Technical Paper: Single-well In-situ Measure of Oil Saturation Remaining in Carbonate after an EOR Chemical Flood

Society: SPE
Paper Number: 141091
Presentation Date: 2011
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The MicroPilot is a log-drill-inject-log sequence of operations designed to evaluate the improvement in oil recovery resulting from the addition of chemicals to the injected water. The fluid to be injected is transported downhole in a sample chamber and injected into the formation through a pencil sized drilled hole, with measurements of the resulting changes in saturation proximal to the well. This technique was first used during 2009 in Oman to perform an in-situ test of alkaline surfactant polymer in high porosity-permeability clean sandstone saturated in medium viscosity oil.

This in-situ measurement is even more relevant for carbonates, as it eliminates the uncertainty associated with restoring mixed wettability in cores prior to laboratory enhanced oil recovery (EOR) floods. However executing a log-drill-inject-log sequence of operations in tight carbonates is more complex than clastics. The issues include small scale heterogeneity, presence of natural or induced micro-fractures, varying residual oil saturations, and the low permeability that requires injecting at pressures above the drilling fluid hydrostatic pressure.

The operation and results of the first use of this EOR screening technology in carbonates is described in this paper in which an alkaline surfactant mixture (AS) was injected into a partially water swept 3mD permeability carbonate containing light oil. Aspects described include the mechanical process of drilling and injecting AS and the petrophysics of measuring changes of oil saturation at a small scale. The saturation changes are compared with other AS flood measurements in a neighboring well test using Single Well Chemical Tracer (SWCT) and cased hole logs.

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