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Evaluation of the Impact of Rock Heterogeneity on the Efficiency of Engineered Salinity Water Flooding

Toupchian, Amin | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54864 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan; Ayatollahi, Shahaboddin
  7. Abstract:
  8. Low salinity water flooding (LSWF) is one of the enhanced oil recovery (EOR) methods that can be applied in both secondary and tertiary recovery techniques. Some reports indicate no incremental oil recovery associated with this method, and the reason can be associated with the binary and tertiary interactions between oil-brine-rock (OBR) systems. In some OBRs, the initial conditions are not favourable in terms of initial wettability. One of the key factors is the local rock heterogeneities in permeability and mineralogy which can affect LSWF performance because the microscopic and macroscopic heterogeneities can impact the flow pattern of the injected water, oil displacement efficiency, and residual oil. In most of the published experimental research in the LSWF area, homogenous rocks are used to help interpret the results. However, there is lack of understanding of the effect of rock grain size heterogeneity on the LSWF performance. This is researched for the first time, to our knowledge, in this thesis. To fullfil this aim, a systematic series of coreflooding experiments were performed using artificial calcite core plugs to investigate the impact of grain size and its heterogeneity on the oil recovery with different brines. High salinity formation water of Koupal oil field of Iran, Persian Gulf seawater, and 4 times diluted seawater were used in the experiments. Homogeneous core plugs with grain sizes ranging from 38 to 75 microns and 75 to 125 microns were fabricated and used to investigate the effect of grain size on the LSWF process, and the heterogeneous core plugs were made with mixing the grains with sizes ranging from 38-75 with 75-125 microns to investigate the effect of grain size heterogeneity.The experimental results revealed that the injection of high salinity water (HSW) in heterogeneous plugs compared to the homogenous cases leads to low oil recovery factors, %39 and 52%, respectively. This result can be attributed to the likelihood of bypassing of the oil and oil trapping in heterogeneous core plugs. In contrast to HSW, the injection of low salinity water (LSW) in the heterogeneous plugs had better performance in oil recovery resulting in a 10% incremental recovery factor compared to HSW. The main finding is that although LSW had a better performance in heterogeneous cores, the overall (ultimate) recovery factor of was lower in these plugs, indicating the significant impact of grain size heterogeneity (or microscopic heterogeneity) on the flooding performance. In other words, grain size heterogeneity will lower the efficiency of the waterflooding process in both HSW and LSW. Another important outcome of this research is that injection of LSW in secondary mode is far better than that in tertiary injection mode after HSW, especially in cores with heterogeneous grain sizes. Thus it is recommended that to inject LSW as early as possible (i.e. secondary mode) to improve the oil recovery
  9. Keywords:
  10. Enhanced Oil Recovery ; Low Salinity Water Flooding ; Wettability ; Grain Size ; Low Salinity/Smart Waterflooding ; Gas Flotation ; Core Heterogeneity

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