柴达木盆地西部地区地温—地压系统演化及其与油气成藏的关系

EVOLUTION OF GEOTEMPERATURE-PRESSURE SYSTEMS AND ITS RELATION TO DISTRIBUTION OF OIL-GAS ACCUMULATION IN THE WESTERN QAIDAM BASIN

综合考虑时间和埋深对孔隙演化的影响,采用孔隙度双元函数模型对柴达木盆地西部地区(以下简称柴西地区)的地层古埋深、古压力进行了恢复,并结合其它研究成果再现了该区两个主要成藏期的地温—地压系统,分析了地温、地压及温压系统的演化特征。将流体势分析与地温—地压研究相结合,分别从定性、半定量到定量,从剖面到平面并从不同的角度分析了地下流体动力场及其对油气运聚成藏的控制作用,探讨了柴西地区油气成藏的特点和规律。发现柴西地区在主要成藏期(中新世中期和上新世末期)都发育高压型复式温压系统,其中,上新世末期的温压系统油气垂向运聚能力较强。在温压系统平面分区内,油气藏基本位于能量相对较低的分区内,高能区也有油气藏分布,但都是封闭及保存条件好的岩性或古构造等原生油气藏。同时论证并提出柴西地区未探明储量主要位于深部高压型温压系统内,深层油气藏勘探应是该区今后重要的勘探领域。

The age of stratum might have an influence on the evolution of porosity, so that the age, as well as the depth of stratum, should be taken in account to solve the restoration of palaeoburial depth, palaeo-geopressure and palaeo-fluid potential of stratum. To synthesize the results of palaeo-geotemperature study, the evolution of geotemperature-pressure systems during the main stages of hydrocarbon accumulation in the western Qaidam Basin was analyzed in detail. Fluid potential, which was combined action on the underground fluid, including geotemperature, geopressure, etc., was introduced to the study of geotemperature-pressure systems in this paper. The underground hydrodynamic field and its control function to hydrocarbon migration and accumulation could be analyzed both qualitatively, semi-quantitatively and quantitatively, also both vertically and planarly. Based on what mentioned above, the oil-gas distribution and the characteristics of oil-gas migration and accumulation were explored. In the western Qaidam Basin, high pressure compound T-P systems developed both in middle Miocene and late Pliocene. The latter had more potential of migration and accumulation. Planarly, the hydrocarbon pools usually occurred in the areas of lower energy. In addition, some pools were discovered in the areas with high energy, which were original ones, such as lithologic hydrocarbon reservoirs and palaeostructure pools with better conservation and better seals. The paper presented that most of undiscovered reserves might be in the deep and high pressure T-P system, and the deep reservoirs should be important exploration targets in future.