Identifying potential gas accumulation sites from Oligocene overpressure data in the Qiongdongnan basin, offshore South China

Journal Article · Sat May 01 04:00:00 EDT 1993 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

DOI:https://doi.org/10.1306/BDFF8D8A-1718-11D7-8645000102C1865D· OSTI ID:6418363

Funing, Liu ^[1]

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1. Nanhai West Oil Corp., Guangdong (China)

Overpressure in Oligocene formations in southern Qiongdongnan basin, offshore China, can be determined either by actual measurements in wells or by calculations using data derived from well logs and seismic surveys. The overpressure is mainly the result of undercompaction of Oligocene rocks during rapid loading by Pliocene and Quaternary sedimentation and of the subsequent thermal expansion of fluids in the Oligocene strata. Every formation possesses its own normal compaction trend (plot of shale-interval acoustic transit times vs. depth). The actual fluid pressures and potential pressures can be computed by the equilibrium-depth method. This method must be corrected for the thermal expansion of fluid. The pressure corrections are based on shale-interval transit times from well logs, interval velocities interpreted from vertical seismic profile (VSP) surveys, and stacking velocity from sonic log data of nearby wells. Gas generated from source rocks is assumed to have moved vertically from strata of higher hydraulic pressure potential to those of lower potentials and to have moved laterally and accumulated within areas where the contour closures of a gas equipotential hydraulic-pressure surface (U curves) have lower values. In the study area, the vicinity of the Yacheng gas field, the potential maps (U, gas, and V, water, maps) and hydraulic head profiles can be plotted from values derived either from actual pressure measurements or from calculations. These maps and profiles show prospective areas of gas accumulation. 5 refs., 10 figs., 1 tab.

• OSTI ID: 6418363
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Vol. 77:5; ISSN 0149-1423; ISSN AABUD2
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
ASIA
CHINA
EXPLORATION
FLUIDS
GEOLOGIC DEPOSITS
GEOPHYSICAL SURVEYS
MAPS
MINERAL RESOURCES
NATURAL GAS DEPOSITS
OFFSHORE SITES
PRESSURE MEASUREMENT
RESOURCE POTENTIAL
RESOURCES
SEISMIC SURVEYS
SOURCE ROCKS
SURVEYS