EOR Process Research Articles

Experimental Study on Nonionic Surfactants for Minimizing Surface Adsorption as an Improved Oil Recovery (IOR) Process

Adsorption of surfactants onto the surfaces during chemical flooding is a major problem in EOR and IOR process. This happens due to blockage of capillary pores and opposite charge on the surface. The objective of this paper is to reduce adsorption of anionic surfactants by application of no nonionic surfactants as an IOR process. The methodology for Selection of surfactants for core flooding has been done based on conductivity and emulsion tests. Nonionic surfactants Ethoxylated Alcohol (EO) of 1000ppm from emulsion test has been chosen to reduce adsorption of anionic surfactants Sodium Dodecyle Sulphate (SDS) of 750ppm determined from conductivity test. Core flooding experiment with anionic surfactants has been conducted with nonionic surfactants and without the influence of nonionic surfactants. Reduction in adsorption of anionic surfactants SDS up to 1.2 pore volume has been observed in the on core flooding experiment.

Foam assisted CO2-EOR: A review of concept, challenges, and future prospects

Abstract Foam assisted CO 2 enhanced oil recovery has attracted increasing attention of oil companies and research institutions, mainly due to the potentially high benefit of foam on CO 2 -EOR performance. Numerous theoretical and experimental studies, limited numbers of pilot tests as well as cases of field applications have indicated that foaming of CO 2 can greatly improve the EOR process, at both the microscopic and macroscopic levels. However, there are still various conceptual and operational challenges, which may compromise the success and application of foaming process. The oil recovery mechanisms involved in a CO 2 foam flood, the complex flow behavior of the system, and the synergy between gas mobility control foaming agent and ultra-low IFT surfactants have been identified as the main challenges of this process. The unavailability of reliable predictive tools due to the less understood concepts and phenomena adds more challenges to the process results and application justifications. A literature review of the foam assisted CO 2 -EOR process is presented in this paper to reveal its strengths, highlight the knowledge gaps, and suggest ways to bring physical understandings of experiments into foam projects׳ performance evaluation and simulation models for potential field application purposes.

ISC Application in Heavy Oil Reservoir after CSS

In order to improve the flowability of crude oil, heavy oil reservoir usually developed by steam injection. While this process produces a lot of greenhouse gases. To deep reservoir, heat loss in the wellbore tends to more severe and thermal efficiency is lower. In-situ Combustion (ISC) is featured by heavy components’ combustion, high thermal efficiency and high oil recovery. Those advantages are outstanding especially in the aspects of improving thermal efficiency and reducing greenhouse gas emissions. This paper researched on ISC EOR process in a complex fault block, including reservoir design and performance evaluation. Remarkable development results have been achieved, which shows the potential for ISC technology and this paper provides a reference for the development of similar reservoirs.

Challenges in adjoint-based optimization of a foam EOR process

We apply adjoint-based optimization to a surfactant-alternating gas foam process using a linear foam model introducing gradual changes in gas mobility and a nonlinear foam model giving abrupt changes in gas mobility as function of oil and water saturations and surfactant concentration. For the linear foam model, the objective function is a relatively smooth function of the switching time. For the nonlinear foam model, the objective function exhibits many small-scale fluctuations. As a result, a gradient-based optimization routine could have difficulty finding the optimal switching time. For the nonlinear foam model, extremely small time steps were required in the forward integration to converge to an accurate solution to the semi-discrete (discretized in space, continuous in time) problem. The semi-discrete solution still had strong oscillations in gridblock properties associated with the steep front moving through the reservoir. In addition, an extraordinarily tight tolerance was required in the backward integration to obtain accurate adjoints. We believe the small-scale oscillations in the objective function result from the large oscillations in gridblock properties associated with the front moving through the reservoir. Other EOR processes, including surfactant EOR and near-miscible flooding, have similar sharp changes and may present similar challenges to gradient-based optimization.

A Review of Early Opportunity-Analysis on CO 2 Sequestration and Enhanced Oil Recovery for Iran

In recent years, greenhouse gases (GHGs) such as carbon dioxide have increased in the atmosphere and caused some concerns about climate change. The table published by International Energy Agency shows that from 1990 to 2007, Iran after China has had the highest rate of increase in carbon dioxide emission. In 1990, Iran produced a total of 175 million tons of carbon dioxide to the atmosphere while in 2007 this rate has reached to 466 million tons. Geological sequestration is one way to reduce the CO 2 content in the atmosphere. There are several options for sequestrating CO 2 in geological sinks. Mature oilfields are one of the most favorable targets for the CO 2 sequestration. Injecting CO 2 into these reservoirs can increase the amount of oil produced in addition to offsetting some of the CO 2 storage expenses. Most of the CO 2 injection aspects into the reservoirs for the purpose of Enhanced Oil Recovery have been known for decades. The economics and incentives for combined EOR and sequestration process are less clear at this time, but a first step in the development process should be to do studies in order to investigate ways for both producing oil efficiently and maximizing storage of the carbon dioxide. This study looks at such scenarios that reduce the CO 2 emissions using the existing oil reservoirs as sink. The goal of this research is to better understand the potential for simultaneous enhanced oil recovery and CO 2 sequestration in oil reservoirs over a range of conditions. Key words : CO 2 sequestration; Enhanced Oil Recovery; Iran

Impact of Plagioclase on the Low Salinity EOR-Effect in Sandstone

The mechanism of the low salinity EOR process in sandstone reservoirs has been debated in the literature for more than a decade. We recently proposed a chemical wettability alteration mechanism for the process, well founded in experimental observations showing that the increase in pH as the high saline water is displaced by the low saline water is a key factor. Even though this chemical understanding is quite well described, there are parameters/factors that can disturb the main process like the following: combinations of certain minerals, temperature, salinity, and composition of formation water could have impact on the low salinity EOR processes. Plagioclase, a polysilicate mineral, which is often present in sandstone reservoir rock, can have a significant effect on the initial pH of the formation water, which will influence the initial wetting condition. In this experimental work, it is shown that the presence of plagioclase in reservoir rock and outcrop material responded differently on the low salinity EOR-effect. The experimental results are discussed in relation to the previously published chemical mechanism for the low salinity EOR process, where changes in pH are believed to promote the wettability alteration of the rock.

Experimental Investigation of Flooding Hydrolyzed–Sulfonated Polymers for EOR Process in a Carbonate Reservoir

The main purposes of this study were to scrutinize experimentally effects of polymer and rock types on the oil recovery using water and polymer flooding processes. Four dynamic flooding experiments were carried out at simulated reservoir condition of temperature and pressure. According to the obtained results, the ultimate oil recovery by water flooding in highly fractured reservoirs was less than reservoirs with the microfractures. The results of polymer flooding showed that in addition the polymer molecular weight, the sulfonation of polymers also affects the oil recovery.

Effect of operational parameters on SAGD performance in a dip heterogeneous fractured reservoir

Steam Assisted Gravity Drainage (SAGD) has been studied theoretically, experimentally and numerically as a promising EOR process. Most of the simulation works have been conducted microscopically in homogeneous non-dipping models. In this communication, the effect of operational parameters on SAGD performance is investigated in a dip heterogeneous naturally fractured reservoir (NFR) with oil wet rock using CMG-STARS thermal simulator. The results indicate that reservoir dip has unfavorable effects on SAGD performance due to overriding effect. Moreover, less oil saturation of matrix causes steam to penetrate into upper blocks. It has also been observed that reservoir thickness controls operational parameters. Furthermore, the results indicate that there is no need for more preheating due to desired heat communication between well pair. As it was expected, higher steam injection rate leads to more oil production. Besides, longer well pairs have no considerable effects on SAGD performance in dip reservoirs. Besides, because of quick reservoir depletion in injection at high pressure, SAGD is not recommended economically in thinner reservoirs.

Factors influencing successful implementation of enhanced oil recovery projects

Tertiary methods in oil production process called 'Enhanced Oil recovery methods' (EOR) are mostly applied in mature oil fields with declining production trend after primary and secondary recovery methods or immediately after primary production phase. These 'Enhanced Oil Recovery' methods implies injection of gases or fluids to mobilize residual oil captured in reservoir rock due to presence of strong viscous and capillary forces and high value of interfacial tension between fluid and rock. Depending on the type of injected fluid, production mechanism, as well as an approach to implementation, EOR methods are divided into thermal methods, chemical methods, miscible/immiscible gas injection methods and other methods that so far have an experimental application. The paper analyzes the key factors influencing the successful implementation of EOR projects: phases of EOR project implementation, the price of crude oil at the world market as a criterion for the beginning and the justification for EOR process application and development of new technologies for more efficient process realization.

Application of ZnO Nanostructures in Improvement of Effective Surface Parameters in EOR Process

ZnO nanosphericals and nanorods have interesting potential applications in various fields such as antibacterial and enhanced oil recovery process. In this work, it was shown that 30 ml of a water-based solution containing 3% of ZnO nanofluids could significantly change the wettability of a carbonate reservoir rock from a strongly oil-wet alter to a strongly water-wet condition, after 3 days aging of the rock at 70°C in the designed solution. Moreover, we have studied air-water and oil-water interfacial tensions of system containing nanofluids. Fluids included ZnO nanoparticles and quantum dots nanostructures (QDOTs ZnO) could effectively decrease the n-decane/water interfacial tension and air/water surface tension. So their efficiency is much higher in comparison with distilled water.The stabilization of various aqueous ZnO nanostructured in mixtures of NaCl, CaCl2, MgCl2 and Na2SO4 salts were investigated, and 50000-163000 ppm transparent and stable nanosalt fluids were fabricated. Wettability of an oil-wet carbonate rock aged for 3 days at 70°C in the designed ZnO nanosalt fluids was studied by measuring the contact angles. The results show a strong change in wettability of carbonate rocks from oil-wet to more water-wet condition. These nanosalt fluids performed an excellent trend of surface tension and IFT reduction in comparison with distilled water too.

Key Technology of Explosion Prevention in Air Injection EOR Process

The article aims at researching on anti-explosion security technique for gas-injection well of air oil drive through the gas associated with crude oil alerting system, and then, making sure safety distance of associated gas explosion. Firstly, experiment the explosion limit of associated gas, then to determine the different alerting threshold and the arrangement of inspection instrument, which are on the basic of different limit requirements of density about gas-injection well head and internal gas-injection well. Secondly, with associated gas explosion in the well, calculate the overpressure of well head through simulation method. Finally, analogy between explosion energy and TNT equivalent, so that determine the level of people casualties and structure breakage for safe distance according to failure criteria of explosive blast.

Experimental analysis of Combustion Assisted Gravity Drainage

Abstract Combustion Assisted Gravity Drainage (CAGD) is a new EOR process that uses dual horizontal wells for the injection of air and the production of heavy oil. One of the important features of CAGD is the properly oriented dual horizontal wells, similar to SAGD, which assists in the development of combustion chamber and stable growth of the combustion front in the reservoir. This research evaluates the potential of CAGD as an attractive alternative to conventional in-situ combustion (ISC). A 3D laboratory model was designed and constructed to study the CAGD process. The combustion cell was fitted with 48 thermocouples. A horizontal producer was placed near the base of the model with a horizontal injector in the upper part. The CAGD process combines the advantages of both gravity drainage and the conventional ISC. Experimental results showed the combustion chamber developed in the wide area of the porous media around the horizontal injector. This combustion chamber consisted of flue gases, injected air and hot oil. The gravity drainage is the main mechanism for oil production and extracting the flue gases from reservoir. Recorded temperatures reached up to 650 °C at the combustion front, with oil recovery more than 82% OOIP. Experimental data showed that improper well distance could cause severe plugging in production well perforations and terminate the process prematurely.

Preliminary Study of In-situ Combustion in Heavy Oil Field in the North of Thailand

A small oil field in the north of Thailand has medium viscous and low gas-content heavy oil. Since conventional production methods are ineffective, thermal recovery is potentially suitable to enhance oil recovery for this reservoir. In -situ combustion is a complex EOR process used for medium to heavy crude oils. The process involves the multi-phase fluid flow through porous media with chemical and physical transition of the crude oil components under high temperature and pressure conditions. The simulation results with STARS were investigated by conducting a number of sensitivity studies with varying the parameters like gridblock sizes, air-injection rates, oxygen concentrations, and injected air temperature. The 0.5m-block size was chosen due to the optimum running time with acceptable accuracy. From the results, it can be concluded that changing injection rate from 100 Mscf/d to 400 Mscf/d does not significantly affect cumulative oil production – less than 6% incremental recovery. Increase oxygen concentration from 29% to 100% shows an increase in 40.67% oil production. Moreover, if the injected fluid temperature is increased from 80˚F to 500˚F, total oil production increases 97.14%. Furthermore, optimal operating conditions to enhance recovery of oil were also studied.

Investigation of hydrocarbon and non-hydrocarbon (CO2, N2) gas injection on enhanced oil recovery in one of the Iranian oil fields

Masjed-I-Suleyman (MIS) field is the first field in the Middle East that has produced oil and has such a long production history (100 years). This field’s production started in 1911. Most of the oil production in the Middle East come from carbonate reservoirs, the majority of which are fractures. These reservoirs tend to produce at high rates in their early production period followed by low rates later on, leading to low overall recovery. The early production rate of this field was 120,000 stb/day, now reaching about 2,000 stb/day. MIS field has produced 1.39 billion stb of oil as of 1 January 2010, which makes it a giant field by world standards. 267 million of this produced oil was re-injected into the reservoir and if the recycled oil re-injected into the reservoir is included, the net total oil produced as of 1 January 2010 would be 1.123 billion stb. Based on original oil-in-place of 6 billion stb, the recovery factor equates to 23.2 % (based on the gross oil production) or 18.7 % (based on the net oil production). So this reservoir is a candidate for an EOR process. It seems the gas injection into oil reservoirs is one of the most effective methods in EOR approaches (Ganji and Haghighi 2006). In this study, the injection technique that was used includes gas injection with different fluids that causes an immiscible process. A compositional reservoir simulator has been used to determine the effect of the gas injection process on reservoir production to optimize the oil recovery for the MIS field. Simulation results show that gas injection is not useful for this field.

Effect of well pattern and injection well type on the CO2-assisted gravity drainage enhanced oil recovery

Fundamental understanding and application of process parameters in numerical simulation that leads to optimized gravity drainage oil recovery at field scale is still a major challenge. Reservoir simulations studying the effects of well patterns and type of gas injection wells have not been reported so far. In first ever attempt, the mechanistic benefits of production strategy on gravity drainage oil recovery are identified in this paper. Effects of irregular and regular well patterns and vertical and horizontal gas injection wells are investigated using a fully compositional 3D reservoir model in secondary immiscible and miscible modes under the conditions of voidage balance, constant pressure of injection and production wells and injection rates below the critical rate. Regular well pattern provided longer oil production time at a constant rate until CO2 breakthrough compared to irregular well pattern. It then dropped almost vertically at the same cumulative oil recovery even at higher production rates. However, gravity drainage oil recovery was higher at higher rate combination after CO2 breakthrough. Results also suggested that the regular pattern could result in horizontal CO2 floodfront parallel to the horizontal producers, maintaining reservoir pressure, thus optimizing the oil recovery by additional 2.5% OOIP. Vertical injection and horizontal production wells in both the immiscible and miscible modes provided nearly identical cumulative gravity drainage oil recovery compared to the combination of horizontal injection and production wells in the regular well pattern. This suggests that the type of injection wells may not be a significant factor to impact the CO2-assisted gravity drainage mechanism. Results obtained herein would help in the optimization of CO2-assisted gravity drainage EOR process.

Technology Focus: Enhanced Oil Recovery (June 2012)

Technology Focus Enhanced-oil-recovery (EOR) operations are what moves EOR processes from the laboratory to the field. They involve a series of activities, from a detailed planning stage to efficient application, consistent monitoring, and results analysis. When reviewing results from field pilots or full-field applications, it is noticeable that significant technical hurdles such as facilities, drilling and completion, and production-technology developments need to be overcome in order to deploy and run a successful EOR operation. Technology developments in water management, intelligent-well completions, and downhole innovation are key for EOR operations to achieve the expected increases in reserves. Over the past year and during the first quarter of 2012, SPE was host to several events focusing on EOR operations, and more than 400 papers were presented. Several of them explored topics related to enhancements associated with the three key areas mentioned. Emphasis in many papers concerns extending the use of smart-well completion technologies to EOR operations, targeting customization to set out an EOR process and provide more flexibility for the solution to unexpected setbacks during process startup. Also, several publications stress the importance of downhole innovation aiming at oil- and gasfield production maximization by continuous optimization of steam and CO2 downhole injection rates in heavy-oil recovery and CO2-EOR processes, respectively. Dealing with EOR operations adequately is a great challenge, and a broad and integrated set of competencies is required. Nevertheless, as some of the papers featured in this issue illustrate, success is attainable with the right use of technology and creativity. I hope that you enjoy reading these paper highlights and will search for additional interesting contributions available in the OnePetro online library. Recommended additional reading at OnePetro: www.onepetro.org. SPE 150477 SAGD Field Trial for a New Intelligent-Well Completions Strategy To Increase Thermal EOR Recoveries by Joel Shaw, Halliburton, et al. SPE 154318 The Design and Execution of an Alkaline/Surfactant/Polymer Pilot Test by A. Sharma, Rex Energy, et al. SPE 154122 Mobility and Conformance Control for CO2 EOR Via Thickeners, Foams, and Gels—A Literature Review of 40 Years of Research and Pilot Tests by R.M. Enick, University of Pittsburgh, et al. SPE 144893 Seventeen Years of Development of Artificial Lift Technology in ASP Flooding in Daqing Oil Field by Yang Yonghua, China University of Petroleum, et al.

An Efficient Methodology for Performance Optimization and Uncertainty Analysis in a CO2 EOR Process

A pragmatic technique is proposed and successfully applied to determine the optimal production–injection scheme in a CO2 flooding reservoir under uncertainty. Well rates of injectors and bottomhole pressures of producers are chosen as the controlling variables. Geological uncertainty is accounted for using the multiple reservoir models. An objective function associated with net present value (NPV) is defined, and a modified genetic algorithm is employed to determine the optimal production–injection scheme. It is shown from a field case study that the optimized scheme can not only increase the expected oil recovery and NPV by 7.8 and 6.6%, respectively, but can also achieve a considerably small range of possible NPVs.

不均質性を考慮した掃攻率改善のための効果的貯留層内ブロッキングの検討

Most of the conventional EOR processes have already been established, and the development of a new innovative EOR process is quite difficult. Therefore, the sweep efficiency improvement (SEI) is more important for an efficient EOR. Several SEI methods have been applied actually in many fields. However, the injected EOR fluid tends to flow selectively in the already swept high permeable zones, and the sweep efficiency is poor as the result. In this case, in-depth profile modification by blocking such the already swept high permeable zones with a polymer gel would be a more effective than already existing SEI methods.In this study, numerical simulations to confirm the effect of the in-depth profile modification on SEI has been conducted to thirty-two heterogeneous reservoir models under the several blocking conditions. The relation between the blocking effect on SEI and the heterogeneity indexes, which are Dykstra-Parsons coefficient for vertical heterogeneity and correlation length for horizontal heterogeneity, is also investigated.From this study, following results have been obtained. First, the blocking effect increases with the increase in the volume of injected polymer gel and the decrease in the volume of chase water. That is to say, the blocking effect increases when the blocking is done more perfectly. Second, the blocking effect increases with the increase in the vertical heterogeneity, and horizontal heterogeneity is less correlated to the blocking effect compared to the vertical heterogeneity.

Chemical Verification of the EOR Mechanism by Using Low Saline/Smart Water in Sandstone

Recently, a chemical mechanism for enhanced oil recovery by low salinity water flooding was suggested. The key step in the mechanism was a localized increase in the pH at the clay surface due to desorption of active cations, especially Ca2+, as the low saline injection water invaded the porous medium. An increase in pH will remove adsorbed acidic and basic material from the clay surface and increase the water wetness of the rock. In the present paper, parametric studies have been performed to verify the different steps in the suggested mechanism. Both dynamic core floods and static adsorption studies of model base and acid on three different clay minerals have been performed. The results from the dynamic experiments were supported by the static adsorption/desorption studies. The main observation regarding adsorption/desorption of basic organic material onto clays was that changes in pH appeared to play a greater role than the salinity of the brine. Thus, both the dynamic and the static studies supported the suggested chemical mechanism for the low salinity EOR process.

Comparison of bio- and synthetic surfactants for EOR

In this work, the performance of three natural surfactants (one produced by a bacteria and two of vegetal origin) in comparison to synthetics surfactants (cationic, anionic, non-ionic and zwitterionic) for its potential use in enhanced oil recovery EOR application was compared. The basis of comparison was basically the surfactant's solutions surface tension (ST) at room temperature, in the presence and absence of brine (salinity of about 4.7%). These measurements were developed to estimate if surfactants will resist reservoir conditions such as 75 °C and high salinities (up to 5%), conditions prevailing in the oil-field of Chicontepec, Veracruz (Mexico). Results of the work showed that biosurfactants could have potential for EOR process. The rhamnolipid produced by Pseudomonas and guar gum natural surfactants developed characteristics as good or even better than the synthetic surfactants normally employed in this process. The rhamnolipid produced by Pseudomonas seems to be a natural surfactant with extremely interesting characteristics. Rhamnolipid solutions yielded quite low ST at low concentrations (i.e. < 30 mN/m), even in the presence of brine for concentrations below 0.08%. Heat treatment applied to rhamnolipid solutions change very slightly the ST values when solutions contained no salts and about of 30% oil when brine was present. Rhamnolipid solutions did not show the higher foam capabilities, but represented half the capability of Polafix CAPB surfactant in producing foam. Neither guar nor locust bean gums showed important diminutions of ST at different concentrations in the solution. Nevertheless, for certain gum concentrations and in the presence of brine, guar gum had a very good performance (0.02%). Neither guar nor locust bean gums produced foam.