元坝气田成藏条件及勘探开发关键技术

Gas accumulation conditions and key exploration & development technologies in Yuanba gas field

梳理元坝超深层生物礁大气田的勘探开发历程可以发现,'开江—梁平陆棚'的厘定奠定了元坝台地边缘生物礁滩发现的基础。通过对油气成藏关键地质条件进行系统解剖,元坝地区礁滩发育具有沿'开江—梁平陆棚'成排成带分布、早滩晚礁、前礁后滩的特点,以侧积、前积迁移生长为主,飞仙关组不发育滩相优质储层,长兴组是主要勘探目的层;三期破裂、三期溶蚀作用和白云石化作用控制了优质储集层的发育;二叠系大隆组与吴家坪组两套烃源岩的有效叠加为大气田的形成提供了充足的气源;微小断层、微裂缝及层间缝共同构成的'三微'立体输导体系能够满足油气运聚的需要;元坝气田的成藏模式为:近凹富集、'三微'输导、岩性控藏、构造控富。针对元坝气田超深层、多压力系统等复杂地质条件,在勘探开发过程中形成了超深层生物礁滩储层精细预测与气水识别、复杂小礁体气藏精细描述和薄储层精细刻画、超深水平井优快钻井技术、复杂礁滩体超深水平井地质导向等关键技术,实现了元坝气田的高效勘探开发,推动了超深层油气勘探领域理论技术与方法的创新。

This paper discusses the exploration and development history and lessons of the large ultra-deep biogenic reef gas field in Yuanba area,where the previous'Kaijiang-Liangping shelf'model provides an insight for the discovery of the biological reef and bank on the platform margin.Systematic analysis of key geological conditions for hydrocarbon accumulation shows that the reef and bank reservoirs in Yuanba area are characterized by row and zonal distribution along'Kaijiang-Liangping shelf',the bank in early and the reef in late,the reef in the front and the bank in the back,and dominated by lateral accretion and progradation.The major exploration target of high-quality reef-bank reservoirs are developed in Changxing Formation instead of in Feixianguan Formation,Three stages of fractures and dissolution,and dolomitization control the development of the high-quality reservoirs.Two sets of effective source rocks(Permian Dalong Formation and Wujiaping Formation)provide sufficient gas source for the large gas field.Three dimensional migration pathway system composed of micro-faults,micro-fractures and interlayer fissures facilitates the hydrocarbon migration and accumulation.The accumulation model of Yuanba gas field is characterized by the near-sag accumulation,three-micro migration pathway system,lithological-stratigraphic reservoirs and tectonics controlling enrichment.According to the complex geological conditions such as ultra-deep reservoirs and multiple pressure systems in Yuanba gas field,several key technologies are developed during hydrocarbon exploration and development,including fine prediction of ultra-deep reef-bank reservoirs and identification of gas and water,fine-scale reservoir description and characterization of complex thin and small reef gas reservoirs,optimal&fast drilling of ultra-deep horizontal well,geo-steering of ultra-deep horizontal well for complex reef and bank.All these technologies resulted in the efficient exploration and development of Yuanba gas field and accelerated the innovation of theoretical technology and methods for ultra-deep reservoirs.