Unconventional resources have significantly transformed the landscape of the oil and gas industry. The primary recovery factor ranges anywhere from 2% to 8% for the various shale plays throughout the United States. Hence, it is imperative to exploit the vast potential of unconventional reservoirs and increase the recovery factors beyond primary depletion by implementing improved and enhanced oil recovery (IOR/EOR) methods. This paper presents detailed review of the advances in IOR/EOR technologies applied to unconventional oil reservoirs. A thorough review of the pertinent published literature on IOR/EOR was performed. Results of EOR application to unconventionals shared by various operators in their investor presentations and press reports were also analyzed. The IOR/EOR studies were classified into laboratory experiments, numerical modeling and field laboratory trials (pilots). In addition, the field trials were also analyzed based on the representative shale plays. Most of the studies performed for the application of EOR technologies to unconventional oil reservoirs have been limited to experimental investigations and numerical simulation studies. The research revealed that miscible gas injection (produced gases, CO2, etc.) is the most promising method among the EOR techniques (miscible gas, water flooding, surfactant, chemical and polymer). Experimental studies showed that CO2 injection had the highest potential of improved recovery in unconventionals followed by produced gas injection and that diffusion was the most predominant mechanism. Surfactant injection showed the next best potential to increase oil recovery by altering the wettability of rock in laboratory experiments. The gas injection pilots showed that sufficient injectivity was achieved mainly due to the injection induced fractures and did not exhibit any significant effect of diffusion. Conformance control remains a big challenge especially due to the channeling of the gas through the fractures. Produced gas injection pilots in the Eagle Ford formation have demonstrated the greatest success in increasing oil recovery. However, there are many inconsistencies between the laboratory investigations and field trials that needs reconciliation. Further research is necessary to bridge the gap and improve the scaling from laboratory to field. This methodical study elicits the learnings and challenges from the application of different IOR/EOR technologies to unconventionals at various scales (micro to macro to field scale). In addition, ideas for future research are recommended to improve the understanding of the complex mechanisms of EOR in unconventional oil reservoirs. These include optimizing gas injection schemes (huff-n-puff, continuous injection) based on key parameters such as permeability and investigating fracture placement for improving the drainage area and inter-well communication.
Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Introduction Billions of barrels of additional reserves have been generated throughwaterflooding, one of the most important methods of improving recovery from oilreservoirs. With the uncertainty of the economic applicability of EORtechniques as a result of oil-price instability, optimization of waterfloodinghas become more significant than ever. The reservoir management aspects ofwaterflooding are not restricted to an initial engineering and geologicalreport, economic justification, and project approval by management. Rather, these ongoing activities span the time before the start of waterflood to thetime when the secondary recovery either is uneconomic or is changed to anenhanced recovery. A reservoir management approach to waterflood surveillanceconsiders a system consisting of reservoir characterization, fluids and theirbehavior in the reservoir, creation and operation of wells, and surfaceprocessing of the fluids. These are interrelated parts of a unified system. Thefunction of reservoir management in waterflood surveillance is to providefacts, information, and knowledge necessary to control operations and to obtainthe maximum possible economic recovery from a reservoir. Initial productionforecasts may not always agree with actual performance. Differences may arisefrom fieldwide averaging of data in the prediction model, inadequate geologicaldescription, and well-completion problems. Thus, attempts should be made toresolve the differences and controlled surveillance should be carried out toimprove field performance. Guidelines for waterflood management should includeinformation on (1) reservoir characterization, (2) estimation of pay areascontaining recoverable oil, (3) analysis of pattern performance, (4) datagathering, (5) well testing and reservoir pressure monitoring, and (6) wellinformation data base. Today, sufficient performance history is available thatsurveillance techniques can be documented in detail. This paper highlightswaterflooding in light of practical reservoir management practices. Casestudies that illustrate the best surveillance practices are referenced. Reservoir Management Reservoir management can be defined as the judicious use of varioustechniques to maximize benefits or economic recovery from a reservoir. Fig. 1 describes the interaction required among the various functions. The reservoirmanagement approach to waterflood surveillance must use a coupled systemconsisting of wells, surface facilities, and the reservoir. All must beconsidered in a balanced way to maximize economic oil recovery. Also, a teameffort involving people from various functional areas is mandatory fordevelopment and implementation of a successful reservoir managementprogram. Key Factors in Waterflood Surveillance Talash and Talash and Strange described the key monitoring points in thetraditional waterflood cycle (Fig. 2). In the past, attention was focusedmainly on reservoir performance. However, with the application of the reservoirmanagement approach, it has become industry practice to include wells, facilities, water system, and operating conditions in surveillance programs. Itis important to consider the following items in the design and implementationof a comprehensive waterflood surveillance program (Table 1).Accurate anddetailed reservoir description.Reservoir performance and ways to estimatesweep efficiency and oil recovery at various stages of depletion.Injection/production wells and their rates, pressures, and fluid profiles.Water quality and treating.Maintenance and performance of facilities.Monthly comparison of actual and theoretical performance to monitor waterfloodbehavior and effectiveness.Reservoir management information system andperformance control (accurate per-well performance data).Diagnosis ofexisting/potential problems and their solutions. JPT P. 1180⁁
Management Unconventional resources have transformed the landscape of the oil and gas industry. The primary oil recovery factor ranges from 2–8% for the various shale plays throughout the US. Hence, it is imperative to develop the vast potential of unconventional reservoirs and increase the recovery factors beyond primary depletion by implementing IOR/EOR methods. This article describes the role of effective reservoir management and summarizes the detailed review of the advances in IOR/EOR technologies applied to unconventional oil reservoirs, as performed by the Energy Industry Partnership Team (EIP) at the University of Houston (Balasubramanian et al. 2018). That review•included: A thorough review of the pertinent published literature on IOR/EOR Results of EOR application to unconventionals shared by various operators in their investor presentations and from press reports Classifying IOR/EOR studies as laboratory experiments, numerical modeling, and field laboratory trials•(pilots) Analysis of field trials based on the representative shale plays. Most studies performed for the application of EOR technologies to unconventional oil reservoirs have been limited to experimental investigations and numerical simulation studies. The research revealed that miscible gas injection (produced field gases, CO2, etc.) is the most promising method among the EOR techniques, including miscible gas, waterflooding, surfactant, chemical, and polymer. Experimental studies showed the following: CO2 injection had the highest potential of improved recovery in unconventionals followed by produced gas injection. Surfactant injection showed the next best potential to increase oil recovery by altering the wettability of rock in laboratory experiments. The produced field gas injection pilots showed that sufficient injectivity was achieved mainly due to the injection-induced fractures and did not exhibit any significant effect of diffusion. Conformance control remains a big challenge due to the channeling of the gas through the fractures. Produced field gas injection pilots in the Eagle Ford formation have demonstrated the greatest success in increasing oil recovery. Many inconsistencies exist between laboratory investigations and field trials that need reconciliation and further research to bridge the gap. This methodical study elicits the learnings and challenges from the application of different IOR/EOR technologies to unconventionals at various scales (micro to macro to field scale). In addition, ideas for future research are recommended to improve the understanding of the complex mechanisms of EOR in unconventional oil reservoirs. Unconventional resources have changed the landscape of oil and gas industry in the US and the world. Oil production from unconventional tight oil reservoirs have accounted for more than 50% of total oil production in the US in the recent years. Todd et al. reported that unconventional oil reservoirs contributed to more than a 4 million•B/D increase in production between 2011 and•2014.
Members SPE-AIME Summary A joint DOE-Gulf oil Corporation Minitest of CO2 miscible flooding was conducted in the Mission Canyon formation of the Little Knife Field, North Dakota. In the five-acre minitest area, a central injection and three observation wells were drilled to form a non-producing, inverted four-spot pattern. A 1:1 CO2 WAG injection sequence (preflush water injection, five alternate slugs of CO2 and water, and drive water injection) was implemented. Prior to the CO2 minitest, a detailed reservoir description of the test area was developed through logging, pulse testing and core analysis. Extensive laboratory pulse testing and core analysis. Extensive laboratory work had been performed to determine miscibility pressure, swelling and viscosity reduction effects. pressure, swelling and viscosity reduction effects. The minitest included continuous bottomhole pressure measurement in all test wells and time-lapse logging to monitor saturation changes as alternate slugs of water and CO2 passed the observation wells. Fluid samples from the observation wells were collected periodically to check for tracers and fluid composition. At the conclusion of drive water injection, a fifth well was drilled behind the CO2, front and pressure-cored to measure the residual oil saturation to the CO2 flood. A Compositional Simulator was used to history match the minitest performance and to evaluate the displacement and sweep efficiency in the project area. Reservoir simulation models were used at various stages of the minitest:to determine the volume and rate of water injection required to raise the reservoir pressure above the minimum miscibility pressure,to calculate co 2 slug size, WAG ratio and project life,to select the location of the fourth observation well behind the CO, front,to predict breakthrough times and concentrations of CO2, and water to decide when to log wells and collect fluid samples,to scale the minitest reservoir description to a typical 160-acre, five-spot pattern for predicting recoveries for a waterflood and the CO2 WAG process, andto perform sensitivity studies for studying the effects of layering, vertical communication and other process parameters. Introduction A joint DOE-Gulf oil Corporation minitest of carbon dioxide miscible flood process was conducted in the Little Knife Field, North Dakota (Figure 1) from December 11, 1980 through September 24, 1981. The objective of this minitest was to show that the CO2, miscible displacement process has potential for commercialization in carbonate oil potential for commercialization in carbonate oil reservoirs in the Rocky Mountain area that have not been extensively waterflooded and have a high remaining oil saturation. A careful monitoring of the field performance of the CO2, minitest using a reservoir simulator was made in order to make a field wide projection of CO2 flood in this field. The Little Knife Field is one of the major reservoirs discovered by Gulf in recent years. The discovery well was completed on February 8, 1977. The original oil-in-place (OOIP) in the Mission Canyon Formation was estimated to be 195 MMSTB. Cumulative oil production through December, 1982 was about 24.4 MMSTB (12.5% of OOIP). The primary recovery mechanism is solution gas drive. primary recovery mechanism is solution gas drive. Currently, there are 124 producing wells on 160 acre spacing, and the average reservoir pressure has been declining from the initial reservoir pressure of 4400 psia to about 2750 psia. It was anticipated that waterflood residual oil saturation would be high and that the CO2, miscible process would be suitable. The work associated with this minitest was divided into five phases: Phase I: Location and Drilling of Minitest Phase I: Location and Drilling of Minitest Pattern Phase II: Laboratory Determination Of CO2/Water Phase II: Laboratory Determination Of CO2/Water Displacement Parameters in Reservoir Cores Phase III: Minitest Area CO2 Simulation Phase III: Minitest Area CO2 Simulation
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