低渗透砂岩中的低对比度油气层类型及成因分析

通过对四川盆地包-界地区须家河组和鄂尔多斯盆地姬塬地区长8段低渗透砂岩油气层测井响应特征的深入分析,结合试油、分析测试和岩心薄片鉴定资料,提出了广义的低对比度油气层的概念。在低渗透砂岩储层中,低对比度油气层包括4种类型:油气层和水层电阻率差异小的低对比度油气层;有自然产能的油气层和干层的孔隙度及电阻率差异小的低对比度油气层;压裂后具工业产能的油气层和干层孔、渗差异小的低对比度油气层;高产油气层和低产油气层的孔隙度和电阻率差异小的低对比度油气层。通过对低对比度油气层岩心NMR和薄片鉴定结果的深入分析表明,导致低渗透砂岩储层中产生上述4种低对比度油气层的主要原因在于其复杂的孔隙结构引起的高束缚水饱和度和成岩相差异。

Types and genesis of low contrast hydrocarbon reservoirs in low permeability sandstones

This paper introduces a general concept of low contrast hydrocarbon reservoir based on deep analyses on log response features of the low permeability sandstone reservoirs in the Xujiahe formation of Bao-jie area,Sichuan Basin and the Chang8 formation in Jiyuan area,Ordos Basin in conjunction with well testing and thin section identification data.In low permeability sandstone reservoirs,there are four types of low contrast hydrocarbon reservoirs: reservoirs with little resistivity difference from aquifer,reservoirs with natural productivity and little differences in porosity and resistivity from dry bed;reservoirs with commercial productivity after fracturing and with little differences in porosity and permeability from dry bed,and reservoirs of high and low productivity with little differences in porosity and resistivity.Analysis of the core NMR and thin section identification results of the low contrast hydrocarbon reservoirs shows that the main cause of the above four types of low contrast hydrocarbon reservoirs in low permeability sandstones lies in high irreducible water saturation due to complicated pore structure and the difference in diagenetic facies.