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Relative permeabilities hysteresis for oil/water, gas/water and gas/oil systems in mixed-wet rocks

Fatemi, S. M ; Sharif University of Technology | 2018

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  1. Type of Document: Article
  2. DOI: 10.1016/j.petrol.2017.11.014
  3. Publisher: Elsevier B.V , 2018
  4. Abstract:
  5. Accurate determination of relative permeability (kr) curves and their hysteresis is needed for reliable prediction of the performance of oil and gas reservoirs. A few options (e.g., Carlson, Killough and Jargon models) are available in commercial reservoir simulators to account for hysteresis in kr curves under two-phase flow. Two-phase kr curves are also needed for estimating kr hysteresis under three-phase flow during water-alternating-gas (WAG) injection. Although, most oil reservoirs are mixed-wet, the existing hysteresis predictive approaches have been developed based on water-wet conditions. Experimentally measured data are needed to assess the performance of these methodologies under more realistic reservoir conditions e.g. low gas-oil IFT and mixed-wet systems. This paper includes two parts. In the first part we review the most valuable works in the literature regarding the effect of hysteresis on two-phase relative permeabilities in different wettability conditions. As will be highlighted most of these data are generated on water-wet or slightly water-wet condition which are most likely not representative of the oil reservoirs. Even the generated two-phase relative permeabilities on mixed-wet and oil-wet conditions are not fully developed for the full hysteresis cycle and/or not for the all three possible systems (oil/water, gas/oil and gas/water) in one place. It is recently recommended by some of the valuable theoretical works in the literature that to enhance the predictions of three-phase hysteresis models, hysteresis for all possible two-phase systems shall be considered in the provided equations. As a result in the second part of this paper, we summarize comprehensive set of experimentally measured relative permeabilities for the two-phase systems of oil/water, gas/water and gas/oil. This set of data can be used with new three-phase hysteresis models such as that presented by Hustad and Browning (2010) to enhance the prediction of the WAG processes in non-water-wet systems. Experiments were performed in 65mD sandstone with mixed-wettability. For the gas/water system, the first set of fluid displacements began by water injection (imbibition: I) in the core saturated with gas and immobile water. This was followed by a period of gas injection (Drainage: D) which was followed by alternating periods of water and gas injections (IDIDI). In the second series, the core was initially 100% saturated with water and the experiment started with gas injection (D) followed by successive imbibition and drainage periods (DIDIDI). Similar sets of displacement experiments were performed for oil/water and gas/oil systems. The gas/oil system in our experiments represents extra low-IFT (near-miscible) system with an IFT value of 0.04 mN.m−1. The measured pressure drop and fluid production data obtained during the experiments were then history matched to estimate kr values for each imbibition and drainage period for each pair of fluids. In the oil/water system (DIDID injection sequence), krw shows cycle hysteresis which is in contrast to the common observations made in water-wet systems in which krw does not show hysteresis. In addition to krw, kro also shows significant hysteresis for the 1st imbibition period compared to the 1st drainage period but after the 1st imbibition period the kro hysteresis was not significant. In the gas/water system (IDIDI), both krg and krw decreased as the alternation between imbibition and drainage continued. The results show significant differences in the kr hysteretic behaviour in gas/water and oil/water systems. We demonstrate that the approach used in some of the three-phase simulations reported in literature, where the oil/water kr curves are used instead of gas/water kr curves (which are not normally measured) is not valid for mixed-wet systems and can lead to significant errors in prediction by reservoir simulators. Irreversible hysteresis loops were observed in our experiments even for the gas/oil system (in spite of the ultra-low gas/oil IFT) whereby krg values during each drainage period lied above the krg of the preceding imbibition. Drainage kro curves were significantly lower than their preceding imbibition kro. The observed kro cycle hysteresis diminished after the 2nd or 3rd injection cycle. The results suggest that in mixed-wet systems it is necessary to consider irreversible hysteresis loops for all phases, and hysteresis behaviour of different systems (oil/gas, water/gas and water/oil) can be different. This behaviour is not predictable by the formulations such as Land, Carlson and Killough models which are currently exist in commercial reservoir simulators. © 2017 Elsevier B.V
  6. Keywords:
  7. Mixed wettability ; Multi-phase flow in porous media ; Forecasting ; Gases ; Hysteresis ; Hysteresis loops ; Low permeability reservoirs ; Oil well flooding ; Petroleum reservoirs ; Porous materials ; Simulators ; Water injection ; Wetting ; Displacement experiments ; Hysteresis behaviour ; Hysteresis effect ; Hysteretic behaviour ; Oil and gas reservoir ; Relative permeability ; Reservoir conditions ; Water-alternating-gas injection ; Petroleum reservoir engineering ; Hydrocarbon reservoir ; Multiphase flow ; Permeability ; Porous medium ; Reservoir rock ; Sandstone ; Three phase flow ; Two phase flow ; Wettability
  8. Source: Journal of Petroleum Science and Engineering ; Volume 161 , February , 2018 , Pages 559-581 ; 09204105 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0920410517308963