Characteristics of Geotemperature-Geopressure System of the Qianjiang Formation in the Qianjiang Depression and Their Relationship with Petroleum Accumulation

Based on the measured temperature, pressure and acoustic log data of more than two hundred wells, the distribution characteristics of geothermal field, geopressure field and the geothermal-geopressure system of the Qianjiang Formation in the Qianjiang depression are analyzed by using the theory of geothermal-geopressure system. The relationship between the systems with petroleum accumulation is also discussed from the perspectives of hydrocarbon generation, preservation and distribution. This research comes to the following results: The Banghu and Zhouji syncline belts have higher geothermal gradient, which is favorable to the maturation of the Qianjiang Formation source rock expulsion. The present pressures of the Qianjiang Formation and stones mostly belong to normal range, whereas the deep Qianjiang Formation mudstones present uncompaction which enhanced its seal ability. In vertical, the T-P system of the Qianjiang Formation includes two kinds of static pressure and overpressure. The static pressure systems mainly distribute at the Qianbei steep slope belt, the eastern slope belt and the western slope belt where the reservoirs were formed by self-generation and self-storage, whereas the overpressure systems exist in the Banghu and Zhouji syncline belts where the reservoirs are distributed mostly at the top of the deep overpressure system and within the shallower normal pressure system. The lateral T-P systems can be divided into 8 subareas, namely, NTHP, LTHP, HTNP, NTNP, LTNP, HTLP, NTLP and LTLP, and the NTNP is the place where petroleum mainly accumulated.