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Collaborating Authors
Drilling Fluids and Materials
Acidizing Workflow for Optimized Well Performance in Zhdanov and Lam Oil Fields Offshore Caspian Sea
Kalabayev, Ruslan (Schlumberger) | Sukhova, Ekaterina (Schlumberger) | Rovshenov, Gadam (Schlumberger) | Kontarev, Roman (Dragon Oil)
Abstract Successful sandstone matrix stimulation treatments require addressing complex mineralogy, correctly identifying formation damage, selecting the best stimulation fluids, and placing these fluids correctly. The objective of this paper is to demonstrate a workflow considering laboratory testing, advanced software modeling including acid and diverter fluid efficiency calibration using field experimental data, field execution, and relevant case studies in two oil fields located in the Cheleken block, offshore Caspian Sea. Implementation of the workflow has led to positive results. Matrix acidizing was selected as the primary method for restoring production of the oil wells drilled into sandstone reservoirs due to the reservoir characteristics. Deep Zhdanov wells and shallower Lam wells possess ~15 and ~250 md permeability and ~90 and ~50°C static reservoir temperature, respectively. The target rock mineralogy in both fields predominantly consists of quartz, chlorite, and carbonate minerals. Fluids selection, stimulation design and job execution followed the above mentioned workflow. Treatment modeling considered calibration factors derived from field testing and incorporated several acid and diverter systems. A mix of bullhead and coiled tubing placed treatments were employed. The first step of the workflow considered characterization of the rock mineralogy and selection of the best-fit treatment fluids. Rock dissolution and X-ray diffraction (XRD) tests were run to develop the optimum formulations for the treatment conditions. Further, the results of the laboratory testing were incorporated into the advanced matrix acidizing simulator to model and optimize the treatment schedules. The recently developed matrix stimulation software incorporates geochemical, thermal, and placement simulations calibrated with experimental data. Offset well stimulation treatment pressure match was done by calibrating the acid and diverter fluid efficiency, and those calibrated values were considered for design simulations for the following acid treatments. In this paper, the term "acid efficiency" is defined as a measure of the relative rate at which the acid can penetrate when it flows in the rock matrix as a function of matrix porosity and the overall acid reactivity. The term "diverter efficiency" is defined as a measure of the viscosity developed by a given diverter when it flows in the rock matrix. Such a calibration method accounts for the actual reservoir large-scale acid-rock reaction kinetics. Finally, diagnostic tests and main acid treatments were executed that enabled achieving the desired levels of skin reduction, reservoir placement, zone coverage, and hydrocarbon production rates. Several acid stimulation operations were conducted including three cases in which a low-temperature well with carbonate damage needed repeated acidizing and two additional cases that involved wells with deep, hot, and clay-rich pay zones. Several fluid schedules were applied including foam diversion technique. The above approach uses a unique method of acid efficiency calibration using field experimental data. It requires good knowledge of reservoir rock mineralogy, porosity, and permeability profiles in the zones of interest. Pretreatment skin is calibrated using production data prior to acid efficiency calibration based on matching the actual treatment pressures. The pressure behavior observed during the following treatments closely matched the design pressures confirming applicability of the approach.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Mineralogy (0.97)
- Asia > Turkmenistan > Caspian Sea > Cheleken Contract Area > Block 2 > Lam Field > Zone 7 Formation (0.99)
- Asia > Turkmenistan > Caspian Sea > Cheleken Contract Area > Block 2 > Lam Field > Zone 6 Formation (0.99)
- Asia > Turkmenistan > Caspian Sea > Cheleken Contract Area > Block 2 > Lam Field > Zone 5 Formation (0.99)
- Asia > Turkmenistan > Caspian Sea > Cheleken Contract Area > Block 2 > Lam Field > Zone 4 Formation (0.99)
Control Over the Fracture in Carbonate Reservoirs as a Result of an Integrated Digital Stimulation Approach to Core Testing and Modeling
Yudin, Alexey (Schlumberger) | Khan, Abdul Muqtadir (Schlumberger) | Romanovskii, Rostislav (Schlumberger) | Alekseev, Alexey (Schlumberger) | Abdrazakov, Dmitry (Schlumberger)
Abstract The oilfield industry is rapidly changing towards reduced CO2 emissions and sustainability. Although hydrocarbons are expected to remain the leading source for global energy, costs to produce them may become prohibitive unless new breakthrough in technology is established. Fortunately, the digital revolution in the IT industry continues at an accelerating pace. A digital stimulation approach for tight formations is presented, using the achievements of one industry to solve the challenges of another. The fracture hydrodynamics and in-situ kinetics model is incorporated in the advanced simulator together with the detailed multiphysics models based on acid systems digitization, including rheology and fluid- carbonate interactions data obtained from the laboratory experiments. Digitization of fluid-rock interaction and fluid leakoff was performed using a coreflooding setup that allowed pumping concentrated acids in core samples at high-pressure/high-temperature (HP/HT) conditions. Varying the testing parameters across a broad range allowed refining the model coefficients in the simulator to obtain high accuracy in the predicted results. The digital slot concept was used to validate physical models in an iterative experimental approach. The software proved efficient at providing validation of multiphysics models used together with advanced slurry transport in the simulator. The fine computational grid allowed accurate predictions of the fracture geometry, etched width, and channel conductivity, resulting in realistic well productivity anticipations. Since multiple fluid systems of the acid stimulation portfolio were digitized and incorporated into the simulator, it was possible to optimize complex acid fracturing designs in the real field operations that included retarded single-phase and multiphase acid systems, self-diverting viscoelastic acids, and fiber- based diverting systems. Several case studies from multiple areas and reservoirs from Caspian and Middle East areas have demonstrated extremely positive oil and gas production results with reduced acid volumes with the digital stimulation workflow compared to conventionally stimulated offset wells. The digital stimulation workflow brings a new approach to acid fracturing optimization based on an integrated cycle in which high-resolution data from several sources are processed by powerful computing capacities. Starting from digitizing acid reactions with the core samples, through digitized rheology and particle transport in multiphysics models, an advanced numerical simulator tailors an optimum design from a number of acid system options, pumping rates, additive concentrations, and stage volumes to achieve best geometry of etched channels inside a fracture.
- Europe (1.00)
- North America > United States > Texas (0.46)
- Asia > Middle East > Saudi Arabia > Eastern Province (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock (0.94)
- North America > Mexico > Veracruz > Veracruz Basin (0.99)
- North America > Mexico > Gulf of Mexico > Veracruz Basin (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- (10 more...)
- Well Drilling > Drilling Fluids and Materials (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Well Completion > Acidizing (1.00)
- (6 more...)
Acid Selection for Volcanic Tuffaceous Sandstone with High Analcime Contents: A Laboratory Study in Kita-Akita Oil Field, Northern Japan
Ueda, Kenji (Inpex Corporation) | Matsui, Ryoichi (Inpex Corporation) | Ziauddin, Murtaza (Schlumberger) | Teng, Ling Kong (Schlumberger) | Wang, Wei Kan (Schlumberger)
Summary Investigation of the effectiveness of matrix‐stimulation treatments for removing drilling‐induced damage in the Akita region of northern Japan is of interest because of the presence of large quantities of acid‐sensitive minerals, such as analcime. A feasibility study of the subcommercial field redevelopment in the Kita‐Akita Oil Field, one of the satellite fields of the main Yabase Oil Fields that produced from 1957 to 1973 and was plugged and abandoned, was conducted. As a part of the studies, matrix‐acidizing laboratory experiments were performed. Conventional mud acids and formic‐acid‐based organic‐mud‐acid systems cause significant permeability damage because of the instability of analcime when exposed to these acids. This study focuses on the development of a treatment fluid that removes drilling‐induced damage and is also compatible with the formation. Petrology studies and core flow tests were used in conjunction with geochemical modeling to achieve this objective. A petrographic analysis on the untreated cores showed abundant tuffaceous pore‐filling mineral phases, ranging from 12 to 20% in volume. Smectite clay and microcrystalline quartz are the major constituents present as alteration products of volcanic glass. Analcime was present in significant quantities in all samples tested. Six core flow tests were performed on formation cores to optimize the acid preflush and main acid stage. Permeability change resulting from treatment fluids was recorded for the tests. Chemical analysis of the effluent was performed on three core flow tests. Core samples before and after acidization were characterized on the basis of thin section, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and mineral mapping. Core flow tests with conventional retarded organic mud acid (ROMA) resulted in only 75% retained permeability. The permeability damage by the ROMA was surprising, because it usually performs well in acid‐sensitive formations. A chelant‐based retarded mud acid was tested next and resulted in minor formation damage. It can be potentially used in a field treatment, because its high dissolving power is expected to more than compensate for the damage. The highest retained permeability was obtained with an acetic‐hydrofluoric (HF) acid system. It was successfully able to remove drilling‐induced damage and was also compatible with the native mineralogy. Core flow tests were used to calibrate the permeability/porosity relationship used in the geochemical simulator. The geochemical simulator was then used to predict the field‐level acid response. The analytic methods presented are general enough to be of interest to sandstone‐acidizing studies, where detailed analysis is needed for damage identification and removal. The fluids developed for this formation are good candidates for other formations where conventional acid systems have not performed well. This study also highlights a close collaboration between the operator and the service company to find a workable solution to a challenging stimulation requirement.
- North America > United States > Texas (0.46)
- Asia > Japan > Honshu Island (0.34)
- Europe > Norway > Norwegian Sea (0.34)
- North America > United States > Michigan (0.28)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)
- Geology > Geological Subdiscipline > Geochemistry (1.00)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Åre Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Tilje Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Ile Formation (0.99)
- (8 more...)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Completion > Acidizing (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (2 more...)
Acid Selection for Volcanic Tuffaceous Sandstone With High Analcime Contents: A Laboratory Study in Kita-Akita Oil Field, Northern Japan
Ueda, Kenji (INPEX Corporation) | Matsui, Ryoichi (INPEX Corporation) | Ziauddin, Murtaza (Schlumberger) | Teng, Ling Kong (Schlumberger) | Wang, Wei Kan (Schlumberger)
Investigation of the effectiveness of matrix stimulation treatments for removing drilling induced damage in Akita region in northern Japan is of interest due to the presence of large quantities of acid-sensitive minerals, such as analcime. Feasibility study of the sub-commercial field redevelopment in the Kita-Akita oil field, one of the satellite fields of main Yabase oil fields, which produced from 1957 to 1973, and were plugged and abandoned, were conducted. As a part of the studies, matrix acidizing laboratory experiments were performed. Conventional mud acids and formic-based organic mud acid systems cause significant permeability damage due to instability of analcime in these acids. This study focuses on the development of a treatment fluid that removes drilling-induced damage and is also compatible with the formation. Petrology studies and core flow tests were used in conjunction with geochemical modeling to achieve this objective. A petrographic analysis on the untreated cores showed abundant tuffaceous pore-filling mineral phases, ranging from 12 to 20% in volume. Smectite clay and microcrystalline quartz are the major constituents as alteration products of volcanic glass. Analcime was present in significant quantities in all samples tested. Six core flow tests were performed on formation cores to optimize the acid preflush and main acid stage. Permeability change due to the treatment fluids was recorded for the tests. Chemical analysis of the effluent was performed on three core flow tests. Core samples before and after acidization were characterized based on thin section, X-ray diffraction (XRD), scanning electron microscopy(SEM) and mineral mapping. Core flow tests with a conventional retarded organic mud acid resulted in only a 75% retained permeability. The permeability damage by the retarded organic mud acid was surprising because it usually performs well in acid-sensitive formations. A chelant based retarded mud acid was tested next and resulted in minor formation damage. It can potentially be used in a field treatment as its high dissolving power is expected to more than compensate for the damage. The highest retained permeability was obtained with an acetic-HF acid system. It was successfully able to remove drilling-induced damage and was also compatible with the native mineralogy. Core flow tests were used to calibrate permeability-porosity relationship used in the geochemical simulator. The geochemical simulator was then used to predict field-level acid response. The analytic methods presented are general enough to be of interest to sandstone acidizing studies where detailed analysis is needed for damage identification and removal. The fluids developed for this formation area good candidates for other formations where conventional acid systems have not performed well. This study also highlights close collaboration between an operator and service company to find a workable solution to a challenging stimulation requirement.
- North America > United States > Louisiana (0.28)
- North America > United States > Texas (0.28)
- Asia > Japan > Honshu Island (0.24)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)
- Geology > Geological Subdiscipline > Geochemistry (1.00)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Åre Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Tilje Formation (0.99)
- Europe > Norway > Norwegian Sea > Halten Terrace > Block 6507/8 > Heidrun Field > Ile Formation (0.99)
- (7 more...)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Completion > Acidizing (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (2 more...)
First Removal of Manganese Tetraoxide Water-Based Mudcake in HP/HT Wells with H2S and CO2 Environment Using Acetic Acid Conveyed with Coiled Tubing
Chendrika, Lusiana (Schlumberger) | Purwitaningtyas, I. M. (Schlumberger) | Fuad, Muhammad (Schlumberger) | Etuhoko, Michael (Husky-CNOOC Madura Limited) | Nurdin, Syaiful (Husky-CNOOC Madura Limited) | Jihong, Lian (Husky-CNOOC Madura Limited) | Rusli, Barne (Husky-CNOOC Madura Limited)
Abstract Manganese tetraoxide (Mn3O4) drilling fluid weighting material was first applied in two high-pressure/high-temperature (HP/HT) Madura Sea, Indonesia wells, BD-A and BD-B. Mn3O4 is less damaging to the environment and formation than other weighting agents. In the BD wells, coiled tubing (CT) will perform Mn3O4 mudcake removal by spotting an acid solution. The main challenges come from the formation characteristics: temperature up to 305°F, pressure of 8100 psi, 5,000 ppm H2S, and 5.5% CO2. Slow-reacting acid was preferred to prevent creating a corrosive environment. The reaction of acetic acid, formic acid, and a chelating agent with Mn3O4 at 305°F was studied. A corrosion test was performed to see the effect of the acid and 5,000 ppm H2S on CT string and completion tubing metal. Viscosimeter and densitometer testing was done on 155 ppb Mn3O4 mud that was mixed at laboratory scale to represent actual drilling mud in the well. Filter cake was made using an HP/HT filter press and 10-micron alloxite disc to represent formation permeability. Using the mix of acetic acid and chelating agent solution, 100% solubility of filter cake was achieved after 6 hours reaction time, giving enough time for CT to spot the acid in the entire 1,000-ft openhole interval and provide a uniform filter cake removal. With additional organic acid inhibitor and H2S inhibitor, the corrosion rate on CT and completion tubing metal after 16 hours test was found acceptable without pitting observed. This method has been proven effective to remove Mn3O4 filter cake with significant pressure drawdown reduction, hence increasing well productivities. The utilization of CT improves cost efficiency by accurately placing a right amount of acid solution across the openhole section. This stimulation fluid system is the first application in the world and was proven to be effective to remove Mn3O4 based filter cake and protect CT and tubing metal against H2S and CO2 in an HP/HT environment.
- Asia (1.00)
- North America > United States (0.93)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Statfjord Group (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Lunde Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Lista Formation (0.99)
- (2 more...)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > HP/HT reservoirs (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
Optimization of Acid Fracturing with Unified Fracture Design
Ravikumar, Arjun (University of Houston) | Marongiu-Porcu, Matteo (Schlumberger) | Morales, Adrian (Schlumberger)
Abstract Acid fracturing is the most recognized and successful reservoir stimulation technique for conventional carbonate formations. Resulting fracture conductivity is the key parameter that controls final well productivity, while the competing diffusion and reaction phenomena control the "vital" acid coverage along the full areal extension of the fracture. However, not all reservoirs lend themselves to the same fracture geometry and conductivity, and this is where the "Unified Fracture Design" (UFD) approach is irreplaceable. Classic fracture design optimization with the UFD approach involves the maximization of well productivity. For any mass of proppant to be injected as part of the treatment, the algorithm determines the unique fracture length and width (with height as a parasitic variable) that will provide the maximum productivity index. In this paper we recast the UFD approach for specific acid fracturing applications, where the maximum productivity index is now determined as a function of the optimum fracture geometry determined for any volume of injected acid. The optimum fracture width profile is then obtained by solving the convection-diffusion equation for acid propagation, and subsequently used to study the required acid coverage through the fracture as a function of such optimum fracture width profile. Acid reaction retardation plays a crucial role in ensuring proper acid coverage throughout the optimum fracture length, and this paper focuses on the two major reaction retardation fluid systems: Acid-Internal Emulsions (AIE) and gelled acids. The workflow presented in this paper provides the basis for designing optimum acid fracturing treatments as a function of the volume of acid injected, the acid injection rate and the selected acid retardation method.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.31)
Improved Fluid Technology for Stimulation of Ultrahigh-Temperature Sandstone Formation
Rignol, Joel (PTT Exploration and Production Public Company Limited) | Ounsakul, Thanawit (PTT Exploration and Production Public Company Limited) | Kharrat, Wassim (Schlumberger) | Fu, Dan (Schlumberger) | Teng, Ling Kong (Schlumberger) | Lomovskaya, Irina (Schlumberger) | Boonjai, Pimterra (Schlumberger)
Abstract Acid stimulation is one of the production enhancement methodologies applicable in both development and exploration fields. Sandstone acidizing requires a sophisticated and well-studied approach to avoid formation damage caused by acid precipitation. Although the industry has made significant technical advancements in treatment fluids over the past decades, high bottomhole temperature still presents one of the biggest challenges. A new chelant-based fluid system was tailored to stimulate sandstone formation effectively under ultrahigh-temperature conditions. The new system has been evaluated extensively in the laboratory. Laboratory work included sequential dissolution, chemical analysis, and core flow tests. Both dissolution and core flow tests were conducted up to 400°F with reservoir core samples to simulate the actual reservoir condition and treatment design. Sequential dissolution results indicated that the new chelant-based system dissolved clay minerals in each sequence without causing silica precipitation due to secondary and tertiary reactions. The increase in the permeability of the reservoir core after core flow tests further demonstrated that the new fluid system is indeed highly effective in removing the damaging clay particles. The major advantage of the new chelant-based system is that it can be pumped in a single stage, which has greatly simplified the field operation and diversion requirement. In addition, because of its mild pH, the new system has low corrosion rate and less tendency to emulsion and sludge formation. This new system is HCl acid free, and therefore it eliminates the high risk of silica precipitation due to reaction with sensitive clays at high temperature. Last, but not least, the chelant fluid is consists of a retarded HF system which enables deeper radial penetration with less near-wellbore deconsolidation and which doubles the effect of clay dissolution and stabilization.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)
Effective Kaolinite Damage Control under Unfavorable Chemical Environment: Field Case
Restrepo, A.. (Equion Energia) | Lastre, M.. (Schlumberger) | Milne, A.. (Schlumberger) | Peñaloza, S. J (Equion Energia) | Castro, E.. (Equion Energia)
Abstract Kaolinite migration is a common but often well treated formation damage mechanism. Undesired secondary reactions leading to precipitates and/or limited treatment coverage related to the presence of additional damage mechanisms are common issues. The present work documents a field case study of kaolinite damage control that included dissolution and stabilization under a very unfavorable environment in which CaCO3 scales and asphaltenes also co-existed. The case herein described is the last development stage after several unsuccessful trials in the same area which included the injection of conventional mud acid and retarded HF sandstone type systems. A new chemistry approach incorporating retarded flouboric acid generation and high performance chelants for metallic ions control was developed. Also key, was realizing fines wettability to oil (through critical rate tests to both water and oil) which allowed including proper pre-flushes on final treatment deployment. Along with a summary of the fines problem description in the area of interest, laboratory protocols, stimulation design approach and field trial results are presented. According to treated well results, up to 50% PI improvement could be now attained in ~60% of total well count where same damage configuration is expected to be present.
- Europe (0.94)
- North America > United States > Louisiana (0.47)
- North America > United States > California > San Francisco County > San Francisco (0.28)
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.67)
- South America > Colombia > Barco Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Statfjord Group (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Lunde Formation (0.99)
- (3 more...)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (0.93)
Summary Fracture acidizing has been a dominant practice in the industry to enhance well productivity in low-permeability carbonate reservoirs. Many acid systems have been developed to improve this stimulation process. The most desirable characteristics for an acid system to be suitable for fracture acidizing are leakoff control and retarded reaction rate. These characteristics are required for deep acid penetration, so that when the fracture closes, long flow channels are etched on the fracture surfaces. Leakoff control can be achieved by pumping a pad containing a viscosifying agent or solid bridging agents to plug wormholes generated by acid dissolution. Reaction retardation is attempted usually by lowering the effective diffusivity of the hydrogen ion. It is well known that during an acid-fracturing operation, the overall reaction rate of hydrochloric acid (HCl) with limestone is mass-transfer-limited. Designing the treatment requires knowing the effective diffusivity of the hydrogen ion in the acid system, which, to the best of the authors' knowledge, has not been determined before. Because of their combined leakoff-control and retardation capabilities, surfactant-based acids have been used in acid-fracturing treatments. Because more carbonate reservoirs are treated by use of this acid system, it is important to obtain the effective diffusivity of H. The rotating-disk device has been used to investigate the reaction kinetics between a reactive solution and carbonate rocks because the thickness of the boundary layer is uniform throughout the disk surface. This paper discusses the reaction-rate data generated recently for surfactant-based acid by use of a rotating-disk apparatus and presents the methodology used to determine the effective diffusivity from the measurements. The results obtained indicated that the viscoelastic surfactant examined (carboxybetaine-type) reduced the dissolution rate of calcite with HCl acid. The surfactant reduced the diffusion coefficient for H. The effect of temperature on the diffusion coefficient did not follow the Arrhenius law.
- North America > United States (1.00)
- Asia > Middle East > Saudi Arabia (0.48)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Completion > Acidizing (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
Abstract Sandstone acidizing is very challenging because of the complex reactions that occur between the multiple-stage treatment fluids and the formation minerals. Such reactions are more likely to occur at elevated temperatures and can result in potentially damaging precipitation reactions. In conventional acid treatments, fluid is usually pumped in multiple stages of pre-flush, main fluid and over flush. The drawback of conventional sandstone acidizing treatments is that the success rate is generally low due to the uncertainty associated with the fluid-formation interactions. This paper presents the results of a laboratory investigation of a single-stage sandstone acidizing fluid designed to address some of the problems associated with conventional sandstone acidizing fluids. The application of the fluid system is sandstone reservoirs with bottom hole static temperatures greater than 200°F. Core flow tests demonstrated that the single acid system minimized the potential for precipitation due to secondary and tertiary reactions. This system did not cause sand deconsolidation, and maintained the integrity of sandstone cores. Corrosion tests conducted for low-carbon steel and 13 Cr coupons demonstrated that the fluid had lower corrosion rates. Introduction Sandstone acidizing is a complex operation because the treatment involves flow and reactions in porous media where the reactive chemicals contact a wide range of minerals.1 The formation may contain various amounts of quartz, clays (aluminosilicates such as kaolinite or illite), or alkaline aluminosilicates such as feldspars, and zeolites, as well as carbonates (calcite, dolomite, ankerite) and iron-based minerals (hematite and pyrite). Recent studies on matrix stimulation have strongly emphasized the importance of secondary and tertiary reactions in determining the success of sandstone acidizing treatments.2–5 However, for acid-sensitive aluminosilicates, these reactions are especially important because they occur at much shorter time-scales than for the non-acid reactive minerals. The presence of acid-sensitive aluminosilicates may dominate treatment design considerations, even though they may be present in small quantities compared to other aluminosilicates. Over the years, many different acidizing systems have been developed for specific applications. In general, the three main drivers for these developments are:6Retard the acid/mineral reactions for deeper acid penetration, Make the acid less aggressive to well completions, and Avoid undesirable reactions that could result in formation damage. Traditionally, hydrofluoric (HF) acid-based systems have been used to dissolve aluminosilicates in sandstone formations. These formulations, typically referred to as mud-acid, are usually composed of hydrochloric acid (HCl) and HF at various concentrations. Examples of these traditional HCl:HF formulations include 6:1.5, and 12:3 mud acid systems. The use of 9:1 or even 13.5:1:5 mud acid systems has been advocated to allow greater dissolutions of secondary reaction products in low pH environments.2,3 In HCl sensitive formations, HCl is replaced with an organic acid such as acetic or formic acid.7 Various methods were suggested to retard the traditional mud acids including the use of buffered-HF systems,8 fluoroboric acid 9 and mixtures of esters and fluorides to generate HF-in-situ by thermal hydrolysis.10 Reactions of some these acid systems with various clays were discussed by Al-Dhahlan et al.11 In general, during sandstone acidizing treatments, the following main precipitation reactions occur that can lead to formation damage.12,13
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral (1.00)
- Well Completion > Acidizing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.89)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.70)
- (5 more...)