川东南地区五峰组-龙马溪组页岩气富集与高产控制因素

Controlling factors on the enrichment and high productivity of shale gas in the Wufeng-Longmaxi Formations,southeastern Sichuan Basin

中美页岩气地质和地表条件的对比分析表明,中国南方海相页岩与北美典型页岩的主要评价指标相近,是页岩气勘探的主攻层系。其中,四川盆地及周缘地区是有利勘探地区。中国石油化工股份有限公司2006年以来,经历6年的研究与勘探探索,2012年在四川盆地涪陵焦石坝地区龙马溪组页岩气获得重大突破,发现了涪陵页岩气田,取得了中国页岩气的首个商业发现。五峰组-龙马溪组页岩气富集与高产的地质因素包括原始沉积条件和后期保存条件,台内坳陷控制优质页岩的形成分布,页岩厚度大、有机质含量高是页岩气选区的首要评价指标。保存条件影响页岩气的富集程度,四川盆地内部总体保存条件较好,有三叠系膏盐岩分布的地区保存条件好,页岩气层段压力系数高,页岩气富集程度高。在选区评价中,原始沉积条件和后期保存条件均有利的地区是页岩气勘探的有利区。通过对典型探井五峰组-龙马溪组页岩气富集条件的分析表明,有机质提供了页岩气富集的物质基础,有机质孔是页岩气富集的主要储集空间,层理(缝)是页岩气水平渗流的高效通道,高硅质含量具有良好的可压性,高压力系数指示页岩气富集程度高。有机质、有机质孔、层理(缝)、硅质含量和压力系数等表征页岩气富集与高产的5种关键参数具有成因联系和统计相关的特征,纵向上又具有"五性一体"的分布特征,从而决定了五峰组-龙马溪组下部富含有机质的优质页岩层段既可以富集页岩气,又有利于页岩气的开发,是开发页岩气的主要层段和水平井轨迹的关键目标层。

Based on a comparison of geological and surface conditions for shale gas in China and America,we conclude that marine strata in South China having similar properties to those of America are targets for shale gas exploration,and the Sichuan Basin and its surroundings are favorable exploration areas.After six years of research and exploration,the Fuling shale gas field,which is the first major commercial shale gas play in China,was finally found in the Sichuan Basin in 2012 and then successfully developed.The shale gas enrichment and high productivity in the Wufeng-Longmaxi Formations is mainly controlled by the original depositional environment which determines organic matter content and post-depositional conditions that promote shale preservation and gas retention within the shale after thermal maturation.Deposition and distribution of the shales are controlled by the platform depression environment.Thickness and TOC content are the evaluation parameters for play.The late preservation conditions control the enrichment of shale gas.There are favorable preservation conditions and high degree of shale gas enrichment in the internal of Sichuan Basin,which are characterized by widely distributed Triassic gypsolyte layers and high pressure coefficient.The areas where both original depositional environment and preservation conditions are favorable should be given priority in play evaluation.Comprehensive analysis of the shale gas reservoir indicates that organic matter content is the principal control on shale gas enrichment,the organic micro-pores are the main reservoir space,horizontal bedding fractures ensure horizontal seepage,and that the high siliceous mineral content ensures good fracturing effect,high pressure coefficient indicates high degree of shale gas enrichment.These five properties have genetic relationships and statistical correlation and are characterized by＂five properties in one position＂distribution features in vertical.The high quality shales with ＂five properties in one position＂feature is conducive to the enrichment of shale gas and benefit for its development,which is the main development of shale gas layer and key objectives of horizontal well trajectory.