Low IFT drainage and imbibition

This paper addresses mathematical modeling of free-fall gravity drainage which is believed to occur in naturally fractured reservoirs after depletion of oil in the fractures or gas injection into the fractured system. Comparison of wetting phase recoveries calculated using existing mathematical models with experimental data indicates the inaccuracy of these models. The causes of error are identified to be the unrealistic assumptions made in formulation of the models. Based on Darcy's law and film flow theory, we have developed a new mathematical model to describe the free-fall gravity drainage process. A simple non-linear governing equation for phase demarcator in dimensionless form was formulated and solved numerically as a function of dimensionless time. Based on the dimensionless demarcator, fluid recovery during free-fall gravity drainage is calculated. Comparisons of wetting phase recoveries given by the new model with 20 sets of experimental data obtained under thermodynamic equilibrium conditions for a variety of fluids and cores show much better accuracy of the model over the existing models. Using the dimensionless time, t D = k e Δρgt/μL, fluid recovery obtained from laboratory studies can be scaled to field applications for estimation of projected oil recoveries in oil fields. We have also applied the new model to simulation of free-fall gravity drainage under non-equilibrium conditions where molecular diffusion between phases is considered. Experimental oil recovery data obtained from CO 2 injection into a Berea core and a reservoir sandstone core, which were saturated with separator oil, have been matched by the model using empirical correlations for fluid properties. The objective of this paper is to provide reservoir engineers with a useful tool for estimating the oil recovery from fractured reservoirs after gas injection.

Mathematical Modeling of Gravity Drainage After Gas Injection into Fractured Reservoirs

This paper discusses the wettability change induced by contact between porous media and drilling fluids and the possibility of eliminating such alterations by cleaning. Three porous media were studied (sandstone, shaly sandstone, and carbonate), as well as various drilling fluids (oil- and water-based). Initially strongly water-wet (hydrophilic) and initially neutral rock/oil/brine systems were evaluated. Wettability was estimated by a test based on spontaneous and forced displacement experiments. The results show that all the oil-based drilling fluids used induce a wettability change inasmuch as the rock is initially water-wet. The rock surface properties are observed to be affected at a distance >0.6 in (>1.5 cm) from the rock/drilling-fluid interface. Cleaning procedures with toluene and methanol circulations can return the rock surface to the original wettability state, but the permeability remains affected. Water-based drilling fluids made no appreciable change in the wettability of the three initially highly hydrophilic porous media.

Effect of Drilling Fluids on Rock Surface Properties

/pdf/influence-of-sequential-changes-in-the-crude-oil-water-134ubwfy.pdf

Influence of sequential changes in the crude oil-water interfacial tension on spontaneous imbibition in oil-wet sandstone

This paper presents an experimental investigation of gas-assisted gravity drainage (GAGD) performance while taking into account the effects of asphaltene deposition. The experiments were conducted at high pressures and high temperature (15–37 MPa and 102 °C) using carbonate cores and real reservoir fluids in the absence of water saturation. An 85% methane-enriched hydrocarbon gas mixture was employed as an injection fluid in the laboratory runs. The final recovery factor for a fairly tall core was 52% of the original oil at immiscible conditions during hydrocarbon gas injection when the operating pressure and the amount of injected gas were 28.3 MPa and 1.2 pore volume, respectively. In all of the experiments, the total amount of asphaltene deposition was less than 2 wt % of the original oil and no considerable reduction in permeability was found. A numerical two-phase (gas–oil) simulator coupled with a deposition model was also developed to evaluate the importance of different parameters contributing to ...

Experimental and Numerical Modeling Study of Gravity Drainage Considering Asphaltene Deposition

Gravity drainage in a fissured reservoir with fluids not in equilibrium

L'objet de cet article est la description d'une methode de laboratoire permettant l'evaluation de la mouillabilite d'une roche-reservoir vis-a-vis d'un couple eau-huile. Dans une premiere partie, on donne une definition du parametre mouillabilite et on precise les conditions requises pour le mesurer valablement, une analyse critique rapide des differentes methodes de mesure est effectuee. Elle permet de justifier le choix d'une methode qui est decrite dans la seconde partie. De nombreux exemples d'application sont donnes a titre d'illustration.

Détermination de la mouillabilité d'un échantillon de roche-réservoir

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Gravity drainage in a fissured reservoir with fluids not in equilibrium

Détermination de la mouillabilité d'un échantillon de roche-réservoir