After Closure Analysis of the Linear Flow Regime in a Fracture Calibration Test
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Date
2016-05-05
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Abstract
After closure analysis (ACA) of a fracture calibration test designed to provide closure pressure and the fracturing fluid leak-off coefficient can provide estimates for formation permeability and pressure if radial flow is visible before the end of the acquired pressure falloff data. In very low permeability formations, the time required for the fracture calibration test to reach radial flow is likely to be impractically long, but the linear flow regime is likely to appear immediately after closure. The objective of this study is to develop equations for estimation of permeability and fracture half-length from the linear flow regime when the radial flow regime is absent.
The formation permeability can be determined when applying after closure analysis (ACA) of Fracture Calibration Test (FCT). The ACA can also offer a means of determining the initial reservoir pressure, fracture length, and closure pressure which are all crucial parameters of hydraulic fracture design in conventional and unconventional reservoirs.
After closure linear and radial flow regimes are easily identified in the log-log diagnostic plot of pressure change and its derivative with respect to the logarithm of elapsed time. We investigate using a flattening departure from the linear flow regime to estimate permeability when the radial flow is absent. We show how the relationship between reservoir permeability and pore pressure can be used effectively to reduce the uncertainty in the formation permeability estimate when an independent estimate exists for the reservoir pressure. We also show how to estimate the fracture half-length from the linear flow regime once an estimate for permeability has been made. We develop equations for estimating permeability and fracture half-length using values that can be read directly from the log-log diagnostic plot.
The value of this work is to provide parameters of interest within a reasonable fall-off duration. This work shows the flaws in current analysis techniques for linear flow regime and indicate how this regime can correctly estimate permeability and fracture half-length even in the absence of radial flow.
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fracture calibration test, linear flow regime, unconventional, gas