徐家围子断陷沙河子组致密砂砾岩气藏的成藏期次及类型划分

下白垩统沙河子组是松辽盆地徐家围子断陷最为重要的气源岩之一,但过去对其致密砂砾岩气藏的油气充注时期及成藏期次等研究较少,制约了对该区致密储层成因机制等的认识。为此,基于19块岩石样品273个流体包裹体的均一温度、盐度等测试数据,结合沉积埋藏史和热演化史分析结果,厘定了该区致密砂砾岩气藏的成藏期次;进而通过分析沙河子组储层致密期与成藏期之间的关系,确定了致密气藏的类型。结果表明:(1)该区流体包裹体的均一温度和盐度分布范围较宽,气藏具有长期充注的特点;(2)徐西—徐东地区第1期天然气充注时期在距今94~100 Ma,第2期在距今80~90 Ma,而安达—宋站地区第1期天然气充注时期在距今82~94 Ma,第2期在距今68~82 Ma;(3)安达—宋站地区沙河子组主要发育"先成型"致密气藏,在东斜坡发育"复合型"致密气藏,而徐西—徐东地区沙河子组则以"复合型"致密气藏为主。

Hydrocarbon accumulation stages and type division of Shahezi Fm tight glutenite gas reservoirs in the Xujiaweizi Fault Depression,Songliao Basin

The Lower Cretaceous Shahezi Fm is one of the most important gas source rocks in the Xujiaweizi Fault Depression, Songliao Basin. In the past, however, hydrocarbon charging periods and hydrocarbon accumulation stages of tight glutenite gas reservoirs in this area were less studied, so the understanding on the genetic mechanisms of tight reservoirs is restricted. In this paper, the hydrocarbon accumulation stages of tight glutenite gas reservoirs in the Xujiaweizi Fault Depression were figured out based on the test data of 273 fluid inclusions in 19 rock samples (e.g. homogenization temperature and salinity), combined with analysis results of burial history and thermal evolution history. Then, the types of Shahezi Fm tight gas reservoirs were determined by analyzing the relationship between tightening stage and hydrocarbon accumulation stage. It is indicated that the homogenization temperature and salinity of fluid inclusions in this area are distributed in a larger range, indicating long-term charging of gas reservoirs. Besides, in the West–East Xujiaweizi area, the first and second charging stages of natural gas reservoir is during 94–100 Ma and 80–90 Ma, respectively; in the Anda–Songzhan area, the stages are during 82–94 Ma and 68–82 Ma, respectively. Moreover, "Antecedent" tight gas reservoirs are mainly developed in the Shahezi Fm of the Anda–Songzhan area. "Complex" tight gas reservoirs are developed in the east slope while dominant in the Shahezi Fm of the West–East Xujiaweizi area.