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Experimental and Modeling Investigation of Liquid Bridge Formation and Stability in Fractures During Gas Injection in Fractured Reservoirs

Harimi, Behrouz | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53619 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Masihi, Mohsen; Ghazanfari, Mohammad Hossein
  7. Abstract:
  8. Gas injection is known as a promising Enhanced Oil Recovery (EOR) method for oil recovery in naturally fractured reservoirs. Gravity drainage is the main production mechanism in such reservoir, which also is affected by molecular diffusion in the case of non-equilibrium gas injection. Formation of liquid bridge in fractures between overlying matrix blocks leads to capillary continuity between blocks and subsequent increase of oil recovery. The aim of this study is to determine the required conditions for formation, stability and fracture capillary pressure of liquid bridge and investigation the role of fracture surface roughness, wettability, oil and gas properties, flow conditions and mass transfer. In this respect, a one-dimensional model based on slender drop theory is employed which holds gravity, viscous and surface tension forces but ignores inertia. This model together with Young-Laplace equation gives the fracture capillary pressure. Then, the effect of liquid influx rate, viscosity, surface tension, density difference, contact angle and contact radius on the shape, critical (or maximum) volume and length of travelling liquid drops is analyzed and is compared with the results in the absence of flow (i.e. pendant drops). Critical length is shown to be an increasing function of both liquid viscosity and influx rate but the effect of surface tension and density is somewhat case dependent. Also, Fracture capillary pressure is shown to be remarkable in thin fractures (with aperture less than 50 microns) embracing liquid bridge. On the other hand, the suspended oil drops, even when reaches to its critical length, cannot provide a considerable capillary pressure. Then, new models of rough-walled fracture are developed and the role of roughness size and frequency on formation of liquid bridge and fracture capillary pressure are investigated. The Young-Laplace equation is numerically solved to characterize the liquid bridge formed in the proposed models of rough fractures. Critical fracture aperture for a range of liquid saturations, various roughness models and wettability conditions, is computed. Moreover, an expression is proposed to predict critical fracture aperture as a function of liquid saturation and contact angle for different models of rough fracture. The results also revealed that fracture capillary pressures as high as 1 psi (6.9 KPa) are viable when liquid saturation in the fracture is low (< 5%) and fracture is sufficiently thin. Increasing wettability to liquid phase decreases the critical fracture aperture and enhances the fracture capillary pressure. Also, a semi-empirical model for capillary pressure as a function of effective fracture aperture, fracture roughness, contact angle and liquid saturation is proposed. Evaporation from the surface of liquid bridge into the surrounding gas could affect the curvature of interface of liquid bridge and in consequence fracture capillary pressure. By the aid of analogy between the diffusive flux and electrostatic potential, a new model for predicting evaporation rate from a liquid bridge inside a horizontal fracture is presented. The proposed model is then coupled with Young-Laplace equation to evaluate volume, shape and capillary pressure of liquid bridge as evaporation proceeds. Close agreement observed between model predictions and experimental data of evaporating liquid bridges confirms reliability of the assumptions and the methodology made in model development. For the first time the impact of presence of solid substrate on evaporation rate as a function of liquid bridge volume, length and contact angle is described by a new mathematical expression. It has been found that transient behavior of fracture capillary pressure for a more realistic mode of evaporating liquid bridge, in which both contact angle and radius change, indicates an initial increase, reaching to a maximum value, which is in contrast to fixed contact angle mode, and finally a sharp decrease before rupture of bridge. For liquid bridges with sufficient initial volume in thin fractures, stability period is prolonged and fracture capillary pressure value are greater, resulting a higher degree of capillary continuity. Results of this study could help to better understand the fundamentals of block-to-block interaction in the presence of liquid bridges which is important to predict oil recovery of fractured reservoirs more precisely
  9. Keywords:
  10. Capillary Continuing ; Fractured Porous Media ; Mathematical Modeling ; Molecular Diffusion ; Experimental Investigation ; Liquide Bridge

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