Reservoir Modeling of Fan Delta with Sparse Wells: A Case from CFD Oilfield in Shijiutuo Uplift, Bohai Bay Basin

Abstract

The third Member of Dongying Formation reservoir in CFD oilfield is steep slope fan-delta deposits; it was penetrated by 6 wells, each well belongs to different fan body. 143 meters oil reservoir was found in well 1, the lithologic combination are complex pebbly sandstone and sandstone with undeveloped interlayer. The reservoir feature is low porosity and low permeability, large thickness with quick lateral variance, and strong internal heterogeneity, which made reservoir characterization challenging. Firstly, high resolution sequence stratigraphic framework of the third Member of Dongying Formation reservoir was established by using of core, log and seismic data, guided by sequence stratigraphy and sedimentology. Then, microfacies classification scheme was determined by actual data and the depositional model. The spatial distribution regularity of fan delta and its microfacies was researched by seismic sedimentology attribute slice and sedimentary numerical simulation. Combined with rock composition features, physical properties, diagenetic characteristics, etc., reservoir classification evaluation was researched. Lastly, a geological model was established for quantitative prediction of the 3d distribution and physical distribution of each reservoir type. The third Member of Dongying Formation reservoir of well 1 block was divided into Lowstand Systems Tract and Transgressive Systems Tract, subdivided into six subsequence sets and 11 subsequences. Good reservoir was mainly distributed in the upper subsequences of Transgressive Systems Tract. Through fine seismic explanation, the plane distribution of each subsequence was determined. The fan delta was divided into six microfacies, including main channel, sheetflood sand beach, braided channel, overflow sand beach, sheet sand and lacustrine mudstone. Middle-fine sandstone and well sorted pebbly coarse sandstone in braided channel and main channel are good reservoir. Based on seismic sedimentology, different strata slicing schemes were used to extract seismic attributes for spatial distribution prediction of good reservoir. Together with sedimentary numerical simulation, the planar distribution and vertical evolution of fan delta and its microfacies were researched, then fan delta sedimentary model of good reservoir developed and Transgressive Systems Tract was established. Based on the study above, the reservoir was divided into four types with different physical characteristics. Then reservoir distribution and physical property distribution of all types were quantitatively predicted by geological modeling. Lastly, a more accurate geological model was provided for oilfield development plan design. Geological model of CFD oilfield was established by comprehensive application of sequence stratigraphy, seismic sedimentology and sedimentary numerical simulation. The modeling method adequately simulated the reservoir heterogeneity and fluid flow characteristics of complex fan delta reservoir with sparse wells in oilfield development plan design stage. The method will be used to guide the fine characterization of more similar oilfields in Bohai Bay Basin.