This project was originally conceived to have four tasks that would clarify the storage mechanisms of gas in shale and outline improved methods for determining gas-in-place from field and laboratory methods. The tasks defined were:
Task 1: Summarize current best practices for field recovery of samples. This has been done, reporting Weatherford’s procedures. To a large extent, all service companies follow similar methodologies.
Task 2: Perform isotherm measurements on end member minerals and kerogen-rich material, at controlled temperatures and water saturations. From these data and supplementary literature develop a predictive model that can estimate gas in place using mineralogy, fundamental geochemical properties and best estimates of current in-situ temperature and pressure. This has been completed, and might provide a viable counterpart/ replacement for comprehensive core measurement programs.
Task 3: The purpose was to carry out controlled isotherm measurements. These measurements would simulate the recovery of a pressurized methane plug from in-situ, replicate a period of lost gas during sample recovery, and simulate subsequent canister desorption. This provided enough information to draw basic conclusions about the validity of lost gas predictions in shale and conceptualized improved methods for diffusivity and gas-in-place determinations.
Task 4: Web page (http://sg2.egi.utah.edu/). As time went on, it was determined that a more logical organization of this report was to consider estimating gas-in-place either by direct or indirect methods. We are used to direct methods – such as canister desorption, where a physical core sample is recovered and the evolved gas is measured. Correcting for gas lost during recovery and residual gas, total gas-inplace can be locally determined. This embodies Task 3.
One type of indirect method is well logging. Another indirect method is the predictive model developed under Task 2 in this program. The predictions rely on mineralogy (from logs, full diameter or sidewall core, cuttings, whatever is available), geochemical properties (TOC and Ro, determined from whatever formation material or log is available) and reservoir properties (temperature and pressure).