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.