中国油气田古岩溶与油气储层

目前,在鄂尔多斯盆地、塔里木盆地、四川盆地等的奥陶系、石炭系、二叠系—三叠系及震旦系等多套地层中均已发现不少典型的古岩溶油气田。这些油气田古岩溶储层常具有以下几个特征:(1)垂向分带明显,地表残积岩溶带、垂直渗流—水平潜流岩溶带等发育齐全。(2)储集空间主要由岩溶作用形成的半充填或未充填残余溶蚀孔洞缝组成。优质储层类型以裂缝—溶蚀孔洞型储层为主,此类储层为各大油气田高产稳产的最重要储层和主力产气层。(3)储层受古岩溶地貌和断层裂缝的控制明显。古岩溶斜坡、古岩溶高地边缘及断层裂缝发育区,古岩溶发育强烈,是溶蚀孔洞层和储层发育的有利地区。(4)埋藏有机溶蚀作用形成的次生孔隙为有敏孔隙,它的发育与烃类的形成、演化和运聚相匹配。(5)古风化壳岩溶作用和埋藏有机溶蚀怍用的多期次叠加和改造,是古岩溶储层及油气藏形成的最佳组合模式。

The Paleokarst Reservoirs in the Oil and Gas Fields in China

Many Ordovician,Carboniferous,Permian,Triassic and Sinian carbonate paleokarst fields that are associated with re- gional unconformities are discovered in Ordos,Tarim and Sichuan basins during oil and gas exploration.Based on analy- sis of the typical paleokarst reservoirs in China,the following characteristics are common:Karst zones including the surface, vadose and the phreatic zones are distinctive in vertical and well developed.Reservoir space is commonly composed of semi-filled or free-filled remnant solution bores,vugs and fis- sures.The reservoirs with fissures and solution-vugs are most favorable for hydrocarbon accumulation,which are the main high-yield oil pays in the giant fields.Distribution of paleokas- tic reservoirs is obviously controlled by karstified morphology and faults or fissures.The intensively karstified areas,such as karstic slopes,marginal paleokarstic highs and fault belts,are the areas most favorable for development of solution-vugged and fissured reservoirs.Effective porosities are the secondary pores resulted from organic dissolution during deep burial for the formation of the pores coincides with the maturation of source rocks,and hydrocarbon evolution and migration.Sever- al alternations of weathering crust karstifications with buried organic dissolution,which is the most important diagenetic process or the best model of the paloekarst reservoirs.