Waterflooding is commonly performed in oil wells for pressure support and increased oil production. Different sources of injection water can be used for waterflooding, such as aquifer water, seawater or produced water. Each of these water sources contain particulates in them that deposit at the injection point forming both an external filter cake on the reservoir face and an internal cake inside the rock surface. The properties of the external and internal filter cake negatively affect injectivity. In order to identify the optimum water filtration specs prior to injection, the contribution of different solid particle types present in the injected water on filter cake properties and injectivity need to be understood. A lab study has been undertaken to gauge the contribution of different solid types, solid sizes, and the presence of oil droplets on filter cake properties and water injectivity. The solid types tested were silica/quartz, clay, iron oxide, barium sulfate and calcium carbonate, with and without oil contamination. Membrane tests were conducted to understand the correlation between the porosity and the permeability of the external filter cake that forms at the formation face for each particulate type. A heavy slurry of selected solid particulate was mixed in brine and was compressed into a membrane under different applied pressures, and the porosity and the permeability of the cake was calculated at each stage. Core tests were designed to look at the combined effects of the external and internal filter cake on reduction in injectivity. Outcrop cores, representative of the field cores, with similar pore throat size, porosity and permeability were used in the core tests, as particle bridging at pore throats is a function of the comparison between the injected particle size and the pore throat size distribution of the reservoir. A slurry of the selected solid particulates in brine was injected into the core system and the permeability drop across the core was monitored as a function of injected water pore volumes. Both types of tests were repeated in the presence of oil contamination in the injected water. The test data from the membrane tests and the core tests were used in the numerical model to obtain the permeability reduction function for the internal and external filter cake.
A two-way coupling methodology between two commercial reservoir simulators and external libraries to simulate complex phenomena occurring in the reservoir during the recovery process is proposed herein. Such methodology was implemented by using two approaches: the first one employs dynamic library loading at runtime; and the second, communication performed via file. These two-way coupling mechanisms allow third party software developers to extend the capability of a commercial simulator. A formulation applied to model Aquathermolysis reactions in a steam flood reservoir model was implemented with this two-way coupling method. This method can be used to model other phenomena, such as in-situ combustion and acidification, among others. The two-way coupling Application Programming Interface (API) provides the reservoir grid cell properties such as pressure, temperature, saturation, composition, pore volume and source terms to the external modules. The external module reads some properties (e.g. temperature and compositions) from the reservoir simulator to compute the reaction terms providing a source term to the reservoir simulator. The frequency of the reaction source term update can be specified at runtime, and it can be for only Newton iteration 0 (explicit) or all Newton iterations (operator splitting sequential implicit). Moreover, the reaction rate constant is modeled as a function of temperature using the Arrhenius equation or a lookup table. The coupling has been tested with commercial reservoir simulators herein designated as A and B. To prove the capability to couple reservoir simulators to an external module, the methodology presented considers both two-way coupling runtime library loading (Simulator A) and two-way coupling file-based (Simulator B) approaches, at time-step (Simulator B) and Newton iteration (Simulator A) levels. Results were evaluated using synthetic cases comparing the coupled solution with a numerical solution obtained by modeling the reactions in Simulator C (a reservoir simulator capable to model the same reactions implemented in the proposed two-way coupling). Results of a field case available in the literature were also evaluated. The great match obtained for the synthetic cases and, together with a good agreement with the field case, proved the capability of the proposed coupling. The simulation time between a coupled solution and a traditional solution without the reactions was compared for both methods and the file-based approach was shown to have a significant impact on simulation time; while using an API showed no significant simulation time increase for the tested cases. The novelty of the proposed coupling is the capability of modeling complex reservoir phenomena using external modules, which is usually not the focus of reservoir simulators. Although the methodology has thus far only been applied to the Aquathermolysis phenomena, it can easily be extended to solve other EOR problems.
Summary The industry is moving away from overboard discharging of produced water and is increasingly selecting produced-water reinjection (PWRI) as the preferred method for waterflooding projects. This does not come without risks because the produced water usually needs to be supplemented by seawater in order to meet injection-volume requirements, increasing the risk of both scaling and souring. PWRI supplemented by seawater was the selected produced-water-management strategy for Field M located in West Africa. Produced water from the adjacent Field K is also being considered for reinjection into Field M. Field M will be waterflooded from the beginning to maintain reservoir pressure close to the bubblepoint. Recent experiences of PWRI in other assets have created a challenging atmosphere because scaling posed a major risk to production. Field M had to go through very detailed and thorough souring and scaling evaluations to justify the feasibility of this project. A consistent formation-water chemistry analysis for these evaluations was obtained by incorporating thermodynamic equilibrium constraints on formation-water composition from reservoir mineralogy and using knowledge of basin formation-water contributions from proximal salt formations. The evaluation of scaling potential was performed using ScaleSoftPitzer. The results show a low risk of scaling when the waters are commingled. Periodic formation scale squeezes are recommended to mitigate the scaling potential. The souring-potential study was conducted using a full-field reservoir-souring simulation model (SourSimRL). SourSimRL superimposes criteria for the generation, partitioning, and transport of H2S. On the basis of the results, the souring potential is predicted to be generally moderate. The souring potential for the field is restricted by the availability of carbon nutrients in the injection waters and the high reservoir temperature of 250°F. These rigorous technical evaluations were instrumental to obtain the support for PWRI and could be used as guidance for other PWRI projects.
The industry is moving away from overboard discharging of produced water and is increasingly selecting produced water reinjection (PWRI) as the preferred method for waterflooding projects. This does not come without risks as the produced water usually needs to be supplemented by seawater in order to meet injection volume requirements, which increases the risk of both scaling and souring. PWRI supplemented by seawater was the selected produced water management strategy for Field M located in West Africa. Produced water from the adjacent Field K is also being considered for reinjection into Field M. Field M will be waterflooded from the beginning to maintain reservoir pressure close to the bubble point. Recent experiences of PWRI in other assets have created a challenging atmosphere as scaling posed a major risk to production. Field M had to go through very detailed and though souring and scaling evaluations to justify the feasibility of this project. A consistent formation water chemistry analysis for these evaluations was obtained by incorporating thermodynamic equilibrium constraints on formation water composition from reservoir mineralogy and using knowledge of basin formation water contributions from proximal salt formations. The evaluation of scaling potential was done using ScaleSoftPitzer. The results show a low risk of scaling when the waters are commingled. Periodic formation scale squeezes are recommended to mitigate the scaling potential. The souring potential study was conducted using a full field reservoir souring simulation model (SourSimRL). SourSimRL superimposes criteria for the generation, partitioning and transport of H2S. Based on the results, the souring potential is predicted to be generally moderate. The souring potential for the field is restricted by the availability of carbon nutrients in the injection waters and the high reservoir temperature of 250 °F. These rigorous technical evaluations were instrumental to obtain the support for PWRI and could be used as guidance for other PWRI projects.
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