Depositional Micro-facies Analysis And Potential Reservoir Prediction In82Block Of Tazhong Uplift

The complexity in carbonate reservoirs is formation heterogeneity due to fractures,vugs, and mixed facies. The lithology distribution is controlled by multiple effects, such assediment source, depositional environment, and diagenesis. Fracture development isinfluenced by lithology, burial depth, local structure and far-field stress. Lithology, ancienttopography, ancient weather, and sea level change control the vugs and Karst development.High-resolution sequence stratigraphy is one of the advanced methods to resolve thelithology challenge with facies identification. The method combines core analysis,conventional logs, outcrop studies, and seismic data to build multiple-ranks sequence andthen predict the sedimentary distribution. However, the analysis results are frequentlyconstrained by the low resolution of the seismic and conventional log data and by limitedcore data.In this paper, we propose a new workflow for high-resolution sequence-stratigraphyanalysis by integrating borehole resistivity images. First, the borehole resistivity images arecalibrated with core data; then the depositional facies are identified from calibratedresistivity-image data combined with multiple-domain data through supervised neuralnetwork method. Second, multiple-ranks base levels are identified from seismic andborehole resistivity image data; and the thickness change of cross bedding and depostionalfacies column are used to classify the strata stacking patterns. Third, the ancient topographymap was built from sequence-stratigaphy analysis and then the vugs and Karst distributionwas summarized within a sequence stratigraphy framework. Finally, the sweet spot waspredicted combining with fracture evaluation from seismic structure.We present a case study where this new approach was implemented in the Block A ofthe Tazhong uplift in the Tarim basin. Seven different depositional facies were identifiedfrom three wells-core data to build the continue facies column for every well after appliedto additional4wells and non-cored intervals.3different base-levels were classified fromborehole resistivity image and seismic data. Sequence framework was built after stratastacking patterns identified. The thickness of top long term base level was used to analyzethe vugs distribution by integrating with single well secondary porosity results fromborehole micro-resistivity image. The local structural curvature controlled the fracture distribution based on single well fracture parameters and curvature computation. The sweetarea was predicted from vugs and fracture potential distribution. A recently drilled wellconfirmed these results and approved the workflow can be applied to similar thickcarbonate reservoirs in shoal-reef margin of a carbonate platform.