致密砂岩气藏损害机理及低损害钻井液优化

针对塔里木盆地B区块致密砂岩气藏储层孔喉细小、渗透性差、束缚水饱和度高、非均质性严重、微裂缝发育、极易受到损害且损害难以解除的难题，模拟地层条件，开展了高温敏感性与水锁损害测试，分析了储层固相损害，系统揭示了致密砂岩气藏损害机理:应力敏感损害、水锁损害、微裂缝固相损害是该储层的主要损害类型。在该区块使用的磺化防塌、钾聚磺钻井液基础上，优选出暂堵剂及可有效降低表面张力的表面活性剂，运用理想充填技术与表面活性剂两者相结合，优化设计“协同增效”型保护致密砂岩气藏的低损害钻井液。通过配伍性测试、动态污染实验对优化钻井液的储层保护性能进行评价发现，优化钻井液与研究区块地层水配伍，岩心渗透率恢复值在85%以上，储层保护效果明显。优化钻井液在B区块B2井巴什基奇克组储层中取得成功应用，钻井后储层表皮系数极大降低，钻井液对储层的污染明显减少。 

Damaging Mechanism of Tight Sandstone Gas Reservoirs and Optimization of Drilling Fluids for Reservoir Protection

The tight sandstone gas reservoir in the Block B in Tarim Basin has small pore throats, low permeability, high bound water saturation, severe heterogeneity and highly developed micro fractures. The reservoir formations are easy to be damaged and the formation damage is difficult to eliminate. To address these problems, tests on the high temperature sensitivity of reservoir formation and water block damage were performed under simulated formation conditions. The mechanisms of formation damage taken place in tight sandstone reservoir are revealed as follows:Reservoir formations are mainly damaged by stress sensitivity, water block and invasion of solids into the micro fractures in reservoir rocks. A temporary plugging agent and a surfactant that effectively reduce surface tension were selected through laboratory experiments for use in polymer sulfonate potassium drilling fluid, which is commonly used in the block of interest. A low damage drilling fluid with "synergetic action" in tight sandstone gas reservoir protection was developed using ideal packing theory and the surfactant selected. Evaluation of the drilling fluid in reservoir protection through compatibility test and dynamic contamination test showed that the drilling fluid is compatible with the formation water in Block B, and the percentage of rock core permeability recovery is at least 85%, indicating that the drilling fluid has good reservoir protection ability. The optimized drilling fluid has been used successfully on the well B2 in Block B in drilling the Bashijiqike formation. The skin factor of the reservoir rocks was greatly reduced after drilling, meaning that drilling fluid-induced reservoir damage was greatly reduced.