COMPUTATION AND 3D VISUALIZATION OF POTENTIOMETRIC SURFACES IN HYDROCARBON-BEARING FORMATIONS ACROSS THE MID-CONTINENT

The determination of formation pressure is extremely valuable to the oil and gas industry as well as an emerging area of interest in carbon dioxide sequestration. To account for land surface elevation changes, regional studies require that pressure be converted to hydraulic head, a parameter commonly used in the field of hydrology. In conventional oil and gas basins, drillstem tests (DSTs) are conducted to record formation pressure for a given depth interval in a well. These DST measurements can be used to calculate hydraulic head values in deep hydrocarbon-bearing formations where water wells do not exist. The resulting calculated hydraulic head values are used to create a potentiometric surface in the same way as hydraulic head measurements from water wells. Unlike hydraulic head measurements in water wells, which have a low number of outliers, only a small subset of the DST data measure true virgin formation pressures. Our goal is to determine a potentiometric surface from DST-calculated hydraulic head values in spite of the erratic data set.

Using 3D imaging capabilities to view and clean the data, we have developed a workflow to create potentiometric surfaces from erratic data sets in hydrocarbon-bearing formations. We have found that the potentiometric surface is more easily defined through human interpretation of the chaotic data set rather than through the application of filtering and geostatistical analysis. Instead of eliminating problematic data points (outliers), we view the data set in a series of narrow, 400-mile-long swaths and systematically select a subset of calculated hydraulic head values interpreted visually along the upper boundary surface in a two-dimensional viewer. The selected subsets for each swath are then combined into one data set for each formation from which three-dimensional potentiometric surfaces are created. We have performed this methodology for multiple formations across the midcontinent of the United States. The final product is an interactive, 3D digital display containing the subsurface structure of the formation, the cluster of DST-derived hydraulic head values, the user selected subset of hydraulic head values that define the potentiometric surface, the resulting potentiometric surface, and the land surface elevation of the region.