中国致密油储层储集性能主控因素分析

摘要

The reservoir property of the tight oil reservoir is one of the key control factors in the formation of the tight oil “geologic sweet spot”and a main reference basis to find the “sweet spot”in the tight oil exploration.The complicated lithology,diversified types,widespread distribution,and overall tightness typify the tight oil reservoirs in China.The reservoir lithologies are largely terrestrial facies lake-basin sandstone and carbonate rock.They can be categorized as four different reservoir types by sedimentary genesis and lithology,that is,the deep-water gravity-flow sandstone,the sandstone of underwater-branched channel in delta,the lake-facies beach-dam and the shoal-facies dolomitic rock,and the lake-facies marl.Different types of tight reservoirs are extensively distributed over China' s terrestrial facies basins with the age from late Paleozoic to Cenozoic era.Affected by the sedimentary environment and diagenesis,the reservoirs are characterized by poor reservoir properties, generally with the porosity smaller than 10%,and the permeability smaller than 1 ×10-3μm2 .The reservoir property of the tight oil reservoirs in China is dependent upon the magnitude of reservoir quality and the fracture development,mainly subject to three control factors:sedimentary facies, diagenetic facies and fractures.The properties of the reservoirs with different geneses are affected by different main control factors.The reservoir of the deep-water gravity-flow sandstone type is subject to the control of the diagenetic facies and tectonic fracture,that of the sandstone of underwater-branched channel in delta to the control of the sedimentary-diagenetic facies,that of the lake-facies beach-dam and shoal-facies dolomitic rock to the control of the lithology and dissolution,and that of the lake-facies marl to the control of the tectonic fracture.The main control factors and their differences of the different properties of tight oil reservoirs aforesaid are the important bases to find different types of tight oil “sweet spots”and target optimization.%致密储层储集性是形成致密油“地质甜点”的关键控制因素之一，是致密油勘探寻找“甜点”的重要参考依据。中国致密油储层岩性复杂、类型多样、分布广、总体致密。储层岩性主要为陆相湖盆砂岩和碳酸盐岩，按沉积成因与岩性，可划分为深水重力流砂岩、三角洲水下分支河道砂岩、湖相滩坝与浅滩云质岩，以及湖相泥灰岩4种储层类型，不同类型致密储层在中国晚古生代至新生代陆相盆地广泛分布。受沉积环境与成岩作用影响，储层储集性差，一般孔隙度＜10％、渗透率＜1×10-3μm2。中国致密油储层的物性好坏与裂缝发育程度决定了储层的储集性能，主要受沉积相、成岩相与裂缝3种因素控制。不同成因储层储集性能主控因素不同，其中，深水重力流砂岩型储层受成岩相与构造缝控制，三角洲水下分支河道砂岩型储层受沉积-成岩相与构造缝控制，湖相滩坝、浅滩云质岩型储层受岩性与溶蚀作用控制，湖相泥灰岩型储层主要受构造缝控制。上述不同致密油储层储集性能主控因素及其差异性是勘探中寻找不同类型致密油“甜点”与目标优选的重要依据。