RESEARCH INTO FLUID PRESSURE FIELD IN DAMINTUN DEPRESSION, LIAOHE BASIN

The mudstone sonic log interval, measured stratigraphic pressure and seismic data are integrated to analyze the underground fluid pressure fields in Damintun depression, Liaohe basin. The research results show the following six points: (1) The mudstone compaction in this region is classified as the following three types: normal compaction-normal pressure, under-compaction and low overpressure in one single interval, and under-compaction and high overpressure in double intervals. (2) The pressure gradient of the oil layers is approximate to 1, so it is often within the normal pressure system. (3) The characteristics of planes and profile pressure fields obtained through the seismic data are of a higher feasibility and reliability. (4) The current profile pressure system consists of normal pressure, low overpressure, and high overpressure from surface to the deep layers. The fault systems, unconformity surfaces, interconnecting pore systems and diapir structures constitute the complex network system of vertical and horizontal transportation within the depression. (5) A distinctive difference exists between the surplus pressures and pressure coefficients on both sides of the relatively large-scale faults controlling greatly the formation, evolution and distribution of the pressures. (6) The under-compaction and hydrocarbon generation are the leading mechanisms for the formation of the overpressure in this region.