Passive control of VOCs using valved well heads: FY1994 report

Abstract

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Analytical Solution for Subsurface Gas Flow to a Well Induced by Surface Pressure Fluctuations

“…These solutions (often adapted from solutions derived for heat conduction) can predict the magnitude and direction of the pressure differential between the surface and subsurface, and have been used for estimating the effective vertical permeability (k z ) of the intervening materials. The one-dimensional analytical solutions match field data remarkably well given the actual complexity of most subsurface systems (Weeks, 1978;Rossabi and Riha, 1994;and Shan, 1995).…”

“…The pressure model can be calibrated by collecting easily measured field data of surface pressure and subsurface pressure through time (Weeks, 1978;Rossabi and Riha, 1994;Shan, 1995;and Rojstacer and Tunks, 1995). Several iterations of the model are then run using different values of λ z .…”

“…This term is analogous to heat conduction equations with a constant diffusivity and is calculated by best fit to the field data during model calibration. Approximately two weeks of logged data has been sufficient for determining the necessary parameters for accurate future prediction using only surface pressure data (Rossabi and Riha, 1994) and λ z .…”

“…Rossabi Riha (1994). Even though this system is strongly layered, the pressure response at a given depth can be modeled with the one-dimensional, homogeneous model using an average value for λ z .…”

“…More detailed discussion of subsurface pressure modeling using one dimensional analytical solutions and the factors affecting results can be found in Weeks (1978,1979), Rossabi and Riha (1994), Shan (1995), and Rojstacer and Tunks (1995).…”