Browsing by Subject "UTCHEM"
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Item Development and application of a parallel chemical compositional reservoir simulator(2015-08) Behzadinasab, Masoud; Ezekoye, Ofodike A.; Sepehrnoori, Kamy, 1951-Simulation of large-scale and complicated reservoirs requires a large number of gridblocks, which requires a considerable amount of memory and is computationally expensive. One solution to remedy the computational problem is to take advantage of clusters of PCs and high-performance computing (HPC) widely available nowadays. We can run large-scale simulations faster and more efficiently by using parallel processing on these systems. In this research project, we develop a parallel version of an in-house chemical flooding reservoir simulator (UTCHEM), which is the most comprehensive chemical flooding simulator. Every physical feature of the original code has been incorporated in the parallel code. The simulation results of several case studies are compared to the original code for verification and performance of the parallelization. The efficiency of the parallelization is evaluated in terms of speedup using multiple numbers of processors. Consequently, we improve the parallel efficiency to carry out the simulations by minimizing the communications among the processors by modifying the coding. The speedup results in comparison to linear speedup (considering the ideal speedup) indicate excellent efficiency. However, using large number of processors causes the simulator speedup to deviate from linear and the efficiency to decrease. The reason for the degradation is that the time devoted to communication between the processors increases with number of processors. To the best of our knowledge, the parallel version of UTCHEM (UTCHEMP) is the first parallel chemical flooding reservoir simulator that can be effective in running large-scale cases. While it is not feasible to simulate large-scale chemical flooding reservoirs with millions of gridblocks in any serial simulator due to computer memory limitations, UTCHEMP makes simulation of such cases practical. Moreover, this parallel simulator can take advantage of multiple processors to run field-scale simulations with millions of gridblocks in few hours.Item An experimental and simulation study of the effect of geochemical reactions on chemical flooding(2010-12) Chandrasekar, Vikram, 1984-; Delshad, Mojdeh; Pope, Gary A.The overall objective of this research was to gain an insight into the challenges encountered during chemical flooding under high hardness conditions. Different aspects of this problem were studied using a combination of laboratory experiments and simulation studies. Chemical Flooding is an important Enhanced Oil Recovery process. One of the major components of the operational expenses of any chemical flooding project, especially Alkali Surfactant Polymer (ASP) flooding is the cost of softening the injection brine to prevent the precipitation of the carbonates of the calcium and magnesium ions which are invariably present in the formation brine. Novel hardness tolerant alkalis like sodium metaborate have been shown to perform well with brines of high salinity and hardness, thereby eliminating the need to soften the injection brine. The first part of this research was aimed at designing an optimal chemical flooding formulation for a reservoir having hard formation brine. Sodium metaborate was used as the alkali in the formulation with the hard brine. Under the experimental conditions, sodium metaborate was found to be inadequate in preventing precipitation in the ASP slug. Factors affecting the ability of sodium metaborate to sequester divalent ions, including its potential limitations under the experimental conditions were studied. The second part of this research studied the factors affecting the ability of novel alkali and chelating agents like sodium metaborate and tetrasodium EDTA to sequester divalent ions. Recent studies have shown that both these chemicals showed good performance in sequestering divalent ions under high hardness conditions. A study of the geochemical species in solution under different conditions was done using the computer program PHREEQC. Sensitivity studies about the effect of the presence of different solution species on the performance of these alkalis were done. The third part of this research focused on field scale mechanistic simulation studies of geochemical scaling during ASP flooding. This is one of the major challenges faced by the oil and gas industry and has been found to occur when sodium carbonate is used as the alkali and the formation brine present in situ has a sufficiently high hardness content. The multicomponent and multiphase compositional chemical flooding simulator, UTCHEM was used to determine the quantity and composition of the scales formed in the reservoir as well as the injection and production wells. Reactions occurring between the injected fluids, in situ fluids and the reservoir rocks were taken into consideration for this study. Sensitivity studies of the effect of key reservoir and process parameters like the physical dispersion and the alkali concentration on the extent of scaling were also done as a part of this study.Item Linear solvers and coupling methods for compositional reservoir simulators(2010-12) Li, Wenjun, doctor of engineering; Sepehrnoori, Kamy, 1951-; Delshad, MojdehThree compositional reservoir simulators have been developed in the Department of Petroleum and Geosystems Engineering at The University of Texas at Austin (UT-Austin): UTCOMP (miscible gas flooding simulator), UTCHEM (chemical flooding simulator), and GPAS (General Purpose Adaptive Simulator). UTCOMP and UTCHEM simulators have been used by various oil companies for solving a variety of field problems. The efficiency and accuracy of each simulator becomes critically important when they are used to solve field problems. In this study, two well-developed solver packages, SAMG and HYPRE, along with existing solvers were compared. Our numerical results showed that SAMG can be an excellent solver for the usage in the three simulators for solving problems with a high accuracy requirement and long simulation times, and BoomerAMG in HYPRE package can also be a good solver for application in the UTCHEM simulator. In order to investigate the flexibility and the efficiency of a partitioned coupling method, the second part of this thesis presents a new implementation using a partition method for a thermal module in an equation-of-state (EOS) compositional simulator, the General Purpose Adaptive Simulator (GPAS) developed at The University of Texas at Austin. The finite difference method (FDM) was used for the solution of governing partial differential equations. Specifically, the new coupled implementation was based on the Schur complement method. For the partition method, two suitable acceleration techniques were constructed. One technique was the optimized choice of preconditioner for the Schur complement; the other was the optimized selection of tolerances for the two solution steps. To validate the implementation, we present simulation examples of hot water injection in an oil reservoir. The numerical comparison between the new implementation and the traditional, fully implicit method showed that the partition method is not only more flexible, but also faster than the classical, fully implicit method for the same test problems without sacrificing accuracy. In conclusion, the new implementation of the partition method is a more flexible and more efficient method for coupling a new module into an existing simulator than the classical, fully implicit method.The third part of this thesis presents another type of coupling method, iterative coupling methods, which has been implemented into GPAS with thermal module, FICM (Fully, Iterative Coupling Method) and GICM (General, Iterative Coupling Method), LICM (Loose, Iterative Coupling Method). The results show that LICM is divergent, and GICM and FICM can work normally. GICM is the fastest among the compared methods, and FICM has a similar efficiency as CFIM (Classic Fully Implicit Method). Although GICM is the fastest method, GICM is less accurate than FICM for in the test cases carried out in this study.Item Modeling and simulation of polymer flooding including the effects of fracturing(2015-12) Li, Zhitao; Delshad, Mojdeh; Wheeler, Mary F.; Pope, Gary A.; Sepehrnoori, Kamy; Huh, ChunChemical enhanced oil recovery (EOR) technology has attracted increasing interest in recent years with declining oil production from conventional oil reserves. Water flooding of heterogeneous reservoirs with viscous oil leaves considerable amount of remaining oil even at high producing water cuts. Polymer flooding is a mature EOR technology for augmenting recovery of moderately viscous oil. Water soluble polymers are used to reduce water mobility and improve sweep efficiency. For very viscous oil, polymer flooding is a potential non-thermal approach for minimizing viscous fingering and improving both displacement sweep efficiency and volumetric sweep efficiency. Polymer manufacturing techniques has been significantly advanced since 1980’s, which provides improved polymer quality and keeps polymer price relatively low. Compared with unconventional oil recovery techniques such as hydraulic fracturing, well planned and optimized polymer flooding can be profitable even at pessimistic oil price. It is thus crucial to have a reservoir simulator that is able to accurately model polymer properties and simulate polymer flooding in complex reservoir systems. Polymer rheological behavior is dependent on polymer molecular structure, concentration, Darcy velocity, brine salinity, hardness, permeability, porosity, etc. We improved polymer rheology modeling for heterogeneous reservoirs where permeability varies for orders of magnitude. For an injection well, a large portion of pressure drop is lost near wellbore where apparent polymer viscosity as a function of Darcy velocity varies drastically. Conventional analytical well models fail to capture the non-Newtonian effect of apparent polymer viscosity and make injectivity predictions widely deviated from true solutions especially for coarse-grid simulations. We developed a semi-analytical polymer injectivity model and implemented it into UTCHEM. This model is able to handle both shear-thinning and shear-thickening polymer rheology. It successfully avoids the grid effect and matches fine-grid simulation results and analytical solutions. Another challenge is to model polymer injectivity under fracturing conditions. To maintain an economic polymer injection rate, wellbore pressure may exceed the fracture initiation pressure. We developed a framework to couple a fracture model with UTCHEM. This coupled simulator is able to model fracture propagation during polymer injection. Finally several simulation studies were conducted to show the impacts of polymer rheological behavior, loss of polymer into aquifer, near wellbore effect and fracture propagation.Item Optimization of steam assisted gravity drainage, electrical Joule’s heating, and thermal-chemical processes for heavy oil reservoirs(2016-05) Ozdingis, Elif; Sepehrnoori, Kamy, 1951; Lashgari , Hamid RezaThermal enhanced oil recovery techniques have been considered as the best approach to produce heavy oil, however, not all thermal methods are appropriate or effective for oil production from every heavy oil reservoir. Therefore, this research study aims to investigate how reservoir and operational parameters affect certain thermal enhanced oil recovery methods (steam assisted gravity drainage, and low frequency electrical heating) and a hybrid thermal-chemical process (method which combines low frequency electrical heating with hot water and alkaline/co-solvent/polymer injection). In this master’s thesis, a compositional reservoir simulator, UTCHEM, was used to build the base case reservoir models. UTCHEM is a three-dimensional, multicomponent, multiphase reservoir simulator, which is mainly utilized to model chemical flooding processes. Besides modeling many features of chemical floods, the simulator can also handle complex phase behavior, heterogeneous porous medium properties. In this study, a modified version of UTCHEM, which includes a thermal module to model thermal recovery processes, was used to design steam assisted gravity drainage, low frequency electrical heating and hot water flooding periods and a geochemical module of UTCHEM was used for simulating chemical flooding part. Simulation results showed that a considerable increase in oil recovery is obtained when multiple SAGD well pairs are used. It is also observed that steam injection rate and heat loss have a significant influence on the steam assisted gravity drainage process. On the other hand, heat loss does not affect low frequency electrical heating method. It is deduced that low frequency electrical heating technique is not economically feasible and not very efficient to heat the reservoir. Therefore, low frequency electrical heating method can be used as a preheating application to lower the oil viscosity and, in turn, increase the injectivity in high viscous oil reservoirs. Finally, simulation results revealed that in the thermal-chemical process at the end of chemical flood, the amount of oil recovered is 80% of original oil in place (OOIP) where the oil recovery is only around 5% after hot water flooding. Thus, combining reservoir (pre)heating and chemical enhanced oil recovery methods has the potential to become a promising oil recovery method for heavy oil reservoirs.Item A polymer hydrolysis model and its application in chemical EOR process simulation(2010-12) Lee, Ahra; Delshad, Mojdeh; Pope, Gary A.Polymer flooding is a commercial enhanced oil recovery (EOR) method used to increase the sweep efficiency of water floods. Hydrolyzed polyacrylamide (HPAM), a synthetic commercial polymer, is widely used in commercial polymer floods and it is also used for mobility control of chemical floods using surfactants such as surfactant-polymer flooding and alkaline-surfactant-polymer flooding. The increase in the degree of hydrolysis of HPAM at elevated temperature or pH with time affects the polymer solution viscosity and its adsorption on rock surfaces. A polymer hydrolysis model based on published laboratory data was implemented in UTCHEM, a chemical EOR simulator, in order to assess the effect of hydrolysis on reservoir performance. Both 1D and 3D simulations were performed to validate the implementation of the model. The simulation results are consistent with the laboratory observations that show an increase in polymer solution viscosity as hydrolysis progresses. The numerical results indicate that hydrolysis occurs very rapidly and impacts the near wellbore region polymer injectivity.Item Simulation of inorganic scales using UTCHEM reservoir simulator(2011-08) Mukhliss, Amroo Essam; Bommer, Paul Michael; Sepehrnoori, Kamy, 1951-Scale deposition, either in the formation or inside the tubing, is a serious problem that can affect the productivity of oil fields. Production sustainability depends on the successful implementation of scale management strategies prior to developing new fields. Such strategies should involve tools capable of addressing the risks of developing scales during the production stage as well as determining the outcomes of possible remediation jobs in the future. UTCHEM, a multi-compositional flow model, was used in this work to present a comprehensive study that includes both precipitation and remediation scenarios. Although there are different mechanisms prompting the deposition of mineral scales, barite and calcite were selected primarily to simulate the effect of mixing incompatible water compositions; an issue that is usually associated with seawater injection. Equilibrium state calculations were carried out using a geochemical model (EQBATCH) to verify the incompatibility of the injection water with the formation water. In this work, we show the evolution, distribution, and remediation of solids over time for several hypothetical cases. The quantity of deposits in the near-wellbore region was found to be less at a highly heterogeneous reservoir model in contrast to the amount precipitated in homogenous reservoirs. This could be critical to wells productivity in the long-run since much of the drop in reservoir pressure occurs near the wellbore. The predictive ability of UTCHEM was extended to include simulating the removal of carbonate scales using a chelating chemical. The optimization of the injected treatment can be achieved mechanically through adjusting the well spacing (during the initial stages of field development) or through adjusting the concentrations of active components in the remediation fluids. The model provides a valuable tool that helps planners to predict scaling-related issues ahead of time, and subsequently to determine the economic viability of the project. This work serves as an opportunity to re-assess this simulator and allows for further work to enhance its capabilities.Item Simulation study of surfactant transport mechanisms in naturally fractured reservoirs(2010-08) Abbasi Asl, Yousef; Pope, Gary A.; Mohanty, Kishore K.Surfactants both change the wettability and lower the interfacial tension by various degrees depending on the type of surfactant and how it interacts with the specific oil. Ultra low IFT means almost zero capillary pressure, which in turn indicates little oil should be produced from capillary imbibition when the surfactant reduces the IFT in naturally fractured oil reservoirs that are mixed-wet or oil-wet. What is the transport mechanism for the surfactant to get far into the matrix and how does it scale? Molecular diffusion and capillary pressure are much too slow to explain the experimental data. Recent dynamic laboratory data suggest that the process is faster when a pressure gradient is applied compared to static tests. A mechanistic chemical compositional simulator was used to study the effect of pressure gradient on chemical oil recovery from naturally fractured oil reservoirs for several different chemical processes (polymer, surfactant, surfactant-polymer, alkali-surfactant-polymer flooding). The fractures were simulated explicitly by using small gridblocks with fracture properties. Both homogeneous and heterogeneous matrix blocks were simulated. Microemulsion phase behavior and related chemistry and physics were modeled in a manner similar to single porosity reservoirs. The simulations indicate that even very small pressure gradients (transverse to the flow in the fractures) are highly significant in terms of the chemical transport into the matrix and that increasing the injected fluid viscosity greatly improves the oil recovery. Field scale simulations show that the transverse pressure gradients promote transport of the surfactant into the matrix at a feasible rate even when there is a high contrast between the permeability of the fractures and the matrix. These simulations indicate that injecting a chemical solution that is viscous (because of polymer or foam or microemulsion) and lowers the IFT as well as alters the wettability from mixed-wet to water-wet, produces more oil and produces it faster than static chemical processes. These findings have significant implications for enhanced oil recovery from naturally fractured oil reservoirs and how these processes should be optimized and scaled up from the laboratory to the field.Item A study of microemulsion viscosity with consideration of polymer and co-solvent additives(2014-05) Dashti, Ghazal; Delshad, MojdehWith the dramatic increase in the worldwide demand for the crude oil and with the fact that the oil and gas resources are depleting, the enhanced oil recovery process plays an important role to increase the production from the existing hydrocarbon reservoirs. Chemical enhanced oil recovery is one of the most important techniques to unlock significant amount of trapped oil from oil reservoirs. Surface agent materials (Surfactants) are used to lower the interfacial tension (IFT) between water and oil phases to ultralow values and mobilize the trapped oil. When surfactant, water, and oil are mixed together they form a thermodynamically stable phase called microemulsion which can be characterized by ultralow interfacial tension and the ability to solubilize both aqueous and oil compounds. Another characteristic of microemulsion solution is its viscosity which plays an important role in the creation and movement of the oil bank. The microemulsion micro-structure is complex and its viscosity is difficult to predict. Various viscosity models and correlations are presented in the literature to describe microemulsion viscosity behavior, but they fail to represent the rheological behavior of many microemulsion mixtures. Most of these models are valid in the lower and higher ranges of solute where one of the domains is discontinuous. The majority of the models fail to calculate the rheology of microemulsion phase in bicontinuous domains. In this work, we present a systematic study of the rheological behavior of microemulsion systems and the effect of additives such as polymer and co-solvent on rheological properties of microemulsions. Several laboratory experiments were conducted to determine the rheological behavior of surfactant solutions. A new empirical model for the viscosity of microemulsion phase as a function of salinity is introduced. The model consists of three different correlations one for each phase type of Windsor phase behaviors. The proposed model is validated using a number of experimental results presented in this document. The proposed viscosity model is implemented in the UTCHEM simulator and the simulator results are compared with the coreflood experiments. Excellent matches were obtained for the pressure. We further improved the proposed viscosity model to incorporate the effect of polymer and co-solvent on the microemulsion viscosity.