Permeability Modification With Sulfomethylated Resorcinol-Formaldehyde Gel System
- Y. Zhuang (Zhengzhou U.) | S.N. Pandey (Indian School of Mines) | C.S. McCool (U. of Kansas) | G.P. Willhite (U. of Kansas)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- October 2000
- Document Type
- Journal Paper
- 386 - 393
- 2000. Society of Petroleum Engineers
- 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.2 Reservoir Fluid Dynamics, 5.4.1 Waterflooding, 4.6 Natural Gas, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.1.2 Separation and Treating, 5.8.7 Carbonate Reservoir, 1.6.9 Coring, Fishing, 5.6.5 Tracers
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The effect of various parameters on the gelation of the resorcinolformaldehyde (RF) system and a newly developed sulfomethylated resorcinol-formaldehyde (SMRF) system was investigated. The SMRF system was more tolerant of salinity, divalent ion content and pH than the RF system. The SMRF system was tested in laboratory core floods conducted at 41°C (106°F) using Berea sandstone cores, Baker dolomite cores and reservoir rock from the Lansing-Kansas City formation.
SMRF forms strong and stable gels at temperatures between 25 and 52°C (77 and 126°F) and in the pH range between 5 and 8.0. Gel times are a function of pH, salinity, concentration of the chemical constituents and temperature, and can be controlled by appropriate adjustment of these parameters. Laboratory data describing the characteristics of the SMRF system in beaker tests are presented.
The SMRF gel system has a viscosity close to water when the reactants are mixed and is easily injected into porous rock. In core tests, the gel system was injected into short cores and allowed to gel in situ. Permeability to brine after in-situ gelation was determined for each core as well as permeability after several pore volumes of brine injection. The SMRF gel system reduced the permeabilities of Berea and Baker dolomite cores by factors on the order of 10,000. The Lansing-Kansas City reservoir rock was plugged by the gel system.
The SMRF gel system is one of a few gel systems that will form a gel in situ in the presence of the strong buffering that occurs when brine is injected into carbonate rock. The SMRF system has potential for treatments of carbonate matrix rock such as that found in the Lansing-Kansas City formations of central Kansas as well as the low-permeability carbonates found in the San Andres formations in west Texas.
The placement of gelant in the targeted zones of a reservoir during permeability reduction treatments is vital to the success of the treatment. Viscosity of the injected gelant defines its mobility, which in turn determines where that fluid will travel in the reservoir. In most situations, a less viscous solution will penetrate low permeability zones to a lesser extent than a more viscous solution.1 Thus, gelants with low, or water-like, viscosity are preferred for permeability reduction treatments. In addition, injectivities are greater for less viscous gelants that enable larger volumes of gelant to be injected.
Most gelants contain polymers that increase the viscosity of the aqueous solvent by factors on the order of 5 to 30. Phenolic-aldehyde systems are a class of gels in which the initial viscosity of the gelant (before gelation occurs) is slightly above that of the aqueous solvent. This feature makes phenolic-aldehyde systems attractive for use in permeability-reduction treatments. Phenolic-aldehyde systems are composed of water-soluble phenols and aldehydes or dialdehydes. A gel is formed through a step-reaction polymerization. Several studies on the performance of phenolic systems have been reported.2-10
In-situ polymerization is also used in the in-situ generated polymer (IGP) conformance-control system11 in which polymerization of a low-toxicity acrylate monomer is initiated with a thermally controlled "azo" activator. This system was used with potassium chloride, fresh water and a pH adjustor to control the in-situ gelation environment for permeability modification of a thief zone in the San Andres formation in west Texas.11
Two phenolic-aldehyde systems were studied in this research. One was composed of resorcinol and formaldehyde (designated the RF system) and the other was composed of sulfomethylated-resorcinol and formaldehyde (designated the SMRF system). The RF system was selected because it was previously studied by Seright and Martin.5 Bottle testing to characterize the RF system revealed the gelation was sensitive to pH, salinity and hardness. At conditions where gelation was less sensitive to these parameters, the gel times were relatively short. The RF system was modified to improve the tolerance to chemical composition by sulfomethylation of the resorcinol to produce the SMRF system. The performance of the SMRF system was superior to that of the RF system in bottle tests. In-situ gelation of the SMRF was studied in several types of core material and was shown to be an effective system to reduce permeability in both sandstone and carbonate rocks when formulated in simulated formation brine.
RF gel systems were prepared as 10 g samples from chemicals and stock solutions of appropriate concentrations. Five grams of brine, 1.00 g formaldehyde solution, 1.00 g of resorcinol and 2.8 g of water were combined in a vial, mixed and the pH of the solution was measured. A combination of 1.0 or 0.1 N NaOH solutions and water was then added to achieve the selected initial pH value and final weight of 10.00 g. The time period for initial pH adjustment was critical for reproducibility. pH adjustments were accomplished over a time period of approximately 1 minute unless otherwise noted. All chemical preparations were done on a mass basis.
SMRF gel solutions were prepared in two steps. The first step was the sulfomethylation of the resorcinol. One part of an aqueous solution containing 7.1% formaldehyde and 19.9% sodium sulfite was added dropwise to 0.56 parts of a stirred aqueous solution containing 67.3% resorcinol. These concentrations are based on weight. The pH of the reaction mixture was adjusted to about 9.5 by adding 50% NaOH. The temperature of the reaction mixture was then increased to 60°C and incubated for 72 hours. Care was taken during the incubation to minimize evaporation losses. The sulfomethylated-resorcinol solution was used to prepare SMRF gel solutions by the same procedure described for the RF solutions. Compositions of SMRF samples are described by the weight percent of resorcinol and the mole ratios, F2:F1:S:R, where F1 , S and R are formaldehyde, sodium sulfite and resorcinol used in the sulfomethylation step, and F2 is the formaldehyde used to prepare the gelant mixture. All values are based on the final gelant mixture.
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