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A laboratory acid treatment modelling in case of hydraulically fractured rocks from tight terrigenous reservoirs

UDK: 622.276.63
DOI: 10.24887/0028-2448-2018-10-84-87
Key words: improved oil recovery, tight shaly terrigenous reservoirs, mud acid treatment efficiency
Authors: A.V. Usoltsev (TNNC LLC, RF, Tyumen), Yu.V. Zemtsov (TNNC LLC, RF, Tyumen), R.S. Neklesa (TNNC LLC, RF, Tyumen)

In general acid treatment can be applied for skin factor reducing, permeability increase of oil well borehole zone and reservoir hydraulic connectivity enhancement. A composition of HCL and HF, or mud acid, is the most efficient and well-known solvent for that purposes in terrigenous reservoirs. However, the efficiency of this agent can vary significantly. The processes of secondary precipitation and gelling of acidizing reaction products in tight reservoirs make goals listed above harder to achieve. Also, there can be pore volume colmatation by solid particles produced by clay minerals swelling and dispergation due to reaction with acid composition. As a result, the permeability of reservoir rock and well efficiency can be reduced, as it can be seen in practice.

This paper introduces the results of mud acid treatment performed on core samples of West Siberian tight shaly terrigenous reservoirs. It is shown that applyingВ  the HCl + HF acid composition with HF concentration more than 3 % on core samples with permeability less than 0.01 mkm2 leads to reduced permeability up to 19,7 – 82,9 %. Wherein the core samples with lowest permeability and acid solutions of a higher concentration provide the most negative effects. The fractured rock acid treatment provides the same effect with permeability reducing up to 40 %. However, if the same experiment is performed on a fractured matrix stabilized with a proppant agent, then positive results can be achieved. Therefore, using fractured and stabilized core samples with permeability of 13.7·10-3 mkm2 and acid solution with 6 % HCl concentration and 1.5 % HF concentration in laboratory tests shows increased permeability up to 0.021 mkm2, i.e. 1.5 times higher. The conclusion of the article declares that using a proppant agent while formation fracturing provides the most efficiency of the following acid treatment.

References

1. Shpurov I.V., Oil: structure and trends of the resource base of Russia (In Russ.), Nedropol'zovanie XXI vek, 2015, no. 6, pp. 40–46.

2. Antonov Yu.F., Mordvinov V.A., Influence of pore sedimentation on filtration properties of rocks (In Russ.), Vestnik Permskogo gosudarstvennogo tekhnicheskogo universiteta. Geologiya. Neftegazovoe i gornoe delo, 2005, no. 6, pp. 64–67.

3. Shelepov V.V., Zemtsov Yu.V. et al., Issues of intensification of oil production in polymictic high clay reservoirs (In Russ.),В  Interval, 1999, no. 7, pp. 2–6.

4. Sergienko V.N., Zemtsov Yu.V., Issues of intensification of oil flow in Jurassic collectors (In Russ.), Interval, 2001, no. 6, pp. 6–7.

5. Sergienko V.N., Tekhnologii vozdeystviya na prizaboynuyu zonu plastov yurskikh otlozheniy Zapadnoy Sibiri (Technologies of impact on the bottomhole formation zone of the Jurassic sediments of Western Siberia), St.Petersburg: Nedra Publ., 2005, 207 p.

6. STO 11-29-2014. Porody gornye. Metodika izmereniy pronitsaemosti po zhidkosti metodom statsionarnoy fil'tratsii (Rock formation. Procedure of measuring the permeability of the fluid by the method of stationary filtration), Tyumen':В  Publ. of TNNC LLC, 2014, 17 p.

7. STO 11-13-2014. Porody gornye. Metodika izmereniy koeffitsienta vosstanovleniya pronitsaemosti plasta posle vozdeystviya tekhnologicheskoy zhidkost'yu (Rock formation. Methods of measuring the coefficient of reservoir permeability recovery after exposure to the process fluid), Tyumen':В  Publ. of TNNC LLC, 2014, 14 p.

In general acid treatment can be applied for skin factor reducing, permeability increase of oil well borehole zone and reservoir hydraulic connectivity enhancement. A composition of HCL and HF, or mud acid, is the most efficient and well-known solvent for that purposes in terrigenous reservoirs. However, the efficiency of this agent can vary significantly. The processes of secondary precipitation and gelling of acidizing reaction products in tight reservoirs make goals listed above harder to achieve. Also, there can be pore volume colmatation by solid particles produced by clay minerals swelling and dispergation due to reaction with acid composition. As a result, the permeability of reservoir rock and well efficiency can be reduced, as it can be seen in practice.

This paper introduces the results of mud acid treatment performed on core samples of West Siberian tight shaly terrigenous reservoirs. It is shown that applyingВ  the HCl + HF acid composition with HF concentration more than 3 % on core samples with permeability less than 0.01 mkm2 leads to reduced permeability up to 19,7 – 82,9 %. Wherein the core samples with lowest permeability and acid solutions of a higher concentration provide the most negative effects. The fractured rock acid treatment provides the same effect with permeability reducing up to 40 %. However, if the same experiment is performed on a fractured matrix stabilized with a proppant agent, then positive results can be achieved. Therefore, using fractured and stabilized core samples with permeability of 13.7·10-3 mkm2 and acid solution with 6 % HCl concentration and 1.5 % HF concentration in laboratory tests shows increased permeability up to 0.021 mkm2, i.e. 1.5 times higher. The conclusion of the article declares that using a proppant agent while formation fracturing provides the most efficiency of the following acid treatment.

References

1. Shpurov I.V., Oil: structure and trends of the resource base of Russia (In Russ.), Nedropol'zovanie XXI vek, 2015, no. 6, pp. 40–46.

2. Antonov Yu.F., Mordvinov V.A., Influence of pore sedimentation on filtration properties of rocks (In Russ.), Vestnik Permskogo gosudarstvennogo tekhnicheskogo universiteta. Geologiya. Neftegazovoe i gornoe delo, 2005, no. 6, pp. 64–67.

3. Shelepov V.V., Zemtsov Yu.V. et al., Issues of intensification of oil production in polymictic high clay reservoirs (In Russ.),В  Interval, 1999, no. 7, pp. 2–6.

4. Sergienko V.N., Zemtsov Yu.V., Issues of intensification of oil flow in Jurassic collectors (In Russ.), Interval, 2001, no. 6, pp. 6–7.

5. Sergienko V.N., Tekhnologii vozdeystviya na prizaboynuyu zonu plastov yurskikh otlozheniy Zapadnoy Sibiri (Technologies of impact on the bottomhole formation zone of the Jurassic sediments of Western Siberia), St.Petersburg: Nedra Publ., 2005, 207 p.

6. STO 11-29-2014. Porody gornye. Metodika izmereniy pronitsaemosti po zhidkosti metodom statsionarnoy fil'tratsii (Rock formation. Procedure of measuring the permeability of the fluid by the method of stationary filtration), Tyumen':В  Publ. of TNNC LLC, 2014, 17 p.

7. STO 11-13-2014. Porody gornye. Metodika izmereniy koeffitsienta vosstanovleniya pronitsaemosti plasta posle vozdeystviya tekhnologicheskoy zhidkost'yu (Rock formation. Methods of measuring the coefficient of reservoir permeability recovery after exposure to the process fluid), Tyumen':В  Publ. of TNNC LLC, 2014, 14 p.


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