窄河道远源致密砂岩气藏断层特征及天然气富集规律——以四川盆地中江气田侏罗系沙溪庙组气藏为例

Fault features and enrichment laws of narrow-channel distal tight sandstone gas reservoirs:A case study of the Jurassic Shaximiao Fm gas reservoir in the Zhongjiang Gas Field, Sichuan Basin

四川盆地中江气田侏罗系沙溪庙组气藏是中国石化西南油气分公司"十二五"天然气增储上产的主要阵地,过去"烃源断层+河道砂岩体+局部构造"的天然气成藏富集模式不能有效地指导勘探井位部署,严重制约了该地区的天然气勘探开发进程。为此,基于断层演化、断层要素、断砂配置(烃源断层与河道砂岩体的配置关系)、圈闭类型、气藏解剖等分析,探讨了区域断层特征及天然气成藏富集规律。结论认为:(1)该区沙溪庙组气藏成藏富集规律主要受"源、相、位"三个因素的控制,具有"源控区、相控带、位控藏"的规律,即"深源浅聚、断砂疏导,多期河道、差异成藏,调整富集、甜点富气";(2)烃源断层和河道砂岩体良好的配置关系是该区天然气成藏的基础条件,天然气在断砂配置好的构造或部位优先富集成藏,后期构造调整形成的单斜构造仍可富气成藏,而多断层夹持区及断层破碎带附近则主产水、不成藏;(3)断层不发育区或远离烃源断层30 km的河道远端含气性差,富气河道砂岩体构造低部位适宜滚动建产。上述新认识可为今后川西地区中浅层天然气勘探目标优选和滚动建产提供指导。

The Jurassic Shaximiao Fm gas reservoir in the Zhongjiang Gas Field, Sichuan Basin, is the main base of Sinopec Southwest Oil Gas Company for gas reserve and production increase during the 12 th Five-Year Plan. However, its natural gas exploration and development process is restricted severely, since the exploration wells cannot be deployed effectively in this area based on the previous gas accumulation and enrichment pattern of ＂hydrocarbon source fault ＋ channel sand body ＋ local structure＂. In this paper, the regional fault features and the natural gas accumulation and enrichment laws were discussed by analyzing the factors like fault evolution, fault element, fault-sandbody configuration（the configuration relationship between hydrocarbon source faults and channel sand bodies）, trap type, and reservoir anatomy. It is concluded that the accumulation and enrichment of Shaximiao Fm gas reservoir in this area is controlled by three factors, i.e., hydrocarbon source, sedimentary facies and structural position. It follows the accumulation laws of source controlling region, facies controlling zone and position controlling reservoir, which means deep source and shallow accumulation, fault-sandbody conductivity, multiphase channel, differential accumulation, adjusted enrichment and gas enrichment at sweet spots. A good configuration relationship between hydrocarbon source faults and channel sand bodies is the basic condition for the formation of gas reservoirs. Natural gas is accumulated preferentially in the structures or positions with good fault-sandbody configuration. Gas reservoirs can also be formed in the monoclinal structures which are formed after the late structural adjustment. In the zones supported by multiple faults or near the crush zones, no gas accumulation occurs, but water is dominantly produced. The gas-bearing potential is low in the area with undeveloped faults or being 30 km away from the hydrocarbon source faults. So a rolling productivity-construction mode is proposed in structural lows of rich gas channel sand bodies. This understanding offers guidance to the future target optimization and rolling productivity construction of shallow-middle gas reservoirs in the western Sichuan Basin.