深层脆性页岩井钻井液漏失机理及主控因素

四川长宁区块页岩气资源丰富,但在水平井钻井中钻井液漏失问题突出,制约了长宁区块页岩气资源勘探开发进程。基于单井测井数据与地震解释数据,建立了长宁区块页岩气地层裂缝、地应力及地层压力展布模型,研究了三者与钻井液漏失情况的响应关系。结果表明:长宁区块构造背斜高部位裂缝密度大,地层埋藏浅地应力小,闭合裂缝的开启临界压力与裂缝延伸临界压力都较小,地层孔隙压力低,钻井液漏失情况严重;构造向斜低部位裂缝密度相对于构造高部位小,地层埋藏较深地应力大,闭合裂缝的开启临界压力与裂缝延伸临界压力都较大,地层孔隙压力高,钻井液漏失情况不突出。长宁区块断层裂缝发育,钻井液漏失主要为压差性漏失和闭合裂缝扩展性漏失。研究结果揭示了长宁区块深层页岩钻井液漏失机理,明确了其主要影响因素,可为长宁区块页岩储层防漏及效益化开发提供科学依据。

Lost Circulation Mechanism and Main Controlling Factors in Deep Brittle Shale Wells

In spite of abundant shale gas resources in Changning Block, Sichuan Province, the severe lost circulation of drilling fluid in horizontal well drilling is prominent restricts the exploration and development of shale gas resources in Changning Block. Based on single-well logging data and seismic interpretation data, a distribution model of shale gas formation fractures, crustal stress and formation pressure of shale gas reservoirs, Changning Block was established, and a study was conducted on the response relationship between them and lost circulation. The results showed that, the fracture density was high in the high position of the tectonic anticline in Changning Block, the formation was buried shallowly, the crustal stress was low, the critical pressure of opening and extension of closed fractures was low, the formation pore pressure was low, and the lost circulation of drilling fluid was severe; the fracture density in the low position of the tectonic syncline was lower than that in the high position, the formation was buried deeply, the crustal stress was high, the critical pressure of opening and extension of closed fractures was low, the formation pore pressure was high, the formation pore pressure was high, and the lost circulation of drilling fluid was subtle. The faults and fractures were developed in Changning Block, and the lost circulation of drilling fluid was mainly caused by pressure difference and closed fracture expansion. The results of the study disclose the lost circulation mechanism of drilling fluid in deep shale in Changning Block, and clarify the main influencing factors, which can be used as a scientific basis for lost circulation prevention and efficient development of shale reservoirs in Changning Block.