Browsing by Subject "Matrix Acidizing"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item A placement model for matrix acidizing of vertically extensive, multilayer gas reservoirs(Texas A&M University, 2008-10-10) Nozaki, ManabuDesign of matrix acidizing treatments of carbonate formation is still a challenge although extensive research has been done on it. It is necessary to estimate acid distribution along the wellbore. This estimation is very important especially for the case where the reservoir properties vary along the wellbore. This work provides development and application of an apparent skin factor model which accounts for both damage and mobility difference between acid and gas. Combining this model with a conventional acid placement model, we develop an acid placement model for vertically extensive, multilayer gas reservoirs. A computer program is developed implementing the acid placement model. The program is used to simulate hypothetical examples of acid placement for vertically extensive, multilayer gas reservoirs. This model will improve matrix acidizing for gas reservoirs and enable realtime monitoring of acid stimulation more accurately.Item A Systematic Study of Matrix Acidizing Treatments Using Skin Monitoring Method(2012-07-16) Pandya, NimishThe goal of this work was to evaluate matrix acidizing treatments of vertical and horizontal wells in carbonate reservoirs. Twenty field cases for acidizing treatments were analyzed by evaluating the skin factor evolution from on-site rate/pressure data during the treatment. A skin monitoring method based on the concept of inverse injectivity (Hill and Zhu, 1996) was used to calculate the skin factor evolution. Viscous diversion techniques were analyzed by using the viscous diversion skin model that accounts for viscosity contrast between the reservoir fluid and the injected fluid. The estimated skin evolution during the treatment was validated using the post-treatment well performance. From the post-treatment analysis, it was observed that emulsified acid was not an efficient viscous diverter because only 27% of the wells treated with emulsified acid showed evidence of viscous diversion. Therefore, other viscous diversion techniques are needed to ensure uniform acid coverage. In addition, treatments that involved diversion techniques such as foam, associative-polymers, and viscoelastic surfactants were also evaluated. Thus, the post-treatment evaluation was used to improve and optimize the acid treatment designs. This study was beneficial to diagnose if excess acid volumes were used, or effective diversion was achieved during the acid treatment.Item Acidizing Dolomite Reservoirs Using HCL Acid Prepared with Seawater: Problems and Solutions(2014-04-28) Arensman, Dennis GSeawater is the only viable water source for many offshore wells with dolomite formations. For these wells it is important to use compatible fluids when stimulating to avoid damaging the formation with calcium sulfate precipitation. Much work has been conducted on this problem for limestone, but there have been no publications about calcium sulfate precipitation within dolomite during matrix acidizing. This work quantifies permeability damage when acidizing using hydrochloric acid mixed with seawater and no scale inhibitors. Scale inhibitors were also tested for effectiveness in reducing calcium sulfate scale during acidizing. Static jar tests of three phosphonate-based, two sulphonated polymer-based, and one polyacrylic-based scale inhibitors in spent acid systems were used to compare the effectiveness at temperatures ranging from 77 to 325?F. Corefloods were conducted to investigate the extent of calcium sulfate precipitation without scale inhibitors and to test permeability improvements with the addition of compatible scale inhibitors at temperatures up to 325?F. This work shows that calcium sulfate precipitation within dolomite during matrix acidizing with seawater and hydrochloric acid will damage the well. Corefloods with seawater showed a permeability reduction of 30% or greater compared to corefloods with freshwater for all temperatures tested when no scale inhibitors were included in the acid solution. Calcium sulfate precipitation was determined to be the cause of the decreased permeability. DTPMP, a phosphonate-based scale inhibitor, and a sulfonated polymer scale inhibitor at concentrations of 150 ppm were shown to effectively reduce calcium sulfate scale with minimal inhibitor/rock reaction during these tests. The ability to improve stimulation effectiveness by the addition of compatible scale inhibitors to the acid solution is critical information to prevent damaging dolomite formations during matrix acidizing with hydrochloric acid and seawater.Item Acidizing High-Temperature Carbonate Formations Using Methanesulfonic Acid(2015-03-25) Ortega, AlexisHydrochloric acid (HCl) is the most commonly used stimulation fluid for high-temperature wells drilled in carbonate reservoirs due to its high dissolving power and low cost. However, the high corrosion rate of HCl on well tubulars could make its use in deep wells non-viable. The current study introduces the novel application of methanesulfonic acid (MSA), a strong organic acid, to increase the permeability of carbonate formations, specifically at temperatures above 200?F. The objective of the experimental study is to evaluate the performance of MSA as stand-alone stimulation fluid for high-temperature limestone and dolomite formations. Coreflood studies were conducted at temperature up to 320?F using limestone and dolomite cores and diluted MSA aqueous solutions. A constant injection rate, ranging from 1 to 25 cm3/min, was maintained during the coreflood tests and the differential pressure through the core was measured until acid breakthrough. Samples of the effluent fluids were collected and analyzed using Inductively Coupled Plasma (ICP) to measure the calcium and magnesium concentrations, and a computed tomography (CT) scan of each core was performed after the acid injection to study the characteristics of the generated wormholes. MSA was found effective in creating wormholes in carbonate cores at the temperatures tested. At low injection rates, face dissolution and conical channels were observed in the cores. At intermediate injection rates, the tendency was to create a few dominant wormholes. At high injection rates, ramified wormhole structures were found, with increased branching for increased flow rates. For each condition tested, an optimum flow rate was identified. Additionally, analysis of the coreflood effluent samples showed no sign of methanesulfonate salts precipitation. Demonstration of the effectiveness of MSA in propagating wormholes in carbonate cores will offer the petroleum industry with another alternative strong acid to HCl for stimulating high-temperature carbonate formations. MSA?s high acidity, solubility of its salts, and thermal stability, along with its readily biodegradable composition provide a beneficial use for MSA as a stimulation fluid in carbonate acidizing techniques. MSA also has a more favorable corrosion profile on metals, such as high chromium alloys, than usual mineral acids employed in well stimulation.Item Design, set up, and testing of a matrix acidizing apparatus(Texas A&M University, 2006-10-30) Nevito Gomez, JavierWell stimulation techniques are applied on a regular basis to enhance productivity and maximize recovery in oil and gas wells. Among these techniques, matrix acidizing is probably the most widely performed job because of its relative low cost, compared to hydraulic fracturing, and suitability to both generate extra production capacity and to restore original productivity in damaged wells. The acidizing process leads to increased economic reserves, improving the ultimate recovery in both sandstone and carbonate reservoirs. Matrix acidizing consists of injecting an acid solution into the formation, at a pressure below the fracture pressure to dissolve some of the minerals present in the rock with the primary objective of removing damage near the wellbore, hence restoring the natural permeability and greatly improving well productivity. Reservoir heterogeneity plays a significant role in the success of acidizing treatments because of its influence on damage removal mechanisms, and is strongly related to dissolution pattern of the matrix. The standard acid treatments are HCl mixtures to dissolve carbonate minerals and HCl- HF formulations to attack those plugging minerals, mainly silicates (clays and feldspars). A matrix acidizing apparatus for conducting linear core flooding was built and the operational procedure for safe, easy, and comprehensive use of the equipment was detailed. It was capable of reproducing different conditions regarding flow rate, pressure, and temperature. Extensive preliminary experiments were carried out on core samples of both Berea sandstone and Cream Chalk carbonate to evaluate the effect of rock heterogeneities and treatment conditions on acidizing mechanisms. The results obtained from the experiments showed that the temperature activates the reaction rate of HF-HCl acid mixtures in sandstone acidizing. The use of higher concentrations of HF, particularly at high temperatures, may cause deconsolidation of the matrix adversely affecting the final stimulation results. It was also seen that the higher the flow rate the better the permeability response, until certain optimal flow rates are reached which appears to be 30 ml/min for Berea sandstone. Highly permeable and macroscopic channels were created when acidizing limestone cores with HCl 15%. In carbonate rocks, there is an optimum acid injection rate at which the dominant wormhole system is formed.Item Evaluation of a New Liquid Breaker for Polymer Based In-Situ Gelled Acids(2012-10-19) Aksoy, GamzeA solid breaker is used to reduce the viscosity of the gel at pH range of 4-5 for in-situ gelled acids with Zr4 cross-linkers utilize. However, the literature survey confirmed that solid breakers caused a premature reduction in the fluid viscosity resulting in a less than desirable productivity. Therefore, an effective liquid breaker that is based on tetrafluoroboric acid was developed. This study was conducted to evaluate this new breaker system under the following conditions: breaker concentration (0-200 ppm), and acid injection rate (0.5-10 cm3/min). The major findings from the performed viscosity measurements and single coreflood experiments can be summarized as follows: the crosslinking of the polymer occurred at a pH value of 1.8. At a pH of less than 2, doubling the breaker concentration did not affect the viscosity of the acid. However, at a pH of greater than 2, the viscosity of acid was reduced by 30 percent. At a breaker concentration of 0 ppm, the appearance of Zr in the core effluent sample was delayed by 0.25 PV compared to the reaction product, while at 100 ppm, Zr was delayed by 0.75 PV. At 200 ppm breaker, no Zr ions were detected in the effluent samples. Additionally, it was observed that as the breaker concentration increased, more Zr remained inside the core, as ZrF4, which is water-insoluble. Increasing the breaker concentration from 100 to 200 ppm reduced the final normalized pressure drop by 50 percent at injection rate of 2.5 cm3/min. Permeability reduction due to gel was reduced by increasing the acid injection rate.Item Matrix Acidizing Core Flooding Apparatus: Equipment and Procedure Description(2012-12-10) Grabski, Elizabeth 1985-Core flooding is a commonly used experimental procedure in the petroleum industry. It involves pressurizing a reservoir rock and flowing fluid through it in the laboratory. The cylindrical rock, called a core, can be cut from the reservoir during a separate core drilling operation or a formation outcrop. A core flooding apparatus suitable for matrix acidizing was designed and assembled. Matrix acidizing is a stimulation technique in which hydrochloric acid (HCl) is injected down the wellbore below formation fracture pressure to dissolve carbonate (CaCO3) rock creating high permeability streaks called wormholes. The main components of the apparatus include a continuous flow syringe pump, three core holders, a hydraulic hand pump, two accumulators, a back pressure regulator, and two pressure transducers connected through a series of tubing and valves. Due to the corrosive nature of the acid, the apparatus features Hastelloy which is a corrosion resistant metal alloy. Another substantial feature of the apparatus is the ability to apply 3000psi back pressure. This is the pressure necessary to keep CO2, a product of the CaCO3 and HCl reaction, in solution at elevated temperatures. To perform experiments at temperature, the core holder is wrapped with heating tape and surrounded by insulation. Tubing is wrapped around a heating band with insulation to heat the fluid before it enters the core. A LabVIEW graphical programming code was written to control heaters as well as record temperature and pressure drop across the core. Other considerations for the design include minimizing footprint, operational ease by the user, vertical placement of the accumulators and core holders to minimize gravity effects, and air release valves. Core floods can be performed at varying injection rates, temperatures and pressures up to 5000psi and 250 degF. The apparatus can handle small core plugs, 1?? diameter X 1?? length, up to 4?? X 20?? cores. The equipment description includes the purpose, relevant features, and connections to the system for each component. Finally documented is the procedure to run a core flooding test to determine permeability and inject acid complete with an analysis of pressure response data.Item The Effect of Heterogeneity on Matrix Acidizing of Carbonate Rocks(2010-07-14) Keys, Ryan S.In matrix acidizing, the goal is to dissolve minerals in the rock to increase well productivity. This is accomplished by injecting an application-specific solution of acid into the formation at a pressure between the pore pressure and fracture pressure. A hydrochloric acid solution is used in carbonate reservoirs, which actually dissolves the calcite rock matrix in the form of conductive channels called wormholes. These wormholes propagate from the wellbore out into the reservoir, bypassing the damaged zone. In matrix acidizing of carbonates, there are four parameters that affect performance: the concentration of calcite present, injection rate of the acid, reaction type, and heterogeneity. Of these parameters, this paper will focus on how rock heterogeneity affects performance. To do this, a coreflood and acidizing apparatus was used to acidize heterogeneous limestone core samples. Rock characterizations and volumetric measurements were considered with the results from these experiments, which made it possible to correlate and quantify the results with rock and volume parameters. It was found that the core samples with more and larger heterogeneities generally required less acid (measured in pore volumes) to achieve breakthrough, that is, a wormhole created axially from one end of the core to the other. This value for pore volumes to breakthrough was one to two orders of magnitude less than more homogeneous samples. The general procedure and best practices for acidizing the core samples is also detailed in this thesis. This procedure was followed for preparation, coreflooding, and acidizing for all core samples.