A Novel Method of Developing In-Depth Permeability Modification Using Surfactant/Alcohol Blends
- Feliciano M. Llave (IIT Research Inst./NIPER) | Thomas E. Burchfield (IIT Research Inst./NIPER) | Randy E. Dobson Sr. (Akzo Chemicals Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- August 1993
- Document Type
- Journal Paper
- 228 - 232
- 1993. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 1.8 Formation Damage, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.5.2 Core Analysis, 4.1.2 Separation and Treating, 5.7.2 Recovery Factors, 5.4.1 Waterflooding, 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology, 5.3.4 Reduction of Residual Oil Saturation, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 1.10 Drilling Equipment, 5.2.1 Phase Behavior and PVT Measurements, 5.3.2 Multiphase Flow, 5.4.10 Microbial Methods
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This paper describes the development of a novel method of in-depthpermeability modification in porous media using specific surfactant/alcoholblends. The unique features of this method come from (1) the development ofpermeability modification primarily resulting from component separation ofinjected blends, primarily resulting from component separation of injectedblends, (2) in-depth penetration of formations without premature injectivityloss, (3) the capability to propagate the permeability barrier farther throughthe porous media, and (4) ease of cleanup of the porous media. Laboratorystudies showed that injecting these porous media. Laboratory studies showedthat injecting these blends into porous media can reduce permeabilitysignificantly. The degree of permeability barrier penetration was controlledexperimentally, and this barrier was propagated in-depth by subsequentinjection of alcohol slugs. The permeability modification potential of theseblends was comparable with that of conventional gelled-polymer treatments.
Several methods for improving reservoir sweep by use of permeabilitymodification have been proposed. In recent years, permeability modificationhave been proposed. In recent years, there has been considerable interest inthe application of crosslinked polymer technology to alleviate problemsassociated with reservoir heterogeneity. The use of polymer technology forpermeability modification has, however, several limitations that have not beenfully addressed. Problems associated with polymer (or gelled-polymer)treatments include (1) polymer precipitation and degradation under harshreservoir polymer precipitation and degradation under harsh reservoirconditions, (2) limited penetration depth, (3) injectivity loss, (4) viscosityloss caused by shear degradation, (5) poor control of polymer gelation rates,and (6) possible effects of crosslinking polymer gelation rates, and (6)possible effects of crosslinking agents on the environment.
In this work, the use of surfactant/alcohol blends was evaluated as analternative method to improve sweep efficiency by modifying permeability inhighly permeable reservoir zones. When injected as a slug, these blends achievein-depth penetration and reduce permeability contrast, diverting injectedfluid. Injectivity loss and formation damage are minimized because the injectedalcohol-rich surfactant-slug viscosity is initially low. Permeabilitymodification is achieved when a sufficiently high Permeability modification isachieved when a sufficiently high solution viscosity develops as the result ofcomponent separation of the surfactant and the alcohol from the originalinjected formulation as the slug traverses the porous media.
Surfactants were selected from Akzo Chemical Inc.'s Armostim PF series ofsurfactants. The alcohols used included methanol, ethanol (ETOH), n-propanol,isopropyl alcohol (IPA), isoamyl alcohol (IAA), n-butyl alcohol, secondarybutyl alcohol, and tertiary butyl alcohol (TBA). These gas chromatography andClass 1B grade batches were used in the formulations without furtherpurification, The oil was from the Mink Unit in the purification, The oil wasfrom the Mink Unit in the Delaware-Childers field, Nowata County, OK, and drybiopolymer was xanthan gum. All solutions were prepared on a weight-to-weightbasis.
Studies were conducted to determine favorable reservoir conditions forapplication of these blends as permeability modification agents to improvewaterflood sweep efficiency to recover more oil. The viscosity scan resultsindicated that blends containing ETOH, IPA, TBA, and IAA yielded relativelyhigher viscosities compared with blends containing the other alcohols. Theresults also showed that solution viscosity or property did not depend onsalinity, allowing a broad range of applications for these blends and testingat up to 8.5% total dissolved solids (TDS). Fig. 1 is a 3D representation ofsolution viscosities measured for the PF-4/IPA blends and shows solutionviscosity dependence on component concentrations. In these experiments, severalblends developed relatively high solution viscosities. A formulation forpermeability modification that has a low initial viscosity and yields arelatively high viscosity in porous media is desirable. porous media isdesirable. Tests were performed to determine the effects of aging, pHvariations, small iron concentrations on solution stability, and conditionsthat would be expected in a typical oilfield waterflood. These experimentsinvolved viscosity measurements and visual observations of the formulations.Two pH levels (6.5 and 8.5) were tested that represented the range of pH valuesfound in most reservoir brines. Results indicated that pH adjustment alone didnot alter the solution viscosity significantly when long-term effects atdifferent temperature conditions were considered. In general, most of thesolutions retained their viscosity with aging. pH adjustment. and Fe+3-ionaddition. pH adjustment. and Fe+3-ion addition. Adsorption experiments wereconducted to evaluate adsorption rates of the blender on various crushedsandstone samples. Bottle tests were performed where these blends were broughtinto contact with a measured amount of crushed sandstone. These test resultsindicated that higher original alcohol concentration yielded higher alcohollosses when the surfactant concentration in the original solution was less than3 wt %. The corresponding surfactant loss was also considerably higher when thealcohol concentration in the original formulation was less than 4 wt %.Overall, the results showed that the presence of alcohol minimized surfactantloss, while lower presence of alcohol minimized surfactant loss, while lowersurfactant concentrations increased alcohol loss.
Slim-Tube Experiments. Slim-tube experiments were conducted to determinewhether the initial penetration depth of these blends can be controlled by theproportion of the components in the formulation. These experiments wereconducted with a 41-ft-long slim tube with intermediate pressure taps. Anexample experiment involved a 0.2-PV injection of a 5-wt% PF-8 surfactant/6-wt%IPA blend, followed by a waterflood cycle and several alcohol/brine slugs.Figs. 2 and 3 show the results of this experiment. Fig. 2 shows a trace ofdifferential pressure, , in each section as a function of PV's injected. Theresults indicated that, before additional alcohol-slug injections, a pressurepeak propagated beyond the 30ft section but not through the end of the slimtube. Subsequent brine injection did not propagate the slug farther butresulted in overall higher pressure levels in each section. The firstalcohol-slug injection helped propagate the surfactant slug beyond the end ofthe slim tube, but additional alcohol slugs did not seem to contribute to anysubstantial surfactant recovery. Fig. 3 shows the relative mobility achievedduring the experiment. For this study, relative mobility, calculated from themobility, ( )/( ), and normalized to 32 darcy brine permeability, was used asthe measure of permeability reduction.
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