Integrated reservoir characterization of Sun Oil and Gas Field, South Texas

Eight stratigraphic units have been identified and correlated within the Frio Formation at Sun Field, South Texas. Seven major depositional systems were recognized, delineated, and mapped. Except for two barrier bar systems developed in the basal units, Frio deposits at Sun Field were dominated by fluvial systems. Specifically, the Gueydan fluvial system was the predominant influence upon Frio deposits at Sun Field. This agrees with the results of previous regional studies of Frio sediments (Bebout and Agagu, 1975; Galloway and others, 1982). The fluvial channels are of various scales. However, they display a fairly uniform convex lower boundary and flat upper boundary geometry, and a multi-story stacking pattern, the phenomenon that has been observed by Feofilova (1954), Fisher and McGowen (1967), and Brown (1969).; A three-dimensional stratigraphic model of the Frio section at Sun Field has been created by stratigraphic modeling. The model dimension is about 5 miles from west to east, 4 miles from south to north, and 1,800 feet in thickness with 139 x 101 x 601 cells. The cell dimension is 200 by 200 feet with an average height of 3 feet. Geological facies distributions, vertical stacking patterns, and rock volumetrics can be imaged and estimated quickly in this 3D earth model.; The relationship between p-wave velocity and rock lithology has been investigated through bivariate and multivariate regression analysis. A normal incidence 3D seismic volume has been created based on the stratigraphic model and on the understanding of rock velocity variations. AVO modeling has been done on an interpreted meandering channel gas reservoir, showing a strong amplitude anomaly as the incidence angle increases. The method may prove especially effective on Frio reservoirs in South Texas due to the predominant gas content and the lack of impedance contrast between the reservoir rocks and background shale. Stratal slicing has proved an effective seismic interpretation technique when interference of surrounding layers is trivial. However, the method does not work well in multi-layer situations (when the interference is strong). In these cases, seismic data inversion is needed to resolve the subtle (reservoir scale) sand patterns.