RESERVOIR PROPERTIES AND FLUID CHARACTERISTICS OF WHJM36-9 GAS FIELD IN YINGGEHAI BASIN, NORTHWESTERN SOUTH CHINA SEA

The WHJM36-9 structure, a mud diapir associated structure extending in south-north direction, is located in southeast of the mud diapir tectonic zone of the Yinggehai Basin, which was formed under the east-west tensile stress derived from the dextral strike-slip movement of the Honghe Fault. The WHJM36-9 Gas Field, that is located in the mud diapir associated structural traps, belongs to a tectonic type of shallow gas reservoir controlled by anticlines and faults. The structural highs of each gas reservoir in this gas field are basically of coincidence, but the deeper structural amplitude is much greater than the shallow ones. The main reservoirs of the gas field are the Quaternary Ledong Formation (Q_pL) and the first member of the Pliocene Yinggehai Formation (N₂Y₁), and dominated by medium-fine sandstone and argillaceous siltstone. Based on the results of core physical property analysis and comprehensive geological evaluation, we found that the first member of Q_pL is the type of reservoir with high porosity and high to mid-low permeability. The second and third members of Q_pL and the first member of N₂Y₁ are the types with high porosity and medium permeability. The low-resistivity gas reservoir of this region is mainly the type of reservoir with high porosity and mid-low permeability. The WHJM36-9 Gas Field is a highly matured dry gas field, of which the main hydrocarbon is CH₄ with low C₂+ (0.49%~2.71%). The formation water is CaCl₂ type for Q_pL and NaHCO₃ type for N₂Y₁. Each gas reservoir has its own formation pressure and gas-water system, and the formation pressure system is normal.