三角洲平原砂岩差异成岩及其对储层分类的控制作用——以鄂尔多斯盆地西南部殷家城地区延安组为例

成岩作用直接影响储层的孔隙演化，控制储层物性及含油性，厘清储层的差异成岩作用及其与油气充注的序列对油气勘探具有重要意义。通过岩芯观察和各类薄片显微镜下鉴定统计，综合X衍射、荧光、物性和压汞等多种测试手段，对殷家城—合道地区延安组三角洲平原砂岩差异成岩演化及其对储层分类的控制作用进行研究。结果显示:原始沉积和成岩流体的差异性是储层差异成岩的主要原因，不同成岩相和储层类型与试油产量均具有较好的对应关系。分流河道中—粗粒砂岩原始孔隙度大，酸性溶蚀作用较强，粒模孔和喉道发育，孔喉连通性好，为大孔喉中孔中高渗储层，多见工业油流井，为Ⅰ类储层；分流河道中—细粒砂岩成岩演化较为缓慢均一，酸性溶蚀产生大量散点状溶孔，孔喉连通性差，为与Ⅰ类储层主要区别，孔隙度相当但渗透率较小，为小中孔喉、中孔中低渗储层，多见低产油流井，为Ⅱ类储层；天然堤含泥细—粉砂岩压实作用强烈，云母弯曲变形，为主要减孔因素，根据方解石含量可将其进一步分为两类，一类无明显方解石胶结，为特小孔喉、低孔特低渗储层，多产水，另一类发育强烈压实作用的同时见大量方解石胶结，为致密无效储层，多为干层，二者均划分为Ⅲ类储层。各类储层的空间分布与单井试油产量间具有较好对应关系，可为下一步储层甜点的预测提供理论支撑。

Differential Diagenesis of Delta Plain Sandstone and Its Control on Reservoir Classification: A case study on Yan'an Formation in Yinjiacheng area,southwestern Ordos Basin

Diagenesis directly affects the pore evolution of reservoirs and controls the physical properties and oil content of reservoirs. It is of great significance to clarify the differential diagenesis of reservoirs and the sequence of hydrocarbon charging. Several techniques were used to study the sandstone reservoir rocks of the delta plain subfacies in the Yan' an Fm (J₁y) in the Yinjiacheng-Hedao area:observation of cores and thin-section optical microscopy, XRD, fluorescence, physical properties, mercury injection, and other testing methods. The study has shown that the differences in the original sedimentary features and diagenetic fluids are the main reasons for the differences in reservoir diagenesis. There is good correspondence between diagenetic facies, reservoir types and oil production.Medium-tocoarse-grained sandstones in distributary channel sedimentary microfacies have large initial porosity, strong acid dissolution, well-developed grain mold pores and throats, and good pore-throat connectivity. The porosity range is 11%18% and the permeability range is (20-1 000)×10-3 μm2. Displacement pressure fluctuates between 0.02 MPa and 0.1 MPa, and the median pressure ranges from 0.04 MPa to 1.3 MPa. The median radius range is 16-27.1 μm. This develops large pores and throats and results in medium-porosity and medium-to-high permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, which produces industrial-grade oil flow and is classified as a Type I reservoir.The diagenetic evolution of medium-to-fine sandstone in distributary channel sedimentary microfacies is relatively slow and homogeneous. Acid dissolution produces a large number of dispersed dissolution pores but the connectivity is poor and therefore its permeability is low. This is its main difference from a Type I reservoir with similar porosity. The porosity range is 11%-17% and the permeability range is (3-60)×10-3 μm2. The displacement pressure fluctuates between 0.03 MPa and 0.41 MPa, and the median pressure ranges from 0.1 MPa to 2.0 MPa. The median radius is 0.8-7.2 μm. Small-to-mesopores and throats are developed, forming medium-porosity and medium to low permeability reservoirs. This type of reservoir rock has undergone phases 1, 2 and 3 hydrocarbon charging, and has low oil flow. It is classified as a Type Ⅱ reservoir.Pelitic fine siltstone in natural levee sedimentary microfacies is strongly compacted, which is the main cause of the small pore size. It is characterized by the bending deformation of mica. This type of reservoir has a porosity from 5% to 13% and a permeability from (0.05-3)×10-3 μm2. The displacement pressure fluctuates between 0.4 MPa and 0.9 MPa; median pressure ranges from 2 MPa to 5 MPa. The median radius ranges from 0.4 μm to 1.3 μm. Such reservoirs are low-porosity and extra-low-permeability reservoirs, or ‘tight’ reservoirs. Depending to the calcite content, this kind of reservoir may be further divided into two types. One kind has no obvious calcite cementation, and because it develops extra-small pore throats, it is regarded as a low-porosity and extra-low-permeability reservoir. This kind of reservoir has undergone stages 1 and 2 hydrocarbon charging, which has high water production. The other kind has developed both strong compaction and a large amount of calcite cementation. This kind has no hydrocarbon display, and is regarded as a ‘dense’ or ‘invalid’ reservoir. This kind of reservoir is a ‘dry layer’. Both of these are classified as Type Ⅲ reservoirs.Strong relationships were found between the spatial distribution of the different reservoir rock types and the oil yields of individual wells, so it is suggested that this study provides theoretical support for the prediction of further productive reservoirs.