Assessment of diverse operational constraints and risk appraisal associated with reservoir heterogeneities are essential foundation of production optimization and oil field development scenarios. Water-flooding performance evaluation that comprises comprehensive numerical simulations is typically cumbersome in terms of time and money, which is not reasonably appropriate for practical decision making and future performance forecasting. Cognitive data-driven proxy modeling practices, which incorporate data-mining techniques and machine learning concepts, offer a fascinating substitute for explicit models of the underlying process that can be instantaneously reassessed, especially for extremely nonlinear system forecasts. In this paper, an exploratory data analysis is applied to create a comprehensive data set from Water-flooding actual field data, which entails different characteristics labeling reservoir heterogeneities and other pertinent operational constraints. Artificial neural network (ANN) is applied as a cognitive data-driven proxy modeling effort to predict Water-flooding production in heterogeneous reservoirs. This study presents the great potential of cognitive data-driven proxy modeling techniques for practical applications and as a feasible add on for investigating a huge quantity of real field data efficiently. In addition, the suggested methodology can be incorporated directly into most present reservoir development decision making routines.
After the development of a numerical fully implicit nonisothermal wellbore/reservoir simulator in Part 1 of this study (Bahonar et al. 2010), this simulator is implemented for a close and detailed study of gaswell pressure-drawdown (DD) and-buildup (BU) tests. Overall, the developed simulator is an accurate and strong tool for design and analysis of transient gaswell testing, particularly for high-pressure/high-temperature (HP/HT) gas reservoirs. Several numerical results will be presented. This includes demonstration of the behaviour of the wellbore-fluid pressure, temperature, density, and velocity and an overall heat-transfer coefficient during DD or shut-in tests for nonisothermal reservoirs and conceptual comparisons with the isothermal counterparts. Thermal effects on the behaviour of derivative plots and the sandface-flow rate of deep nonisothermal gas reservoirs will be studied. A significant effect of neglecting the heat capacity of tubular and cement materials on the wellhead-temperature simulation, and thus transient well tests, will be demonstrated. A sample case to show that neglecting the thermal effects in the gaswell tests of composite reservoirs leads to unreliable results in well-testing analysis will be presented. Several other numerical experiments, including the presence of a variable wellbore-storage coefficient, gas backflow from the wellbore to the reservoir, and other thermal effects during the gaswell tests, are also presented. Hundreds of millions of dollars are spent every year on well testing around the world (Hawkes et al. 2001). A proper design and truthful interpretation of these tests can be achieved by a reliable coupled wellbore/reservoir simulator, which in turn can save a large portion of the required costs.
Quality and productivity of tight formations are heavily dependent on the degree of fracture development. In fact, hard and dense carbonate formations may not be considered as net pay without presence of fractures which conduct fluids towards wellbore. The evaluation of fractures is a key to reservoir effectiveness characterization for well drilling, completion, development and simulation of fractured reservoirs. Although new imaging technologies such as Formation Micro-Scanners and Imagers (FMS and FMI) provide the information of fracture properties (dip angle, porosity, aperture and permeability), image logs are very expensive and cannot be available in all wells. In this paper, fracture parameters are estimated using conventional Dual Laterolog (DLL) resistivity, which includes shallow (LLS) and deep (LLD) responses. This technique is based on electrical resistivity anomalies because of separation of shallow and deep laterolog curves. Fracture parameters that can be calculated by DLL include dip angle, aperture, porosity, permeability and cementation factor. The accuracy of the calculated parameters using DLL is validated by the results of FMI in one well in one of Iranian fractured reservoirs. Despite the image logs, the conventional DLL is routinely run in all of the drilled wells. This makes the constructed fracture model on the basis of DLLs more reliable than the corresponding model founded on limited and insufficient image logs. Furthermore, DLL has an advantage of much deeper evaluation of fractures in comparison with the immediate borehole investigation of image logs.
A numerical fully implicit nonisothermal wellbore/reservoir simulator is developed. The model entails simultaneous solution of transient coupled mass-, momentum-, and energy-balance equations within the wellbore; energy-balance equations for the tubular and cement materials and the formation surrounding the wellbore; and mass-balance and flow-rate/pressure equations for the reservoir formation. A wellbore heat-loss model that is a strong feature of this study is developed and employed in the model to improve the accuracy of the simulator and to be able to estimate the casing temperature and formation-temperature distribution. The model formulation is completed with an equation of state (EOS) to estimate fluid properties and appropriate friction-factor correlations in the wellbore tubing to compute the frictional pressure drop for different flow regimes.The developed model has several applications in the petroleum industry, particularly in the gas-well testing design and interpretation of both isothermal and nonisothermal gas reservoirs.This nonisothermal simulator is validated through comparisons to both analytical models and an equivalent numerical isothermal coupled wellbore/reservoir simulator that is also developed in this paper. Applications of this simulator to analyzing gas-well testing problems, in addition to several important observations, are extensively studied in Part 2 of this research work (Bahonar et al. 2010).Currently, it has been well accepted that the applicability and significance of a reservoir simulator depend on the behaviour of the wellbore and interaction between the wellbore and reservoir. A robust, accurate coupled wellbore and reservoir simulator is an invaluable tool for the petroleum engineer to help the petroleum industry understand production behaviour, make a meaningful prediction, and make correct decisions in all field-development and production stages. Fig. 2-Schematic representation of the Jacobian matrix.
Summary Naturally fractured reservoirs (NFRs) represent more than 20% of the world's oil and gas reserves. However, their characterization is complex and presents unique challenges in comparison with conventional reservoirs. It is immensely difficult to achieve the best results in the secondary-recovery process for NFRs. This paper presents a successful development of waterflooding to overcome the complex geological characterization of the White Tiger field, the largest fractured basement reservoir to date on the continental shelf of Vietnam. This reservoir has a complicated geological structure, with high heterogeneity, high temperature, and high closure stress. The total oil initially in place (OIIP) of this field reached nearly 4 billion bbl from 2000 m of oil-bearing thickness, and the field has been produced by more than 100 wells, 10 of which have flowed at the rate of approximately 1,000 B/D. The geological study and fractured model have been carefully investigated in both micro- and macroscale to improve waterflooding performance. The authors have analyzed the advantages and disadvantages of injection systems in this basement reservoir during 20 years of production history, and an artificial water buffer solution has been proposed to improve the waterflooding process. The authors have described the establishment and association of local artificial water buffer in the basement reservoir. An effective method to optimize the injected-water volume has also been discussed. Promising results from the White Tiger field have shown that the average reservoir pressure and total oil recovery have increased significantly in comparison with previous injection schemes. This paper presents useful guidelines to solve some typical problems of waterflooding in fractured basement reservoirs: What can be applied in waterflooding for a fractured basement reservoir? What is the optimal injection rate and injected volume for the fractured basement reservoir? How do we evaluate the probability of high water cut in production wells during the waterflooding process? How do we predict the rise of an artificial water/oil contact (AWOC)?
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