随钻地质与地球化学分析在四川威远页岩气开发中的应用

四川威远是国家级长宁—威远页岩气开发示范工程的重点开发地区,页岩气目的层为下志留统龙马溪组优质页岩发育层段。页岩气水平井钻进过程中,传统的地质录井及随钻测井方法难以对优质页岩气储层进行实时有效的分析与评价,降低了优质储层的钻遇率,增加了钻井施工的风险。通过研究区水平井随钻过程中大量岩屑样品的地质与地球化学录井分析,结合相应取心井分析资料,建立了水平井储层地质评价方法,应用TOC辅助地层界面卡取,应用TOC、吸附气含量、气测全烃参数评价储层含气性,再结合储层脆性矿物含量进行有利页岩气开发层段评级和优选;同时建立了水平井地质导向辅助方法,通过TOC、Ca含量、气测全烃等关键参数的相对区间变化,指导工程人员进行水平井着陆入靶调整和水平井窗体控制。现场应用表明,该套技术方法提高了威远地区页岩气水平井开发效率,同时可为同类页岩气储层的有效开发提供技术参考。

Application of geological and geochemical analysis while drilling in shale gas development in Weiyuan area,Sichuan Basin

Weiyuan area is an important block of the national shale gas development demonstration project in Changning-Weiyuan area,with the main target of high quality shale in Lower Silurian Longmaxi Formation.Traditional mud logging and LWD(logging while drilling)methods have difficulties in effectively analyzing and evaluating shale gas reservoir in real time,which reduce the penetration rate of high quality reservoir and increase the risks during drilling operations.This paper establishes the geological evaluation methods for shale gas reservoir in horizontal wells through geological and geochemical logging analysis from a large number of cuttings samples while drilling and based on the lab test data from offset coring wells.Firstly,TOC is used to support thin layer identification.Then,parameters of TOC,adsorbed gas content and total hydrocarbon content of gas logging are applied to evaluate the gas-bearing property of shale gas reservoir.Finally,shale gas reservoirs are graded and favorable targets selected combining with the parameter of brittle mineral content.Meanwhile,this paper establishes auxiliary methods for horizontal well geosteering,that is,by analyzing the relative variation range of the key parameters—TOC,Ca element content,total hydrocarbon content and so on,adjustment of horizontal trajectory landing in target and controlling of horizontal well window can be achieved by drilling engineer.Field application indicates that these methods improve the development efficiency of shale gas horizontal well in Weiyuan area,and also provide technical reference to the efficient development of similar shale gas reservoirs.