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Brian Horsfield - One of the best experts on this subject based on the ideXlab platform.
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induced mobility of inorganic and organic solutes from black shales using water extraction implications for shale gas exploitation
Applied Geochemistry, 2015Co-Authors: Franziska D H Wilke, Andrea Viethhillebrand, Rudolf Naumann, Jorg Erzinger, Brian HorsfieldAbstract:Abstract The study reported here evaluates the degree to which metals, salt anions and organic compounds are released from shales by exposure to water, either in its pure form or mixed with additives commonly employed during shale gas exploitation. The experimental conditions used here were not intended to simulate the exploitation process itself, but nevertheless provided important insights into the effects additives have on solute partition behaviour under oxic to sub-oxic redox conditions. In order to investigate the mobility of major (e.g. Ca, Fe) and trace (e.g. As, Cd, Co, Mo, Pb, U) elements and selected organic compounds, we performed leaching tests with black shale samples from Bornholm, Denmark and Lower Saxony, Germany. Short-term experiments (24 h) were carried out at ambient pressure and temperatures of 100 °C using five different lab-made Stimulation Fluids. Two long-term experiments under elevated pressure and temperature conditions at 100 °C/100 bar were performed lasting 6 and 2 months, respectively, using a Stimulation Fluid containing commercially–available biocide, surfactant, friction reducer and clay stabilizer. Our results show that the amount of dissolved constituents at the end of the experiment is independent of the pH of the Stimulation Fluid but highly dependent on the composition of the black shale and the buffering capacity of specific components, namely pyrite and carbonates. Shales containing carbonates buffer the solution at pH 7–8. Sulphide minerals (e.g. pyrite) become oxidized and generate sulphuric acid leading to a pH of 2–3. This low pH is responsible for the overall much larger amount of cations dissolved from shales containing pyrite but little to no carbonate. The amount of elements released into the Fluid is also dependent on the residence time, since as much as half of the measured 23 elements show highest concentrations within four days. Afterwards, the concentration of most of the elemental species decreased pointing to secondary precipitations. Generally, in our experiments less than 15% of each analysed element contained in the black shale was mobilised into the Fluid.
Hisham A. Nasr-el-din - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Iron Interaction with Viscoelastic Surfactant VES-Based Stimulation Fluid
Day 3 Wed March 20 2019, 2019Co-Authors: Salar Afra, Hamidreza Samouei, Hisham A. Nasr-el-dinAbstract:Abstract Viscoelastic surfactant (VES) have been successfully applied as acid-diversion Fluids. However, high temperature, interaction of VES and Fe(III), addition of alcohol-based additives, and chelating agents all interfere with the apparent viscosity of the VES-based acid and reduce its efficiency. In the present study, the interactions of Fe(III) with a new type of VES-based acid system, which can be applied effectively for diversion at high temperatures, were characterized. Viscosity measurements were conducted on the VES-based acid in the presence of different concentrations of Fe(III) to characterize the rheological properties of the VES-based acid. The results showed that addition of Fe(III) in the concentration range of 2000 to 10000 ppm, lead to increase in the viscosity of the VES-based acid even at room temperature. Higher concentration of Fe(III) (more than 40000 ppm) lead to phase separation of VES out of the acid and formation of a brown gel-like material, which is considered as the main cause of formation damage by VES-based diversion Fluids. IR spectroscopy was employed to understand the nature of the VES interactions with Fe(III) in live acid conditions. Also, UV-vis spectroscopy was conducted to determine stoichiometry of the reaction as well. The results show that interaction of amide part of the VES with Fe(III) that results in screening the repulsion forces between surfactant head groups and formation of wormlike micelles is the primary reason for increase in the viscosity. To the best of authors' knowledge, although Formation damage caused by VES-based system due to iron contamination were reported previously both in the laboratory studies and field applications, the present paper is the first mechanistic attempt to characterize and understand the nature of a VES-based system interaction with Fe(III) as the driving force for the occurrence of reported formation damage. The findings of the present study can be utilized to further investigation of the effects of additives on the performance of VES-based systems.
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Modeling Flow of Chelating Agents During Stimulation of Carbonate Reservoirs
Arabian Journal for Science and Engineering, 2014Co-Authors: Mohamed Mahmoud, Hisham A. Nasr-el-dinAbstract:Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and hydroxy ethylene diamine triacetic acid (HEDTA) have been used as stand-alone Stimulation Fluids. These Fluids can be used to stimulate water injectors, oil, or gas producers. In this study, an analytical model was developed to describe the flow of HEDTA and EDTA chelating agents and propagation inside calcite formations. The analytical model can be used as a pre-design tool before the treatments. The developed model can be used to predict the volume of the chelant required to create wormholes in calcite formations at different temperatures. The temperature affects the diffusion coefficient of the chelating agent, wormholing rate, and wormhole shape and size. The dissolving power of different forms of HEDTA can be determined using the model. The optimum injection rate based on optimum wormholing conditions was identified. Also, the model can be used to predict the wormholing rate of different chelating agents in calcite formations. The analytical model can be used to predict the performance of the chelating agent in calcite Stimulation. The volume of chelating agent required to stimulate calcite formation per foot thickness was determined using the developed model. The optimum injection rate was determined for different chelating agents using the model, and the results were compared with experimental results from previous work and there was a good agreement between the measured and the predicted values. The model can be used to determine the best Stimulation Fluid based on the temperature and fracture pressure of the target zones.
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HT Stimulation Fluid Based On GLDA Meets Productivity, Environmental Need
Journal of Petroleum Technology, 2013Co-Authors: Hisham A. Nasr-el-dinAbstract:Technology Update Industry operations are shifting toward high-temperature (HT) downhole set-tings, expensive tubular metallurgy, and extended reach wells, while health, safety, and environmental requirements become stricter. Consequently, conventional Stimulation treatments, such as applications using hydrochloric acid-based Fluids, will no longer meet the industry’s needs as operational environments evolve. A new Stimulation Fluid developed by AkzoNobel, Dissolvine StimWell, is based on glutamic acid diacetic acid (GLDA) and has been successfully applied in the field. GLDA has high thermal stability and low corrosion potential, and is an effective Stimulation Fluid without adverse environmental impact. A vertical gas well in a deep, sour carbonate reservoir was successfully stimulated using GLDA. Previous matrix Stimulation treatments with conventional acids in this HT gas well did not sustain the performance, and a fracture treatment was considered for the well. However, the case proved that matrix acidizing with the GLDA-based Fluid was the best Stimulation method for the well in terms of cost-effectiveness and regulatory issues. Stimulation Purpose The object of Stimulation is to remove the production zone damage caused by the drilling and completion processes in sandstone reservoirs, and to create channels or wormholes in carbonate reservoirs. Although an industry workhorse for decades, hydrochloric acid (HCl) often produces subpar Stimulation results, especially at high temperatures, because of its fast reaction near the wellbore, low acid penetration, and high corrosivity. Many problems may occur during sandstone acidizing with HCl/hydrofluoric mud acid, such as decomposition of clays in HCl acids, precipitation caused by the presence of fluoride, silica gel filming, and colloidal silica gel precipitation. As a result, mud acid may cause significant damage to sandstone reservoirs, especially for those with a high content of calcite or clays such as illite. The desirable alternative Stimulation Fluid would be suitable for all of these conditions, be globally applicable, and have an acceptable environmental profile. Fluids based on GLDA meet those requirements. The Fluids are effective in improving permeability in carbonate and sandstone formations. Many additives such as iron control agents that are required in other Fluids are not needed in GLDA-based Stimulation Fluids.
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Improved Health, Safety and Environmental Profile Of A New Field Proven Stimulation Fluid
All Days, 2012Co-Authors: Wolfgang Braun, Corine De Wolf, Hisham A. Nasr-el-dinAbstract:Abstract Acidizing treatments can help significantly improve the productivity of a well. Safe handling of commonly used corrosive acids, however, is a significant challenge to properly manage during the execution of the treatments. The additives, such as corrosion inhibitors, iron control agents, etc., typically used to mitigate the corrosive impact of acids and other un-wanted reactions during the treatments adds to the complexity of safe handling, while further aggravating the environmental impact of the overall treatment. Higher dosages of additives that are needed at higher treatment temperatures and pressures further compound the challenge. With the industry needs trending to high temperatures & pressures, and stricter health, safety & environmental (HSE) considerations, an alternative Stimulation Fluid that is suited for all the challenging conditions and be globally applicable with an acceptable environmental profile would be ideal. Recent studies and field applications with a new Stimulation Fluid based on glutamic acid diacetic acid (GLDA) has shown that GLDA can improve permeability in carbonate and sandstone formations even at tough field conditions and can maintain the integrity of wells made of various tubular metallurgies. In the present paper the health, safety and environmental profile of GLDA is reviewed and compared against conventional Stimulation Fluids such as hydrochloric acid, acetic acid, hydrofluoric, etc., along with the commonly used additives. GLDA is to a large extent based on a natural amino acid made from sustainable resources. It is biodegradable in both fresh and seawater. GLDA has a very favorable eco-tox profile and very low toxicity levels. In contrast to other Stimulation Fluids and frequently used additives, GLDA does not have any hazard classification and therefore requires no adverse safety labeling. GLDA can be handled easily and safely in the field with just standard chemical handling precautions in place. Overall, GLDA is a safe, environmentally friendly and effective Stimulation solution that can help improve productivity of a well with the least possible well integrity or HSE concerns.
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Modeling of the Flow of Chelating Agents in Porous Media in Carbonate Reservoirs Stimulation
All Days, 2012Co-Authors: Mohamed Mahmoud, Hisham A. Nasr-el-dinAbstract:Abstract Different Fluids have been introduced in the oil industry to be used as alternatives to HCl. Chelating agents such as EDTA (ethylenediaminetetraaceticacid), and HEDTA (hydroxy ethylene diamine triacetic acid) have been used as stand-alone Stimulation Fluids. These Fluids can be used to stimulate water injectors, oil, or gas producers, therefore, the effect of the type of reservoir Fluid on the Stimulation process should be investigated. In this study, an analytical model was developed to describe the flow of HEDTA and EDTA chelating agents and propagation inside carbonate formations. The analytical model can be used as a pre-design tool before the treatments. The developed model can be used to predict the volume of the chelant solution required to create wormholes in calciteformations at different temperatures. The temperature affects the diffusion coefficient of the chelating agent, wormholing rate, and wormhole shape and size. The dissolving power of different forms of HEDTA chelating agent can be determined using the model. The optimum injection rate based on optimum wormholing conditions was identified for the chelating agents. Also, the model can be used to predict the wormholing rate of different chelating agents in carbonate formations. The analytical model can be used to predict the performance of the chelating agent in carbonate Stimulation. The volume of chelating agent required to stimulate carbonate formation per foot thickness was determined using the developed model. The optimum injection rate was determined for different chelating agents using the model and the results were compared with experimental results from previous work and there was a good agreement between the measured and the predicted values. The model can be used to determine the best Stimulation Fluid based on the temperature and fracture pressure of the target zones.
Franziska D H Wilke - One of the best experts on this subject based on the ideXlab platform.
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induced mobility of inorganic and organic solutes from black shales using water extraction implications for shale gas exploitation
Applied Geochemistry, 2015Co-Authors: Franziska D H Wilke, Andrea Viethhillebrand, Rudolf Naumann, Jorg Erzinger, Brian HorsfieldAbstract:Abstract The study reported here evaluates the degree to which metals, salt anions and organic compounds are released from shales by exposure to water, either in its pure form or mixed with additives commonly employed during shale gas exploitation. The experimental conditions used here were not intended to simulate the exploitation process itself, but nevertheless provided important insights into the effects additives have on solute partition behaviour under oxic to sub-oxic redox conditions. In order to investigate the mobility of major (e.g. Ca, Fe) and trace (e.g. As, Cd, Co, Mo, Pb, U) elements and selected organic compounds, we performed leaching tests with black shale samples from Bornholm, Denmark and Lower Saxony, Germany. Short-term experiments (24 h) were carried out at ambient pressure and temperatures of 100 °C using five different lab-made Stimulation Fluids. Two long-term experiments under elevated pressure and temperature conditions at 100 °C/100 bar were performed lasting 6 and 2 months, respectively, using a Stimulation Fluid containing commercially–available biocide, surfactant, friction reducer and clay stabilizer. Our results show that the amount of dissolved constituents at the end of the experiment is independent of the pH of the Stimulation Fluid but highly dependent on the composition of the black shale and the buffering capacity of specific components, namely pyrite and carbonates. Shales containing carbonates buffer the solution at pH 7–8. Sulphide minerals (e.g. pyrite) become oxidized and generate sulphuric acid leading to a pH of 2–3. This low pH is responsible for the overall much larger amount of cations dissolved from shales containing pyrite but little to no carbonate. The amount of elements released into the Fluid is also dependent on the residence time, since as much as half of the measured 23 elements show highest concentrations within four days. Afterwards, the concentration of most of the elemental species decreased pointing to secondary precipitations. Generally, in our experiments less than 15% of each analysed element contained in the black shale was mobilised into the Fluid.
M. W. Conway - One of the best experts on this subject based on the ideXlab platform.
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Minimize formation damage by rapid, inexpensive method of completion- and Stimulation-Fluid selection
Spe Production Engineering, 1992Co-Authors: D. R. Underdown, M. W. ConwayAbstract:Minimizing or removing formation damage is a major objective in completion and Stimulation operations. Formation damage is minimized by selection of nondamaging Fluid systems and operations on the basis of petrographic analysis and field experience. A technique know as the capillary suction time (CST) test, adopted from the drilling-Fluid industry, provides a quick and inexpensive method for qualitative selection or screening of the least damaging Fluid system for a particular formation. The CST test is a fundamental filtration method for determining the electrolyte concentration that will produce the maximum inhibiting effect on formation. The method uses an instrument to measure the time required for a liquid to travel a calibrated distance on a standard porous filter paper. The CST procedure currently is used very successfully to select completion Fluids and to evaluate Stimulation-Fluid additives. This paper explains the procedure, discusses limitations of the test, and presents laboratory and field data to sto show the value of the technique.
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Minimize Formation Damage by Rapid, Inexpensive Method of Completion- and Stimulation-Fluid Selection
SPE Production Engineering, 1992Co-Authors: D. R. Underdown, M. W. ConwayAbstract:Summary Minimizing or removing formation damage is a major objective in completion and Stimulation operations. Formation damage is minimized by selection of "nondamaging" Fluid systems and operations on the basis of petrographic analysis and field experience. A technique known as the capillary suction time (CST) test, adopted from the drilling-Fluid industry, provides a quick and inexpensive method for qualitative selection or screening of the least damaging Fluid system for a particular formation. The CST test is a fundamental filtration method for determining the electrolyte concentration that will produce the maximum inhibiting effect on a formation. The method uses an instrument to measure the time required for a liquid to travel a calibrated distance on a standard porous filter paper. The CST procedure currently is used very successfully to select completion Fluids and to evaluate Stimulation-Fluid additives. This paper explains the procedure, discusses limitations of the test, and presents laboratory and field data to show the value of the technique. Introduction The CST test, used by some mud companies to determine the optimum salinity for drilling through sloughing shales,1-4 is now used for completion-Fluid selection. As formation damage becomes more of an issue with operators, the need for a quick and easy method of screening Fluid/rock interactions is becoming apparent. The most commonly accepted method to determine the extent of formation damage is to run a core flow test with different Fluids and to observe the change in permeability. This technique is very effective but very time-consuming and expensive, especially as a screening method. The core flow tests also have the disadvantage that generally only a very few tests are run because of the limited amount of whole-core material available for suitable core plugs. The CST test allows screening of several Fluids with a limited amount of formation material before more costly core flow tests are run. The tests are quick and easy and provide semiquantitative information about the Fluid/rock interaction. CST Test The CST test is a filtration method for determining the electrolyte concentration that will produce the maximum inhibition of a formation. The method uses an apparatus shown in Fig. 1 to measure the time required for a liquid to travel a calibrated distance in a standard porous paper. The measurement is made by placing 5 to 7 mL of a Fluid/rock slurry into a cylinder that is resting on a standard porous paper. Electrodes are located 0.5 and 1.0 cm from the edge of the cylinder and connected to a timer that measures the time required for the filtrate to travel from the electrode closest to the cylinder to the furthest electrode. The time interval measured depends on the amount of free water in the rock/Fluid slurry and the permeability of the filter cake deposited. The more flocculated (less dispersed) the rock/Fluid slurry, the more permeable the filter cake and the shorter the time interval. Formation material that contains water-sensitive minerals will adsorb free water and disperse, forming a relatively impermeable filter cake and a longer CST. A good example of this is the "swelling" experienced when smectite imbibes and adsorbs free water. Water-sensitive minerals flocculate when cations or anions are introduced into the slurry. The flocculated minerals form a more permeable filter cake and the CST is reduced. Consistent results are obtained by standardized sample preparation and test procedures. One factor affecting CST is the surface area of the ground sample. Care is needed in grinding the sample to ensure that the technique used produces similar surface areas from one sample to another. The sample usually is ground gently in a mortar and sieved through a 30- or 40-U.S.-mesh screen. This process is repeated until all the sample passes through the screen. One of the most significant factors affecting reproducibility is the method of sampling the disaggregated material. For good sampling, individual boats are laid out for all the samples. The bulk sample is mixed thoroughly and about 1/10th of the required sample is added to each weigh boat. This step is repeated until the proper amount of sample is in each boat. The ratio of solid to liquid to form the slurry also is very important. Experience shows that a 1:20 ratio of sample to liquid gives reproducible results. Significant variation from this ratio results in poor-quality filter cakes and statistically less reliable data. The mixing time and degree of mixing are very important to the reproducibility of the results. One of the more controlled methods of mixing involves use of a Hamilton Beach mixer controlled by measurement with a strobe light. The mixing time is usually kept at 15 minutes. It is important to keep the mixing time and degree of mixing constant from one sample to the next to ensure comparable results. Most of the results reported in this paper are from samples sieved through a 30-mesh screen and mixed at a liquid/solid ratio of 20:1 for 15 minutes on a Hamilton Beach blender at 500 rev/min. It is important to obtain the sample while the slurry is mixing to ensure a representative composite at the end of the mixing period. This is best accomplished with a disposable plastic pipette. The results are compared by normalizing the CST's of the Fluid/rock slurry to that of the liquid blank to eliminate the effects of the liquid, such as viscosity and surface tension. Normalization of CST's The CST test involves the capillary suction of a Fluid through a porous medium. The following equation shows the relationship between CST, Fluid viscosity, and pressure differential5: Equation (1) Eq. 1 shows that CST is proportional to Fluid viscosity and inversely proportional to the pressure differential across the filter cake and through the CST paper. The pressure differential is related to capillary pressure and surface tension by the LaPlace-Young equation6: Equation (2) Therefore, CST is expected to increase with Fluid viscosity and decrease with decreasing surface tension. Test results show that it is very difficult to separate the relative effects of each of these parameters.
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Minimize formation damage by rapid, inexpensive method of completion- and Stimulation-Fluid selection
1992Co-Authors: D. R. Underdown, M. W. ConwayAbstract:Minimizing or removing formation damage is a major objective in completion and Stimulation operations. Formation damage is minimized by selection of «nondamaging» Fluid systems and operations on the basis of petrographic analysis and field experience. A technique known as the capillary suction time (CST) test, adopted from the drilling-Fluid industry, provides a quick and inexpensive method for qualitative selection or screening of the least damaging Fluid system for a particular formation. The CST test is a fundamental filtration method for determining the electrolyte concentration that will produce the maximum inhibiting effect on a formation
Mohamed Mahmoud - One of the best experts on this subject based on the ideXlab platform.
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Reaction of Chelating Agents and Catalyst with Sandstone Minerals During Matrix Acid Treatment
Arabian Journal for Science and Engineering, 2018Co-Authors: Mohamed MahmoudAbstract:Chelating agents were used recently to stimulate sandstone formations in oil and gas reservoirs. Chelating agents replaced the old sandstone acidizing Fluids such as mud acid (HF $$+$$ + HCl). Mud acid has several problems such as high corrosion rate, reservoir unconsolidation problems, and incompatibility with the reservoir rocks. The objective of this study is to introduce different chelating agents diluted in deionized water and seawater combined with potassium carbonate as a catalyst and clay stabilizer to stimulate sandstones reservoirs. In this paper, solubility experiments were performed for Bandera and Berea sandstone rocks in high pH DTPA, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylenediaminetriacetic acid (HEDTA) solutions. The optimum concentrations of both chelating agent and potassium carbonate were determined through the solubility experiments. Chelating agents were diluted using seawater and deionized water from an initial concentration of 40 wt%. Coreflooding experiments were performed on Berea and Bandera sandstone cores to assess the performance of the new formulation. Corrosion tests were conducted on actual tubing coupons made of L-80 alloy to check the corrosion rate of the new formulations. The enhancement in the core permeability was recorded after using the chelating agent and the catalyst to investigate the effectiveness of the formulation in sandstone acidizing. The solubility results showed Berea and Bandera sandstone have good solubility in HEDTA, EDTA, and DTPA chelating agents. EDTA chelating agent combined with potassium carbonate enhanced the permeability of both sandstone cores. EDTA chelating agent combined with catalyst has a corrosion rate of $$0.01\,\hbox {lbm/ft}^{2}$$ 0.01 lbm/ft 2 at $$350\,^{\circ }\hbox {C}$$ 350 ∘ C compared to $$0.65\,\hbox {lbm/ft}^{2}$$ 0.65 lbm/ft 2 for the mud acid plus 3 vol% corrosion inhibitor at the same temperature. The corrosion inhibitor additives will be eliminated in the new formulation which will reduce the cost of the Stimulation Fluid.
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Evaluation of using HEDTA chelating agent to clean up long horizontal heterogeneous sandstone wells without divergent
Journal of Petroleum Exploration and Production Technology, 2018Co-Authors: Salaheldin Elkatatny, Mohamed Mahmoud, Badr BageriAbstract:The removal of the calcium carbonate water-based filter cake and the associated formation damage after drilling is a very difficult task, especially in horizontal and extended reach wells. The horizontal section length could be 20,000 ft or more with different permeability distributions, which makes the damage caused by the drilling Fluid vary from one section to another. The filter cake removal in heterogeneous long horizontal lateral needs diverters to distribute the cleanup Fluid through the entire section. In this paper, a smart Fluid (HEDTA of 20 wt% and pH 4, hydroxyethyl ethylenediamine triacetic acid trisodium salt) was evaluated to remove the damage caused by calcium carbonate weighted drilling Fluid for the horizontal and extended reach wells without adding gelling agents. This Fluid will react with the calcium carbonate in the filter cake and the calcium carbonate in the formation to produce high viscosity Fluid that will divert the fresh flow through the less permeable sections in the horizontal well. Parallel coreflooding experiments were used to confirm the diversion ability of this chemical through two sandstone cores with different permeability. The results obtained showed that the viscosity of the Stimulation Fluid increased at least 3 times after the treatment of the sandstone cores and the parallel coreflooding showed good ability of diversion for the Fluid. The experimental results were used to describe the process of diversion using this Fluid mathematically. HEDTA chelating agent showed good ability to remove the damage caused by drilling Fluid from different sandstone cores with different permeabilities.
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Evaluation of using HEDTA chelating agent to clean up long horizontal heterogeneous sandstone wells without divergent
Journal of Petroleum Exploration and Production Technology, 2018Co-Authors: Salaheldin Elkatatny, Mohamed Mahmoud, Badr BageriAbstract:The removal of the calcium carbonate water-based filter cake and the associated formation damage after drilling is a very difficult task, especially in horizontal and extended reach wells. The horizontal section length could be 20,000 ft or more with different permeability distributions, which makes the damage caused by the drilling Fluid vary from one section to another. The filter cake removal in heterogeneous long horizontal lateral needs diverters to distribute the cleanup Fluid through the entire section. In this paper, a smart Fluid (HEDTA of 20 wt% and pH 4, hydroxyethyl ethylenediamine triacetic acid trisodium salt) was evaluated to remove the damage caused by calcium carbonate weighted drilling Fluid for the horizontal and extended reach wells without adding gelling agents. This Fluid will react with the calcium carbonate in the filter cake and the calcium carbonate in the formation to produce high viscosity Fluid that will divert the fresh flow through the less permeable sections in the horizontal well. Parallel coreflooding experiments were used to confirm the diversion ability of this chemical through two sandstone cores with different permeability. The results obtained showed that the viscosity of the Stimulation Fluid increased at least 3 times after the treatment of the sandstone cores and the parallel coreflooding showed good ability of diversion for the Fluid. The experimental results were used to describe the process of diversion using this Fluid mathematically. HEDTA chelating agent showed good ability to remove the damage caused by drilling Fluid from different sandstone cores with different permeabilities.
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Determination of the optimum wormholing conditions in carbonate acidizing using NMR
Journal of Petroleum Science and Engineering, 2017Co-Authors: Mohamed MahmoudAbstract:Abstract The current optimum wormhole injection rate during acid Stimulation treatment in a carbonate formation is defined as the injection rate that creates a dominant wormhole with the minimum acid volume. Wormholes are created to connect the reservoir to the wellbore by bypassing the drilling Fluid damage and to enhance the wellbore productivity by increasing the effective wellbore radius in carbonate formations. Currently, the pressure drop and computed tomography scan (CT scan) are used to define the acid optimum injection rate and wormhole shape in the stimulated carbonate rock cores. However, these two techniques assess the interconnectivity of the created wormhole to the rest of the pore system in the reservoir in a coarse way. In this paper and for the first time new definitions and new approach to the optimum injection rate and wormhole evaluation during carbonate Stimulation are introduced. Coreflooding experiments were performed using 3-inch Indiana limestone cores at 100 °C at different injection rates. A suite of Stimulation Fluids such as emulsified acid, hydrochloric (HCl) acid, gelled HCl acid systems based on polymers and viscoelastic surfactant (VES), and chelating agents were used in this study. Nuclear Magnetic Resonance (NMR) was used to evaluate the efficiency of different Stimulation Fluids in creating wormholes and their interconnectivity with the surrounding pore distributions in the rock. A new dimensionless number, pore interconnectivity number, is introduced to describe the interconnectivity between the created wormhole and the rest of the pore size distributions in the rock. Optimum wormhole shape is determined at the highest interconnectivity number. The optimum injection rate for a specific Fluid can also be determined at the highest interconnectivity number. Detailed NMR scanning of the core was found to be a good assessing tool for the type of the Stimulation Fluid and locating the optimum wormholing generating conditions. For example, using a 3-inch length Indiana limestone core, conventional coreflooding experiments showed that 2 cm 3 /min injection rate generates the minimum acid volume HCl/VES acid system, however, NMR scan showed an injection rate of 3 cm 3 /min generates the highest pore interconnectivity for the wormhole. Gelled acidizing Fluids such as HCl based on polymers created wormholes that were clearly identified by CT scan and pressure drop but the NMR scan showed that these wormholes are completely isolated from the rest of the surrounding pore system due to polymer residue plugging the pores. This isolation will reduce the production rate due to minimal radial Fluid entry at the wormhole surface. Radial flooding experiments through the wormhole and production from the side of the core confirmed the findings of NMR scan regarding the interconnection between the wormholes and other pores in the rock. Strong relationship was found between the interconnectivity number and core radial permeability around the wormhole.
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Modeling Flow of Chelating Agents During Stimulation of Carbonate Reservoirs
Arabian Journal for Science and Engineering, 2014Co-Authors: Mohamed Mahmoud, Hisham A. Nasr-el-dinAbstract:Chelating agents such as ethylenediaminetetraacetic acid (EDTA) and hydroxy ethylene diamine triacetic acid (HEDTA) have been used as stand-alone Stimulation Fluids. These Fluids can be used to stimulate water injectors, oil, or gas producers. In this study, an analytical model was developed to describe the flow of HEDTA and EDTA chelating agents and propagation inside calcite formations. The analytical model can be used as a pre-design tool before the treatments. The developed model can be used to predict the volume of the chelant required to create wormholes in calcite formations at different temperatures. The temperature affects the diffusion coefficient of the chelating agent, wormholing rate, and wormhole shape and size. The dissolving power of different forms of HEDTA can be determined using the model. The optimum injection rate based on optimum wormholing conditions was identified. Also, the model can be used to predict the wormholing rate of different chelating agents in calcite formations. The analytical model can be used to predict the performance of the chelating agent in calcite Stimulation. The volume of chelating agent required to stimulate calcite formation per foot thickness was determined using the developed model. The optimum injection rate was determined for different chelating agents using the model, and the results were compared with experimental results from previous work and there was a good agreement between the measured and the predicted values. The model can be used to determine the best Stimulation Fluid based on the temperature and fracture pressure of the target zones.