珠江口盆地西江33洼古近系油藏地质特征与成藏解剖

Geological Characteristics and Hydrocarbon Accumulation Mechanism of Paleogene Reservoir in Xijiang 33 Subsag,Pearl River Mouth Basin

珠江口盆地西江33洼油气勘探的主要目的层系和探明储量均集中在古近系,而古近系油气藏由于埋藏深、钻井成本高导致该区勘探程度低,至今没有建立开发平台。XJ-A古近系油藏位于西江33洼南部斜坡带,该油藏的储层物性较差,横向与纵向变化均较大,具有"低孔渗"特征,而且发育多个断块,各个断块油气独立成藏,无统一的油水界面,给油藏的精细刻画带来了极大的困难。本文以XJ-A古近系油藏为例,系统分析了该油藏的油气成藏规律,研究表明:①西江33东西次洼生成的油气均可向XJ-A油藏供烃;②XJ-A油藏为复杂断块油藏,储层以辫状河三角洲沉积为主,上恩平组湖沼相沉积是该油藏的区域盖层;③XJ-A油藏在主排烃期具有油气早期充注特征,表现为"中高孔渗"储层形成常规油气藏,主排烃期后储层边致密化边成藏。总体而言,XJ-A油藏具有"双源供烃,旁生侧储,断砂输导、早期充注、断块成藏"的特征。

The petroleum exploration targets and proved reserves in Xijiang 33 Subsag of Pearl River Mouth Basin focus on Paleogene strata.The exploration degree in Paleogene reservoir is relatively low because of deep burial depth and high drilling cost,and the development platform has not been built so far.XJ-A Paleogene reservoir locates in the southern slope belt of Xijiang 33 Subsag.The reservoir has the characteristics of poor reservoir physical property,large horizontal and vertical variation, "low porosity and permeability",and many fault blocks developed.Each block has independent hydrocarbonaccumulation without unified oil-water interface.These bring great difficulties to the fine depiction of the reservoir.The hydrocarbon accumulation characteristics of the XJ-A Paleogene reservoir is systematically analyzed,and the results show that :①The oil and gas generated in Xijiang 33 eastern and western subsags can be supplied to XJ-A reservoir;② XJ-A reservoir is a complex fault block one with braided river delta deposited mainly.The limnetic sedimentation in upper Enping Formation is the regional cap of the reservoir;③In the main hydrocarbon expulsion period,XJA reservoir had the characteristics of hydrocarbon charging in early stage,and the reservoirs with "medium-high porosity and permeability" may from conventional oil-gas reservoirs,but the reservoir was densified with hydrocarbon accumulation after the major hydrocarbon expulsion period.In general,XJ-A reservoir has the characteristics of "bidirectional effective hydrocarbon generation,side generation and side storage,fault-sandstone carrier,early charging,hydrocarbon accumulation in fault block".