Gas‐producing wells in the Barnett Formation show a steep decline from initial production rates, even within the first year, and only 12–30% of the estimated gas in place is recovered. The underlying causes of these production constraints are not well understood. The rate‐limiting step in gas production is likely diffusive transport from matrix storage to the stimulated fracture network. Transport through a porous material such as shale is controlled by both geometry (e.g., pore size distribution) and topology (e.g., pore connectivity). Through an integrated experimental and theoretical approach, this work finds that the Barnett Formation has sparsely connected pores. Evidence of low pore connectivity includes the sparse and heterogeneous presence of trace levels of diffusing solutes beyond a few millimeters from a sample edge, the anomalous behavior of spontaneous water imbibition, the steep decline in edge‐accessible porosity observed in tracer concentrations following vacuum saturation, the low (about 0.2–0.4% by volume) level presence of Wood's metal alloy when injected at 600 MPa pressure, and high tortuosity from mercury injection capillary pressure. Results are consistent with an interpretation of pore connectivity based on percolation theory. Low pore connectivity of shale matrix limits its mass transfer interaction with the stimulated fracture network from hydraulic fracturing and serves as an important underlying cause for steep declines in gas production rates and a low overall recovery rate.
Trace-metal abundances and ratios (Sr/Ca, Mg/Ca, Ba/Ca) in speleothems can be indicators of the hydrogeochemical processes active in overlying epikarst and serve as valuable proxies for precipitation amount and source, water residence time, and vegetation cover. However, conventional methods of trace element acquisition can be expensive, time-consuming, and destructive. A semi-portable µ-XRF system is compared to other methods, as it is non-destructive, rapid, and has the capacity to provide high quality datasets. A suite of test scans was performed in order to define the appropriate methodology for the application of µ-XRF in trace metal analysis of speleothems. Statistical analyses were performed on an experimental dataset in order to assess the precision with which data were obtained and determined that there is no evidence for time-dependent behavior within the data and there is no evidence that the data do not follow a Poisson distribution. The optimal count time varies from sample to sample, as it was determined to be a function of the desired level of analytical uncertainty. Sr results for a speleothem obtained through LA-ICP-OES show a high degree of comparability to results obtained through µ-XRF and demonstrate the suitability of this non-destructive method. Sr counts can also be converted to concentration [ppm] via Xray-tube-dependent calibration curves.
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