibited 12% hydrochloric acid with 4% of volume of multifunctional surface-active substance Neftenol (mark NK-FD), viscosity under temperature 20 = 3,6 MP.s; 4) Formation water model, density 20 = 1,096 kg/m3, mineralization- 140 g/l, viscosity under temperature 20 =1,301 MP.s. Experimental stages: 1. Filtration through formation water model under room temperature. Determination of initial permeability. 2. Gel injection under room temperature and different filtration rates. 3. Injection of 0,3 porous volume of 12% solution of iInhibited hydrochloric acid with addition of 4% of Neftenol (mark NK-FD) volume. 4. Injection of formation water under different filtration rates. 5. Conditioning under room temperature for 15 hours with further filtration of formation water and determination of resistance factor R. 6. Injection in reverse direction of carbon oil to wash the model off asphalt-tarry paraffin depositions and determination of resistance factor Rres. 7. Model conditioning for 2 days with further filtration of carbon oil and determination of final resistance factor Rres.

SPE 117366 7

Experiment 2

Objective: Estimation of acid treatment impact on gel cementing properties Sample: filling water saturated model filling silica sand fraction diameter 3,09 sm cross-section area 7,50 sm2 viscosity of formation water under temperature 20 1,301 MPas Initial model parameters: model length 63,11 sm initial water permeability 15,73 mkm2 porous volume 161,1 sm3 porosity 34,03 % Reagents under study: 1) gelling complex Khimeco-H-based hydrocarbon gel, composed on base of stock oil (20 oil = 825 kg/m3) Volume of reagents, l/m3: Gelling agent Khimeco-H 16,0 activator Khimeco-H18,0; gel viscosity under temperature 20 = 68,83 MP.s under shear rate 656 s-1; 2) Carbon oil, viscosity under temperature 20 = 1,16 MP.s 3) Inhibited 12% hydrochloric acid with 4% of volume of multifunctional surface-active substance Neftenol (mark NK-FD), viscosity under temperature 20 = 3,6 MP.s; 4) Formation water model, density 20 = 1,096 kg/m3, mineralization- 140 g/l, viscosity under temperature 20 =1,301 MP.s. : 1. Filtration through formation water model under room temperature. Determination of initial permeability. 2. Gel injection under room temperature and different filtration rates. 3. Injection of 0,3 porous volume of 12% solution of iInhibited hydrochloric acid with addition of 4% of Neftenol (mark NK-FD) volume. 4. Injection of formation water under different filtration rates. 5. Conditioning under room temperature 15 hours with further filtration of formation water and determination of resistance factor R. 6. Injection in reverse direction of carbon oil to wash the model off asphalt-tarry paraffin depositions and determination of resistance factor Rres.

8 SPE 117366

Studies showed, that while injecting gel decrease of permeability of porous medium sample due to high viscosity of gel takes place, but even higher decrease of permeability takes place during further acid injection due to sludging of asphalt-tarry paraffin depositions, whilst the highest decrease is reached by using higher concentration of acid. So, while injecting 12% acid residual resistance factor made up 17,63; and while injecting 24% acid residual resistance factor made up 93,88. Necessary to mention that during first contact with acid resistance factor grows much higher. Decrease of permeability due to sludging of asphalt-tarry paraffin depositions takes place, and in case acid volume increases permeability increases, which is explained possibly by the impact of surface-active substances in acid formulation while formation water injection has practically no impact on resistance factor (see experiment 1, fig.3). Carbon oil injection in reverse direction with further conditioning significantly decreases resistance factor to 5,74 and 9,39 for 12% and 24% acid respectively, and during light gasoil injection-to 2,2 (experiment 2 fig.4). For purity of experiment filtration studies were carried out using porous medium, simulating the conditions of terrigenous reservoir for eliminating negative influence of carbonate reservoir and hydrochloric acid interaction. The idea of using hydrocarbon gel for hydrochloric acid fracturing with water shutt-off is in formation of hydrocarbon-dissoluble sludges of asphaltenes and tars during interaction of hydrocarbon gel and hydrochloric acid in the process of by-turn injection of hydrocarbon gel pill and part of 12-24% hydrochloric acid, treated with 40 l/m3 of multifunctional surface-active substance Neftenol K (mark NK-FD). This lets on one hand to create a fracture by formation hydraulic fracturing and on the other hand selectively shut it off. Though, acid treated with Neftenol K (mark NK-FD) in contact with pure oil doesnt sludge which is proved by carried tests, shown in the table 1.

So, we purposefully shut-off big fractures where hydrocarbon gel comes to. Thereby hydrocarbon sludges are dissoluted while diluting with oil, which shows selective water shut-off.

SPE 117366 9

0,01

0,1

1

10

100

0 5 10 15 20 25 30 35 40

Relative cumulative injection volume,Vinjec/Vpor

Perm

eabi

lity,

mkm

2

Experiment 1 Experiment temperature 20 . Initial water permeability - 18,11 mkm2

Form

. w

ater

in

ject

ion

Gel injectionForm. water

injection Carbon oil injection in reverse direction

Acid injection

FlR

=600

sm3 /h

FlR=300sm3/h FlR=200sm3/h

FlR=80sm3/h

FlR

=600

sm3 /h

FlR

=400

sm3 /h

FlR=200sm3/h

FlR=600sm3/h

FlR=600sm3/h

FlR=200sm3/h

Conditioning2 days

Conditioning 15 hours

Rres =5,74

Rres =1,00

Rres=17,63

Fig. 3 Change in permeability of water saturated model after injection of gel based on gelling complex "Khimeco -" and stock oil, and 12 % inhibited hydrochloric acid with addition

of Neftenol (mark NK -FD, 4% of volume ), formation water and carbon oil

0,0

0,1

1,0

10,0

100,0

0 2 4 6 8 10 12 14 16

Relative cumulative injection volume, Vinjec/Vpor

Perm

eabi

lity,

mkm

2

Experiment 2 Experiment temperature 20 . Initial water permeability - 15,73 mkm2

Fig. 4 Change in permeability of water saturated model after injection of gel based on gelling complex "Khimeco- " and stock oil, and 24% inhibited hydrochloric acid

with addition of Neftenol K (mark NK-FD, 4% of volume ), formation water, carbon oil and light gasoil

FlR=600sm3/h

FlR=400sm3/h

FlR=300 sm3/h

FlR=200sm3/h

FlR=80sm3/h

FlR=200sm3/h

Formation water injection

Gel injectionCarbon oil injection in

reverse direction

Rres =9,39

Rres =7,11

Acid injection

Rres =93,88

Conditioning 15 hours

Rres =2,22

FlR=200sm3/h

Light gasoil injection

10 SPE 117366

Table 1

Results of studies of interaction of acid compositions with stock oil (20= 825 kg/m3) and formation water

Studied fluid Acid composition , Sludging of

asphalt-tarry paraffin

depositions 1 2 3 4 5

1. Stock oil 20= 825 kg/m3

HCl 24% 50 yes


HCl 12% 50 yes


HCl 12% +Neftenol K (NK-FD)

50 no


HCl 24% + Neftenol K (NK-FD)

50 no


HCl 12% 90 yes


HCl 24% 90 much



90 no



90 no

9. Stock oil 20= 825 kg/m3+ formation water

HCl 12% 50 no


HCl 24% 50 much



50 no



50 no

13. Stock oil 20= 825 kg/m3 + formation water

HCl 12% 90 no


HCl 24% 90 yes

SPE 117366 11

Table 1 (continuation) 1 2 3 4 5



90 no

16. Stock oil 20= 825 kg/m3+formation water


90 no

Application of developed technology of hydrochloric acid fracturing with water shut-off in greatly watered well of Berezinskoye oil field let increase fluid inflow and, at the same time, decrease well water cut from 88,4 to 51,8%. The results are given in table 2.

In the process of working we have created a technology of mixing hydrocarbon gel based on gelling complex Khimeco H and stock oil, and surface-active substance-acid solution composed of inhibited hydrochloric acid solution and Neftenol K (NK-FD) and also technology of their injection into formation during hydrochloric acid fracturing with water shut-off by the set of equipment of Production Assiciation Belorusneft.

12 [Paper Number]

Table 2

Efficiency of hydrochloric acid fracturing with water shut-off as of 01.06.2008

Well number, oil

field

Ending date of treatm

ent

Working parameters before hydrochloric

acid fracturing

Working parameters after hydrochloric acid

fracturing Work efficiency

Note Qfl, t/d

Qoil, t/d

Watercut, %

Qfl, t/d

Qoil, t/d

Watercut, %

Production rate

increase, t/d

Incremental

production, t

1 3, Berezinskoye

31.07.2007 3,27 0,38 88,4 5,56 2,4 51,8 1,99 601

Effect continues

2 56, Marmovichskoye

07.03.2008 4,45 3,81 14,3 6,65 6,29 4,9 2,48 196

Effect continues

In total we have mixed and injected 30 m3 of hydrocarbon gel based on stock oil with density 810 kg/m3, effective viscosity of gel under 100 rotations/minute was within 200-300 MPas, and 50 m3 of 18% hydrochloric acid, containing 4% of Neftenol K (NK-FD) volume. Injection was performed in stages as follows: pill of hydrocarbon gel-15 m3, pill of hydrochloric acid-30 m3, again pill of hydrocarbon gel-15 m3, again pill of hydrochloric acid-20 m3; flushing was performed by oil-based water-oil emulsion with density 843 kg/m3 and fresh water in proportion 1:1 using emulsifying agent Neftenol NZ-1% of volume, effective viscosity of emulsion under 100 rotations/minute was within 60 80 MPas. Applying this technology in a well of Marmovichskoye oilfield with lower water cut (14,3%) the effect of water cut decrease (4,9%) was also reached.

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