--> Application of Geophysical Technologies Assemblage in Evaluation of Deepwater Fields in the Northern South China Sea

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Application of Geophysical Technologies Assemblage in Evaluation of Deepwater Fields in the Northern South China Sea

Abstract

Several big deepwater gas fields (such as Liwan, Liuhua and Linshui) have been discovered in northern South China Sea. These discoveries have proven the excellent hydrocarbon accumulation in this area. However, because of complicated seafloor topography and reservoir inhomogeneity, it is difficult to precisely image, evaluate and effectively develop these deepwater gas fields. This paper provides a set of geophysical technologies and workflows that have proven to be effective in addressing these problems. Firstly, to solve the problem of seismic imaging, anisotropic pre-stack depth migration process provided high quality and precise depth-domain seismic data. Full 3D visualization and interpretation of the prestack depth-migrated seismic data helped characterize the structural features and build the spatial concept of regional depositional setting and geometry in the study area. Comparisons with analogs of world-wide deepwater reservoirs then helped establish the depositional model. The visualization and interpretation of 3D seismic data indicated that three types of deepwater reservoirs including basin floor fan, confined channel and channel complexes are developed in this area. Petrophysical properties of these reservoir sands and encasing shales are remarkably different in the different parts of the depositional system. Prestack seismic inversion provides the link between petrophysical properties and seismic data and was used to accurately describe the lateral distribution and thicknesses of the main gas-bearing sands. Analysis indicates that different kinds of AVO anomalies occur in the Liwan and Liuhua gas fields and these are useful for delineating the gas-bearing areas. Finally, based on the integrated depositional, structural and reservoir information, 3D geological models were built to conduct reservoir simulation. Based on these models, the original gas in place (OGIP) and recoverable resources were calculated, and the appraisal and development wells were designed. This paper illustrates the effectiveness of these geophysical technologies and workflows using two examples from the Liwan and Liuhua gas fields. The prognoses matched the actual drilling results quite well. It reduced the evaluation risk and pushed forward the process of the deepwater gas development. Liwan gas field went into production in 2014 and the production dynamics so far are as predicted.