Title: Log-derived Petroleum Geochemistry Applied to the Lewis Shale
Speaker: by James R. Lancaster
Date: Friday, September 7, 2001
Publication: The Outcrop, September 2001, p. 4
Two previously published techniques are combined to assess the production potential of basin-center gas resources in carbonaceous silty and sandy “shale” lithologies using a normal suite of wireline logs. A technique for determining gas-storage capacity from total organic carbon (TOC) using only core and cuttings is combined with a method of using wireline logs to compute TOC and other petroleum geochemical properties. This presentation will include a brief discussion regarding the development of log-based TOC, using computer software called “Petroleum Geochemistry using Wireline Logs.”
Data are analyzed for three wells in the Late Cretaceous Lewis Shale: one in the San Juan Basin of New Mexico and two in the Sand Wash Basin in northwestern Colorado. The San Juan Basin well is an example of gas production that was developed from previously unrecognized fractured Lewis Shale intervals in a pioneering effort by Burlington Resources. This presentation will include very good comparisons of computed TOC and gas-storage capacity with laboratory TOC and gas-storage capacity in scf/ton on the San Juan Basin well. Production testing in the Lewis Shale in the Sand Wash Basin would help to establish the combined techniques as viable when operators are evaluating source rock/reservoir combinations in other basins.
The results of the log-based evaluations suggest that the combination of these two techniques is an excellent way to assess the potential for hydrocarbon production directly from source rocks. In addition, reliable log-derived TOC can be inexpensively employed in the computation of volumes of adsorbed gas. The greater availability of wireline logs compared to that of cuttings and cores extends the applicability of these combined techniques in any global geologic setting with similar fine-grained carbonaceous lithologies. Finally, log determinations of TOC and the conversion to volumes of adsorbed petroleum products are viable means for the preliminary identification of widespread, yet commonly overlooked, resources.