The transient flowmeter test: Theory and sensitivity analysis

A hydrologic analog of a semi-analytic transient flowmeter test (TFMT) petroleum engineering model for confined layered systems is developed and validated by comparing its performance to that of a numerical finite-difference model. It accounts for inter-layer crossflow, wellbore storage, and a thick skin surrounding a fully penetrating well.; In conjunction with a modified Levenberg-Marquardt algorithm the semi-analytic TMFT model is used to interpret TFMT measurements in synthetic studies. It produces relatively accurate estimates of the hydraulic conductivity and the specific storativity of each layer in the aquifer zone. The skin hydraulic conductivity estimates are also relatively accurate for damaged (low-conductivity) skins and within an order of magnitude otherwise. The skin specific storativity estimates are highly inaccurate.; A sensitivity analysis is performed for three semi-analytic TFMT models. Logarithmic sensitivities are calculated and used to obtain the plausible relative errors as a measure of information content in the well response from each model. The analysis results for synthetic homogeneous aquifers show that the plausible relative errors in aquifer hydraulic conductivity are generally the smallest compared to other parameters. In addition, the plausible relative errors in the hydraulic conductivity of a normal skin (skin conductivity greater than aquifer conductivity) may be more than an order of magnitude greater than the plausible relative errors in aquifer hydraulic conductivity. For damaged skins (skin conductivity smaller than aquifer conductivity), on the other hand, the plausible relative errors in skin hydraulic conductivity are of the same order of magnitude as the plausible relative errors in aquifer hydraulic conductivity. Additionally, plausible relative errors in aquifer specific storativities are an order of magnitude or more greater than the plausible relative errors in aquifer hydraulic conductivities.; For synthetic two-layer aquifers, the sensitivity analysis yields results analogous to those found for homogeneous aquifers. Furthermore, for layers with damaged skins, the plausible relative errors in skin layer horizontal hydraulic conductivities are comparable to those in the aquifer layer horizontal hydraulic conductivities. Whereas for layers with normal skins, these errors may be an order of magnitude greater than the plausible relative errors in aquifer layer horizontal hydraulic conductivities. In addition, the plausible relative errors in aquifer layer vertical hydraulic conductivities may be up to two orders of magnitude larger than the plausible relative errors in aquifer layer horizontal hydraulic conductivities. (Abstract shortened by UMI.)...