东胜气田锦58井区下石盒子组致密砂岩气藏气水关系

Gas-water relation in tight sandstone gas reservoirs of Lower Shihezi Formation,Jin 58 wellblock,Dongsheng gasfield

为了明确鄂尔多斯盆地东胜气田锦58井区下二叠统下石盒子组致密砂岩气藏气水分布关系及影响因素,以气藏地质特征为研究基础,分析了下石盒子组气藏地层水的化学特征和赋存状态。研究结果表明:①地层水型为高矿化度氯化钙型,地层水地球化学特征参数反映出储层封闭条件好,有利于天然气的聚集和保存;②地层水分为边底水、透镜状水体及滞留水3种类型;③平面上以气水同层、含气水层分布为主,纵向上多个气水系统共存,无统一的气水界面。结论认为:①气水关系主要受生烃强度、储层连通性、储层非均质性及局部构造的共同影响,其中储层连通性越好越有利于天然气聚集成藏,反之易形成透镜状水体;②储层非均质性导致纵向剖面呈现"气层-干层-水层"的叠置分布;③局部构造微断裂、微裂缝既是有利的天然气运移通道,又是储层改造沟通它层水体的主要途径,而局部构造高点或构造隆起是天然气的相对富集区。

In Jin 58 wellblock,Dongsheng gasfield of Ordos Basin,in order to clarify the gas-water distribution in tight sandstone gas reservoirs of Lower Permian Lower Shihezi Formation and its influencing factors,some chemical characteristics and occurrence states of formation water in these reservoirs were analyzed based on their geological characteristics.Results show that(1)the formation water is one type of chloride calcium with high salinity,and its geochemical parameters reflect better sealing conditions favorable for gas accumulation and preservation;(2)it may be classified into three types,i.e.,edge/bottom water,lens-shaped waterbody,and detained water;and(3)gas/water layer or gas-bearing water layer are areally dominant and multiple gas-water systems coexist vertically without a united gas-water interface.In conclusion,the gas-water relation is mainly under the joint control of hydrocarbon-generating intensity,reservoir connectivity and heterogeneity,and local structure,in which better the reservoir connectivity,more favorable for gas accumulation,otherwise the lens-shaped waterbody tends to form.Heterogeneity leads to the superimposed distribution of"gas layer-dry layer-water layer"in the vertical profile.Some local structures such as microfault and microfracture are not only the favorable migration pathway but also the main way to communicate waterbody with some other layers through reservoir reform whereas others including high point and uplift belong to certain belts relatively rich in natural gas.