Abstract
The process of drilling mud filtrate invading into a reservoir is time dependant. It causes dynamic invasion profiles of formation parameters such as water saturation, salinity, and formation resistivity. Thus, the responses of a high-definition induction log (HDIL) tool are time dependent. The logging time should be considered as an important parameter during logging interpretation for the purposes of determining true formation resistivity, estimating initial water saturation, and evaluating a reservoir. The time-dependent HDIL responses are helpful for log analysts to understand the invasion process physically. Field examples were illustrated for the application of present method.
Highlights
Resistivity log is an effective method to estimate the critical properties of a reservoir in petroleum exploration
Since the radial distribution of formation resistivity varies with time, the apparent resistivity of high-definition induction log (HDIL) measurement at time t is determined by resistivity invasion profile Rf(t, r)
It is important that the process of drilling mud filtrate invading into a reservoir is time related, so that the invasion profiles vary with time as well
Summary
Resistivity log is an effective method to estimate the critical properties of a reservoir in petroleum exploration. Induction log is an important tool to measure the formation resistivity. The HDIL instrument is a typical multiarray induction logging tool that measures the formation resistivity simultaneously with six arrays. Conventional invasion model is the static step-invasion profile [3] that presumes that the resistivity varies sharply at the boundary between invaded zone and uncontaminated formation. The present work focused on the influence of dynamic invasion process on HDIL measurements. The theoretical model of dynamic invasion and the geometry factor theory for resistivity log were used to calculate the time-dependant responses of a HDIL device. The present results can give a reasonable interpretation for the difference of resistivity responses at various measurement times. Examples of field applications were illustrated to determine the true-formation resistivity and initial saturation and to evaluate a reservoir
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