THE LITHOFACIES AND MICROFACIES OF HBJM39-1 GAS RESERVOIR IN YINGGEHAI BASIN OF NORTHWESTERN SOUTH CHINA SEA

Based on drilling data from the wells of HBJM39-1-1, HBJM39-1-2A, HBJM39-1-3 and HBJM39-1-4, in connection with the seismic sequences, we deeply studied the lithofacies of HBJM39-1 gas reservoir in the Yinggehai Basin. Results show that the lithofacies of the HBJM39-1 gas reservoir is characterized by deep color and fine grained deposits with bioturbation and intercalation of storm deposits, formed under weak hydrodynamic conditions. Palaeogeomorphological reconstruction with seismic and core data indicate that the HBJM39-1 gas reservoir was formed in a relatively deepwater environment. Littoral and shallow marine facies dominate the sequences from the 1st member of Yinggehai Formation of Pliocene up to the 3rd member of the Quaternary Ledong Formation. However, facies analysis based on water chemistry, ichnofacies, lithology and logging facies reveal that there also occurs subtidal subfacies. No foreshore and shoreface deposits have been found so far. We also studied in this paper the permeability of the reservoir based on mud and sand ratio. And offshore marine subfacies are also deeply studied.