四川盆地渝西大安地区灰质源岩气勘探突破与资源潜力

Exploration breakthrough and resource potential of limy source rock gas in Da’an area in the western Chongqing,Sichuan Basin

四川盆地渝西大安地区茅口组一段(茅一段)灰质源岩气勘探取得了重大突破,对灰质源岩气的源内非常规勘探具有重要借鉴和示范意义。DB1H井是四川盆地针对茅一段暗色灰质源岩非常规气藏评价部署的首口水平井,通过酸化压裂试气获得高达55.6×10^(4) m^(3)/d的测试产量。系统介绍了渝西大安地区茅一段灰质源岩气的发现历程,展望了四川盆地茅一段灰质源岩气的资源前景。通过对渝西大安地区茅一段灰质源岩地质特征研究,认为该层系岩性主要为中缓坡相深灰色—黑灰色富有机质泥晶生屑灰岩,且区域稳定分布,是中国南方中上扬子地区重要的海相灰质源岩地层。茅一段灰质源岩气整体经历了富有机质碳酸盐岩沉积—成岩—成烃—成储—成藏—赋存“源内一体化演变”成藏过程,具有“源储一体、原位富集、连续型展布”的成藏特征。以微米级为主体的源内微观孔隙及与断层伴生的溶蚀孔洞、微缝网体系为气体主要储集空间,构成了基质孔隙型(原生型)和裂缝—孔隙型(改造型)两类储层,建立了“源储一体为主兼构造转折带短距离运移富集”的灰质源岩气成藏模式和甜点评价体系。富有机质暗色灰质源岩的发育、有利的古隆起和现今背斜构造背景,及与古断层有关的断控型岩溶、张性应力微裂缝的发育叠置,为茅一段灰质源岩新型储层富集高产的关键。初步估算四川盆地茅一段灰质源岩气资源量可达2×10^(12)m^(3),将成为盆内现实增储上产战略意义的非常规勘探新领域。

A major breakthrough has been made in the exploration of limy source rock gas in the first member of Maokou Formation(Mao 1 member)in Well DB1H in Da’an area in the western Chongqing,Sichuan Basin,which has important reference and demonstration significance for the intra-source exploration of limy source rock unconventional gas in the Basin.The first horizontal well DB1H was drilled to evaluate the dark limy source rock gas reservoir in Mao 1 member in Sichuan Basin and a high gas rate of 55.6×10^(4) m^(3)/d was tested after acidizing and fracturing.The discovery process of limy source rock gas in Mao 1 member in Da’an area has systematically been introduced,and the resource prospect in Sichuan Basin has been estimated.The analysis of geological characteristics of limy source rock gas in Mao 1 member in Da’an area in the western Chongqing shows that the main lithology is composed of medium-gentle slope facies deep gray-black organic-rich micritic bioclastic limestone,with stable distribution in the region,which is an important marine limy source rock in the Middle and Upper Yangtze region in South China.The hydrocarbon accumulation process of limy source rock gas in Mao 1 member showed an“intra-source integrated evolution”of organic-rich carbonate rock deposition,diagenesis,hydrocarbon generation,reservoir formation,hydrocarbon accumulation and preservation,which had characteristics of“source rock and reservoir integration,in-situ hydrocarbon enrichment,and contiguous gas distribution”.The micro-sized pores in source rock,and the dissolution pores and micro-fracture network system associated with faults served as the main reservoir space,forming two types of reservoirs,i.e.,matrix porosity type(primary)and fracture-porosity type(transformed).The hydrocarbon accumulation pattern of“mainly source rock and reservoir integration and enrichment in local structural transition zone after short-distance migration”has been established and the sweet spot evaluation system has been constructed.The key factors for gas enrichment and high-yield production in the new type of limy source rock reservoir in Mao 1 member include the development of organic rich dark limy source rock,favorable paleo uplift,anticlinal tectonic settings at present,and fault-controlled karst and extensional micro-fractures.The estimated resources of limy source rock gas in Mao 1 member are 2×10^(12)m^(3)in Sichuan Basin,which is a new unconventional field for increasing reserves and production in the basin.