摘要
"甜点"的识别对确定页岩气有利区分布,进而实现大规模经济开发具有重要的意义。为此,基于国内外大量优质含气页岩的分析资料和研究数据,比较分析了页岩气藏的地质特征,阐述其"甜点"的地质要件:含气页岩有效厚度、有机碳含量(TOC)、有机质类型与成熟度(R_o)、岩石骨架及其物性(孔隙度及渗透率)特征、天然裂缝发育状况等。然后,结合页岩气经济开采的特点以及各要素间的相关性,以四川盆地长宁地区的相关资料为基础,综合考虑四川盆地威远区块的情况,总结了页岩气富集的地质规律,明确了该区海相页岩气藏有利"甜点"的构成要素及其分布值:①有效页岩连续厚度大于30 m、TOC>2.0%、R_o介于2.4%~3.5%,保证了气源岩的质量;②脆性矿物含量介于30%~69%、黏土矿物含量小于30%、夹层厚度介于0.1~1.0 m,保证了储层的质量;③孔隙度大于2.0%、渗透率大于50 nD、含气量大于1.45 m~3/t、地层压力介于常压—超压,决定了生产方式与产能。最后进一步分析了页岩气藏"甜点"的主次控件,并探讨了其相互制约关系。
Identification of sweet spot is of great significance in confirming shale gas prospects to realize large-scale economic shale gas development.In this paper,geological characteristics of shale gas reservoirs were compared and analyzed on the basis of abundant data of domestic and foreign shale gas reservoirs.Key elements of sweet spots were illustrated,including net thickness of gas shale,total organic carbon(TOC) content,types and maturity(R_o) of organic matters,rock matrix and its physical properties(porosity and permeability),and development characteristics of natural fractures.After the data in Changning and Weiyuan blocks,Sichuan Basin,were analyzed,the geologic laws of shale gas enrichment were summarized on the basis of the economic exploitation characteristics of shale gas and the correlation between the elements.The elements of favorable "sweet spots" of marine shale gas reservoirs in Changning block and their distribution characteristics were confirmed.Firstly,the quality of gas source rocks is ensured with the continuous thickness of effective gas shale larger than 30 m,TOC > 2.0%and.R_o=2.4-3.5%.Secondly,the quality of reservoir is ensured with the brittle minerals content being 30-69%,the clay mineral content lower than 30%and a single lamination thickness being 0.1-1.0 m.And thirdly,the porosity is higher than2.0%,the permeability is larger than 50 nD,gas content is higher than 1.45 m~3/t,and formation is under normal pressure-overpressure system,which ensures the production modes and capacities.Finally,the primary and secondary elements that control the "sweet spots" of shale gas reservoirs were further analyzed and their restrictive relationships with each other were also discussed.
引文
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