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ABSTRACT: Reservoir Delineation by Geophysical Methods in the Suizhong 36-1 Oil Field, Bohai Gulf, Previous HitChinaNext Hit

John B. Gustavson, Xin Shi Gong

The Suizhong 36-1 oil field is located in Liaodong Bay, People's Republic of Previous HitChinaNext Hit. Oligocene fluvio-deltaic and lacustrine sandstones contain over 1 billion barrels of oil-in-place in a combination Previous HitstructuralNext Hit-stratigraphic trap. An international effort to delineate the reservoirs by geophysical methods was completed in June 1989. Three hundred and fifty kilometers of Previous HitseismicNext Hit Previous HitdataNext Hit were reprocessed and interpreted.

An attempt was made to reprocess vertical Previous HitseismicNext Hit profile (VSP) Previous HitdataNext Hit to better relate Previous HitseismicNext Hit Previous HitdataNext Hit to subsurface reservoir parameters. Unfortunately, incomplete field Previous HitdataNext Hit and/or documentation made such an effort infeasible.

Synthetic seismograms were used for correlation and for wavelet processing of the Previous HitseismicNext Hit Previous HitdataNext Hit. Previous HitSeismicNext Hit-petrophysical analyses were carried out to relate the measurable Previous HitseismicNext Hit parameters to the subsurface rock and fluid parameters.

Previous HitSeismicNext Hit Previous HitdataNext Hit processing comprised conventional reprocessing, special processing primarily for hydrocarbon indicators, and Previous Hit3-DNext Hit velocity analysis. The reprocessing of the Previous HitseismicNext Hit Previous HitdataNext Hit improved Previous HitdataNext Hit quality over that of the original processing. Amplitude versus offset (AVO) processing revealed no obvious hydrocarbon indicators in the main reservoir zones. Velocity analysis produced a Previous Hit3-DNext Hit velocity field that was the key to the interpretation and engineering work that followed.

Stratigraphic and Previous HitstructuralNext Hit interpretation were carried out on a GeoQuest workstation and iterated several times to obtain a consistent match with the wells. Previous HitSeismicNext Hit attribute generation and analysis were used primarily to reveal patterns associated with the depositional environments.

Two kinds of Previous HitseismicNext Hit trace Previous HitinversionNext Hit processes were used to obtain quantitative estimates of the subsurface acoustic impedance distribution. One, the approximate or pseudo-Previous HitinversionNext Hit method developed by Lindseth, was Previous HitappliedNext Hit to 300 km of Previous HitseismicNext Hit Previous HitdataNext Hit and was the basis for all the reservoir parameter estimates. The other, the generalized linear Previous HitinversionNext Hit approach developed by Backus and Gilbert, was Previous HitappliedNext Hit to 20 km of Previous HitseismicNext Hit Previous HitdataNext Hit in the center of the field as part of the special processing requirement.

Three principal approaches to the detection of hydrocarbons were tried in an effort to map oil-water contacts in the field. Relative Amplitude Profiles (RAP) sections and normal-incidence P-wave profiles were analyzed for amplitude anomalies. AVO gradient profiles were analyzed for amplitude gradient anomalies. These efforts failed to detect hydrocarbon presence or oil-water contact levels conclusively.

In order to estimate hydrocarbon reserves and reservoir parameters, seismically derived values of acoustic impedance were converted first into estimates of porosity using the relationships derived Previous HitfromNext Hit Previous HitseismicTop-petrophysical analysis. Next, the porosity distribution was transformed into maps of net reservoir thickness, permeability, and oil saturation. At each stage, the results were calibrated back to the wells to ensure consistency of the estimates. The results suggest that accurate predictions of oil-in-place are possible with this methodology.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990