Characteristics of Shanghe sandbody reservoirs and high-solution sequence stratigraphic control in Huimin sag

Abstract：Based on theories and techniques of high-solution sequence stratigraphy and reservoir geology, the authors made a synthetic study of sequence stratigraphy, reservoir characteristics and the control factors of the lower subsection of the 2nd Member of Shahejie Formation (Es22) in Shanghe area by such means as drill core observation, slice identification, property analysis of drill core, logging curve interpretation and mercury-injection analysis, with the purpose of detecting the distribution regularity, the properties and the control factors of Shanghe sandbodies in Huimin sag. It is found that the Es22 could be divided into 3 middle base-level cycles. Sandstone reservoirs with relatively good properties occurred mainly in the early stage of the ascending middle base-level cycle and the late stage of the descending middle base-level cycle, and that the properties of sandstone reservoirs in the descending middle base-level cycle are commonly superior to those of the ascending middle base-level cycle. The following conclusions could be drawn： the properties of the reservoirs are closely related to sedimentary microfacies, i.e., reservoirs in subaqueous distributary channel sandbodies and bayou sandbars have the best properties, but with poor inhomogeneity; far sandbars and front sheet sandstone have relatively inferior properties, and beach-sandstone and interdistributary bay sandstone with strongest inhomogeneity have the worst properties. Planar distribution and inhomogeneity of sandbody reservoirs are mainly controlled by types and distribution of sedimentary microfacies. Therefore, the transference and evolution of the sedimentary facies belt and the vertical inhomogeneity of the reservoirs are all controlled by ascending and descending fluctuation of the base-level. As a result, spatial distribution and inhomogeneity of reservoirs are under the control of ascending and descending fluctuation of base-level cycles.