Browsing by Subject "Permeability in wells"

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Assessment of permeability from well logs based on core calibration and simulation of mud-filtrate invasion
(2004-05-22) Salazar Luna, Jesus Maurcio; Torres-Verdín, Carlos
This thesis describes the application of a novel methodology to estimate permeability of clastic rock formations based on the physics of mud-filtrate invasion. The methodology assumes a key well with a complete suite of well logs and laboratory measurements of porosity, permeability, capillary pressure, and relative permeability. For additional wells in the same field, absolute permeability is estimated by matching the shallow resistivity well log with the electrical resistivity in the flushed zone yielded by the simulation of mud-filtrate invasion. We show the successful application of this methodology for the estimation of permeability in three wells penetrating the same over-pressured tight-gas sands of the East Texas Bossier formation. Conventional core porosity and permeability, along with capillary pressure, are used to determine rock types and flow units in the cored key well. Estimates of permeability based on a modified version of Winland’s equation agree with the measured permeability of the available rock-core samples. Simulations of mud-filtrate invasion account for the process of immiscible flow between mud-filtrate and in-situ gas as well as for salt mixing between mud-filtrate and connate water. Moreover, the simulations properly reproduce the effect of mudcake buildup along the borehole wall. Two-dimensional cross-sections of water saturation and salt concentration obtained from the simulations are used to calculate cross-sections of electrical resistivity. The latter are checked against the measured shallow, medium, and deep resistivity logs to calibrate time of invasion and Archie’s saturation and cementation exponents Based on the analysis in the key well (Well 1), a petrophysical assessment of flow units is performed in two nearby wells (Wells 2 and 3) within the same gas field. Initial Winland permeability values are progressively adjusted until the calculated cross-sections of electrical resistivity agree with the shallow array induction resistivity readings. For Well 2, the estimated permeability is equal to the initial guess, whereas for Well 3 the estimated permeability is approximately 50-80% higher than the initial guess. The permeability values estimated with the methodology described in this thesis are consistent not only with the petrophysical properties of the near-borehole region but also with the length of investigation and vertical resolution of wireline induction logs