Reservoir sedimentary characteristics and reservoir prediction in the shelf margin delta of the Zhuhai Formation in the southern subsag of the Baiyun sag in the Pearl River Mouth Basin
SHU Liangfeng, ZHANG Lili, LEI Shenglan, GAO Zhongliang, HAN Xiao, YU Sa
Research Institute, Shenzhen Branch of China National Offshore Oil Corporation Limited, Shenzhen 518054, Chin
The shelf margin delta of the Zhuhai Formation in the southern subsag of the Baiyun sag in the Pearl River Mouth Basin is a focus for domestic deep-water research and an important deep-water exploration target. Based on the surrounding drilled wells, thin section and physical property analysis data, the characteristics of the reservoirs in Zhuhai Formation are investigated, the main factors affecting physical properties are discussed and favorable reservoir distribution is predicted. The result shows that reservoirs with good physical properties had developed in all the delta intervals of the Zhuhai Formation, and the physical properties of the reservoirs decrease with an increase of burial depth. The 1st and 2nd Members of the Zhuhai Formation have the best physical properties. These are mainly medium-high porosity and medium-high permeability. The 3rd and 4th Members of the Zhuhai Formation have medium-high porosity, extra low permeability- high permeability. The 5th and 6th Members of Zhuhai Formation are relatively poor, and have mainly low porosity and low permeability-extra low permeability. The reservoirs on the shelf margin delta of the Zhuhai Formation are controlled by sedimentary facies belts, compaction, and basin heat flow background. Sedimentary facies belts provide the material basis of the reservoirs, and high-quality reservoirs are developed in the high-energy facies belts of the delta front. The compaction was only strong before the 4th Member of the Zhuhai Formation, and the compaction was not strong during the main development period of the shelf margin delta. The high geothermal gradient in the southern subsag of the Baiyun sag promotes the acceleration of diagenesis and the deterioration of the physical properties of the reservoir, but it also has led to secondary pore development zones. The threshold of the burial depth of the reservoir physical properties is 2400~2600 m, indicating that the physical properties of the 4th Member and above of the Zhuhai Formation are relatively good. Favorable reservoirs in the Zhuhai Formation are characterized by high thermal sag, shallow burial and superior facies. They are mainly high-energy facies belts at the front of the shelf margin deltas and deep-water fans near the delta, the physical properties of deep-water fans relatively far from the delta have deteriorated. The shelf margin delta front and deep water fans from the 3rd Member to the 1st Member of the Zhuhai Formation form favorable reservoirs. The most favorable reservoirs developed in the 1st Member of Zhuhai Formation because of its large scale and best physical properties and they can be key exploration targets. The 5th and 6th Members of the Zhuhai Formation are mainly important reservoirs when superior facies and secondary pore development zones exist.
Key words：
shelf margin delta; physical properties; prediction of favorable reservoirs; Zhuhai Formation; southern subsag of the Baiyun sag
