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Steam generation for the purposes of thermal recovery includes facilities to treat the water (produced water or fresh water), generate the steam, and transport it to the injection wells. A steamflood uses high-quality steam injected into an oil reservoir. The quality of steam is defined as the weight percent of steam in the vapor phase to the total weight of steam. The higher the steam quality, the more heat is carried by this steam. High-quality steam provides heat to reduce oil viscosity, which mobilizes and sweeps the crude to the producing wells.
Abstract Two (2) steam flood vertical injection wells are under operation for the last 15 months in a two- pattern pilot. Previous steam injection experience in this reservoir did not indicate serious issues due to the short injection periods for cyclic steam stimulation (CSS) but several well integrity issues have been faced during the steam flood period. Key issues include high wellhead growth, steam leak to the annulus A, annulus between 7” production casing and 4-1/2” injection tubing, and groundwater vapor behind 9.625” surface casing. Negative impacts from these issues on the continuity and effectiveness of the steam flood are recognized and need to be resolved comprehensively. All wells in the steam flood pilot were drilled and completed based on designs and procedures according to thermal well compliance including well equipment, and cementing specification. Production casing was equipped with thermal expansion collars to support reduction in wellhead growth. Completion strategy uses seal bore packer with bore extensions to accommodate tubing movement and Vacuum-Insulated-Tubing to provide maximum thermal insulation. However, the presence of a total- loss zone near the surface (starting from 50 m depth) affects the cement isolation between surface casing and 12.25” open hole. Daily monitoring is performed on each well where key injection parameters and well responses are recorded. Maximum wellhead growth reached 61 cm within the first week and steam leak from the injection string to annulus A started after 6 months of steam injection. Soon after that, groundwater vapor starts to arise from the gap between 9.625” casing and 12.25” open hole. These series of failures occurred in both injection wells within 3 months apart from each other. It is believed that the steam leak to annulus A resulted in thermal transmission to groundwater vapor. Hoist entries to both injectors indicated that Injector-1 has tubing seal assembly stuck inside seal bore and resulted in parted tubing collar while Injector-2 has tubing seal assembly damage. Both wells have thick oil covering the retrieved seal bore packer. Remedial actions were performed, including a complete change-out of the seal bore packer assembly and top-job cement fill up to surface using fast-set cement to isolate the gap between 9.625” casing and 12.25” open hole to reduce wellhead growth. As a result, the maximum wellhead growth became only 19 cm and 4 cm in Injector-1 and Injector-2, respectively. These remedial actions also led to restoring well and thermal integrity. Retrieved seal bore packer was sent back to manufacturer for appropriate failure analysis and providing useful feedback reports on the above issues. Monitoring and observation data along with failure analysis should provide vital information and possible improvement in completion strategy for steam injection wells that are planned for continuous steam flood projects in similar reservoirs.
A data-driven approach to successfully analyze and evaluate production-fluid impact during facility system divert events is presented. The work flow effectively identifies opportunities for prompt event mitigation and system optimization. The methodology used includes data streaming, advanced computations on high-frequency data, visualization, data mining, and rules extraction. The paper demonstrates that applied data-driven analytics led to learnings and observations that had a positive effect on the management of facility systems during divert events. The subject field is a heavy-oil reservoir, using steam for enhanced oil recovery.
Steam injection in heavy oil recovery often reaches the economical limit. Factors such as steam-oil ratio, generation costs, formation injectivity, reservoir pressure and heat losses are critical for the viability of these projects. This works presents a workflow to develop a scheme of surface facilities for different field conditions, that allows the capture, storage and usage of flue gas generated by steam generators and use it in a steam-flue gas injection process, which is going to mitigate the CO2 emissions, increase oil production and improve the results of steam injection alone in terms of energy efficiency.
The proposed workflow has 4 phases: 1) material balance to estimate the composition of flue gas generated based in generator parameters as gas feed, energy capacity and air excess; 2) numerical simulation of the involved processes as combustion, compression and heat exchange to study thermodynamic properties of the flue gas generated; 3) integrity analysis for equipment selection; and 4) determination of the most adequate scheme for flue gas managing according to field requirements.
Different case studies for surface facilities development are presented. High initial flue gas temperatures (400°F) and corrosion rates mainly by the presence of CO2 and O2 were identified as critical operation parameters. Since above 140°F corrosion rate gets higher compromising the integrity of the equipment, optimal relation between the gas feed used and an excess of air (15%) might allow a full combustion process decreasing the CO and hydrocarbons fraction in flue gas stream. Cooler units are required after the gas is compressed since the temperature raises, H2O separation has to be done after the first cooling process in order to mitigate the possible formation of carbonic acid on the stream; facilities dimensions are related to the capacity of steam generators and availability of flue gas volumes. The development of an adequate scheme of surface facilities requires an analysis of the conditions described before. Considering that each field has its own characteristics, the current workflow allows to develop optimal facilities for different projects using numerical simulation of multiple processes.
The methodology presented allows to determine the adequate facilities for different field conditions, in order to implement a steam flue gas enhanced oil recovery project that increases production and mitigates environmental impacts.
This paper focuses on the benefits of utilizing waste heat recovery units (WHRUs) in offshore oil and gas applications. Today, a high number of offshore installations use gas turbines (GTs) for power generation and as mechanical drivers for critical equipment, such as compressors. Most installations, however, do not employ any form of waste heat recovery. This results in wasted energy and increased emissions, as hot exhaust gases from the GT are vented to the atmosphere.
One of the factors that has contributed to the limited use of WHRUs on offshore facilities has to do with weight and space limitations. The paper discusses how original equipment manufacturers (OEMs) are addressing that challenge through both design standardization and modularization. For illustrative purposes, the paper discusses a line of standardized WHRUs which are designed for industrial and aeroderivative gas turbines in the 10–70 megawatt (MW) range. The WHRUs can be used for thermal fluids or applied as a drum-type steam generator (DTSG) or once-through steam generator (OTSG). Their vertical compact layout makes them particularly well suited for offshore installations, such as floating, production, storage, and offloading (FPSO) vessels, where weight and footprint of topsides modules are of particular importance.
By standardizing the WHRU/DTSG/OTSG and leveraging a high degree of modularization, the units can be easily modified per project. Construction time can also be reduced by up to ~ 70% when compared to traditional horizontal gas turbine heat recovery designs. Standardization also enables a reduction in engineering efforts during project execution – resulting in increased product quality and lower CAPEX.
Abstract Hydrate formation in production and control lines has been a serious issue in the oil industry, especially in the deepwater offshore market. This article focuses on a compact temporary plant designed to be assembled on offshore rigs for heating and injecting high flow rate water to break hydrates. Hydrates are formed under determined conditions (high pressure at low temperature) in which natural gas hydrocarbon molecules are trapped in ice molecules, forming crystal structures and plugging or choking lines, causing operational problems. When preventive solutions, such as chemical inhibitors or thermal insulation, do not work, the formed hydrate must be broken or dissociated to set the lines free. One option is active heating, in which hot fluid is circulated to increase the temperature and break the hydrate ice structures. Consequently, a compact plant, with combined direct and indirect heating, was designed to deliver a customized solution for an offshore rig. Drill or salt water pumps were used to supply cold water at 12 bpm at 25 °C, and two steam generators were used to inject steam into the flow, mixing inline and delivering water at 49 °C at the mud tanks. This tank water was pumped through mud pumps at 12 bpm, passing through four steam heat exchangers (SHE) to deliver water at a final temperature of 90 °C. The total process used six steam generators and four SHE to heat water from 25 to 90 °C at 12 bpm. The compact design for the high flow rate injection plant was only possible with combined and independent processes. Direct heating by steam injection was used inline downstream from the drill water pump to preheat the water to 49 °C while feeding the mud tank. Indirect heating used four SHE downstream of the mud pump to deliver water at 90 °C at the seabed.
Liu, Yigang (CNOOC China Ltd, Tianjin Branch) | Zou, Jian (CNOOC China Ltd, Tianjin Branch) | Han, Xiaodong (CNOOC China Ltd, Tianjin Branch) | Wang, Qiuxia (CNOOC China Ltd, Tianjin Branch) | Zhang, Hua (CNOOC China Ltd, Tianjin Branch) | Liu, Hao (CNOOC China Ltd, Tianjin Branch) | Wang, Hongyu (CNOOC China Ltd, Tianjin Branch) | Wu, Wenwei (China University of Petroleum, Beijing) | Wang, Cheng (China University of Petroleum, Beijing)
Abstract Steam and flue gas stimulation technology has been applied for heavy oil exploitation in Bohai Oilfield for almost ten years. For the special fuel and water requirement of the current thermal generator, large amount of diesel and desalinated seawater are needed during the thermal injection process. Besides, treatment of the produced oily wastewater on the platform becomes more difficult as the oil output increases. Aimed at solving the existing problems and taking the advantage of characteristics of the supercritical water, a new type of supercritical steam and flue gas generator for offshore oilfield is proposed and studied. The newly proposed generator is mainly consisted of two sections, which are the supercritical water gasification reactor and combustion reactor, respectively. The produced oily wastewater could be directly used for steam generation. A series of experiments are carried out for its feasibility research and structure optimization. A prototype of the generator is made for indoor experiment. During the gasification process, wastewater and the organic material mixed inside is placed in the supercritical conditions in the gasification reactor whose temperature and pressure are about 600-700°C and 23MPa, respectively. And the reaction product would be mainly H2, CO2 and water. Gasification Experiments of both the diesel and oily wastewater are conducted. And the combustion experiment is also conducted and the gasified gas is reacted with O2 under conditions of 25MPa and 500-550°C. Composition of the produced fluid in each experiments are analyzed. Besides, the structure of the generator is also designed and optimized for improving its working efficiency. The proposed new-type supercritical steam and flue gas generator has the characteristics of high efficiency, waste water treatment and higher temperature and pressure delivery capacity. And there would be a promising perspective for its application on offshore platform.
Hashim Noori, Wildan (Istanbul Technical University) | Cinar, Murat (Istanbul Technical University) | Salehian, Mohammad (Istanbul Technical University) | Alkouh, Ahmad (College of Technological Studies)
Abstract Steam injection is one of the well-known thermal recovery processes that has been extensively applied to heavy oil reservoirs. Several efforts have been made to understand theoretical and practical aspects of steam injection and alkali flooding. However, the detailed information about the performance of steam-alkali flooding in field applications has not been deeply addressed yet. In this sense, in order to shed light on the background and applications in this area, this study comparatively investigates the efficiency of different strategies of pure steam injection and cyclic steam-alkali flooding in Bati Raman oil field, Turkey. Three experiments were conducted to evaluate the advantage of steam-alkali injection compared to pure steam injection for an 11.6° API Bati Raman crude oil. The steam injection system consists of two reservoirs for water and the alkali solution, an electrical pump, and an electric steam generator. Those three experiments are as follows; conventional pure steam injection, cyclic injection of steam and alkali solution 4.0 wt%, and cyclic injection of steam and alkali solution 8.0 wt%. Steam was injected with the rate of 10 ml/min at 110°C and the system pressure was set to be the atmospheric pressure. The liquid produced from the separators is sampled periodically to determine the oil recovery. Observation of sand packs after the experiments indicates the tendency for steam channeling in the vertical direction around the upper thermocouple. Since the upper thermocouple was inserted after the sand packing operation by pressing and rotation, steam could be passed through these channels without entering the all pores in the porous media. The average oil recovery by conventional pure steam injection, steam-alkali solution 4.0 wt% injection, and steam-alkali solution 8.0 wt% are 8%, 3% and 5.5% OOIP (original oil in place), respectively. This indicates that although the oil recovery in conventional pure steam injection was maximum, increasing the alkali concentration in the aqueous solution from 4% to 8% has caused the improvement in the recovery. The theoretical and practical information is supported by the experimental examples to evaluate the performance of different steam-alkali flooding strategies with Borax in heavy oil reservoirs of Bati Raman. This study also examines the challenges of steam-alkali flooding in extremely heavy oil reservoirs and explains that the pure steam injection is preferred due the insufficient change in interfacial tension during Borax injection process.
Abstract The cost per barrel is higher for Heavy Oil developments, and particularly thermal developments than for Conventional. Specific attention needs to be paid to the cost of Heavy Oil developments to ensure economic viability. The current cost basis for the heavy oil project shows that energy costs constitute some 45% of Unit Technical Cost and more than 65% of the OPEX per barrel. An OPEX cost improvement plan has been conceptualized to reduce the cost per barrel. Hence, the improvement plan focusses on Alternative Energy sources for steam generation. In addition to the cost optimization, those initiatives will contribute heavily in achieving HH the Emir of Kuwait vision to cover 15% of Kuwait’s peak load with renewable energy by 2030". Based on current field development plans a feasibility study was carried out to determine the maximum practical and economic fraction of energy that can be contributed by renewables in heavy oil development. The bulk of the work was executed developing a model to study the supply-demand balance, as well as the gas prices ranges within the alternative energy solutions are viable. To optimize the fuel gas consumptions two options were studied by utilizing the alternative energy solutions (solar steam and cogenerations) to generate steam instead of conventional boilers. On the power optimization side the study focused on the solar photovoltaic and wind energy. The lowest cost solution is to use direct solar steam and allow the steam injection at a variable rate - this may require some upgrades to allow fully- automatic flow control throughout the steam distribution system. With this method (and a typical weather year) solar fractions of approximately up to 40% may be possible. It may be possible to increase this further if the requirements for minimum steam flow in the steam distribution network can be reduced. With the use of thermal storage, the solar fraction can be increased to approximately 60-80%, however steam from storage is likely to cost significantly more than direct steam, especially as direct molten-salt coupled with oilfield- quality water has not yet been proven commercially. As renewable power alone will not be able to meet the full demand of Heavy Oil field development, hence the utilization of cogeneration will be a feasible solution in order to supply the required steam demands in addition to solar and also to supply the required power in addition to solar PV. The redundant power generated by the cogeneration may be supplied to the Electrical Grid. The economics analysis illustrates that all renewable options considered have positive NPV. The economics for both PV and wind are robust, where maximum deployment is advised, subject to grid connection constraints. For solar steam, the economics are partially affected by the once-through steam generators (OTSG) CAPEX already spent, but still show positive NPV. Anticipated costs reductions for solar steam technology as a consequence of greater deployment of the technology over the next few years could further improve the NPV. Including the cogeneration, solar steam and less conventional steam generators in the future projects will maximize the NPV of the heavy oil.
Abstract Heavy oil extraction requires heat introduction to the reservoir to enhance the mobility of oil. While steam injection is one of the most reliable thermal EOR methods for heat introduction, it has several operational, technical, economic, and environmental limitations. This study investigates the effectiveness of a newly developed downhole steam generator which not only minimizes the heat losses due to distance the between generation and injection but accomplishes oil production with lower steam and energy requirements. A test of the downhole steam generator took place in a small 20 acre area northeast Texas with 13 wells accessing a shallow (540 feet TVD) heavy oil bearing sandstone. The viscosity and API gravity of the heavy oil was reported as 3,000 cP at 100 °F and 19 °API. The initial oil and water saturation were approximately 65% and 35% respectively. Steam injection was started in April of 2013 at steam rates of up to 1300 bbl/day of 600°F steam, producing a total of 540 million BTU per day. The steam front was carefully monitored with temperature readings through oil sampling, both on an individual well basis. According to the temperature readings, steam front movement was faster than typical steam flooding cases in such high viscosity oil reservoirs. Preferential steam propagation occurred towards the northwest of the field due to reservoir dipping towards the southeast. The oil production increased on both the 20 acre test site and wells outside of the test site. The varying distances between injection wells and production wells enabled us to observe steam propagation at varying length. Thus, we could acquire produced oil sampling at varying steam exposure times at different locations and depths. Viscosity, density, and compositional analyses were carried out on the produced oil samples. It has been observed that the viscosity and density of produced oil were not improved due to emulsion formation which is a common concern for any steam injection project. However, further analysis revealed that emulsion breaking is possible with the use of asphaltene insoluble solvents or cationic surfactants. Since the novel design of the downhole steam generator allows injection of any additional chemical with steam during the process, these chemicals could be added to the steam stream to enhance the effective steamed area and reduce the flow assurance related problem. The new downhole steam generation tool provides an opportunity to generate steam in-situ and co-inject steam with additional chemicals to prevent emulsion formation and asphaltene precipitation. Thus, this study proves that downhole steam generation can be feasible for heavy oil extraction, even for small, low-rate fields, if all drawbacks (such as emulsion formation and asphaltene precipitation) are considered and the chemicals injected with steam are selected properly.