论准噶尔盆地东部地区油气分布的基本规律

准噶尔盆地东部是一个新含油气区。主力生油层为上二叠统、油气分布受晚古生代拗陷的控制。被隆起分开的北部大井拗陷和南部昌吉拗陷东段,表现为两个独立的含油气单元,类似于两个独立的合油气盆地,油气分布的方式各不相同。 北部大井拗陷为自生自储型含油拗陷,平地泉组(P2p)是唯一的自生自储自盖的含工业性油气的地层单元。拗陷中心就是生油中心。在生油中心内,中等隆起幅度的共成熟型背斜,是最有利的含油圈闭。岩性因素亦不可忽视,属典型的构造—岩性油藏。油水界面参差不齐,而压力系统一致。 南部昌吉拗陷东段则属他生他储型含油拗陷,含油地层单元多,油气藏的形成过程很复杂。二叠系生油层的平面厚度变化大,且进入成熟门限的时间先后不一;其中缺乏孔隙性砂层,排烃不畅,油气运移难受大;主要生油中心仅限于山前的狭长地带,早燕山运动以后,回返隆升成剥蚀区,失去了油源区的意义。中生界煤系在拗陷西部也可生油。从北三台南坡至阜康断裂下盘,油气来自山前生油中心,形成于白垩纪前,以残余油藏的稠油为主,部分为迟到油气。吉木萨尔凹陷内的重粘油,来自凹陷內低—未成熟的生油岩。北三台北断鼻的油气来自阜康凹陷北部的二叠系,是经二次运移的异地油,保存好,不是残余油藏。北三台西坡的油气以低密、低粘为特点. 是来自阜康凹陷的晚熟晚到油气, 也不是老油试破坏后的残余。预计还可能在北部五彩湾及火东两个负性构造区找到一些小型油气藏: 南部在阜康断裂带有潜力, 可惜都是些分散的中小型复杂油气藏; 吉木萨尔凹陷不可忽视: 北三台西坡的晚期油气藏很重要, 有可能使南部局面改观。

ON RADICAL RULES OF OIL AND GAS DISTRIBUTION IN THE EASTERN AREA OF JUNGGAR BASIN

The eastern Part of Junggar basin is a new oil and gas-bearing area with principal source bed being upper Permian series. The Distribution of oil and gas here was controlled by late-palaeozoic depressions. The north Dajin g depression and east of the south Changji depression seperated by an uplift appear to be two independent oil and gas-bearing units, resembling two independent oli and gas-bearing basins where distribution patterns of oil and gas are not uniform. The Dajing depression, located in the north area is an oil-bearing depression where source rock and reservoir rock are the same bed.Pindiquan formation is only srratigraphic unit bearing industrial oil and gas. The formation itself is source bed and reservoir rock as well as caprock. Therefore, the centre of depression was the centre of source area. In the centre of source area anticlines with middle uplift size and mature synchronous with hydrocarbon are the best oil-bearing traps. The lithologic characters, however, is a faactor which should not be neglected. They are tyoal strucral-lithologic oil pools in which oil-water interfaces are uneven whereas reservoir pressures uniform. In the south area, the east part of Changji depression is characterized with source and reservoir rocks are not the same beds. Here, more oil - bearing stratigrraohic units exist, and formation course of oil and gas reservoir is very complicated. Variations of the thickness of Permian source rock are very rapid laterally, and times when the source rock came into maturity threshold are not uniform. Porous sand-stones were so tack in the source rock that expulsion of hydrocarbons was impeded. This resulted in great difficulty of oil-gas migration. The main centre of source area of Permian was only situated within the limite of a long, narrow piedmont of Bogeda mountain. After early Yenshan movement this zone rose, becoming an erosional area, hence lost meaning of a source area. In the west depression Mesozoic coal-series was a kind of source rocks. From the south slope of north Santai uplift to the downthrow of Fukang fault, oil and gas came from source centre of the piedmont and gathered into traps before Cretaceaus, and then were eroded Here. heavy. viscous oil of remaining old oil reservoirs was principal with part of oil and gas came in late. In Jimusar depression heavy and viscous oil came from the unmature-low mature source rocks within the depression. The oil and gas in north faulted-nose at north Shantai uplift came from Permian in the north part of Fukang depression, and was a sort of exotic petroleum experienced secondary migration. It is still well preserved and isn't remanent reservoir, The oil and gas in the west slope of north Shantai uplift is characteristic of low density and low viscosity.This is a kind of late mature and late arriving oil and gas coming from Fukang depression. It is not the remainders of destroyed oil depositeither. It is anticipated that some small oil and gas reservoirs might be discove-red in Wucaiwan depression and Hodong syncline of the northern area. In the southern area where Fukang fault zone has greater potential unfortunately,however, there are only many scattered, complex, middle and small oil and gas reservoir. Oil potential in Jimusar depression can not be neglected. Later oil and gas accumulations in the west slope of north Shantai uplift might be soimportant that it could change significance of the southern area.