Browsing by Subject "Acidizing"
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item Acid Diversion in Carbonate Reservoirs Using Polymer-Based In-Situ Gelled Acids(2012-07-16) Gomaa, Ahmed Mohamed MohamedDiversion in carbonates is more difficult than in sandstones because of the ability of acid to significantly increase the permeability in carbonates as it reacts in the pore spaces and flow channels of matrix. In-situ gelled acids that are based on polymers have been used in the field for several years and were the subject of many lab studies. An extensive literature survey reveals that there are conflicting opinions about using these acids. On one hand, these acids were used in the field with mixed results. Recent lab work indicated that these acids can cause damage under certain conditions. There is no agreement on when this system can be successfully applied in the field. Therefore, this study was conducted to better understand this acid system and determine factors that impact its performance. Lab test of polymer-based in-situ gelled acids reveal that polymer and other additives separate out of the acid when these acids are prepared in high salinity water. In coreflood tests, in-situ gelled acid formed a gel inside 20? long core samples, and the acid changed its direction several times. Unexpectantly, the core's permeability was reduced at low shear rate. Wormhole length increased as the shear rate was increased; while the diameter of the wormhole increased as the acid cumulative injected volume was increased. CT scan indicated the presence of gel residue inside and around the wormhole. Gel residue increased at low shear rates. Material balance on the cross-linker indicated that a significant amount of the crosslinker was retained in the core. Based on the results obtained from this study the in-situ gelled acids should be used only at low HCl concentrations (5 wt percent HCl). Acid should be prepared in low salinity water and the acid injection rate should be determined based on the expected shear rate in the formation. A core flood experiment is recommended to confirm optimum injected rate. Well flow back is needed to minimize the residual gel inside the formation. The data obtained in this study can be used as a guideline for injection rate selection.Item Effect of droplet size on the behavior and characteristics of emulsified acid(Texas A&M University, 2008-10-10) Almutairi, Saleh HaifEmulsified acids have been extensively used in the oil industry since 1933. Most of the available research and publications discussed mainly the application of emulsified acid in the field. A fair number of the published work also discussed in depth some of the emulsified acid properties such viscosity, stability and reactivity. However, all of the available research discussed the emulsified acid without sufficient details of its preparation. Beside their chemical composition, the ways emulsified acids are prepared cause significant differences in their physical properties. The characterization of emulsified acid by its droplet size and size distribution complements its chemical composition and gives the emulsified acid a unique description and thus reproducible properties. No previous study considered the impact of the droplet size on the characteristics and properties of emulsified acid. Therefore, the main objective of this research is to study the effects of the droplet size on various properties of emulsified acid such as viscosity, stability and reactivity. Results showed that the droplet size and size distribution have a strong effect on the stability, viscosity and diffusion rate of the emulsified acid. The results of this work are important because knowledge of the effect of the droplet size on major design parameters will guide the way emulsified acid is prepared and applied in the field.Item Formation Damage due to Iron Precipitation in Acidizing Operations and Evaluating GLDA as a Chelating Agent(2012-02-14) Mittal, RohitIron control during acidizing plays a key role in the success of matrix treatment. Ferric ion precipitates in the formation once the acid is spent and the pH exceeds 1-2. Precipitation of iron (III) within the formation can cause formation damage. Chelating agents such as EDTA and NTA are usually added to acids to minimize iron precipitation. Drawbacks of these chelating agents include limited solubility in strong acids and poor environmental profile. Hydroxy EDTA was introduced because of its higher solubility in 15 wt% HCl. However, its solubility in 28 wt% HCl is low and it is not readily biodegradable. In this study we studied the formation damage caused by iron precipitation in acidizing operations and tested the chelate L-glutamic acid, N,N-diacetic acid (GLDA). This chelant is soluble in higher concentrations of HCl. It is readily biodegradable, and is an effective iron control agent. A study was conducted to study the concentration of iron at different pHs ranging from 1-4 without the presence of any chelating agent at room temperature. A similar study was conducted in the presence of a chelating agent. To simulate field conditions, coreflood tests were conducted on Indiana Limestone, Austin Chalk and Pink Desert. Tests were conducted with and without the chelant. Samples of core effluent were collected and iron and calcium concentrations were measured using atomic absorption spectroscopy (AA). The cores were scanned using X-ray before and after acid injection. Results indicated that precipitation of iron can cause serious reduction in core permeability. The chelate was found to be very effective in chelating iron upto 300 degrees F. No permeability reduction was noted when GLDA was added to the acid. Material balance calculations show that significant amount of the iron that was added to the injected acid was produced when GLDA was used. This chelant is effective, environmentally friendly and can used up to 300 degrees F.Item Impact of Acid Additives on Elastic Modulus of Viscoelastic Surfactants(2012-02-14) Khan, Waqar AhmadIn live acid solutions at concentrations of HCl namely 15-20 wt% HCl, elastic modulus remained quite low as compared to 10-12 wt% HCl concentrations. At 10 wt% HCl concentration, elastic modulus was 3.4 Pa observed whereas at 20 wt% HCl concentration, elastic modulus was 0.03 Pa. 0.5- 1.0 wt% concentrations of NaCl and CaCl2 showed negligible effect on the elastic modulus while 3-10 wt % concentrations, substantially reduced the elastic modulus. As little as 0.5 wt% Fe (III) concentration reduced elastic modulus quite significantly. In live acids, increase in temperature resulted in viscous modulus dominating the elastic modulus. Corrosion inhibitor reduced values of elastic modulus significantly, at 10 wt% HCl concentration elastic modulus dropped from 5.1 Pa to 3.4 Pa. Preparation of acid solution with sea water showed negligible effect at higher concentrations of HCl (> 10 wt% HCl) whereas at lower concentrations of HCl the elastic modulus fell sharply. For spent acid solutions, the elastic modulus at room temperature was quite low. Increase in temperature resulted in the increase in elastic modulus up to 130 F after which it decreased. At 190 - 205F and 18.8 rad/s, elastic modulus for 12 wt% HCl concentrations was 0.4 Pa whereas at 130 F, it was 2.25 Pa. At high temperatures (>130 F), the maximum elastic modulus shifted to higher concentrations of HCl namely 20 wt% HCl concentration. At 160 F, elastic modulus of 20 wt% HCl concentration at 18.8 rad/s was observed to be 2.6 Pa, whereas for 12 wt% HCl concentrations, it was 1.27 Pa. Throughout the HCl concentration and temperature range tested, viscous modulus dominated the elastic modulus for spent acid solutions. The effects of organic acids namely, formic and acetic acid, on the elastic modulus of viscoelastic surfactants have also been investigated.Item Investigating the Effects of Core Length on Pore Volume to Breakthrough (PVBT) Behavior in Carbonate Core Samples during Matrix Acidizing with Hydrochloric Acid(2014-05-06) Nour, MohamedMost literature contains Hydrochloric acid (HCl) carbonate acidizing experiments performed on short (2 - 6 inch) cores. These cores do not accurately represent reservoir conditions, as spent acid is not propagated for any appreciable distance along the length of the sample. In this work, HCl injection experiments are performed on both short (6 inch) and long (20 inch) calcite cores to investigate the pore volume to breakthrough (PVBT) behavior. PVBT is defined as the volume of acid necessary to propagate the wormhole network from the inlet to the outlet of the core sample, divided by the pore volume of the core. HCl (5 and 15 percent by weight) injection core flood experiments were performed on 6 inch and 20 inch calcite (Indiana Limestone) cores. The cores were CAT scanned before and after acid injection to observe wormhole propagation. Core outlet effluent samples were collected and their calcium concentration was measured using Inductively- Coupled Plasma. Results from core flood experiments show an increased PVBT for 20 inch cores compared to the 6 inch samples. Results from CAT scan experiments show enlarged worm-holing and face dissolution on the 20 inch cores compared to the 6 inch cores, due to increased acid spending at the same acid concentration, flow rate, and injection temperature. Results from experiments performed at various flowrates indicate the existence of an optimum injection rate for 20 inch cores, just as in 6 inch cores. This study summarizes and explains the results obtained from the aforementioned experiments.Item Surfactant Screening to Alter the Wettability and Aid in Acidizing Carbonate Formations(2013-02-26) Yadhalli Shivaprasad, Arun KumarSurfactant flooding in carbonate matrix acidizing treatment has been widely used for changing the wettability of the rock and to achieve low IFT values. Optimizing the type of surfactant and concentration for the specific oil field is very important in order to avoid formation damage and to reduce the treatment cost. We built an experimental procedure for screening the right surfactant to alter the wettability and aid in acidizing of Pekisko formation, Canada, which is strongly oil-wet and has high viscosity oil. Five surfactants were tested out of which three are cationic, one amphoteric and the other one was a fluoro-surfactant. Measurements were made of interfacial tension with different surfactant types/concentrations in brine with the oil and xylene, critical micelle concentration of each surfactant, solubility characteristics of the surfactants, compatibility of the chemical additives, wettability of the core after treating with surfactants, and core flooding in the laboratory to simulate matrix acidizing. From the results obtained we noted that the fluoro-surfactant can cause formation damage due to precipitation in the brine. So the compatibility of every chemical additive should be tested first. The use of xylene as a pre-flush solution lowered the CMC and hence reduced the cost of the surfactant treatment. Aromox, an amine based surfactant was best suited for matrix acidizing treatment of the Pekisko formation.Item Well Productivity Enhancement of High Temperature Heterogeneous Carbonate Reservoirs(2014-05-08) Wang, GuanqunAcidizing is one of the most popular techniques for well productivity enhancement during oil and gas production. However, the treatment method is not very effective when the wellbore penetrates through multiple layers of heterogeneous reservoirs. Uneven acid distribution always results in productivity enhancement under expectation. When such a well is drilled, the temperature of the well could be too high to keep the acid reaction under control. The acid used in the treatment fluid, most commonly HCl, would react with the tubular and the formation at a very high rate. Rather than creating long wormholes to bypass the damaged area, face dissolution, loss of pipelines, and potential damage are the outcomes after the treatment. Thus, several new techniques were proposed in this study to solve the issues discussed above. To address the heterogeneity of the reservoir, viscoelastic surfactants (VES) were used as diverting agents during acidizing treatments. A recently developed chelating agent, L-glutamic acid-N,N-diacetic acid (GLDA), was evaluated as a possible alternative for the traditional HCl. Coreflood tests and measurements of rheology properties of the treatment fluids were used to investigate the performance of the treatment fluids based on the two new systems. In total, two VES were evaluated for their diverting abilities. The first VES was based on amine oxide. It was found that the live VES-based acids had the highest apparent viscosity when the concentration of HCl was 5 wt%. During the coreflood tests, the VES-based acid was only able to build up pressure drop across the core at injection rates less than 1 cm_(3)/min. A significant amount of the VES was left inside the core after the treatment, which reduced the efficiency of production enhancement. The other VES, based on carboxysulfobetaine, can tolerate high temperatures up to 325?F. According to the viscosity measurements of the spent VES-based acid, the addition of various corrosion inhibitors lowered the fluid viscosity at temperatures above 150?F. Mutual solvent was able to break the wormlike micelles formed by the VES in the presence of calcium chloride. The diverting ability of the VES was proved through coreflood tests. For the GLDA-based treatment fluids, two additives were added into the system in effort to improve the efficiency of the treatments. Polymers and VES were added into the GLDA to achieve even fluid distribution during treatment. A significant viscosity increment was observed with the help of the viscosifier, which could expand the application of the GLDA.