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

Abstract

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. *Mark of Schlumberger

Evaluation of Residual Oil Saturation in the Secondary Gas Cap of a Mature Carbonate Reservoir from Multi-Dimensional Magnetic Resonance Logging

“…There are several methodologies available to estimate ROS/Sor from logs (Al-Harbi, 2011; Schmitt, 2011) from a single pass, including Resistivity, NMR, PNL (Pulsed Neutron logs, C/O and Sigma) and dielectric logs; or from multiple passes, including NMR LILfor shortening or "killing" the water signal by doping the mud (Horkowits, J.P., 1997;Hassoun, T.H., 1997), and Micro injectivity pilot for in-situ injection with a Wireline Formation Tester (Arora, 2010;Edwards, 2011). In the case of the gas cap in Mauddud there is an additional complication, because three fluid phases co-exist in the reservoir: gas, oil and water.…”

Feasibility of an EOR MicroPilot for Low-Salinity Water Flooding

“…Cherukupalli et al (2010) presented flow modeling of the first MicroPilot showing that the saturation changes measured by the logs could be successfully matched by a relatively simple model of the ASP process. Finally, Edwards et al (2011) recently reported on the second application of the technique, which was conducted in a light-oil carbonate reservoir using an alkaline-surfactant mixture as EOR fluid.…”