Browsing by Subject "Waterflooding"

Now showing 1 - 8 of 8
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    A Mechanism of Improved Oil Recovery by Low-Salinity Waterflooding in Sandstone Rock
    (2013-05-02) Nasralla, Ramez
    Injection of low-salinity water showed high potentials in improving oil recovery when compared to high-salinity water. However, the optimum water salinity and conditions are uncertain, due to the lack of understanding the mechanisms of fluid-rock interactions. The main objective of this study is to examine the potential and efficiency of low-salinity water in secondary and tertiary oil recovery for sandstone reservoirs. Similarly, this study aims to help in understanding the dominant mechanisms that aid in improving oil recovery by low-salinity waterflooding. Furthermore, the impact of cation type in injected brines on oil recovery was investigated. Coreflood experiments were conducted to determine the effect of water salinity and chemistry on oil recovery in the secondary and tertiary modes. The contact angle technique was used to study the impact of water salinity and composition on rock wettability. Moreover, the zeta potential at oil/brine and brine/rock interfaces was measured to explain the mechanism causing rock wettability alteration and improving oil recovery. Deionized water and different brines (from 500 to 174,000 mg/l), as well as single cation solutions were tested. Two types of crude oil with different properties and composition were used. Berea sandstone cores were utilized in the coreflood experiments. Coreflood tests indicated that injection of deionized water in the secondary mode resulted in significant oil recovery, up to 22% improvement, compared to seawater flooding. However, no more oil was recovered in the tertiary mode. In addition, injection of NaCl solution increased the oil recovery compared to injection of CaCl2 or MgCl2 at the same concentration. Contact angle results demonstrated that low-salinity water has an impact on the rock wettability; the more reduction in water salinity, the more a water-wet rock surface is produced. In addition, NaCl solutions made the rock more water-wet compared to CaCl2 or MgCl2 at the same concentration. Low-salinity water and NaCl solutions showed a highly negative charge at rock/brine and oil/brine interfaces by zeta potential measurements, which results in greater repulsive forces between the oil and rock surface. This leads to double-layer expansion and water-wet systems. These results demonstrate that the double-layer expansion is a primary mechanism of improving oil recovery when water chemical composition is manipulated.
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    A new reservoir scale model for fracture propagation and stress reorientation in waterflooded reservoirs
    (2016-12) Bhardwaj, Prateek; Sharma, Mukul M.
    It is now well established that poro-thermo-elastic effects substantially change the magnitude and orientation of in-situ stresses. Fractures induced in injectors during water injection for waterflooding or produced water disposal have a profound impact on waterflood performance. These effects, coupled with injectivity decline due to plugging caused by injected particles, lead to permeability reduction, fracture initiation and propagation. Models are available for fracture propagation in single injection wells and single layered reservoirs that account for these effects. However, the impact of fluid injection and production on fracture growth in multiple wells and multi-layered reservoirs with competing fractures, has not been systematically modelled at a field scale. In this work, a three-dimensional, two-phase flow simulator with iteratively coupled geomechanics has been developed and applied to model the dynamic growth of injection-induced fractures. The model is based on a finite volume implementation of the cohesive zone model for arbitrary fracture propagation coupled with two-phase flow. A dynamic filtration model for permeability reduction is employed on the fracture faces to incorporate effects of internal damage and external filter cake build-up due to the injection of suspended solids and oil droplets. All physical phenomena are solved in a single framework designed for multi-well, field-scale simulation. The pressure distribution, saturation profile, thermal front, mechanical displacements and reservoir stresses are computed as fluids are injected and produced from the reservoir. Simulation results are discussed with single as well as multiple fractures propagating. Stress reorientation due to poroelastic, thermoelastic and mechanical effects is examined for the simulated cases. The orientation of the fractures is controlled primarily by the orientation of the stresses, which in turn depends on the pattern of wells and the rates of injection and production. The sweep efficiency of the waterflood is found to be impacted by the rate of growth of injection-induced fractures. Heterogeneities in multi-layered reservoirs strongly govern the expected vertical sweep and fluid distribution, which impacts the cumulative oil recovery. This is the first time a formulation of multiphase flow in the reservoir has been coupled with dynamic fracture propagation in multiple wells induced by solids plugging while including poro-thermo-elasticity at the reservoir scale. The model developed in this work can be used to simulate multiple water injection induced fractures, determine the reoriented stress state to optimize the location of infill wells and adjust injection well patterns to maximize reservoir sweep.
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    Experimental investigation of the effect of increasing the temperature on ASP flooding
    (2011-12) Walker, Dustin Luke; Pope, Gary A.; Weerasooriya, Upali
    Chemical EOR processes such as polymer flooding and surfactant polymer flooding must be designed and implemented in an economically attractive manner to be perceived as viable oil recovery options. The primary expenses associated with these processes are chemical costs which are predominantly controlled by the crude oil properties of a reservoir. Crude oil viscosity dictates polymer concentration requirements for mobility control and can also negatively affect the rheological properties of a microemulsion when surfactant polymer flooding. High microemulsion viscosity can be reduced with the introduction of an alcohol co-solvent into the surfactant formulation, but this increases the cost of the formulation. Experimental research done as part of this study combined the process of hot water injection with ASP flooding as a solution to reduce both crude oil viscosity and microemulsion viscosity. The results of this investigation revealed that when action was taken to reduce microemulsion viscosity, residual oil recoveries were greater than 90%. Hot water flooding lowered required polymer concentrations by reducing oil viscosity and lowered microemulsion viscosity without co-solvent. Laboratory testing of viscous microemulsions in core floods proved to compromise surfactant performance and oil recovery by causing high surfactant retention, high pressure gradients that would be unsustainable in the field, high required polymer concentrations to maintain favorable mobility during chemical flooding, reduced sweep efficiency and stagnation of microemulsions due to high viscosity from flowing at low shear rates. Rough scale-up chemical cost estimations were performed using core flood performance data. Without reducing microemulsion viscosity, field chemical costs were as high as 26.15 dollars per incremental barrel of oil. The introduction of co-solvent reduced chemical costs to as low as 22.01 dollars per incremental barrel of oil. This reduction in cost is the combined result of increasing residual oil recovery and the added cost of an alcohol co-solvent. Heating the reservoir by hot water flooding resulted in combined chemical and heating costs of 13.94 dollars per incremental barrel of oil. The significant drop in cost when using hot water is due to increased residual oil recovery, reduction in polymer concentrations from reduced oil viscosity and reduction of microemulsion viscosity at a fraction of the cost of co-solvent.
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    Generalized Correlations to Estimate Oil Recovery and Pore Volumes Injected in Waterflooding Projects
    (2012-02-14) Espinel Diaz, Arnaldo Leopoldo
    When estimating a waterflood performance and ultimate recovery, practitioners usually prepare a plot of log of water-oil ratio vs. cumulative production or recovery factor and extrapolate the linear section of the curve to a pre-established economic limit of water production. Following this practice, engineers take the risk of overestimating oil production and/or underestimating water production if the economic limit is optimistic. Engineers would be able to avoid that risk if they knew where the linear portion of the curve finishes. We called this linear portion the "straight-line zone" of simply SLZ. In this research, we studied that ?straight-line zone? and determined its boundaries (beginning and end) numerically using mathematics rules. We developed a new procedure and empirical correlations to predict oil recovery factor at any water/oil ratio. The approach uses the fundamental concepts of fluid displacement under Buckley-Leverett fractional flow theory, reservoir simulation, and statistical analysis from multivariate linear regression. We used commercial spreadsheet software, the Statistical Analysis Software, a commercial numerical reservoir simulator, and Visual Basic Application software. We determined generalized correlations to determine the beginning, end, slope, and intercept of this line as a function of rock and fluid properties, such as endpoints of relative permeability curves, connate water saturation, residual oil saturation, mobility ratio, and the Dykstra-Parsons coefficient. Characterizing the SLZ allows us to estimate the corresponding recovery factor and pore volumes injected at any water-oil ratio through the length of the SLZ . The SLZ is always present in the plot of log of water-oil ratio vs. cumulative production or recovery factor, and its properties can be predicted. Results were correlated in terms of the Dykstra-Parsons coefficient and mobility ratio. Using our correlations, practitioners can estimate the end of the SLZ without the risk of overestimating reserves and underestimating water production. Our procedure is also a helpful tool for forecasting and diagnosing waterfloods when a detailed reservoir simulation model is not available.
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    Impact of fracture creation and growth on well injectivity and reservoir sweep during waterflooding and chemical EOR processes
    (2012-05) Lee, Kyung Haeng; Sharma, Mukul M.; Huh, Chun; Balhoff, Matthew T.; Pope, Gary A.; Bonnecaze, Roger T.
    During waterflooding, or chemical EOR processes with polymers, fractures are frequently generated in injectors. This can have a profound impact on the process performance and reservoir management. A fracture growth model was developed and linked to a reservoir simulator that incorporates the effect of (i) particle plugging due to filtration of solids and oil droplets in the injected fluids; (ii) non-Newtonian polymer rheology (shear-thinning and -thickening) for polymer injection; and (iii) thermal stresses induced by cold water injection. Dynamic fracture growth, which results from the pore pressure increase due to particle plugging or complex polymer rheology, affects the well injectivity and reservoir sweep significantly. With the fracture growth model, simulations can be made not only to make more accurate reservoir sweep and oil recovery predictions, but also to help identify well patterns that may improve reservoir performance. In homogeneous reservoirs, the injectivity is significantly affected by the propagation of an injection induced fracture; but the ultimate oil recovery and reservoir sweep are relatively unaffected. In multi-layered reservoirs, however, reservoir sweep and oil recovery are impacted significantly by the fracture growth. The oil recovery results from our fracture growth model differ substantially from those obtained based on the assumption of no fracture generation or a static fracture. For polymer injection processes, the shear rate dependence of the polymer viscosity is critical in determining the injectivity, fracture growth, and oil recovery. In addition to vertical injection well fractures, horizontal injection well fractures have been simulated by using the fracture growth model. The reservoir stress distribution determines the fracture orientation near a horizontal well. When the minimum horizontal stress orientation is perpendicular to the horizontal injector, a longitudinal fracture is generated, while with the minimum horizontal stress orientation parallel to the injector, a transverse fracture is developed. The impact of static and dynamic transverse/longitudinal fractures on well injectivity and reservoir sweep has been investigated. The impacts of (i) lengths of horizontal injector and producer; (ii) location of water oil contact; (iii) sizes of transverse and longitudinal fractures; (iv) particle concentration in the water, were further investigated. The well injectivity model was validated successfully by history matching injection of water (with particles) and shear rate dependent polymer injection. The history match was performed by adjusting the effective particle concentration in the injected water or the shear rate dependent polymer rheology. Based on history matching the long-term injection rates and pressures, estimates of the fracture length were made. These fracture dimensions could not be independently measured and verified. Based on the simulation results recommendations were made for strategies for drilling well patterns, water quality and injection rates that will lead to better oil recovery.
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    Modeling and remediation of reservoir souring
    (2011-08) Haghshenas, Mehdi; Bryant, Steven L.; Sepehrnoori, Kamy, 1951-; Delshad, Mojdeh; Huh, Chun; Liljestrand, Howard M.
    Reservoir souring refers to the increase in the concentration of hydrogen sulfide in production fluids during waterflooding. Besides health and safety issues, H₂S content reduces the value of the produced hydrocarbon. Nitrate injection is an effective method to prevent the formation of H₂S. Although the effectiveness of nitrate injection has been proven in laboratory and field applications and biology is well-understood, modeling aspect is still in its early stages. This work describes the modeling and simulation of biological reactions associated with reservoir souring and nitrate injection for souring remediation. The model is implemented in a general purpose adaptive reservoir simulator (GPAS). We also developed a physical dispersion model in GPAS to study the effect of dispersion on reservoir souring. The basic mechanism in the biologically mediated generation of H₂S is the reaction between sulfate and organic compounds in the presence of sulfate-reducing bacteria (SRB). Several mechanisms describe the effect of nitrate injection on reservoir souring. We developed mathematical models for biological reactions to simulate each mechanism. For every biological reaction, we solve a set of ordinary differential equations along with differential equations for the transport of chemical and biological species. Souring reactions occur in the areas of the reservoir where all of the required chemical and biological species are available. Therefore, dispersion affects the extent of reservoir souring as transport of aqueous phase components and the formation of mixing zones depends on dispersive characteristics of porous media. We successfully simulated laboratory experiments in batch reactors and sand-packed column reactors to verify our model development. The results from simulation of laboratory experiments are used to find the input parameters for field-scale simulations. We also examined the effect of dispersion on reservoir souring for different compositions of injection and formation water. Dispersion effects are significant when injection water does not contain sufficient organic compounds and reactions occur in the mixing zone between injection water and formation water. With a comprehensive biological model and robust and accurate flow simulation capabilities, GPAS can predict the onset of reservoir souring and the effectiveness of nitrate injection and facilitate the design of the process.
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    Reservoir characterization, performance monitoring of waterflooding and development opportunities in Germania Spraberry Unit.
    (Texas A&M University, 2005-08-29) Hernandez Hernandez, Erwin Enrique
    The Germania Unit is located in Midland County, 12 miles east of Midland, Texas and is part of the Spraberry Formation in the Midland Basin which is one of the largest known oil reservoirs in the world bearing between 8.9 billion barrels and 10.5 billion barrels of oil originally in place. The field is considered geologically complex since it comprises typically low porosity, low permeability fine sandstones, and siltstones that are interbedded with shaly non-reservoir rocks. Natural fractures existing over a regional area have long been known to dominate all aspects of performance in the Spraberry Trend Area. Two stages of depletion have taken place over 46 years of production: Primary production under solution gas drive and secondary recovery via water injection through two different injection patterns. The cumulative production and injection in Germania as of July 2003 were 3.24 million barrels and 3.44 million barrels respectively and the production level is 470 BOPD through 64 active wells with an average rate per well of 7.3 BOPD and average water cut of 60 percent. This performance is considered very low and along with the low amount of water injected, waterflood recovery has never been thoroughly understood. In this research, production and injection data were analyzed and integrated to optimize the reservoir management strategies for Germania Spraberry Unit. This study addresses reservoir characterization and monitoring of the waterflood project with the aim of proposing alternatives development, taking into account current and future conditions of the reservoir. Consequently, this project will be performed to provide a significant reservoir characterization in an uncharacterized area of Spraberry and evaluate the performance of the waterflooding to provide facts, information and knowledge to obtain the maximum economic recovery from this reservoir and finally understand waterflood management in Spraberry. Thus, this research describes the reservoir, and comprises the performance of the reservoir under waterflooding, and controlled surveillance to improve field performance. This research should serve as a guide for future work in reservoir simulation and reservoir management and can be used to evaluate various scenarios for additional development as well as to optimize the operating practices in the field. The results indicate that under the current conditions, a total of 1.410 million barrels of oil can be produced in the next 20 years through the 64 active wells and suggest that the unit can be successfully flooded with the current injection rate of 1600 BWPD and pattern consisting of 6 injection wells aligned about 36 degrees respect to the major fracture orientation. This incremental is based in both extrapolations and numerical simulation studies conducted in Spraberry.
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    A sensitivity study on modified salinity waterflooding and its hybrid processes
    (2016-05) Bissakayev, Beibit; Sepehrnoori, Kamy, 1951-; Kazemi Nia Korrani, Aboulghasem
    Waterflood is one of the most widely used techniques in enhanced oil recovery. In 1990s researchers came to conclusion that the chemistry of the injected water can be important in improving oil recovery. The low salinity water injection (LoSal® ) has become one of the promising topics in the oil industry. It is believed that the main mechanism for incremental oil recovery in low salinity flooding is wettability alteration. Several papers discussed that the wettability alteration from oil-wet to mixed- or water-wet takes place due to clay swelling and expanding of double layer in sandstones and calcite dissolution along with rock surface reactions in carbonates. However, there is no consensus on a single main mechanism for the low salinity effect on oil recovery. The main objective of this research is to conduct sensitivity analysis on main parameters in low salinity waterflooding and its hybrid processes affecting oil recovery in carbonates. We compare results by using coupled reservoir simulator UTCOMP-IPhreeqc. UTCOMP is the compositional reservoir simulator developed at the Center for Petroleum and Geosystems Engineering in The University of Texas at Austin. IPhreeqc is the module-based version of the PHREEQC geochemical package, a state-of-the-art geochemical package developed by the United States Geological Survey (USGS). We investigate the effect of low salinity water and carbon dioxide on oil recovery from carbonates by modeling the processes through the UTCOMP-IPhreeqc simulator. We perform sensitivity analysis on continuous gas injection (CGI), water-alternating-gas (WAG) flooding, and polymer-water-alternate-water (PWAG) flooding. We study the significance of reservoir parameters, such as reservoir heterogeneity (Dykstra-Parsons coefficient, Vdp, and crossflow, kv/kh), the salinity of injected water, the composition of gas, and polymer concentration in polymer-water solution on cumulative oil recovery. Moreover, we study the importance of inclusion of the hydrocarbon CO2 impact on the aqueous-rock geochemistry by comparing two scenarios where in one scenario the hydrocarbon CO2 effect is included in UTCOMP-IPhreeqc whereas in the other one the effect is neglected. Finally, we perform sensitivity analysis on PWAG flooding for most influential design parameters using Design of Expert software. The reservoir parameters, such as average reservoir permeability, reservoir heterogeneity, and crossflow and injected polymer-water solution parameters, such as polymer concentration and salinity of injected water are optimization parameters in this study.