Publications

Seismic methods can assist gas and oil field development in a number of ways: predicting structure, predicting abnormal pressure by velocity analysis, predicting drilling hazards such as faults, slump zones and gas pockets using shallow seismic data, defining more precisely small faults and other features which affect accumulations, and indicating hydrocarbon accumulations by change in amplitude, frequency content, lowering of velocity, etc. Color displays of amplitude, frequency and velocity measurements can often help define reservoir limits. Development activities often do not make maximum use of seismic data even where such data are already available. Seismic sections processed for exploration objectives may not be optimal for development decisions. Improvements in seismic data processing have been so great in recent years that most data more than 4-5 years old can be enhanced significantly by reprocessing, especially in the light of specific objectives determined from a discovery well. Major companies now often have geophysicists on their development staffs to advise on use of seismic data, but smaller companies may not involve geophysicists with development problems. Approaches to seismic interpretation of hydrocarbon accumulations involve both (1) modeling so as to predict the expressions which situations should produce, and (2) observingwhich are often associated with hydrocarbon accumulations. There are problems in both types of approach because of incomplete understanding of the earth, approximations necessary to make problems tract- able, ambiguities which preclude unique answers, etc. Despite these problems, seismic data can indicate where changes in reservoirs should be expected, lessen the risk of development well failures and suggest adjacent reservoirs. The understanding of reservoir geometry is often very incomplete prior to the drilling of development wells, the additional information obtainable from seismic data can reduce the risks involved and lead to more optimal locating of development wells. It is difficult to determine precisely the circumstances associated with prediction successor failure, Documentation of hydrocarbon prediction is almost completely lacking, at least in the public domain. "Success" often involves a non-sequitor, it is usually measured by economic profitability whereas prediction is usually of lithology, porosity, fluid content, etc., which do not necessarily assure profitability. Several types of phenomena are often associated with hydrocarbon accumulations: - changes in amplitude: - brightening or dimming, - lowering of frequency, - changes in waveshape, phasing or polarity reversal, - lowering of velocity, and delays of deeper data because of this, - flat spots, - association with trapping situations, faults or other structural features.