鄂尔多斯盆地黄陵地区深水砂岩中碳酸盐胶结物特征、成因及分布规律

Characteristics,origin and distribution of carbonate cements in deep-water sandstones in Huangling area,Ordos Basin

碳酸盐胶结物是影响致密砂岩储层质量的一个重要因素。为预测储层“甜点区”的分布,提高油气勘探开发效率,利用岩心、常规测井、微观岩石薄片等资料,分析黄陵地区长6段致密砂岩中碳酸盐胶结物特征、成因和分布规律。结果表明碳酸盐胶结主要有早期方解石和白云石胶结,中期铁方解石胶结,晚期铁白云石胶结,其中早期方解石占主要含量,分析成因主要为内源成因,中、晚期碳酸盐胶结为内源和外源综合作用的结果。碳酸盐胶结物的分布样式主要有:砂体顶部、底部和中部3种形式,其中砂体底部和顶部延伸较远,中部延伸距离短,规模小。顶部钙质层主要分布在浊流成因砂体中,中部和底部钙质层主要为砂质碎屑流成因砂岩中。碳酸盐胶结物分布明显受沉积和成岩作用的控制因素,钙质层在基准面下降半旋回中较上升半旋回发育,与深湖相泥岩相接触的砂岩更易于钙质层分布;差异成岩演化影响着钙质层分布。

Carbonate cement is an important factor affecting the quality of tight sandstone reservoirs.In order to predict the distribution of reservoir“sweat area”and to improve oil and gas exploration and development efficiency,the characteristics,origin and distribution of carbonate cements in Chang 6 member were analyzed by using the data of core,logging,thin section.The results show that the carbonate cementation consisted mainly of early calcite and dolomite,mid-diagenetic ferroan calcite and late-diagenetic ferroan dolomite in the study area,in which the early calcite was the main content.The main cause of the early calcite was internal sources,while the middle and late carbonate cementation was the result of internal and external sources.Three distribution forms of carbonate cements were identified:the top,bottom and middle of the sand body,among which the bottom and top of sand body extended far,while the middle extended short on a small scale.The top calcareous layers were distributed in the sandstone of turbidity current,and the middle and bottom calcareous layers were mainly in the sandy clastic flow.The types and distribution of carbonate cementation were obviously controlled by sedimentation and diagenesis.Calcareous layers were developed more in the base-level descending cycle than upward cycle.Sandstones in contact with deep-water mudstones were more prone to the concentration and distribution of carbonate cementation.Differential diagenetic evolution affects the calcareous layer distribution.