In April’s AAPG Annual conference and exhibition, Roxanna Oil Company executives presented a paper on a “quick look” determination of oil-in-place shale resource plays.
A Quick Look Determination of Oil-in-Place in Oil Shale Resource Plays
Quantitative measurements of gas-in-place volumes for coal gas and shale gas resource plays have been important and powerful starting points for planning optimized economic gas extraction. Quantitative desorption measurements of gas-in-place have strongly assisted investor confidence in the exploitation of coal gas and shale gas plays. Gas-in-place measurements provide the resource target that can justify on-going technical and business investments in gas shale resource plays.
With recent successes in apparent commercial extraction of oil from shale, such as in the Eagle Ford Shale of South Texas and the Woodford Shale of southern Oklahoma, the question arises as to the efficiency of oil recovery using current completion and drilling technologies. Given the high likelihood that these plays will prove to be long-term endeavors, it is a strategic and economic imperative that recovery efficiency be optimized, the starting point being the reliable definition of the size of the oil-in-place resource. While this approach does not determine how much oil can be recovered, it provides a measurement of the maximum amount of oil-in-place, the target volume of the play area.
We propose a quantitative measure of oil-in-place from measurements of the distillable oil in an oil shale, specifically from the S1 measurements of a standard Rock-Eval analysis. The measurements obtained may then be up-scaled to calculate oil-in-place for a given formation, trend or basin. By comparing these estimates to estimates of ultimate recovery per well-bore based on decline curve analysis, operators may glean greater insight into their recovery efficiency, and as a result, determine the need for, and lay plans to carry out the minimum amount of drilling and formation fracturing to ensure the maximum amount of oil extraction. The ultimate recovery efficiency will be determined over time by iterative applications of technology.
In testing the technique, measurements were made in the Eagle Ford Shale of South Texas and in the Woodford Shale of southern Oklahoma. Comparisons were made between immature, mature and over-mature source rocks and between core derived measurements and those obtained from drill cuttings. Guidelines are proposed for a simplified quick-look approach with pointers to avoid potential pitfalls and ensure accuracy.