An Experimental Method Applicable to the Prediction of Borehole Stability in Brittle Rock Gas Drilling
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: 2016-02-10
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 described below in conjunction with accompanying drawing:
[0035] The first step is to use the cores obtained from adjacent drilled wells to make standard cylindrical core specimens, and carry out more than 2 groups of quasi-triaxial confining pressure experiments under simulated downhole temperature conditions and different confining pressures on the rock rigidity testing machine;
[0036] The second step is to draw the corresponding rock stress-strain curve, such as figure 1 , to determine whether the rock is a brittle material, and obtain the maximum principal stress (σ a1 , σ b1 ,…) and minimum principal stress (σ a3 , σ b3 ,...);
[0037] The third step is to make the Mohr circle and its envelope of the rock, such as figure 2 , and then obtain the maximum failure compressive stress σ when the rock reaches the fracture limit c1 :
[0038] σ c 1 ...
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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 well wall stability of brittle rock gas drilling, and mainly relates to the fields of oil and 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 it has many advantages that drilling fluid drilling does not have. Using gas as the circulating medium, on the one hand, can greatly increase the drilling speed of the drilling machine and the drilling footage of a single drill bit; on the other hand, the gas used as the circulating medium has a low density, and the pressure on the wellbore is relatively low, which can effectively solve the problem of long open holes. Drilling fluid lost circulation and other complex problems in low-pressure fractured formations; at the same time, it has obvious technical advantages in preventing differential pressure stic...
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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