川东石炭系天然气成藏地质条件再认识及其勘探潜力预测

Restudy of geologic conditions and prediction of exploration potential in the Carboniferous gas reservoirs of the eastern Sichuan Basin

四川盆地东部石炭系是盆地内天然气的主要高效产层,随着构造圈闭落实的难度增大,勘探方向的选择成为其发展的新问题。为此,开展了以岩性地层气藏为目标的新一轮地层、沉积微相、储层、烃源岩、构造、成藏与圈闭等方面的研究。分析认为:川东石炭系气源充足,白云岩储层广泛发育,并具有明显的非均质性与不连续性特征。这种非均质性与不连续性不仅是白云化、沉积微相、成岩溶蚀与构造作用共同作用的结果,而且也是构造?地层复合圈闭及岩性圈闭发育的重要条件。因此,川东石炭系不仅还存在构造圈闭勘探的新区带,而且还存在构造—地层复合圈闭、岩性圈闭等有利勘探目标。其中构造气藏产量高而稳定,产能建设见效快,仍是近期勘探增储上产的主要气藏类型;构造—地层复合圈闭是近期勘探的主要新类型,一定坡度的构造围斜区是有利于天然气勘探的新方向;岩性体多发育于致密区,虽然单个规模小,但可以叠置广泛发育,是老区滚动勘探与挖潜的重要新类型。

Carboniferous reservoirs have become the major pay zones in the eastern Sichuan Basin after more than 30 years' exploration and development.However,because of the increasing difficulty in delineating structural traps along with exploration getting mature,it becomes a new issue how to select the target for further Carboniferous gas exploration here.With the identification of lithologic-stratigraphic traps as a goal,studies are carried out in respect of stratigraphy,sedimentary microfacies,reservoirs,source rocks,structures,and hydrocarbon accumulation and traps.It is believed that,in the eastern Sichuan Basin,source rocks are highly developed and dolomite reservoirs are widely distributed and have strong heterogeneity and discontinuity,these two features of which are not only the results of combined action of dolomitization,sedimentary microfacies,diagenetic dissolution and tectonism,but important conditions for the development of composite structural-stratigraphic traps and lithologic traps.Therefore,there are both new structural traps and composite structural-stratigraphic traps and lithologic traps.The structural traps are still the major type for reserve growth and production increase in the near term,while the structural-stratigraphic traps are the major target of future exploration and the superimposed and widely developed lithologic traps in tight zones are the important new target for rolling exploration in mature fields.