Accurate In-Situ Fluid Analysis Aids in Reliable Reservoir Evaluation in Pearl River Mouth Basin

This paper will present two case studies accurate in-situ fluid analysis aids in reliable reservoir evaluation in Pearl River Mouth basin. In the first case, no reliable pressure gradient was achieved to indicate formation fluids due to severe supercharging despite an extensive pressure survey. Five in-situ fluid analysis stations including three sampling stations were conducted. Comparison of the in-situ fluid analysis data, including C1, C2, C3–C5, C6+, CO2, gas/oil ratio (GOR), and density, indicates excellent tool resolution. The vertical variation of oil properties reveals a more complex system than the initially expected single oil column. Two tendencies of oil property variations may be controlled by two depositional systems. Vertical compartmentalization was then characterized. A second case involves a gas reservoir containing significant CO2 with a thin carbonate layer between the upper and lower sections. Accurate in-situ density measurements combined with pressure transient analysis enabled reconstructing the fluid gradients and gas/water contact. In-situ fluid measurements indicate that the thin carbonate could act as a vertical barrier. These case studies demonstrate that the use of reservoir fluid properties can be extended from standalone PVT results to delineation of important geological features such as compartmentalization and petroleum systems.