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Collaborating Authors
Successful Application of an End-to-End Advanced Workflow for Reservoir Stimulation: Case Studies from a High-Temperature Gas Formation in Ukraine
Abdrazakov, Dmitriy (Schlumberger) | Eswein, Edmund (Schlumberger) | Witek, Jakub (Schlumberger) | Agee, Daniel (Schlumberger) | Bruce, Brian (Schlumberger) | Dorokhov, Maksym (DTEK Oil & Gas) | Trokhymets, Dmytro (DTEK Oil & Gas) | Prokhorenko, Stanislav (DTEK Oil & Gas)
Abstract An end-to-end workflow was developed for optimization of a carbonate stimulation treatment in a high-temperature environment. The workflow includes advanced core testing, treatment fluid and design considerations, and production simulations. A case history validated the workflow and production results. A well in central Ukraine was selected by an operator as a candidate well for a production stimulation feasibility study. The reservoir and well information were reviewed, and a reservoir model was built in an advanced matrix stimulation simulator. Core flow tests with 3D wormhole geometry visualization were used to calibrate the simulator's fluid-rock interaction parameters. Various skin and permeability profiles were subjected to iterations in the simulator with different fluids and treatment schedules. Optimum fluids were chosen according to the risk analysis, and key design objectives were considered based on the drilling records, mud type, workover history, and petrophysics. Analysis of the drilling history revealed the necessity of using special stimulation fluids for removing damage from the oil-based mud. Analysis of the well and reservoir conditions showed that the use of nonmodified, emulsified, and organic acids was not recommended. Instead, a single-phase retarded stimulation fluid was chosen as the main reactive agent. Use of chelates was declined due to higher cost-to-efficiency ratio in comparison with the single-phase retarded stimulation fluid. The core flow tests along with 3D wormhole geometry visualization allowed optimizing the treatment parameters with respect to wormholing efficiency. The core flow test data were used to calibrate the matrix stimulation simulator with representative fluid-rock interaction curves. Due to interval length and heterogeneity, the use of diverters was recommended to increase wellbore coverage during the treatment. A polymer-free viscoelastic surfactant-based diverter was selected to alter the injection profile. An optimum treatment schedule developed in the matrix simulator included cleanout by coiled tubing equipped with a high-velocity jet, a low-rate coiled tubing matrix treatment, and a high-rate bullhead treatment. The designed treatment was successfully pumped. The post-stimulation production showed a significant increase in productivity index, without issues in cleanup. Similar workflow stimulation treatments were deployed on five subsequent wells, which have also shown very positive production response. This work provides validation that a sound and rigorous engineering approach with advanced modeling and novel chemistry solutions can revive and significantly increase productivity of carbonate reservoirs. It was the first application of such a workflow and described stimulation fluid technology in Ukraine and Europe.
- Asia (0.93)
- Europe > Ukraine (0.91)
- North America > United States > Texas (0.46)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/9b > Bruce Field > Turonian Limestone Formation (0.97)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/9b > Bruce Field > Statfjord Sandstone Formation (0.97)
- Europe > United Kingdom > North Sea > Northern North Sea > East Shetland Basin > Block 9/9b > Bruce Field > Bruce Sandstone Formation (0.97)
- (6 more...)
Abstract Hydrocarbon production enhancement by means of acid stimulation in Kazakhstan requires application of a more effective approach to address challenges associated with acid placement and reservoir contact in long pay zones of high-temperature carbonate reservoirs, thereby improving return on investment. Several robust chemical product solutions, coupled with comprehensive modeling in a new advanced simulator, have been successfully implemented to tackle the challenges and successfully increase the efficiency of matrix acidizing. To improve the productivity of stimulated wells by improving the effectiveness of acid treatments, a detailed study of reservoir rock and its reaction to various acid and fluid systems has been made via laboratory testing and software modeling. Sensitivity analyses involving multiple treatment schedule scenarios incorporating various acid and diverter fluid systems are considered. Enhanced modeling of a novel retarded acid, viscoelastic diverting acid and particulate diverting systems demonstrated more uniform zone coverage, as well as deeper wormhole penetration. The above optimizations were field tested in several oil fields. Prior to any acid stimulation, the formation injectivity and damage profiles were calibrated based on the well pre-treatment production profile taken from production logs. As the first step, performance of the retarded acid was tested in several treatments. The bottomhole injection pressure decline behavior indicated that a slower reaction takes place during injection of the retarded acid compared to the stages of conventional hydrochloric acid, confirming the retarded nature of the acid as seen from the core tests. Secondly, viscoelastic self-diverting acid was added to the schedule for treatment of long intervals, replacing conventional gelled acid with shorter viscosity peak and lower retained permeability features. Better zone coverage, observed from injection pressure slope changes upon arrival of each diverter stage downhole, and improved post-acidizing formation cleanup were achieved as a result of this implementation. Third, field trials were made using combined application of the viscoelastic diverting acid and degradable particulate diverter pills. Full and uniform coverage of the entire zone of interest has been observed after pressure matching the actual treatments’ schedule and was validated by post-stimulation production logs. Field application of the approach supports the theoretical findings. Substantial improvement in well productivity was monitored after the application of each optimization step. The above approach demonstrates the value of thorough integration of laboratory testing, comprehensive software modeling and application of enhanced stimulation fluids. The efficiency of the approach is supported by multiple successful field case studies and is the recommended way forward for carbonate acidizing.
- North America > United States (0.95)
- Asia > Kazakhstan (0.71)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Tengiz Formation (0.99)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Korolev Formation (0.99)
Integration of Latest Laboratory, Software and Retarded Acid Technologies to Increase Efficiency of Acid Treatments in Carbonates: Case Studies from Central Asia
Abdrazakov, Dmitriy (Schlumberger) | Ziauddin, Murtaza (Schlumberger) | Vernigora, Denis (Schlumberger) | Beletskaya, Anna (Schlumberger) | Yakimchuk, Ivan (Schlumberger) | Olennikova, Olesya (Schlumberger) | Usoltsev, Dmitriy (Schlumberger) | Nikolaev, Max (Schlumberger) | Panga, Mohan (Schlumberger) | Burlibayev, Askhat (Almex Plus LLP)
Abstract Acidizing treatments in carbonates often result in significant skin decrease due to high reactivity of the formation with acids. Noticeable production increase or inability to run analysis tools after the treatment may lead to the conclusion that the matrix acidizing job was performed efficiently, when, in fact, the job was not optimized in terms of fluid volumes, acid types, wellbore coverage, and pumping rates. As a result, the final skin is not as low as it could be, and, most importantly, medium - and long-term post-acidizing production decline is faster than it could be with an optimized treatment. To overcome these concerns, an integrated approach to acidizing treatments was implemented for different oil fields in Kazakhstan. The integrated approach consists of comprehensive laboratory testing, which includes core flow tests with subsequent 3D computer tomography scanning. The tests help to determine wormholing regimes and channel geometry while providing calibration points for acid-rock interaction curves. These coefficients are used in the acidizing modeling software, which enables optimization of fluid volumes, pumping rates, and diversion strategy. The approach suggests the use of a single-phase retarded acid system is the most effective method of keeping the treatment in the dominant wormhole regime, especially at elevated temperature. The integrated approach loop is closed by the analysis of the distributed temperature sensor data to calibrate the efficiency of diversion and reservoir injectivity profile. The approach was introduced for different oil fields in Kazakhstan, with a variety of conditions: depths up to 5000 m and temperatures up to 145°C. The approach helped to optimize acid volumes by as much as 44% to achieve an optimum skin. In the mid-term perspective, this approach helped to reduce the production decline rate by at least 20%, and ongoing post-treatment analysis is even more promising.
- Asia > Kazakhstan (0.68)
- North America > United States > Texas (0.28)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (0.48)
Abstract Oil and gas companies operating carbonate oil and gas condensate fields in Kazakhstan have been carrying out acid stimulation activities leading to a substantial increase in hydrocarbon production. Nearly all treatments were considered a success. Nevertheless, a certain level of optimization in the production enhancement methods that could, potentially, have brought additional technical and financial benefits, were overlooked due to various reasons. A comprehensive review of historical treatments on several fields located in West-Kazakhstan region was performed to identify areas to improve post-stimulation well performance. This review identified improvements including "cleaner" fluid selection, optimised design and treatment schedules. Historical treatments in the oil field typically used straight hydrochloric acid as the main acid, polymer-gelled (self-diverting) acid as the chemical diverter, and linear guar gel for displacement, and diagnostic tests. The application of a modern single-phase retarded acid to replace the straight hydrochloric acid was identified as a key improvement that would yield more efficient wormhole generation and an improved stimulation ratio. Another opportunity for improvement was to upgrade the chemical diversion system from polymer-based self-diverting acid to a viscoelastic surfactant-based (polymer-free) diverting acid system. The use of an oil-based displacement fluid with high retained permeability instead of linear gel and to reduce the hydrostatic pressure post-acidizing, thereby improving flowback, was also employed. Extended core flow testing for regained permeability and solubility were carried out with several acid systems to compare their capabilities and efficiency to create conductive wormholes, and their dissolution capacities. Additionally, emulsion, and sludging tendency upon contact with wellbore tubulars and formation crude was checked to verify the acids’ compatibility with hydrocarbons produced from the target reservoir. After the prerequisite laboratory testing, field trials commenced applying various combinations of fluid technologies in high-rate matrix stimulation treatments. The optimizations resulted in higher (normalized) post-stimulation productivity index (PI), facilitated formation cleanup, and enabled more efficient operations. A similar approach is, currently, being implemented in other stimulation projects in the region, and the results are being replicated. As has been mentioned above, one of the main enhancements implemented as part of this work is the employment of the single-phase retarded acid. Most of the published literature discussing application of the acid covers the cases of stimulation of relatively hot reservoirs (BHST>100°C) as acidizing of high-temperature carbonate rock using traditional hydrochloric acid is a great challenge. The current paper provides details of the case studies, where the acid system was successfully implemented in combination with several other stimulation technologies for mid-temperature ranges. One of the objectives was also to assess whether application of reduced volumes of the retarded and diverting acids would still lead to improved wells’ productivity. Positive results of the laboratory studies, treatment modeling, and field trials were validated by the increasing normalized post-stimulation PI with each optimization step.
- Asia > Kazakhstan > West Kazakhstan Region (0.24)
- North America > United States > Louisiana (0.15)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Tengiz Formation (0.99)
- Asia > Kazakhstan > Mangystau Oblast > Precaspian Basin > Tengiz Field > Korolev Formation (0.99)
Single-Phase Retarded Inorganic Acid Optimizes Remediation of Drilling Formation Damage in High-Temperature Openhole Horizontal Carbonate Producer
Fawzy, Ahmed Mohamed (ADNOC Onshore) | Talib, Noor Nazri (ADNOC Onshore) | Makhiyanov, Ruslan (ADNOC Onshore) | Naseem, Arslan (ADNOC Onshore) | Molero, Nestor (Schlumberger) | Khan, Rao Shafin (Schlumberger) | Enkababian, Philippe (Schlumberger) | Belkadi, Wafaa (Schlumberger) | ElAttar, Ahmed (Schlumberger) | Ibrahim, Amer (Schlumberger)
Abstract In high-temperature carbonate producers, conventional hydrochloric (HCl) acid systems have been ineffective at delivering sustainable production improvement due to their kinetics. Retarded acids are deemed necessary to control the reaction and create effective wormholes. This scenario is even more critical in wells completed across long openhole horizontal intervals due to reservoir heterogeneity, changing downhole dynamics, and uniform acid placement goals. Out of the different retarded acid options, emulsified acid is one of the preferred choices by Middle East operators because of its excellent corrosion inhibition and deep wormhole penetration properties. However, it also brings other operational complexities, such as higher friction pressures, reduced pump rates, and more elaborate mixing procedures, which in some cases restrict its applicability. The recent introduction of a single-phase retarded inorganic acid system (SPRIAS) has enabled stimulation with the same benefits as emulsified acids while eliminating its drawbacks, allowing friction pressures like that of straight HCl and wormholing performance equivalent to that of emulsified acid. A newly drilled oil producer in one of the largest carbonate fields in onshore Middle East was selected by the operator for pilot implementation of the SPRIAS as an alternative to emulsified acid. The candidate well featured significant damage associated with drilling, severely affecting its productivity. The well was completed across 3,067 ft of 6-in. openhole horizontal section, with a bottomhole temperature of 285°F, permeability range of 0.5 to 1.0 md, and an average porosity of 15%. Coiled tubing (CT) equipped with fiber optics was selected as the fluid conveyance method due to its capacity to enable visualization of the original fluid coverage through distributed temperature sensing (DTS), thus allowing informed adjustment of the stimulation schedule as well as identification of chemical diversion and complementary fluid placement requirements. Likewise, lower CT friction pressures from SPRIAS enabled the utilization of high-pressure jetting nozzle for enhanced acid placement, which was nearly impossible with emulsified acid. Following the acidizing treatment, post-stimulation DTS showed a more uniform intake profile across the uncased section; during well testing operations, the oil production doubled, exceeding the initial expectations. The SPRIAS allowed a 40% reduction in CT friction pressures compared to emulsified acid, 20% optimization in stimulation fluids volume, and reduced mixing time by 18 hours. The experience gained with this pilot well confirmed the SPRIAS as a reliable option to replace emulsified acids in the region. In addition to production enhancement, this novel fluid simplified logistics by eliminating diesel transportation, thus reducing equipment and environmental footprints. It also reduces friction, thus enabling high-pressure jetting via CT, leading to more efficient stimulation with lower volumes.
- North America > United States (0.70)
- Europe (0.68)
- Asia > Middle East > UAE (0.29)