临兴区块致密砂岩气储层损害机理及钻井液优化

致密砂岩气储层钻井过程中，钻井液入侵将造成严重的储层伤害难题。通过岩心分析技术、岩心流动实验等系统分析了临兴区块致密砂岩气储层主要损害机理，统计并分析了现场钻井液存在的技术难题，并优化出具有良好性能的致密砂岩气储层保护钻井液。研究结果表明，临兴区块致密砂岩气储层岩石具有中-粗砂状结构，胶结致密，孔喉细小，含敏感性黏土矿物，储层潜在严重的水锁伤害与中等偏强的水敏性及应力敏感性损害（临界压力为7.0 MPa），潜在中等偏弱的速敏性（临界流速为0.75 mL/min）、盐敏性（临界矿化度为7500 mg/L）、碱敏性（临界pH值为10.0）及土酸敏感性损害；临兴区块主要存在储层损害、钻井液漏失、井眼垮塌、摩阻扭矩大与井眼清洁等钻井液技术难题。优化出的钻井液封堵性能良好，滤液表面张力低（23.3 mN·m-1），能减少固相侵入，削弱水锁效应，提高岩石渗透率恢复值至91.3%，具有良好的储层保护性能。现场应用结果表明，该储层保护钻井液完全满足复杂井段或水平井段钻进的钻井液技术要求。 

Damage Mechanisms Determination for Tight Sands Gas Reservoir in Block Linxing and Drill-in Fluid Optimization for Protection of the Reservoir

Drilling fluid invasion during drilling in tight sands gas reservoirs causes serious formation damage problem. Using core analysis and core flow experiment technologies, main damage mechanisms were determined for the tight sands gas reservoir in Block Linxing. Technical difficulties in field drilling fluid operations were summarized and analyzed, and a drill-in fluid for the protection of the reservoir was formulated based on optimization. Laboratory study showed that the rocks in the tight sands gas reservoir in Linxing have medium-coarse sand structure, compact cementation, fine pore throat and sensitive clay minerals. Several kinds of formation damage are found in the reservoir rocks, such as serious water block damage, moderately strong water sensitivity and stress sensitivity damage (critical pressure is 7.0 MPa), moderately weak flow rate sensitivity (critical flow rate is 0.75 mL/min), salt sensitivity (critical salinity is 7,500 mg/L), sensitivity to alkalinity (critical pH value is 10.0) and sensitivity to mud acid. Technical difficulties found in Linxing include formation damage, mud losses, wellbore collapse, high torque and drag, and hole cleaning. The optimized drill-in fluid has good plugging capacity and low surface tension of filtrate (23.3 mN/m), and is thus able to minimize the invasion of particles and to weaken water block effect. The percent recovery of permeability of reservoir rocks was raised to 91.3% of the original value, demonstrating the reservoir protection capacity of the drill-in fluid. Field application of the drill-in fluid showed that the optimized drill-in fluid met the needs of drilling in complex formations or horizontal drilling.