Abstract

A vertical pulse test was conducted in a water injector in the Goldsmith San Andres Unit (GSAU) in West Texas for determining the integrity of a low permeability barrier separating two carbonate facies. This test was conducted as part of a CO2 pilot project. The effective vertical sweep efficiency is controlled by the barrier and is important to quantify.

The pulse test design was tempered by tailing it with a standard interference sequence to mitigate unforeseen situations. This proved useful as the reservoir pressure was lower than anticipated and the well went on vacuum. The data was interpreted using conventional techniques and numerical modeling. The numerical model was tuned to provide transient quality results by comparing against standard analytical solutions before using it to interpret the pulse test.

This paper presents the conduct, analysis and interpretation of the vertical pulse test and discusses some of the learnings. Sensitivity analysis was performed on slab, layercake and geostatistical models for the flooding pattern, to understand the influence of small scale heterogeneity on short tests. The results indicate that one can distinguish between a casing leak and reservoir vertical communication from a pulse test. The vertical permeability governs the peak arrival and magnitude of the pulses whereas the horizontal permeability controls the magnitude and shape of the fall off portions of the test.

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