松辽盆地北部地下水热对流及油气聚集模型

松辽盆地北部与油气有关的地下水活动可分为沉积水运动和渗入水初生水对流运动两个阶段。地下水矿化度在盆地边缘地区随埋深的增大而增加,中间地区则出现了低→高→低的现象,中央地区随埋深增大地下水矿化度递减。该区地下水矿化度的“倒转”分布规律是因地下水的热对流运动而形成的。根据盆地地下水热对流地质模型建立的油气聚集模型可将油气聚集场所分为3大类:盆地边缘为地下水流动急剧变化区,地下水所携带的油气在有利的圈闭中聚集成藏(C类);盆地中间为由流线Ⅲ-Ⅲ'限制的“死循环”区,流体不与外界发生交替,具有好的油气保存条件(B类);盆地中央区上部为地下水的区域排泄区,利于油气聚集(A2类),中央区下部为两个流动系统交汇区,易形成油气聚集(A1类),此处亦为无机成因气藏的可能分布区。这3类油气藏(A、B、C类)分属不同的油气系统。 

HYDROTHERMAL CONVECTION MODEL OF GROUNDWATER AND THE CORRESPONDING HYDROCARBON-ACCUMULATION MODEL FOR THE NORTH SONGLIAO BASIN

The movement of groundwater related to hydrocarbon in the North Songliao Basin can be divided into two stages: the movement of sedimentary water and the convection of infiltration water and juvenile water.The TDS (total dissolved solids) of groundwater in the marginal area of the basin increases with depth.It shows a low-high-low phenomenon in the middle area.In the central area of the basin,it decreases with depth. The "reversed" distributive rule of TDS for the groundwater in this area is contributed to the hydrothermal convection of groundwater.According to the hydrocarbon-accumulation model based on the hydrothermal convection geologic model of groundwater in the basin,there are three types of hydrocarbon-accumulation sites.The margin of the basin is the rapid change area of groundwater flow,in which the hydrocarbon carried by groundwater accumulates into pools in favorable traps (type C).The middle of the basin is the "dead circulation" area limited by Ⅲ-Ⅲ' flowline,in which fluid has no exchange with the outside and good hydrocarbon-preservation conditions exist (type B).The upper part of the central area in the basin is the regional drainage area of groundwater which is advantageous to hydrocarbon accumulation (type A2),and the lower part is the confluence area of two flow systems which is liable to form hydrocarbon accumulation (type A1) and is the possible distributive area of inorganic-genetic gas pools.The three types of hydrocarbon pools (type A,B and C)belong to different hydrocarbon systems respectively.