A New Gelling System for Acid Fracturing

Woo, G.T.; Lopez, H.; Metcalf, A.S.; Boles, Joel L.

doi:10.2118/52169-ms

Cited by 24 publications

(5 citation statements)

References 2 publications

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“…This could improve the sweep efficiency of the acid. However, Woo et al (1999) indicated the plugging problems were inherent with the conventional crosslinked acid gellants. Chang et al (2001) noted that in-situ gelled acid caused a loss in the permeability in tight carbonate cores because of polymer gel retention at the core face.…”

Section: Introductionmentioning

confidence: 99%

Application of Novel Polymer Assisted Emulsified Acid System Improves the Efficiency of Carbonate Acidizing

Zakaria

Nasr‐El‐Din

2015

SPE International Symposium on Oilfield Chemistry

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In highly heterogeneous carbonate reservoirs, several acid systems have been used to enhance acid diversion during matrix acidizing treatments. Viscosified acid with polymer increases the viscosity of the acid system to improve the wellbore coverage. However, the injection of such acid at low rates had a negative effect on the spending rate and it initiates filter cake formation which inhibits the wormhole growth. On other hand, relatively low viscosity emulsified acid is diffusion retarded which makes it an effective wormholing agent at the low injection rates that occur, for example in low permeability, or damaged formations. None of the studies in the literature address an acid system that uses both advantages.The objective of this work was to investigate the behavior and the performance of a new acid system, polymer assisted emulsified acid, as a self-diverting acid by conducting viscosity measurements thorough coreflood study and acid diversion experiments. The system was 15 wt% gelled acid emulsified in diesel with a 70:30 acid/diesel volume ratio.Coreflood experiments using Indiana limestone were conducted at 230°F at different injection rates and the core samples were imaged using a computed-tomography (CT) scan technique after each coreflood experiment. Also, a 0.5 PV of the polymer assisted emulsified acid was injected to assess the effect of the acid on the permeability of the cores before breakthrough. Finally, two acid diversion experiments at 1 cm 3 /min were conducted into pairs of low and high permeability cores to test the effect of polymer concentration in the acid internal phase on diversion.The viscosity measurements and acid diffusivity measurements showed that increasing the polymer concentration in the acid internal phase of the emulsified acid from 0 to 1.5 vol% significantly enhanced the viscosity of the emulsified acid and reduced the diffusion coefficient by one order of magnitude. Coreflood results showed that the polymer assisted emulsified acid was an effective wormholing fluid at low injection rates while maintaining the high viscosity of the acid system for zonal coverage.Also, it was shown that the emulsion/polymer retention was the main source for permeability damage. However, flowback with mutual solvent removed any remaining damage and permeability enhancement was achieved.Acid diversion experiments are presented that show the self-diverting ability of the polymer assisted emulsified acid into the low permeability cores.

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Section: Introductionmentioning

confidence: 99%

Application of Novel Polymer Assisted Emulsified Acid System Improves the Efficiency of Carbonate Acidizing

Zakaria

Nasr‐El‐Din

2015

SPE International Symposium on Oilfield Chemistry

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“…This is primarily due to the onsite blending and mixing of the base gel and the time that is necessary to produce a consistent base gel. The gelling process is often deliberate to prevent the unhydrated polymer in the reservoir due to the rapid hydration of the polymers …”

Section: Introductionmentioning

confidence: 99%

Copolymer MCJS as a retarder of the acid–rock reaction speed for the stimulation of deep carbonate reservoirs

Quan

Huang

et al. 2014

J of Applied Polymer Sci

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The fast reaction rate between hydrochloric acid and carbonates causes the most acid consumption near the wells, and the acid cannot penetrate the deeper places of the carbonate reservoir; this limits the application of acidizing modifications for the reservoir. In this study, we chose acrylamide, 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), allyl alcohol polyoxyethylene ether (APEG), and N-dimethyl-N-vinyl nonadecan-1-aminium chloride (DMAAC-18) to synthesize a quadripolymer (MCJS) that could reduce the reaction rate mentioned previously. The molecular structure of MCJS was characterized by Fourier transform infrared and 1 H-NMR spectroscopy. The molecular weight and molecular weight distribution of MCJS was determined by gel permeation chromatography. Carbonate rock was analyzed by X-ray diffraction and energy-dispersive X-ray spectroscopy. The retarding properties of the acid mixed with MCJS (MCJS acid) were investigated, and the resulting reaction rate between the acid and carbonate decreased obviously, even at a low viscosity. Scanning electron microscopy and core flood experiments showed that the MCJS could be adsorbed on the carbonate rock surface and form a hydrated film that delayed the reaction.

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“…For heterogeneous reservoirs and for large contrast in permeability, acid diversion is necessary to enhance the outcome of the matrix acidizing treatments (Woo et al 1999;Chang et al 2001;Kalfayan and Martin 2009). Several methods were introduced, tested in the laboratory, and applied in the field such as foambased acids, surfactant-based acids, and in-situ-gelled acids (Smith et al 1969;Nasr-El-Din et al 2006;Yeager and Shuchart 1997).…”

Section: Introductionmentioning

confidence: 99%

HCl/Formic In-Situ-Gelled Acids as Diverting Agents for Carbonate Acidizing

Rabie

Gomaa

Nasr‐El‐Din

2012

SPE Production &Amp; Operations

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In highly heterogeneous carbonate reservoirs, several acid systems have been used to enhance acid diversion during matrix acidizing such as surfactant-based acids and in-situ-gelled acids. In-situgelled acids are also used to reduce leakoff rate in acid fracturing. The main acid used in this system is hydrochloric acid (HCl). However, high reaction rates and severity of corrosion problems, especially for wells completed with Cr-based tubulars, limit the use of HCl at high temperatures. On the other hand, mixing organic acids with HCl either increases the acid penetration or reduces the necessary strength of HCl and the necessary load of the corrosion inhibitors. A few studies addressed the systems that use both advantages.The objective of this work is to investigate the behavior and the performance of different in-situ-gelled HCl/formic acid blends as diverting agents by conducting viscosity measurements, reactionrate measurements using the rotating-disk apparatus, and through coreflood study.Formic acid was blended with HCl, and four in-situ-gelled acids were examined. Formic acid concentration varied from 0 to 6.31 wt%, and HCl concentration ranged from 0 to 5 wt%. Pink Desert limestone was used for reaction-rate and coreflood experiments. The rotating-disk apparatus was used to measure the reaction rate at 250°F at disk rotational speeds of 100 and 1,000 rev/min. The effect of formic acid concentration and zirconium crosslinking on the reaction rate was examined. Coreflood experiments were conducted at 250°F using two different rates of injection (2 and 10 cm 3 /min), and the core samples were imaged using a computed-tomography (CT) scan technique after each coreflood experiment.Increasing formic acid concentration decreased the reaction rate of in-situ-gelled HCl/formic acid with calcite at both low and high disk rotational speeds. This was confirmed by viscosity measurements, which showed that increasing formic acid concentration increased the viscosity of the live acids and decreased the viscosity of the spent acids. Coreflood results showed that increasing formic acid concentration in HCl/formic acid blends reduced acid ability for diversion. In the selected range of acid concentration and for the type of polymer and crosslinking agent used, the insitu HCl/formic acid behaved more like gelled acid and reached a breakthrough in all coreflood experiments. The higher the formic acid concentration, the higher the pore volume of the acid required to break through.

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A New Gelling System for Acid Fracturing

Abstract: This paper was prepared for presentation at the 1999 SPE Mid-Continent Operations Symposium held in Oklahoma City, Oklahoma, 28-31 March 1999.

Cited by 24 publications

References 2 publications

Application of Novel Polymer Assisted Emulsified Acid System Improves the Efficiency of Carbonate Acidizing

Application of Novel Polymer Assisted Emulsified Acid System Improves the Efficiency of Carbonate Acidizing

Copolymer MCJS as a retarder of the acid–rock reaction speed for the stimulation of deep carbonate reservoirs

HCl/Formic In-Situ-Gelled Acids as Diverting Agents for Carbonate Acidizing

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