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Estimating Rock Permeability from a Leak-off Test and Its Uncertainty
( Nghiep Quach ),( Hyung-mok Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2
Rock permeability is a fundamental parameter not only to understand underground fluid flow in porous media but also to evaluate geomechanical stability through an effective styress concept such that a realiability of rock permeability estimation is important in cases of injection, production, and charaterizing rock formation. In this study, we apply different approaches such as an analytic approach, numerical analysis, inverse analysis and history matching to estimate and compare rock permeability using a leak-off test. The test, that was carried out at constant flow rate of water injection from surface, was run at 4 m open-hole interval below a casing shoe, where the rock formation is mudstone. The analytic approach here is permeability estimation using a diffusion equation which is known to define a transient fluid flow in porous media, and we could obtain the pressure evolution in the form of Theis's equation by solving the equation in specific conditions. TOUGH2 and iTOUGH2 were used for numerical simulation of the test data and for the estimation of uncertain parameters in terms of inverse analysis, respectively, which solves a mas conservation from multiphase Darcy's flow using an integral finite difference method. nSIGHTS was employed as a history matching approach, which had been developed for a well hydraulic test analysis. From the comparision of permeability estimations, we investigated the uncertainties in estimating formation permeability through demonstrating how differently the estimated permeabilities are obtained depending on diferent approaches and how much a flow model may influence these estimations.
Rock Permeability Estimation from Hydraulic Injection Tests in a Sealed Borehole Interval
( Nghiep Q. Quach ),( Yeonguk Jo ),( Chandong Chang ) 대한지질공학회 2018 지질공학 Vol.28 No.1
We propose a borehole test technique to estimate permeability of rocks in borehole. The borehole tests are hydraulic injection tests such as leak-off test and hydraulic fracturing tests, which are originally conducted for stress or casing integrity assessment and not for permeability measurement. We use one-dimensional radial diffusion equation to interpret fluid injection test results in terms of permeability. We apply this technique to a leak-off test conducted at a depth of 700 m in a wellbore, where rock formation is mudstone. The estimated permeability is at an order of 10<sup>-16</sup> m<sup>2</sup>, which is somewhat high but within the range reported for mudstones previously. Quantitative rick assessment suggests that an accurate measurement of open hole section length is important to improve reliability of results. More data may be needed to ensure the reliability of this technique. If validated, however, this technique can provide cost-effective estimation of in situ permeability without conducting independent permeability tests in borehole.