鄂尔多斯盆地麻黄山西区北部长4+5～长6油层组成岩作用及对储层影响

Study of Diagenesis and Its Effect on Reservoir Properties of Chang 4+5～6 Layer in the North of Western Mahuangshan Area of Ordos Basin

鄂尔多斯盆地麻黄山西区北部长4+5～长6油层组油气显示普遍,但试油水多油少。为搞清储层微观孔渗特征,通过岩心薄片观察及化验资料综合分析,该储层属于特低孔低渗储层,孔喉结构表现为小孔细喉型,孔隙以次生溶蚀孔隙为主。颗粒接触呈现线-凹凸接触。机械压实、压溶作用、钙质沉淀胶结及自生粘土矿物的沉淀造成储层原生孔隙减少;而泥质胶结物的溶蚀与成岩裂缝形成的次生孔缝,尤其顺千枚岩排列方向的溶缝成为油气的主要储集空间。按照成岩阶段划分标准,长4+5～长6油层组大部分层段处于中成岩B期,较强的成岩作用是造成储层低孔低渗的主要原因。结合油气充注时间,认为造成该区油层组含油性差的主要原因是油气充注的时间早于碳酸岩胶结物大量溶蚀的时间,从而部分溶蚀孔不含油。

There were wide indications of oil and gas in the Chang 4+5~6 reservoir in the western Mahuangshan Area of Ordos Basin,it was proven that there was more water and less oil in well test.To understand the characteristics of micro-pore permeability of reservoirs,the reservoirs belonged to the lowest porosity and lowest permeability reservoirs which was indicated by observation of core section and comprehensive analysis of laboratory data.Its pore structure was small pore-thin throat type.The secondary dissolution porosity was dominated.Particle contact shows in line-concave-convex contact .Mechanical compaction,pressure solution,cementation and precipitation of calcium and precipitation of authigenetic clay minerals caused the decrease of primary porosity.The secondary porosity was formed by dissolution of the argillaceous cement and the diagenetic cracks,in particular dissolved fracture ranged along the direction of phyllite became a major space of oil and gas storage.According to the latest criteria for the classification of diagenetic stage of clastic rocks,most of layers are currently in Medium diagenetic phase of B.Intensive diagenesis was the main reason of low porosity and low permeability reservoirs.In combination with oil and gas filling time,analysis shows that the reason of poor oil saturation is that the time of oil and gas filling is earlier than that of massive dissolution of calcareous cement ,therefore there contains no oil in part of the dissolution holes.