Evaluation of High Dissolving-Power Retarded Acid Recipes for Carbonate Acidizing

Development of retarded acid recipes that can have both adequate dissolving power and controllable reaction rate is desired to maximize the effectiveness of matrix stimulation treatments for oil and gas wells. Hydrochloric acid (HCl) has high dissolving power, however, the reaction rate with carbonate rock is uncontrollable and can cause face dissolution. Organic acids have low dissolving power and controllable reaction rate. The objective of this paper was to compare the effectiveness of three low viscosity retarded acid recipes with dissolving powers of 15 wt% and >20 wt% HCl equivalent. The examined acid recipes were 15/28 wt% emulsified acids, retarded acid recipes #1, #2 and #3, and 15/26 wt% HCl. The emulsified acids were at 30:70 ratio of diesel to acid. The retarded acid recipes were prepared at different dissolving power. Retarded acid recipe #3 was equivalent to 15 wt% HCl while retarded acid recipes #1 and #2 were equivalent to >20 wt% HCl. The calcite disc dissolution rate with retarded acids #1 and #2 was significantly lower than 26 wt% HCl and comparable to 15 wt% HCl at 75°F. The solubility of calcite discs in the retarded acid recipe #3 showed acid retardation higher than retarded acid recipes #1 and #2. The corrosion rate of retarded acid recipes #1 and #2 were 0.003-0.015 lb/ft2 at 250°F and 6 hrs, lower than both examined 26-28 wt% HCl and emulsified acids. The pitting indices of retarded acid recipes #1, #2, and #3 were 4, 2, and 1 respectively at 300°F. The pore volumes to breakthrough (PVBT) of retarded acid recipes #1 and #2 were slightly higher than retarded acid recipes #3 at 200°F. The PVBT values for 15 wt% and 28 wt% emulsified acid was comparable to retarded acid recipes #1, #2, and #3, confirming their retardation was effective.

Diverting from the Status Quo: Leveraging Acid Retardation for Production Enhancement in Offshore Carbonates in UAE

With the expanding offshore rig activity in United Arab Emirates leading to an increased number of horizontal wells and longer drains, coupled with changing rock fabrics, it became imperative to diverge from the existing stimulation methods to deliver more consistent and reliable results. These results were achieved via the introduction of single-phase retarded acid (SPRA) and viscoelastic diverting acid (VEDA) to both active and shut-in wells offshore. The introduction of SPRA and VEDA was possible after extensive laboratory testing including core flow tests, solubility tests, emulsion tendency testing, and corrosion inhibition tests to evaluate and benchmark the performance of these blends in comparison to the existing acid recipes such as plain HCl and polymer-based diverted acid. These tests showed that a combination of SPRA and VEDA would allow maximizing lateral coverage and enhance acid penetration due to the reduced rate of reaction and chemical diversion capabilities from thief zones. Combining the introduction of SPRA and VEDA with a shift to bullheading and higher pumping rates enabled the delivery of previously unachievable production results at sustainable wellhead pressures or even well revival of shut-in wells. In addition, reduction of acid content for dolomite stimulation was possible due to the implementation of acid retardation, which also allowed protecting wellheads from exposure to higher acid concentrations while bullheading. Treatment parameters such as volumes, rates, and acid/diverter sequence and ratio were then adjusted for optimal wormhole penetration across all zones using a new carbonate matrix acidizing modeling software. Post-treatment evaluation for the cases of previously shut-in wells has proven the success of the SPRA and VEDA combination. Shut-in wells that were unable to produce sustainably at the required tubing-head pressure (production flowline pressure), were able to produce sustainably with a 100% increase in production compared to prestimulation testing. Similarly, for gas wells, the combination of SPRA and VEDA resulted in a 50% increase in production at a similar bottomhole pressure. In addition, water injectors have also exhibited sustainably increased levels of injectivity compared to prestimulation levels, leading to better sweepage. The novelty of this paper is the comparison between historical carbonate stimulation results in UAE using plain HCl acid with polymer-based diverted acid and using SPRA with VEDA. It also sheds light on the game-changing solutions that suit the ever-increasing challenges observed in offshore oil and gas wells including well placement, lithology, permeability contrast, and type of hydrocarbon within the various target sublayers.

Acid Retardation method of separation for closed-circuit processing of alumina-containing raw materials with the use of salt-acid digestion

A brief overview and critical analysis of acid and acid-salt methods for processing alumina raw materials, including high-silica bauxite, nepheline and clay is presented. The basic approaches to the creation of closed and reagent-less or low-reagent-consumption processes are demonstrated. The results obtained in the course of long-term systematic laboratory and bench studies are presented, and they display the prospects for the creation of new technologies for the production of alumina from high silica bauxite and aluminum silicates with the use of different nitrate and sulfate reagents. In the case of using acids, the sorption method of «Acid Retardation» in nano-porous media is shown to be successfully used for recycling them into the process head and to ensure soft conditions for the removal of iron components. This stage is realized with the use of strong base anion exchanger, preliminarily equilibrated with the macro-anion composition of solutions to be processed and washed with water or diluted acid solution. The AR process in three phase systems including organic liquids immiscible with water solutions (“New Chem” method) is also described, a this is also important to provide the complete insulation of concentrated salt solution and to simplify its farther treatment. A circular process with the recovery and consumption of the same amount of salt reagent in each cycle is demonstrated. A comparison of digestion methods is given in terms of the completeness of reagent recycling, the quality of product and the complexity of the process. Advisable conditions for the production of alumina from non-traditional raw with salt-acid decomposition are shown. As it is shown, the most in demand are the processes, which fully or partially can be «inscribed» in modern equipment design and process conditions corresponding to the standard Bayer method or its industrial modifications

Recovery and Reuse of Sliver and Sulfuric Acid from Waste Liquid of COD Determining

Silver sulfate in waste liquid of COD determining could be recycled by NaCl-H2SO4 technology, the recovery rate could be reached 80.5 %. Make a comparison between recyclable Ag2SO4 and commercially available Ag2SO4, and make seven kinds of wastewater COD experiment. The result of basic statistic analysis showed that recyclable Ag2SO4 could be recycled available for the determination of COD in water. The sulfuric acid in COD waste liquid (except silver) could be recycled by acid retardation technology, the recovery rate could be reached 91.7 %. Ag2SO4 and sulfuric acid in COD waste liquid was effectively recycled by NaCl-H2SO4-acid retardation coupling technology.

Waste Steel-Pickling Sulphuric Acid Removal Treated by Freezing Crystallization-Acid Retardation Coupling Technology

Waste steel-pickling sulphuric acid was treated by freezing crystallization acid retardation coupling technology. Under the optimal conditions(temperature was -5 °C, rotational speed was 4000 rpm, TulsionA-32 as Acid Retardation reagent), the concentration of sulfuric acid reached 20～25 % and the concentration of FeSO4·7H2O fell to 15～20 g/L in the waste steel-pickling sulphuric acid which achieved the standard for sulfuric acid reuse. Polymeric ferric sulfate prepared by recyclable ferrous sulfate was accord with the first type of standard water clarfying agent polymer ferric sulfate(GB14591-2006)．