A simplified formula is given for the gravity effect of a horizontal semi‐infinite block truncated by a dipping plane. This formula is used to obtain curves illustrating the gravity anomalies for blocks having different thicknesses and depths truncated by planes dipping at various angles. By combining two blocks, results are obtained for faulted horizontal beds for a wide range of bed thicknesses and depths, fault displacements and dips. These should be useful as guides in interpreting fault anomalies, and in planning gravity programs intended to map faults. The most striking feature of the curves is the marked effect of the dip of the fault plane on the curves for faulted beds. The asymmetry of the fault curves is related mainly to the dip and can be used to determine dips between 30 and 90 degrees. If the dip of the fault, density contrast, and bed thickness are known, the depths to the bed on the two sides of the fault are given by the sizes and positions of the gravity maximum and minimum.

The Fourier transform formula for a two‐dimensional fault truncating a horizontal bed at an arbitrary angle of inclination is derived. The amplitude spectrum of the Fourier transform is found to give information about the depth to the top of the upper part of the faulted bed and the inclination of the fault‐plane. Under suitable conditions the thickness and the displacement of the bed involved can be obtained. With actual field data, these transforms can be obtained at discrete points by a Fourier analysis of the gravity anomaly. A field example from the Logan fault area near Montreal, Que., Canada, is given.

Geologic problems encountered in four U.S. DOE-sponsored EOR projects in clastic reservoirs were analyzed. The reservoir heterogeneities were grouped into four categories: depositional, diagenetic, structural, and formation-fluid composition/distribution. Each category had a variable effect on the performance of the EOR projects.Requirements for developing one static geologic model for each category of heterogeneity are proposed. The interrelationship of geologic factors and the effect of heterogeneities resulting from the origin and timing of geologic events are described.Besides heterogeneities associated with the depositional environment, which has a significant effect on EOR performance, diagenetic effects resulting from geochemical alterations and different types and polymorphs of clays are also important but are often neglected. The structural component of the model needs to be improved through the application of new methodology or improvements in existing technology (e.g., remote sensing, high-resolution seismic). A realistic prediction of fluid movement in clastic reservoirs subjected to EOR requires the integration of the four models that define all the heterogeneities.

This paper synthesizes geologic information, acquired from the literature and field studies, and provides detailed maps of geologic heterogeneities, obtained from log and core data, of the Bell Creek field, MT. Geologic heterogeneities were correlated with fluid production data to identify the heterogeneities that have a dominant effect on fluid production. Integration of new and existing information from various geological, geophysical, and engineering disciplines allowed us to identify heterogeneities that influence production during different recovery operations.

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