沁南地区高煤阶煤储层水敏效应及其控制因素

在煤层气开发过程中,工作液与煤储层不匹配时会造成水敏效应,导致煤储层渗透率降低,影响煤层气井产能。对煤储层进行水敏效应评价并探讨其主控因素,对提高煤层气开发效率具有重要意义。沁南地区高煤阶煤储层具有低孔低渗透特征,常规水敏实验方法已不适用,因此研究提出了煤储层水敏评价的新方法,采用气测渗透率取代传统的水测渗透率来表征煤岩水敏损害程度,并对沁南地区典型煤岩样品进行了测试。结果表明:沁南地区煤储层水敏损害率介于弱敏感到中等偏强之间,且以弱敏感为主;制约水敏效应的因素有煤储层渗透率、粘土矿物含量和粘土矿物赋存方式;煤储层渗透率越低,粘土矿物含量越高,水敏损害率越大。煤储层中粘土矿物的赋存方式有2种:煤岩裂隙填充与煤岩基质中植物细胞腔填充,且粘土矿物填充于煤岩裂隙的水敏损害程度高于填充于煤岩基质的水敏损害程度。

Water sensitivity and its controlling factors on high-rank coal reservoirs in southern Qinshui basin

During the coalbed methane (CBM) development process, the incompatilbility between working fluid and coal reservoir will result in water sensitivity, leading to a reduction in coal reservoir permeability and serious effects on the production of CBM wells.Therefore, water sensitivity evaluation of coal reservoirs and disscution on its controlling factors have a significant importance in improving the development efficiency of CBM. High-rank coal reservoirs in the southern Qinshui basin are characterized by low porosity and low permeability, and the conventional water-sensitive experimental method is no longer applicable in this area. This research proposed a new method for the evaluation of coal reservoir water sensitivity by using gas permeability instead of the traditional water permeability. Typical coal samples in the southern Qinshui basin were tested based on this method. Results show that: the water sensitivity in the study area is weak to moderate and is dominated by low water sensitivity; the controlling factors of water sensitivity in the southern Qinshui basin are permeability, clay mineral content and the occurrence type of clay minerals. The lower the coal reservoir permeability, the higher the clay mineral content and the higher the water sensitivity. The clay minerals in coal reservoirs have two types of occurrence: fracture filling and cavity filling of plant cells in the coal matrix, and the water sensitivity caused by fracture filling is higher than that caused by cavity filling.