准噶尔盆地阜康凹陷侏罗系超压成因、垂向传导及油气成藏

Origin of Overpressure,Vertical Transfer and Hydrocarbon Accumulation of Jurassic in Fukang Sag,Junggar Basin

沉积盆地中超压广受关注,但对超压传导规律认识的不足制约了高压领域的油气勘探.以准噶尔盆地阜康凹陷侏罗系为例,通过超压类型地质综合判识、关键超压表征参数的理论计算及流体包裹体压力恢复,首次认识到了垂向传导对于储集层超压的重要贡献,结合压力垂向传导机制及过程,探讨了油气藏的运聚及泄露意义.研究结果表明,侏罗系超压由4类超压环境中7种致压因素引起,经历2期大规模压力跨层垂向传导,储集层段发育以垂向传导为主因的复合超压,形成3类不同动力特征的油气藏.压力垂向传导是储集层超压的主要成因机制,断-盖的力学性质、差应力及流体压力等3类因素控制压力垂向传导,传导背景下,形成3类与传导作用有关的油气藏:受断层垂向传导控制的超压油藏、受连通砂体侧向传导控制的超压油藏以及超压界面上的常压油藏,上述3类油气藏的运聚及泄露特征差异较大.

Overpressure in sedimentary basins is widely concerned, but the lack of understanding of mechanism of the overpressure transfer restricts the exploration of oil and gas in the over-pressured reservoir of sedimentary basins. Taking Jurassic overpressure of Fukang sag in Junggar basin as an example, the important contribution of vertical transfer overpressure to reservoirs was recognized for the first time through the comprehensive geological studies of overpressure type, the theoretical calculation of characterization parameters of overpressure and the fluid inclusion pressure recovery. Combined with the overpressure vertical transfer mechanism and process, the application for oil migration and accumulation and leakage in the over-pressured reservoir is discussed. The research results indicate that the Jurassic overpressure in Fukang sag is caused by seven kinds of pressure factors in four different overpressure environments. Furthermore, basin modelling and fluid inclusions pressure recovery results show that two stages of overpressure vertical transfer in Jurassic can be conformed to well explain the superposition phenomenon of multiple cause types of over-pressured reservoirs. Theoretical analysis indicates that pressure vertical transfer are controlled by three kinds of factors, such as the geomechanical properties of the seals or sealing faults, the differential stress and the fluid pressure. Under the control of the factors above, three types reservoirs related to the overpressure vertical transfer are formed: over-pressured reservoirs related to fault vertical transfer;hydrostatic pressure reservoirs related to oil and water differentiation on overpressure interface and over-pressured reservoirs related to sandstone lateral transfer. The migration, accumulation and leakage characteristics of the above three types of reservoirs are quite different in their potential beneficial target areas.