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Braided River Delta Sand-Body Distribution and Reservoir Predication in a Transfer Zone: Example From the Paleogene Wenchang Formation, HZ-A Block, Huizhou Sag, Pearl River Mouth Basin, China

Abstract

The Pearl River Mouth Basin, is one of the most important petroliferous basins in China. The Paleogene Wenchang Formation is an important hydrocarbon-bearing stratigraphic unit (buried depth > 3500m). HZ-A block, located in the south of Huizhou Sag, covered with 3-D seismic data and only four drilling wells. However, the seismic data is characterized by narrow effective-frequency band and low resolution. Therefore, sedimentary body features including thickness and physical property, which cannot be described precisely and quantitatively by techniques of sequence stratigraphy or seismic sedimentology technology alone. A high resolution inversion technique named seismic phase-controlled Previous HitnonlinearNext Hit random invertion has the advantage of seismic prediction for thin sandstone. It is not limited to the constraint of an initial model and provides inversion results with clear geologic meaning. By using 3-D seismic data and well data, taking techniques of seismic phase-controlled Previous HitnonlinearTop random invertion, combined with sequence stratigraphy and seismic sedimentology, sedimentary facies and sand body distribution of the SQ2 of Wenchang formation has been analyzed in detail. The results are as follows: (1) Braided river delta of three periods are identified in the transfer zone (from base to top: namely D-1, D-2 and D-3), the delta was deposited jointly by the provenances, which controlled different periods of delta. The major oil reservoir is located in the D-2, and the thin sandstone layer of 8~15m can be distinguished in inversion profile. (2) The underwater distributary channel and mouth bar are the favorable reservoirs. We also depicted the thickness map of sand-body (porosity>8%) distribution of D-2. (3) Finally the structural-lithologic trap under the complex geological conditions is identified. In continental basins, the sedimentary facies change quickly, the thickness of sand body is usually thin and the seismic quality of deep-baried formation is often not good, which bring great difficulties to the predication of sand-reservoir. This study demonstrates that facies architecture and sand-body distribution analysis using sequence stratigraphy, seismic sedimentology and high resolution inversion may serve as an effective approach for petroleum exploration in areas lacking of wells or outcrop data.