Technology and application of reservoir fine description via drilling-seismology-dynamic integration for offshore areas with scarce wells in the PH Oilfield, Xihu Sag

In recent years, with the improvement of exploration and development, offshore oilfields have gradually entered the evaluation stage of potential reservoirs. However, the reservoir research of offshore oilfields faces problems in general such as sparce drilling data, large burial depth, low resolution of seismic data, and thin reservoir thickness. Fine description of the reservoir in offshore areas with sparce wells has gradually become one of the main bottlenecks restricting the exploration and development. Based on relatively abundant drilling data, well logging data, high-quality OBN seismic data, and production dynamic data in the PH Oilfields, we proposed a method of fine description of reservoir by integrating geology, logging, seismic, and reservoir engineering in the P4-4 layer in the Oligocene Pinghu Formation as a case. First, based on the core facies, we determined that the P4-4 layer in the target area is dominated by distributary channel-crevasse sedimentary system of delta plain; combined with the modern sedimentary model, the sedimentary microfacies combination of distributary channel-crevasse channel-natural levee-crevasse splay was proposed. Secondly, the single-layer fine correlation technology based on geological genesis was developed, the P4-4 layer was divided into four single-layer sand bodies, and the single-layer thickness was defined into 2 m in precision, and the vertical evolution model of distributary channel-crevasse sedimentation was established. Thirdly, based on high-quality OBN seismic data, −90° phase shift and frequency-division RGB fusion technology was applied to characterize the distributary channel-crevasse splay sand bodies with different thicknesses. Finally, multi-data mutual verification among cores, single well profile, and inter-well correlation was conducted to realize semiquantitative to quantitative characterization of the distributary channel-crevasse splay sand bodies. Therefore, the rolling evaluation strategy of lithologic gas reservoir in the PH Oilfields was proposed, based on which the deployment of Well X19 has been proved a successful breakthrough in lithologic gas reservoir field, presenting a meaningful guidance for the rolling evaluation of lithologic gas reservoir in other offshore oilfields.