This paper focuses on life-cycle optimization of oil field development plan under uncertainty. The optimization problem included a wide range of design variables and control rules related to wells and platform in a realistic benchmark case (UNISIM–II–D) with a known ground truth reservoir model, UNISIM–II–R, that resembles Brazilian pre-salt fractured carbonate reservoirs in their early development stage. The design variables were the number and location of wells, the fluid processing capacity of the platform, and the location of internal control valves (ICVs), whereas the control rules were the setting of ICVs, production and injection rates, and the duration of the water-alternating-gas (WAG-CO2) cycle. An iterative sequential optimization framework was developed to deal with the massive search space and complex parameterization. The optimization further took into consideration the subsurface, operational and economic uncertainties, and used iterative discrete Latin hypercube method as the search algorithm. The robust optimization was carried out on a subset of representative models derived from the reduction of a large ensemble of data-assimilated models. As a low-fidelity representation of the compositional fluid model, a black-oil model was used to reduce simulation runtime. To validate our optimization framework, we applied the optimal development strategy to the ensemble of compositional simulation models, as well as the ground truth model. The true model’s responses were within the ranges predicted by the compositional ensemble, confirming the optimization framework’s reliability. The general methodology developed in this study, as well as our findings, can be used to optimize other similar real-world complex and high-risk field development projects, and are especially useful in closed-loop field development and management practices.
Autor: João Lucas Braga Da Silva
Binary well placement optimization using a decomposition-based multi-objective evolutionary algorithm with diversity preservation
In binary multi-objective well placement optimization, multiple conflicting objective functions must be optimized simultaneously in reservoir simulation models containing discrete decision variables. Although multi-objective algorithms have been developed or adapted to tackle this scenario, such as the derivative-free evolutionary algorithms, these methods are known to generate a high number of duplicated strategies in discrete problems. Duplicated strategies negatively impact the optimization process since they: (i) degrade the efficiency of recombination operators in evolutionary algorithms; (ii) slow the convergence speed as they require more iterations to find a well-distributed set of strategies; and (iii) perform unnecessary re-evaluations of previously seen strategies through reservoir simulation. To perform multi-objective well placement optimization while avoiding duplicated strategies, this paper investigates the application of a newly proposed algorithm named MOEA/D-NFTS, with a modified diversity preservation mechanism that incorporates prior knowledge of the problem, on a multi-objective well placement optimization problem. The proposed methodology is evaluated on the UNISIM-II-D benchmark case, a synthetic carbonate black-oil simulation model in a well placement optimization problem using a binary strategy representation, indicating the presence or absence of a given candidate well position in the final strategy. The objective functions are the maximization of the Net Present Value, the maximization of the Cumulative Oil Production, and the minimization of Cumulative Water Production. The modified MOEA/D-NFTS performance is compared with a baseline algorithm without diversity preservation, and the evidence shows that the MOEA/D-NFTS produces statistically significant superior results, and is suitable for binary multi-objective well placement optimization.
Prototyping visualizations as a support for selecting representative models of petroleum reservoirs
Petroleum engineers usually create a set of hundreds of models of a given oil reservoir under analysis to represent its uncertainties. Assisted optimization approaches may help engineers to select a subset of these models (a.k.a. representative models, or RMs for short), which is used in computational flow simulations in replacement of the original set, aiming to reduce the total simulation runtime without changing the quality of these results. Despite the power of visualization techniques to help people to understand multidimensional datasets like the ones provided in this scenario, we noted a few efforts that use these techniques to help petroleum engineers to assist the selection of RMs. In this context, our research aims to test the hypothesis that it is possible to improve how interactive visualization resources are currently used to aid decision-making regarding the selection of RMs, mainly in the presence of multiple sets of RMs or multiple variables (obtained from running model simulations). This work presents our first steps towards this goal: (a) literature review and (b) definition of visualization prototypes that aim to help the analysis of RMs regarding the values of the variables provided by simulation outputs, and the risk curves associated with these variables. As preliminary results, we present our proposed interactive visualizations and briefly point out the design rationale behind these prototypes.
Experimental Investigation Of The Shear Effect On Oil-Water Emulsion Flow In Pipelines
Emulsion flows have been a severe flow assurance issue, mainly in mature oil fields. Its formation occurs due to shear on oil-water flows caused by artificial lift methods, such as Electrical Submersible Pumps (ESP), and/or valves. The shear rate has an important role in emulsion flow behavior related to its relative viscosity and phase inversion. Therefore, this work presented an experimental investigation of the shear effect on three emulsion systems flowing in a pipeline. The shear element used was a combination of an 8-stage ESP and a glob valve. The emulsion systems analyzed were unstable emulsion and stable emulsion with and without a demulsifier. The experimental investigation was carried out for two ESP rotational speeds, 2400 and 3500 rpm, and one total volumetric flow rate, varying the water cut. From this study, it was observed that phase inversion occurred with increasing shear. Moreover, the effective viscosity was the same regardless of the surfactant presence for the three emulsion systems tested.
Flow Visualization In The Impeller And Diffuser Of A Centrifugal Pump Using Time-Resolved Particle Image Velocimetry
The present paper describes an experimental study on the flow dynamics within a centrifugal pump impeller. A transparent pump prototype made of acrylic parts was firstly developed for flow visualization purposes. Then, single-phase flow experiments were conducted in different impeller rotational speeds and water flow rates. A time-resolved particle image velocimetry (TR-PIV) system was used as the flow visualization method. As a result, velocity fields were obtained in the whole impeller. They reveal that the flow behaviour is dependent on the pump operational condition. When the pump works at the best efficiency point (BEP), the flow is uniform and the streamlines follow the blade curvature. However, when the machine works at off-design conditions, the flow becomes complex, with the presence of turbulent structures which cause a reduction in the pump performance. This type of result may be useful to validate numerical simulations and support the proposition of new mathematical models, new impeller geometries, among other applications.
Visualization Of Oil-Water Emulsion Formation In A Centrifugal Pump Stage
Electrical submersible pumps are assembled in oil wells to act as artificial lift methods. When water is present in the reservoir, oil-water emulsions are formed in the pump. These two-phase mixtures affect the performance and promote instabilities that lead the machine to operate inefficiently and fail prematurely. Therefore, this paper aims to investigate the formation of emulsions and behavior of mineral oil drops in a transparent centrifugal pump through a flow visualization approach. Shut-off, best efficiency point, and open-flow condi tions are investigated at three impeller rotational speeds with high-speed imaging and particle image velocimetry. As the oil fraction increases, large drops accumulate in the impeller channels, while some escape to the volute and circulate until the water flow carries them out of the pump stage. Regions with vortices and water recirculation explain the accumulation of oil drops in the impeller and reduced pump performance at low water flow rates. Intense velocity fluctuations at the impeller and impeller-volute boundary indicate the main causes for oil drop rotation, deformation, and fragmentation at high water flow rates. The new findings can be used to improve models and numerical simulations for pumps operating with multiphase flows and help the creation of new pump designs.
Evaluation of the effect of wax concentration in crude oils on the dimensionless temperature plateau
One of the main challenges regarding crude oil production under low temperatures in deep seas concerns the wax deposition in pipelines. This issue presents a high level of complexity and the governing mechanism is still under investigation. Considering the deposition phenomenon and seeking to improve the knowledge about the governing mechanism and the main variables influencing the final behavior, the present work analyzes how different oil compositions and mixtures, under different flow conditions, impact the deposit wax thickness. It also compares the dimensionless temperature for different wax concentrations, which allows to evaluate the behavior of the temperature gradient, and verifies the behavior of the plateau under different Reynolds numbers. Finally, the mechanism proposed in this work is compared with the behavior proposed by the main governance mechanisms discussed in the literature in the last decades.
Experimental Investigation on Velocity Fields, Vorticity, and Turbulence within the Stage of an Electrical Submersible Pump (ESP)
This paper presents an experimental study on the flow dynamics within an Electrical Submersible Pump (ESP) stage. An ESP prototype with transparent impeller and diffuser was designed and manufactured to allow flow visualization, which was achieved by using a Time-Resolved Particle Image Velocimetry (TR-PIV) system. Single-phase water flow tests were conducted in various flow rates corresponding to percentages of the Best Efficiency Point (BEP). The average velocity fields, vorticity contours, and turbulent kinetic energy values obtained in the whole impeller reveal that the flow behaviour is very dependent on the ESP operational condition. Energy losses due to turbulence are lower when the pump works at the BEP. But when the device operates at off-design conditions, the flow becomes complex, with high vorticity and turbulence which cause a reduction in the performance. This type of investigation may be useful to validate numerical simulations, support the proposition of mathematical models, or help create improved impeller designs.
Understanding ESP Performance Under High Viscous Application and Emulsion Production
Although being widely used as an artificial lift method for heavy oil field developments, Electrical Submersible Pump (ESP) system performance in high viscous applications is not fully understood. A miscomprehension of challenges and equipment performance in such conditions might lead to operation inefficiencies and equipment failures. This paper presents results of single-phase and multiphase tests performed by University of Campinas (UNICAMP). It also presents operation data, lessons learnt, and failure examples gathered over 10 years of ESP operation in Peregrino field which is a heavy oil, high viscous oilfield offshore Brazil operated by Equinor.
Affinity laws commonly used for ESP simulations don’t hold true for high viscosity applications. Hydraulic performance of centrifugal pumps is affected by fluid parameters like viscosity and density; operation parameters such as flow rate and rotational speed; and specific stage design characteristics. To determine degradation in head and efficiency as well as power requirement increase in viscous applications, Equinor performs one-phase high viscosity flow loop test to qualify each stage type prior to deployment in Peregrino field.
For the qualification of ESPs, single phase qualification tests are performed using mineral oil with viscosities specifically chosen to cover the viscosity range of the specific field. Each stage type is qualified using a prototype with reduced number of stages due to flow loop limitations. Qualification tests for the Peregrino field confirmed that affinity laws are not accurate for high viscous applications and provided important insights regarding pump performance that are used in equipment specification and system surveillance.
The UNICAMP research team has designed and performed multiphase flow tests to evaluate emulsion formation inside centrifugal pump stages and effective viscosity behavior. Phase inversion phenomenon investigation was also included in studies. Studies performed using a prototype stage allowed visualization and evaluation of oil drops dynamics inside the impeller in different rotational speeds. Two phase flow loop tests investigated the shear forces influence in effective viscosity inside pump stages and downstream pump discharge. Phase inversion phenomenon was also a point of great interest during the studies. Data gathered during lab tests was used to evaluate accuracy of mathematical models existing in the literature when a centrifugal pump is added to the system. Hysteresis effect associated to catastrophic phase inversion (CPI) was confirmed and replicated during flow loop tests. Such behavior can be related with operation parameters instabilities and equipment failures noticed in actual application in Peregrino field which are also presented in this paper.