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Mechanistic Investigation of Enhanced Oil Recovery by Engineered Water Using Computational Fluid Dynamics at Pore Scale

Namaee Ghasemi, Arman | 2022

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55895 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering Department
  6. Advisor(s): Ayatollahi, Shahaboddin; Mahani, Hassan
  7. Abstract:
  8. Despite the proven advantage of the engineered water flooding technique, a coherent and mechanistic understanding of the fundamental phenomena occurring at pore scale is lacking. Most of the available simulation models have a phenomenological approach and have limited predictive capability. One of the key questions is how to justify and relate large (Darcy) scale observations to effects and phenomena that essentially occur at much smaller scales (i.e. pore and molecular level). Furthermore, two-phase flow dynamics and the effect of complex interplay between wettability, capillary number, and ions dispersion in a heterogeneous porous medium on the trapping and mobilization of oil at pore scale are not well understood. A deeper investigation of the pore scale as an intermediary scale and the phenomena governing it can have a crucial role in resolving the existing ambiguities. In this dissertation, the mechanistic simulation of engineered water flooding at pore scale of is pursued in order to obtain a deeper and fundamental understanding of the ongoing phenomena and parameters affecting oil recovery. Two-phase flow is modeled by direct solution of the governing equations using the volume-of-fluid method coupled with species transfer in OpenFOAM software. The effect of engineered water is captured in the flow model by means of conceptual wettability alteration models and then through implementation of a mechanistic model using in-situ contact angle calculation from augmented Young-Laplace equation based on the DLVO theory, disjoining pressure notion, and double-layer expansion. Moreover, the slow process of wettability alteration from oil-wet to water-wet was taken into account via appropriate boundary conditions at the rock-brine-oil interface. Fundamental and well-known porous media models such as pore-doublet and successive pore-throats were used to carry out the simulations. In the first part of the results, the interplay between the effects of wettability, salt dispersion, and capillary number was studied. In the second part, the interplay and relationship between the pore structure, time scale, and injection scenario in the engineered water method were also investigated. The results show that even in a simple pore structure, various low-salinity recoveries and pore-filling sequences are obtained based on the pore geometrical factors, wettability alteration trend, effective salinity range, time effects, backward mixing, and injection scenarios. Based on the wettability state (especially at the outlet side of the system), balance of forces, and dispersion regime, the mobilized oil may flow past the conjunctions (favorable) or in the backward direction (unfavorable) and get retrapped. Moreover, backflow and backward mixing were introduced as a significant phenomenon in the effectiveness of LSWF. In tertiary mode, the salt dispersion pattern in the flowing region controls the wettability distribution and the rate and magnitude of oil recovery from the stagnant region. Secondary LSWF, on the other hand, results in higher ultimate oil recovery since both small and large pores are accessible to flow, dispersion and mixing of the injection front is lower, back-flow occurs to a lesser extent, and ultimately, breakthrough time is delayed. Moreover, it was observed that the low salinity effect on oil recovery becomes more pronounced when capillary number is less than 10-5, and the dispersion regime is in the power-law interval. Therefore, it is essential to carry out the simulations at a low capillary numbers such as 10-6 and 10-7. According to the pore-throat geometry, the case with large pores connected by large throats generally exhibits higher ultimate recovery. However, the geometry with large pores connected via small throats leads to a higher incremental recovery by tertiary engineered water flooding. Furthermore, there exists an optimal time scale in secondary engineered water flooding, while in the tertiary case, faster low-salinity effect will result in higher oil recovery. Based on this, the proposed mechanistic approach is able to improve the previous models, correctly account for the engineered water effect, and closely predict its subsequent flow dynamics. Ultimately, the proposed model is capable of capturing the low salinity effect, and providing more accurate and realistic predictions of the flow dynamics, pore-filling patterns, and oil recovery mechanisms. On this basis, the results of this research can be regarded as an important step towards better predictions, with the aim of designing and applying the engineered water flooding method to increase oil recovery at reservoir scale
  9. Keywords:
  10. Pore-Scale Model ; Direct Numerical Simulation (DNS) ; Two-Phase Flow Modeling ; OpenFOAM Software ; Derjaguin-Landau-Verwey-Overbeek (DLVO)Theory ; Disjoining Pressure ; Wettability Alteration ; Wettability Alteration Time-Effect ; Salt Dispersion ; Mechanistic Wettability Alteration ; Pore-Doublet Model

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