Test method for predicting well wall stability of gas drilling in brittle rock
A technology of stability prediction and gas drilling, which is applied in the direction of wellbore/well components, earthwork drilling and production, etc., and can solve problems such as complex calculation process
Active Publication Date: 2014-01-15
CHINA PETROLEUM & CHEM CORP +1
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Therefore, the wellbore stability prediction method for gas drilling proposed in this patent is basically suitable for formations with post-peak softening characteristics, but it has certain limitations for brittle rocks such as igneous rocks, carbonate rocks, metamorphic rocks, and tight sandstones. , and the calculation process of this method is more complicated
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[0034] The present invention will be further explained below in conjunction with the drawings:
[0035] In the first step, use the cores obtained from adjacent drilled wells to make standard cylindrical core specimens, and carry out more than 2 sets of quasi-triaxial confining pressure experiments under different confining pressures under simulated downhole temperature conditions on the rock rigidity testing machine;
[0036] The second step is to draw the corresponding rock stress-strain curve, such as figure 1 As shown, determine whether the rock is a brittle material, and obtain the maximum principal stress (σ) that the rock can withstand under different confining pressures a1 , Σ b1 ,...) and the minimum principal stress (σ a3 , Σ b3 ,...);
[0037] The third step is to make the Moore circle and its envelope of the rock, such as figure 2 As shown, the maximum failure compressive stress σ when the rock reaches the fracture limit is obtained c1 :
[0038] σ c 1 = σ ...
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The invention provides a test method for predicting the well wall stability of gas drilling in brittle rock and mainly relates to the industrial fields of oil and gas drilling, geological prospecting, mine drilling and the like. The method comprises the following steps that a rock core is obtained from an adjacent drilled well, a standard cylindrical rock core test piece is made of the rock core, and a quasi-triaxial confining pressure test is conducted, wherein the down-hole temperature condition and different confining pressure are simulated; a corresponding stress-strain curve of the rock is drawn and whether the rock is a brittle material or not is judged; the Mohr circle of the rock and the envelope line of the Mohr circle are drawn so that the largest failure pressure stress sigma c1 when the rock reaches the break limit can be obtained; the largest primary stress sigma 1 borne by a well in a researched stratum is compared with the largest failure pressure stress sigma c1 of the rock and whether the sigma 1 is smaller than the sigma c1 is judged; if the sigma 1 is smaller than the sigma c1, the result that the well wall can be kept stable is obtained; if the sigma 1 is larger than the sigma c1, the result that the well wall is unstable is obtained; if the sigma 1 is equal to the sigma c1, the result that in the process of gas drilling, the well wall is in the state of critical instability is obtained. According to the test method, the factors such as the temperature of the researched stratum, the overburden pressure and the ground stress are taken into account, and calculation is simple, accurate and reliable.
Description
Technical field [0001] The invention relates to an experimental method suitable for predicting the stability of the borehole wall of brittle rock gas drilling, and mainly relates to the fields of petroleum and natural gas drilling, geological exploration, mine drilling and the like. Background technique [0002] Gas drilling is currently one of the fastest and most economical drilling methods, and has many advantages that drilling fluid drilling does not have. Using gas as a circulating medium can greatly increase the drilling speed of drilling machinery and the drilling footage of a single bit; on the other hand, the gas as a circulating medium has low density and relatively low pressure on the wellbore, which can effectively solve long open holes. Complex problems such as lost circulation of drilling fluids in low-pressure fractured formations; meanwhile, it has obvious technical advantages in preventing pressure sticking, discovering and protecting low-pressure producing zones...
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IPC IPC(8): E21B49/00
Inventor 王宗钢韩来聚孙铭新冯光通刘新华唐洪林赵洪山
Owner CHINA PETROLEUM & CHEM CORP