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Method for stabilizing shale formation by adjusting activity of drilling fluid

A drilling fluid and mud shale technology, which is used in earth-moving drilling, wellbore/well components, etc., can solve the problems of lack of quantitative basis for the addition of salt substances, failure to achieve activity balance, waste and other problems. The effect of large-scale promotion and application, stabilization of shale formation, and avoidance of material waste

Active Publication Date: 2020-02-04
中石化石油工程技术服务有限公司 +2
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AI Technical Summary

Problems solved by technology

The main application of activity adjustment technology in water-based drilling fluids is the application of inorganic salts and organic salt systems, but the application of inorganic salts and organic salt systems is more concerned with the use of ion exchange to diffuse the electric double layer by compressing clay. To achieve the purpose of inhibiting the hydration and dispersion of clay, the salts did not play the role of activity balance; and the addition of salts in this type of drilling fluid system is usually based on past experience or consideration of the conventional performance of the drilling fluid. Calculation and design are carried out according to the activity of the formation. Adding too little salt will fail to achieve the purpose of activity balance, and adding too much will cause waste. There is no quantitative basis for the addition of salt, which is not conducive to the formation of standardized specifications. Promote application

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0017] At a well depth of 3000m, the formation temperature is 100°C, the effective pressure difference is 24MPa, the gas constant is 8.314, and the molar volume of water is 1.8×10 -5 m 3 mol -1 . Formulate the drilling fluid formula for stable formation activity as follows:

[0018] (1) Determine the activity of the drilling fluid. According to the calculation formula of formation water activity, The formation water activity is obtained to be 0.9275.

[0019] (2) Because the core cannot be obtained, according to statistics, the tensile strength of shale is the smallest, usually 2-10MPa, and the minimum value of 2MPa is taken as the minimum strength of rock.

[0020] (3) According to the relationship that the osmotic pressure is greater than the minimum strength of the rock, the osmotic pressure is equal to 2MPa, and the osmotic pressure calculation formula ΔP = αRT / V is used w ln(a m / a s ), taking the semipermeable membrane efficiency as 1, the drilling fluid activit...

Embodiment 2

[0023] The core of a well at a depth of 4000m was obtained, the formation temperature was 125°C, the formation pressure was 32MPa, and the water saturation was 1.68%. Formulate the drilling fluid formula for stable formation activity as follows:

[0024] (1) Determine the activity of the drilling fluid. Under simulated formation conditions, the formation activity measured by a high-performance adjustable laser water activity meter is 0.8563.

[0025] (2) Take the cores of the same formation in adjacent wells, and measure the tensile strength as 2.5MPa, the shear strength as 6MPa, and the compressive strength as 43MPa, and take the minimum value of 2.5MPa as the minimum rock strength.

[0026] (3) According to the relationship that the osmotic pressure is greater than the minimum strength of the rock, the osmotic pressure is equal to 2.5MPa, and the calculation formula of osmotic pressure is ΔP = αRT / V w ln(a m / a s ), taking the semipermeable membrane efficiency as 1, the ...

Embodiment 3

[0029] At a well depth of 3500m, the formation temperature is 110°C, the effective pressure difference is 28MPa, the gas constant is 8.314, and the molar volume of water is 1.8×10 -5 m 3 mol -1 . Formulate the drilling fluid formula for stable formation activity as follows:

[0030] (1) Determine the activity of the drilling fluid. According to the calculation formula of formation water activity, The formation water activity is obtained to be 0.8967.

[0031] (2) According to the rock strength test experiment in the adjacent well, the minimum strength of the rock is 3.2MPa in tensile strength, and the minimum value of 3.2MPa is taken as the minimum strength of the rock.

[0032] (3) According to the relationship that the osmotic pressure is greater than the minimum strength of the rock, the osmotic pressure is equal to 3.2MPa, and the osmotic pressure calculation formula ΔP = αRT / V is used w ln(a m / a s ), taking the semipermeable membrane efficiency as 1, the drillin...

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Abstract

The invention relates to a method for stabilizing shale formation by adjusting the activity of drilling fluid. The method comprises the steps that (1) the water activity of a formation is determined;(2) the minimum strength of rock is determined; (3) the drilling fluid activity capable of balancing the activity of the formation is calculated according to the relation that osmotic pressure is larger than the minimum strength of the rock and by using the osmotic pressure calculation formula that deltaP is equal to alphaRT / Vwln(am / as); and (4), according to the calculated activity value of the drilling fluid, the addition amount of an activity regulator in the drilling fluid is determined. According to the method, the activity of the drilling fluid required to stabilize the shale formation can be accurately determined through quantitative calculation so that the addition amount of an activity regulator type treatment agent can be accurately controlled, the aims of effectively balancing the activity of the formation and stabilizing the shale formation can be achieved, and the problems of material waste, increased cost, unstable drilling fluid performance and the like caused by excessive addition can be avoided. Meanwhile, establishment of a quantitative program is beneficial to realizing standardization and modularization of operation, and large-area application and popularizationare facilitated.

Description

technical field [0001] The invention relates to a method for stabilizing mud shale formations during drilling, in particular to a method for stabilizing mud shale by reducing the activity of drilling fluid in the drilling process so that the activity of drilling fluid and formation activity are moderately balanced stratum method. Background technique [0002] As early as 1911, Donnan, a British physical chemist, proposed the Donnan equilibrium theory of drilling fluid activity, and then many scholars carried out research on the relationship between drilling fluid activity and shale hydration. Studies have shown that mud shale subjected to strong compaction or mud shale with low porosity can act as a semi-permeable membrane by itself. Therefore, reducing the activity of water in the drilling fluid can reduce the tendency of water to diffuse, infiltrate, and react with formation minerals near the wellbore wall in the shale formation, which is conducive to stabilizing the well...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): E21B49/00
CPCE21B49/00
Inventor 张敬辉李公让于雷乔军刘宝锋李海斌郑成胜刘振东吴雄军张守文李波季一冰
Owner 中石化石油工程技术服务有限公司
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