西湖凹陷黄岩区深层低渗天然气藏差异聚集规律及成因浅析

Differential Accumulation Law and Genesis of Deep Low Permeability Natural Gas Reservoirs in Huangyan Area of Xihu Sag

针对西湖凹陷黄岩区“区域成藏、一层多藏”的天然气规模成藏与差异成藏现象,基于钻井资料、流体预测、断裂解析及低渗天然气藏运聚方式等分析,提出区内“翼部主运、核部调节”的天然气差异聚集特征。具体表现为:当构造核部小断层不发育时,核部为天然气汇聚优势区,易形成气藏富集区;当构造核部小断层较发育时,断层面附近易形成非渗透区,靠近深大断裂的构造翼部易形成气藏富集区。这种现象是先伸展后挤压的地质背景、背斜-似花状断裂构造及低渗储层天然气“体积流”充注富集共同形成的。黄岩区的油气评价应遵循“一核两翼、近断富集”的思路。

Many oil and gas bearing structures in Huangyan area of Xihu Sag show the phenomenon of large-scale and differential natural gas accumulation of"regional accumulation and multiple reservoirs in one layer".The differential accumulation characteristics of natural gas of"transporting in wings and regulating in core"in the study area are put forward based on the analysis of drilling data,fluid prediction,fracture analysis and natural gas migration and accumulation mode.The specific manifestations are as follows:when the small faults in the structural core are not developed,the core is the dominant area of natural gas accumulation,where it is easy to form gas accumulation area;When small faults are developed in the structural core,impermeable areas are easy to form near the fault plane,and natural gas accumulation areas are easy to form near the structural wings of deep and large faults.This phenomenon is formed under the combined action of the geological background of first extension and then compression,anticline-flower-like fault structure and the"volume flow"filling and enrichment of natural gas in low-permeability reservoirs.Therefore,the oil and gas evaluation idea of"one core,two wings and accumulation near faults"in Huangyan area is put forward in this paper.