Development of an integrated compositional wellbore-reservoir simulator for flow assurance problems




Abouie, Ali

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Flow assurance problems such as asphaltene and geochemical scale precipitation and deposition are among the major operational challenges encountered during oil production. The variations in thermodynamic conditions such as pressure, temperature, and/or fluid composition can result in formation and deposition of solid particles (e.g., asphaltene and scale particles) in the reservoir and wellbore. Although asphaltene and scale precipitation and deposition can occur in the reservoir and near-wellbore regions, this problem is mainly observed in the production wells. Precipitation and deposition of asphaltene and scale particles in the wellbore can cause partial or total plugging of tubing. Asphaltene and scale precipitation from the reservoir fluids can also cause formation damage problems (i.e., pore throat plugging and wettability alteration) in the reservoir and near-wellbore region. These factors affect the economics of the project by lowering the production rate and requiring remediation. Application of improved oil recovery techniques such as waterflooding and miscible gas flooding has also increased the chances of scale and asphaltene formation in the wellbore and near-wellbore region. In this dissertation, we developed an integrated compositional coupled wellbore-reservoir simulator to accurately predict the detrimental effects of asphaltene and scale deposition on production performance of the oilfields. The simulation results illustrate the time and the location at which asphaltene and scale deposition damage the efficiency and productivity of the production wells. This prediction is highly crucial to monitor the production performance of the field, to optimize the field operating condition which leads to minimum asphaltene or scale formation, and to propose the effective remediation techniques. The developed wellbore model has the flexibility to work in standalone mode or in conjunction with the reservoir simulator. To accurately model the asphaltene phase behavior as a function of pressure, temperature, and hydrocarbon fluid composition, PC-SAFT equation-of-state is implemented into a non-isothermal, multiphase, multi-component compositional wellbore simulator (UTWELL). PC-SAFT models asphaltene precipitation by performing a three-phase flash calculation to determine the formation of the second-liquid phase or asphaltene-rich phase. Flocculation and deposition models are also integrated with the thermodynamic models to mimic the dynamics of asphaltene deposition during multiphase flow in the wellbore. In addition, the computational time of the reservoir simulator (UTCOMP) with PC-SAFT EOS was improved by parallelizing the phase behavior module. To investigate the dynamics of asphaltene deposition under fluid flow condition, several mechanisms such as asphaltene precipitation, asphaltene deposition, porosity and permeability reduction, wettability alteration, and viscosity modification were included in the developed model. For mechanistic modeling of scale deposition in the wellbore, a detailed procedure is presented through which a comprehensive geochemical package, IPhreeqc, is integrated within the wellbore simulator. The integrated model has the capability to model reversible, irreversible, and ion exchange reactions under non-isothermal, non-isobaric, and local equilibrium or kinetic conditions inside the wellbore. In addition, the effects of hydrocarbon components and weak acids dissolutions in the aqueous phase are included in the integrated model to accurately predict scale deposition profile. Moreover, the developed wellbore model and the reservoir simulator were coupled to investigate the effects of key parameters such as pressure, temperature, hydrocarbon fluid composition, aqueous phase composition, breakthrough time, particle transportation, and flow dynamics on asphaltene/scale precipitation and deposition. The coupled wellbore-reservoir model can also be applied to achieve the optimum solution (e.g., operating condition, injection water composition, injection gas composition) with minimum asphaltene/scale problems in the production system. Finally, continuous chemical injection model was implemented within the wellbore simulator to investigate the effectiveness of chemical injection on prevention of asphaltene precipitation. The simulation results revealed that proper selection of the type and injection rate of solvent can minimize asphaltene deposition in the wellbore


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