The Liuhua reservoir consists of alternating high- and low-porosity zones of shallow-water algae-foram packstones and grainstones. Horizontal sections of the development wells of this field are drilled in the top of the reservoir and reach up to 2700 feet in length. In order to maximize well length drilled through high-productivity zones, the porosity stratification of the reservoir must be understood in detail. To that end, all development wells are drilled with MWD and LWD tools. In addition, wireline logs were acquired from two wells from opposite ends of the field for LWD calibration.

Subzones in the “attic” of the reservoir do not have any distinctive biostratigraphic or lithologic character that would allow unequivocal identification of thin (3-8 feet thick) individual zones. However, repeated penetrations of these subzones throughout the field suggest that their thickness and sequence seem to remain surprisingly constant over a scale of several kilometers even though the primary depositional facies is shallow water and high energy. Porosity stratification is interpreted as being due to diagenetic processes during minor sea-level fluctuations and periodic exposure of the Liuhua carbonate bank, resulting in porosity enhancement and reduction at the sea water - atmosphere interface.

Interpretation of logs, cuttings, and drilling parameters during and after drilling allow the construction of high-resolution cross-sections which improve our understanding of reservoir architecture and flow behavior. This, in turn, is essential for optimization of well locations, reservoir management, and future investment decisions.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah