Basinwide facies distributions of Leonardian (Lower Permian) producing units generated by a core-calibrated, wireline cross-plot technique, Midland Basin, West Texas

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Presenter

David Carr
Research Scientist Associate IV
Bureau of Economic Geology
Jackson School of Geosciences
The University of Texas at Austin

Description

David L. Carr & H. Scott Hamlin*
Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin
*retired

Deep-water Leonardian (Lower Permian) strata have been prolific Midland Basin, west Texas oil producers since the Spraberry Field discovery in the 1940’s. The thin-bedded, very fine-grained siliciclastic sandstones and siltstones of the Dean and the Lower and Upper Sprayberry units represent lowstand (LST) tracts that alternate with shaly, carbonate-bearing highstand (HST) strata known as the Wolfcamp A (aka Lower Leonard), Middle Leonard (aka L. Spraberry Shale), and the Middle Spraberry units. Thus far, the HST units have been the top producing units driving the current, unconventional Permian Basin oil boom. However, the intervening LST “sandstones” have played large roles in past conventional oil production, and it is likely that these tight, oil-bearing sandstone-siltstone units will be further exploited as unconventional development matures in the Midland Basin. Successfully developing these unconventional targets requires detailed knowledge of structure, gross thickness and internal distribution of lithofacies.

We used wireline log data from over 5,000 wells to make stratigraphic correlations for the Leonardian strata and made wireline facies estimates for 2,100 of these wells throughout the Midland Basin. The wireline facies methodology utilizes a relatively simple, gamma ray (GR) vs. deep resistivity (R_d) cross plot, which after core calibration, provides information and insights into the depositional environments, depositional histories, and oil production potential of Leonardian strata. In wireline facies cross sections and maps, we have observed that Leonardian HST units share general characteristics that set them apart from LST strata. In addition, the geographic distributions and volumes of specific wireline facies in our maps correlate to trends observed in first-year production maps. In this talk, I will discuss the cross-plot/core calibration methodology, present examples of cross sections and maps created using it, and how these products can be useful as exploration and production tools in the Midland Basin.