In-Situ Visualization of Multidimensional Imbibition in Dual-Porosity Carbonates

Abstract

Summary Oil recovery by waterflood is usually small in fractured carbonates because of selective channeling of injected water through fractures toward producers, leaving much of the oil trapped in the matrix. One option to mitigate the low recovery is to reduce fracture uptake by increasing the viscosity of the injected fluids by use of polymers or foams. Another option, that is the objective of this work, is to inject surfactant solutions to reduce capillary effects responsible for trapping oil and allow gravity to segregate oil by buoyancy. Analysis of gravity and capillary forces suggests that such segregation is achievable in the laboratory, provided that cores are moderately long and oriented vertically. Besides investigating the role of gravity on oil recovery, the effect of surfactant-flood mode (secondary-flood mode and tertiary-flood mode) on the ultimate recovery (UR) was also investigated. To investigate the predictions of this analysis, coreflood experiments were conducted by use of carbonate cores and monitored by an X-ray computed-tomography (CT) scanner featuring true vertical positioning to quantify fluid saturation history in situ. Novel aspects of this work include cores that are oriented both horizontally and vertically to maximize gravitational effects as well as a special core holder that mimics aspects of fractured systems by use of the whole core. This paper discusses the contrast in experimental results in vertical and horizontal orientation with and without surfactant. To study gravity effects, surfactant reduced interfacial tension (IFT) from 40 to 3 mN/m. For this mode of recovery, ultralow IFT is not preferred because some capillary action is needed to aid injectant transport into the matrix. The vertical experiment showed that gravity has the potential of improving oil recovery at low IFT. Another surfactant was used to study the flood-mode effect; this surfactant reduced IFT from 40 to 0.001 mN/m (ultralow IFT). In this study, two experiments were conducted: a tertiary-surfactant-flood experiment and a secondary-surfactant-flood experiment. The secondary-flood experiment showed an improvement in recovery with the early implementation of the surfactant flood relative to the tertiary-flood experiment. This work highlights the importance of gravity at low IFT in terms of mobilizing trapped oil and also the effect of flood mode on UR. Moreover, this work emphasizes the use of surfactant solutions as a method of enhancing oil recovery in fractured resources not necessarily because of wettability alteration but mainly because of gravity effects. Experimental results are presented primarily as 1D and 3D reconstructions of in-situ oil- and water-phase saturation obtained by use of X-ray CT.

Micro X-ray fluorescence reveals pore space details and spatially-resolved porosity of rock-based microfluidic devices

“…The carbonate porosity is comparable to reported literature values of 23.8–25% from core plug measurements. 50…”

“…The carbonate porosity is comparable to reported literature values of 23.8-25% from core plug measurements. 50 Thin sections of both rocks, with thicknesses of 200 μm, were obtained by mechanical cutting. The unconfined thin sections were then placed in the static polycarbonate cell, and their connected pore space was invaded with Krypton.…”

Oil Recovery Performance by Surfactant Flooding: A Perspective on Multiscale Evaluation Methods

“…In this method, 1D saturation profiles are produced by scanning the rock sample from the injection end to the outlet end at different flooding stages. From the CT scanner, the porosity and oil saturation can be calculated suing eqs and as follows: ϕ = CT wet − normalCT dry normalCT normalw − CT air S normalo = normalCT x − CT wet ϕ ( CT o − CT w ) where CT dry and CT wet are the CT numbers of the core before and after saturation, respectively CT w , CT o , and CT air are the CT numbers of water, oil, and air, respectively; and CT x is the CT number of the core measured during the flooding process. Figure shows a typical setup for a coreflooding system equipped with an X-ray CT scanner.…”