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Abstract The expected loss of useful alkalinity caused by, the slow dissolution of silica from pure quartz sand is shown for some typical alkaline flooding solutions (about 1 % NAOH or 1.25% sodium orthosilicate) to be only about 10 to 20%. This conclusion is based on the observation that alkaline solutions equilibrate with quartz and on the methodology proposed here for determining the useful alkalinity of a solution. Furthermore, the dissolution of quartz in alkaline flooding can be eliminated by the use of solutions saturated in silica with respect to quartz. Such formulations may be useful in controlling the erosion of the wellbore and gravel pack. Introduction Research results emphasize the importance of silica dissolution reactions, both in steamflooding and in alkaline flooding. Rapid dissolution of silica can quickly form a large cavity adjacent to the injection well. In unconsolidated reservoir sands, this cavity could collapse and produce lateral stresses that sever the well casing. Furthermore, for alkaline flooding it is uncertain whether alkaline pulses can propagate through reservoir sands before hydroxide concentrations drop to ineffective levels. Although many mechanisms that consume alkali exist in the reservoir, a recent paper by Bunge and Radke proposed that the slow silica dissolution reaction is of primary proposed that the slow silica dissolution reaction is of primary importance. When scaled to reservoir residence times, their calculations for the dissolution of silica by alkali predict dire conclusions: for many practical well predict dire conclusions: for many practical well spacings and flow rates, hydroxide concentrations drop to ineffective levels after - 15% of the interwell distance is traversed. Important assumptions inherent in their calculations are thatthe dissolution of silica by hydroxide can be treated as an irreversible reaction because the solubility of amorphous silica is not approached, which allows short-term dissolution rates to be extrapolated to reservoir times, and loss of hydroxide ion concentration (or pH,) with time is the critical parameter in estimating alkaline-pulse migration. In this paper, alkaline dissolution experiments are performed with a pure quartz sand. A methodology is performed with a pure quartz sand. A methodology is proposed for estimating the amount of useful alkalinity lost proposed for estimating the amount of useful alkalinity lost because of silica dissolution, and estimates for wellbore erosion are given. It is not the intent of this paper to determine the total alkaline consumption for reservoir sands. Consumption reactions important for reservoir sands such as precipitation of alkali by multivalent cations, and clay transformations-are not considered. However, discussions of the effect that clay minerals and cation precipitation might have on silica dissolution are presented. precipitation might have on silica dissolution are presented. Experimental Procedure Static bottle experiments in which quartz sand is contacted with alkaline solution are used to study silica dissolution. A basic argument in this paper is that the accumulation of silica in alkaline solution during storage with sand at elevated temperatures mimics silica accumulation in a given fluid element as the fluid propacates through the reservoir sand. Two assumptions are inherent in this statement: fluid flow at reservoir rates ft/D f - 0. 3 m/d]) has no effect on the chemical reaction of alkali with solid silica. and the surface area of sand in the static bottle tests does not drop significantly as dissolution proceeds. The first assumption is certainly reasonable, but the second deserves comment. Subsequent results show that the maximum silica dissolution observed in these experiments corresponds to only 0.5% of the quartz sand present in the bottles. Assuming spheres, such a dissolution reduces the surface area of sand grains by about 0.4%; thus the second assumption is also valid. This experimental approach is to determine the changes in soluble silica concentration and alkalinity with increasing time. For this pure quartz sand, soluble silica accumulations can be related directly to reaction rates. (In the absence of clays, aluminum is not present to cause the precipitation of silica in the form of aluminosilicate precipitation of silica in the form of aluminosilicate minerals.) Acid titrations of the alkaline solutions can be particularly useful because they reveal the effects that soluble particularly useful because they reveal the effects that soluble silica has on total alkalinity and buffering capacity. Methods Static Bottle Tests. For static bottle tests, 75 quartz sand (Clemtex No. 5, - 100 mesh) was stored with 33 g of alkaline solution in tightly sealed Teflon bottles at constant temperature. Special inserts were fabricated and placed in the necks of the bottles to [minimize vapor loss. placed in the necks of the bottles to [minimize vapor loss. The bottles were not agitated during storage because sufficient mixing is accomplished by Brownian diffusion and because agitation results in the abrasion or grinding of the sand grains, a phenomenon not encountered in reservoir flooding. Calculations show that Brownian diffusion completely distributes concentration changes caused by silica dissolution through the aqueous phase in 3 days. SPEJ P. 857
- Research Report > New Finding (0.68)
- Research Report > Experimental Study (0.54)
Abstract Establishing the amount of alkali loss by rock reactions is critical because successful application of most alkaline flooding techniques requires that hydroxide propagate through a large portion of the reservoir. This paper presents a mathematical analysis of the chromatographic movement of alkaline pulses when they are scaled to reservoir flow rates and distances. Using only this analysis and laboratory data, we show how to estimate the distance an alkaline pulse traverses under field conditions before its concentration diminishes to ineffective levels. Laboratory core tests and X-ray analyses identify the various mineral reactions and their rates. For clayey sands a fast, reversible, sodium/hydrogen ion exchange retards alkali concentration velocities. Fine silica and quartz are suggested as important dissolving minerals, with slower-dissolving clays and clay minerals releasing soluble aluminum, which may redeposit with soluble silica as new aluminosilicate minerals. While new mineral formation influences the aqueous aluminum and silica concentrations, hydroxide consumption appears to be controlled mainly by the dissolution reaction. First-order kinetics most closely represent the dissolution behavior, lumped-parameter rate constants are reported for Huntington Beach and Wilmington sands and for a Berea sandstone. Introduction Recent studies of alkaline interactions with reservoir rock, both in steamflooding and in caustic flooding, report the importance of slow mineral dissolution. The question arises: Can alkaline pulses propagate completely through a reservoir, or do hydroxide concentrations diminish to ineffective levels shortly after injection? We address this question by outlining a mathematical analysis for the migration of a pulse of alkali, which simultaneously ion exchanges and dissolves reservoir minerals. Since the computational results are presented in a nondimensional form, a new tool is now available to estimate how long an alkaline pulse remains active for reservoir flow rates and well spacings, with data obtained only from laboratory studies. When ascertaining potential chemical loss by rock consumption, it is tempting to screen various reservoirs with either dynamic column or static batch experiments (i.e., beaker or jar tests) and to report a single number for chemical loss (e.g.. in meq/100 g of rock). Such a procedure has validity when the rock reactions go to completion during laboratory time scales. SPEJ P. 998^
- North America > United States > California (0.28)
- North America > United States > West Virginia (0.25)
- North America > United States > Pennsylvania (0.25)
- (3 more...)
- North America > United States > California > Los Angeles Basin > Huntington Beach Field (0.99)
- North America > United States > West Virginia > Huntington Field (0.89)
- North America > United States > California > Los Angeles Basin > Wilmington Field (0.89)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.94)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (0.86)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (0.66)
Abstract The polymerization of dissolved silica in aqueous solutions up to 100 degrees C and containing up to 1 M NaCl has been studied experimentally, and theoretically. In this paper, the results of this work are presented in a form suitable for practical use in interpreting and predicting the chemistry of silica in geothermal brines. Empirical equations for calculating the rate of molecular deposition of silica on surfaces as a function of silica concentration. temperature, pH. and salinity are presented. Theoretically calculated type curves that depict the decrease of dissolved silica concentration by homogeneous nucleation and particle growth are presented, along with the procedures for using them to predict the course of this process under different conditions. Introduction Usually, silica precipitates from geothermal brines as colloidal amorphous silica (AS). The process of AS precipitation consists of the following steps. 1. Random growth of silica polymers past critical nucleus size. Above this size, the polymers become colloidal AS particles that are large enough to grow spontaneously and without interruption. This process is called homogeneous nucleation. 2. Growth of the supercritical AS particles by further chemical deposition of silicic acid on their surfaces. 3. Coagulation or flocculation of the colloidal particles to give a floc-like precipitate or gel. 4. Cementation of the coagulated particles by chemical bonding and further deposition of silica between them to form silica scale and other solid deposits. The preceding sequence of processes occurs when the concentration of dissolved silica is high enough for homogeneous nucleation to occur at a significant rate. Very roughly, this requires supersaturation by a factor of 2.5 or more. If this condition is met, rapid polymerization occurs, and massive precipitation or scale deposition may follow. This is the case with the brine at Niland (CA). Cerro Prieto (Mexico), and Wairakei (New Zealand). after it has been flashed down to atmospheric pressure. The voluminous floc-like silica deposits encountered in these areas consist of colloidal AS that has been flocculated by the salts in the brine. The crumbly gray and white scales associated with this material are cemented aggregates of colloidal silica. If the concentration of dissolved silica is too low for rapid homogeneous nucleation to occur, relatively slow heterogeneous nucleation and the deposition of dissolved silica directly on solid surfaces become the dominant ploymerization processes. The product of the latter process (essentially Step 2 of the preceding sequence alone) is a dense vitreous silica. At higher temperatures, this process may produce scale at a significant rate. This paper has two purposes: to summarize succinctly and quantitatively what we have learned in our kinetic studies of silica polymerization and to demonstrate by example how our results may be applied to studying practical problems in geothermal energy utilization. Because it is a summary, actual experimental data and most details of derivation have been omitted, they may be found elsewhere. Because some of the material in this paper is condensed from an earlier paper, it is partly of a review nature. It is an updated version of an earlier article. Studies of the actual formation of silica scale and the removal of colloidal silica from geothermal brines have been reported elsewhere. Molecular Deposition on Solid Surfaces By molecular deposition we mean the formation of compact, nonporous AS deposits by chemical bonding of dissolved silica directly onto solid surfaces. This is also the mechanism by which colloidal silica particles grow once nucleated. SPEJ P. 9^
- North America > Mexico > Baja California (0.25)
- Oceania > New Zealand > Waikato > Wairakei (0.24)
Field Tests of Organic Additives for Scale Control at the Salton Sea Geothermal Field
Harrar, J.E. (Lawrence Livermore Natl. Laboratory) | Locke, F.E. (Lawrence Livermore Natl. Laboratory) | Otto, C.H. (Lawrence Livermore Natl. Laboratory) | Lorensen, L.E. (Lawrence Livermore Natl. Laboratory) | Monaco, S.B. (Lawrence Livermore Natl. Laboratory) | Frey, W.P. (Lawrence Livermore Natl. Laboratory)
Harrar, J.E., Lawrence Livermore Natl. Laboratory Locke, F.E., Lawrence Livermore Natl. Laboratory Otto Jr., C.H., Lawrence Livermore Natl. Laboratory Lorensen, L.E., Lawrence Livermore Natl. Laboratory Monaco, S.B., Lawrence Livermore Natl. Laboratory Frey, W.P., Lawrence Livermore Natl. Laboratory Abstract A pilot-size brine handling system was operated from Magmamax Well 1 in southern California to study the characteristics of siliceous scale deposition and to evaluate the possibility of treating the brine with chemical additives to control scaling. The rates of formation, chemical constitution, and morphology of the scales were examined as functions of temperature, brine salinity, substrate material, and antiscalant additive activity. Potential antiscalant compounds were screened using a silica-precipitation inhibition test at 90 deg. C. The most active classes of compounds were those containing polymeric chains of oxyethylene and polymeric nitrogen compounds that are cationic in character. The best single compound was Corcat P-18 TM (Cordova Chemical Co. polyethylene imine, molecular weight 1,800). This compound had no effect on the scale formed at 220 deg. C but it reduced the rates of scaling at 125 and 90 deg. C by factors of 4 and 18, respectively, and it also functioned as a corrosion inhibitor. The best additive formulation for the brines of the Salton Sea Geothermal field (SSGF) appears to be a mixture of an organic silica-precipitation inhibitor, a small amount of hydrochloric acid, and a phosphonate crystalline deposit inhibitor. Introduction Interest in utilizing the geothermal resources of the Imperial Valley in California for the generation of electricity has accelerated rapidly in recent years. One resource in particular, the SSGF, is attractive because of its high temperature and size. Recent estimates of its potential for electrical power generation range between 1,300 and 8,700 MW per year (over a 20-year period). The fluid of this resource, however, is a highly corrosive, high-salinity brine containing several constituents that form deposits of scale on power plant components as the brine is cooled. Economical utilization of the SSGF will require techniques for limiting scaling and corrosion to acceptable levels. Scale deposition control at SSGF is particularly difficult because the scale that forms in the portions of the brine handling equipment operating at low pressures and temperatures (100 to 150 deg. C) is predominantly silica and it deposits at rates approaching 0.2 in./D. (Energy extraction systems in which the brine is flashed and injected at high temperature mitigate this problem, but considerable energy is discarded.) Chemical treatment scheme to retard the low temperature scale have been considered, but until recently there have been no systematic investigations of this approach. In 1976, Owen and coworkers demonstrated effective control of the siliceous scales by acidification of the brine with hydrochloric acid, and this technique has been verified in New Zealand by Rothbaum et al. However, for SSGF brines, acidification has several disadvantages:because concentrations >300 ppm of HCl are required, chemical costs are high; the pH of the brine must be lowered from 6 to 3 for complete scale control, and this sharply increases corrosion rates, and acidification tends to interfere with effluent brine treatment Processes involving sludge-bed reactor clarification. Other methods of scale control such as seeding with a silica sludge and the use of scale adhesion inhibitors also have been examined briefly. In this paper we present the results of tests of organic chemical agents for silica scale control in hypersaline geothermal brines. Prior to this work, virtually no knowledge existed on the types of compounds that would interact with silica under the severe geothermal conditions of high temperature, high ionic strength, and high fluid shear rates. Accordingly, to screen a large number of substances rather rapidly, we designed a small-scale flash system as a brine treatment test apparatus and operated it from SSGF Magmamax Well 1 and Woolsey Well 1. SPEJ P. 17^
- North America > United States > California > Riverside County (0.61)
- North America > United States > California > Imperial County (0.61)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.90)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.88)
Abstract In our experiments, supersaturated brines were passed through columns packed with several forms passed through columns packed with several forms of silica (crystalline -quartz, polycrystalline quartz, and porous Vycor). Also, silica deposition on ThO2 microspheres and titanium powder was studied under controlled conditions of supersaturation, pH, temperature, and salinity. The residence time was varied by adjustments of flow rate and column length. The silica contents of the input and effluent solutions were determined colorimetrically by a molybdate method that does not include polymers without special pretreatment.The following observations have been made.1. Essentially identical deposition behavior was observed once the substrate was coated thoroughly with amorphous silica and the Brunauer-Emmett-Teller (BET) surface area of the coated particles was taken into account.2. The reaction rate is not diffusion-limited in the columns.3. The silica deposition is a function of the monomeric [Si(OH)4] concentration in the brine.4. The deposition on all surfaces examined was nucleated spontaneously.5. The dependence on the supersaturation concentration, hydroxide ion concentration, surface area, temperature, and salinity were examined. Fluoride was shown to have no effect at pH 5.94 and low salinity.A cursory study of the effect of salinity showed little difference for 0.09 and 1.0 molal NaCl solutions; however, increasing the concentration to 4.0 molal increased the deposition rate by more than one order of magnitude. The empirical rate equation that describes our data in 1 molal NaCl in the pH ranges to 8 and temperatures from 60 to 120 deg. C is ........(1) where A is the amorphous SiO2 surface area in square centimeters per kilogram of water in column voids; t is minutes; and the concentrations are in molal units. Hydroxide concentration was derived from the measured pH and the ionization quotient for water. In the expression given above, the rate constant is essentially independent of temperature over the range 60 to 120 deg. C. Introduction This paper reports on work conducted at the Oak Ridge National Laboratory (ORNL) to examine silica deposition behavior in dynamic geothermal systems from hydrothermal brines found in the western U.S., with particular emphasis on the factors affecting the kinetics of deposition impact columns. We begin this report with a general discussion on the behavior of silica. Behavior of Silica In dilute aqueous solutions, silica generally occurs in the acidic-to-neutral pH range as Si(OH)4. In basic solutions, the anionic species SiO(OH)3-, SiO2(OH)2/2-, and Si4(OH)2/18 have been observed in two potentiometric studies. The equilibrium reactions among these anions and the neutral silicic acid have been studies in detail in sodium chloride solutions to 300 deg. C. Also, the fluoride ion interacts with silicic acid in relatively acidic solutions, producing principally the SiF2/6- complex.* The producing principally the SiF2/6- complex.* The stability of the complex decreases as the temperature increases. SPEJ P. 239
Abstract Just a few years ago, there existed a great uncertainty regarding the durability of oilwell cements in geothermal wells. Limited, and at times apparently unreliable, information suggested that conventional well cements may not be sufficiently resistant to geothermal well fluids and temperatures for the expected 20- or 30-year service life of the average geothermal well. Therefore, we began to investigate the performance of numerous oilwell cementing compositions in actual geothermal environments.Duplicate samples were exposed to actual geothermal well temperatures and fluids in the Baca, NM, and Imperial Valley, CA, geothermal fields for periods of up to 1 year.A novel testing procedure for geothermal cements was developed and successfully applied in these experiments. Laboratory evaluation of the exposed samples measured the durability of various compositions.The work indicated that some oilwell cements apparently can be rendered sufficiently resistant to geothermal well conditions for the service life of a geothermal well. Introduction The research completed and reported here was prompted primarily by uncertainty about the durability of any cement to be applied in geothermal wells with bottomhole temperatures ranging from 400 to 750 deg. F (204 to 399 deg. C) or produced flashing brine. The required well-service life ranged from 20 to 30 years. Several problems existed. First, the literature contained little applicable information about high-temperature hydrothermal cement chemistry. Prediction of the service life of cements in geothermal environments on the basis of known cement chemistry clearly was impossible. Prediction was of vital concern to operators responsible for safe, as well as competent, geothermal wells, particularly when serious cement-strength retrogression and deterioration generally was known to occur at elevated temperatures.Second, results of an early field test [which exposed samples of oilwell cements as 2-in. (5-cm) precured cement cubes to 600 deg. F (316 deg. C) brine in a geothermal well for periods up to 1 year] strongly suggested that even the three best cementing compositions tested might deteriorate to less than minimum acceptable compressive strengths within 3 to 9 years during geothermal well service. Other field experiments with oilwell cements in contact with produced geothermal fluids also yielded information showing extremely rapid (30- to 60-day) cement deterioration in strength and permeability. Thus, an API Class G cement (without silica) completely disintegrated (to granular size) in 30 days when exposed to 460 deg. F (238 deg. C) steam. Significantly we found that this sample contained (on X-ray diffraction analysis) both dicalcium silicate hydrate and large amounts of calcium hydroxide and carbonate. In another sample of this cement, compressive strength degraded by 77% from 5,050 to 1,150 psi (34.8 to 7.93 MPa) and permeability increased from 0.012 to 8.3 md in 60 days of aging in a produced geothermal brine of only 320 deg. F (160 deg. C) temperature. SPEJ P. 233^
Abstract The thermodynamic aspect of sandstone acidizing by hydrofluoric acid (HF) is examined. It is shown that silica dissolution, with a first order in HF concentration leads almost exclusively to the formation of fluosilicic acid. Clay and feldspar dissolution is much more complex; after a uniform alteration of the crystalline lattice, partial precipitation of silicic species occurs when the precipitation of silicic species occurs when the acid is spent. An approach to the kinetic aspect is made by defining, for a naturally complex medium, a reactivity profile that is a characteristic of the medium instead of a single reaction-rate constant. Experimental data enable a correlation between permeability, porosity, and reactivity. Also, a permeability, porosity, and reactivity. Also, a qualitative interpretation of acid response curves is given. The numerical simulation of the acidizing process satisfactorily reproduces the experimental process satisfactorily reproduces the experimental results. When extended to radial flow, the model shows the influence of stimulation parameters, injection rate, concentration, and time. Introduction Use of acids for increasing well productivity has been well established since the description of the first acid treatment appeared at the end of the last century. However, commercial development of acidizing as a stimulation technique became widespread around 1930. Since then, extensive research has broadened the number of techniques and chemical additives that not only improve the operation, but also extend applications to more complex reservoirs under severe pressure and temperature conditions. These applications are extended by the use of special corrosion inhibitors and organic acids for deep well treatment (with or without the cool-down technique) by the handling of high-strength acids recommended in offshore operations where it is advisable to use small volumes, and by the development of acid mutual-solvent technique to prevent fine particles from migrating near the wellbore, improving stimulation response. In As present state, the acidizing process largely involves empirical methods primarily because of insufficient understanding of the physical, chemical, and physicochemical phenomena involved. As a result, the anomalous behavior of some acid-response curves used for predicting treatment efficiency has not yet received a satisfactory explanation. The chemistry of the dissolution of detritic materials by acids is, in fact, not entirely understood because of the great number of equilibria between the reagent and the different species in solution derived from the native rock. The thermodynamic aspect of the problem is examined first giving a qualitative and quantitative description of chemical phenomena and attaining the solubilization mechanism of silica, feldspars, and clays. Conclusions of this study enable interpretation of the phenomena observed when an acid flows through a natural porous sandstone (dynamic experiment). The kinetic aspect is considered, along with the definition and the measurement of the matrix reactivity, a concept as characteristic of this matrix as porosity and permeability. THERMODYNAMIC CONSIDERATIONS Sandstone acidizing is based on the unique quality of HF to attack silica and alumina-silicates. Although this property has long been known (since HF is used in the glass-engraving method), its application to well stimulation quickly revealed the complexity of the problem, especially the possibility of side reactions that may affect formation permeability. The thermodynamic aspect is permeability. The thermodynamic aspect is approached in the following manner. The system formed by HF in water solution and a mineral occuring in a sandstone, such as silica, clay, or feldspar, is considered. There is a chemical reaction; that is, a consumption of the reagents and a solubilization of the mineral constituents (silicon, aluminum, potassium, etc.), which are then involved in a great number of chemical equilibria. SPEJ P. 117
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)