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This technique of linking geochemistry and geophysics is especially valuable in pre-drilling evaluation of hydrocarbon potential in frontier or difficult areas where well data are not
available owing to economic, environmental, or political reasons. Also it is a useful technique for a realistic assessment of hydrocarbon potential in a drilled area for two reasons. First, the proposed method is applicable to the evaluation of hydrocarbon potential in an off-structure area where most of the hydrocarbon generation occurred but where the conventional geochemical methods are useless because of lack of samples. Second, the technique incorporates subtle lateral changes in geothermal gradients--hence maturation level--due to variation in thickness and lithology of sediments.
The proposed method involves three major steps. (1) The thermal conductivity of a formation in a basin is determined from the seismic interval velocity. Then the subsurface temperature is calculated from heat flow (measured or estimated) and the thermal conductivity. (2) The calculated temperature is combined with geologic age derived from seismic stratigraphic or related data to calculate maturation level in terms of vitrinite reflectance (Ro) using our modified Lopatin's method. (3) The calculated Ro value is incorporated with burial history curve to reconstruct organic maturation history diagram. This diagram forms the basis for determining the timing of oil generation and depth interval of the oil window.
We have tested the modeling technique in several sedimentary basins using measured vitrinite reflectance value, DST temperature, and fluid inclusion as checks.
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