长宁区块强封堵油基钻井液技术研究及应用

分析清楚长宁区块龙马溪组和五峰组井眼失稳的原因，提出强化井眼稳定的钻井液技术对策，对该区块水平井水平段的钻进至关重要。基于X射线衍射、扫描电子显微镜、页岩膨胀、滚动分散试验，揭示了复杂地层的井眼失稳机理，提出了“强化封堵微观孔隙、抑制滤液侵入和阻缓压力传递”协同的井眼稳定技术对策。采用砂床滤失仪、高温高压滤失模拟装置、微孔滤膜等试验装置，优选了以封堵剂为主的长宁区块油基钻井液处理剂，构建了适用于长宁区块的强封堵油基钻井液体系，其抗温135 ℃，抗盐10%，抗钙1%，抗劣土8%，400 μm宽裂缝的承压能力达5 MPa，0.22和0.45 μm孔径微孔滤膜的滤失量均为0，封堵效果突出，综合性能优于常规油基钻井液。该钻井液在长宁区块现场试应用10余口井，龙马溪组和五峰组水平段均未出现井眼失稳的问题；与同区块采用常规钻井液的已钻井相比，复杂地层的井径扩大率平均降低10.82%，建井周期平均缩短4.5 d。研究结果表明，强封堵油基钻井液技术解决了长宁区块水平井龙马溪组和五峰组水平段的井眼失稳问题，具有较好的推广应用价值。 

Technical Research and Application of Oil Base Drilling Fluid with Strong Plugging Property in Changning Block

It is crucial for drilling the horizontal sections of horizontal wells in Changing Block to uncover the reasons for borehole instability in Longmaxi and Wufeng fromations and put forward the countermeasures of drilling fluid technology to strengthen the borehole stability. Based on X-ray diffraction, scanning electron microscopy, shale swelling, and rolling dispersion tests, the mechanism for the borehole instability of complex strata was revealed and a coordinative borehole stability method was proposed, i.e., "strengthening plugging of micropores, inhibition of filtrate invasion, and retardation of pressure transfer". With the test devices such as sand-bed filtration testers, high-temperature and high-pressure filtration simulators, and microporous membranes, the treatment agent of oil base drilling fluid in Changning Block, which was dominated by plugging agents, was selected. And a drilling fluid system with strong plugging property, which was suitable for Changning Block, was developed. The system had a temperature resistance of 135 ℃, salt resistance of 10%, calcium resistance of 1%, poor-soil contamination resistance of 8%, bearing capacity of 5 MPa for 400 μm fractures, and filtration loss of 0 for both 0.22 μm and 0.45 μm microporous membranes. Its plugging effect was significant, and its comprehensive performance was better than that of ordinary drilling fluid. The drilling fluid was applied to more than 10 wells in Changning Block and borehole instability was not encountered in the horizontal sections of Longmaxi and Wufeng formations. In comparison with the drilled wells applied with the conventional drilling fluid technology in the same block, the hole diameter enlargement rate of complex formations was reduced by 10.82% on average, and the construction cycle was shortened by 4.5 days on average. The research results demonstrated that the oil base drilling fluid technology with strong plugging property can effectively solve the borehole instability problem in the horizontal sections of Longmaxi and Wufeng formations in Changning Block, and it is worthy of promotion and application.