Pore-Scale Modeling of Wettability Effects and Their Influence on Oil Recovery

Abstract

The wettability of a crude oil/brine/rock system influences both the form of petrophysical parameters ͑e.g., P c and k rw /k ro ) and the structure and distribution of remaining oil after secondary recovery. This latter issue is of central importance for improved oil recovery since it represents the ''target'' oil for any IOR process. In the present study, we have developed a three-dimensional network model to derive capillary pressure curves from nonuniformly wetted ͑mixed and fractionally wet͒ systems. The model initially considers primary drainage and the aging process leading to wettability alterations. This is then followed by simulations of spontaneous water imbibition, forced water drive, spontaneous oil imbibition and forced oil drive-i.e., we consider a complete flooding sequence characteristic of wettability experiments. The model takes into account many pore level flow phenomena such as film flow along wetting phase clusters, trapping of wetting and nonwetting phases by snapoff and bypassing. We also consider realistic variations in advancing and receding contact angles. There is a discussion of the effects of additional parameters such as the fraction of oil-wet pores, mean coordination number and pore size distribution upon fractionally and mixed wet capillary pressure curves. Moreover, we calculate Amott oil and water indices using the simulated curves. Results indicate that oil recovery via water imbibition in weakly water-wet cores can often exceed that obtained from strongly water-wet samples. Such an effect has been observed experimentally in the past. The basic physics governing this enhancement in spontaneous water imbibition can be explained using the concept of a capillarity surface. Based on these theoretical calculations, we propose a general ''regime based'' theory of wettability classification and analysis. We classify a range of experimentally observed and apparently inconsistent waterflood recovery trends into various regimes, depending upon the structure of the underlying oil-and water-wet pore clusters and the distribution of contact angles. Using this approach, numerous published experimental Amott indices and waterflood data from a variety of core/crude oil/brine systems are analyzed.

Network Modeling of EOR Processes: A Combined Invasion Percolation and Dynamic Model for Mobilization of Trapped Oil

“…Network modeling is now used to study wide range of phenomena such as simulation of drainage and imbibition processes (Singh and Mohanty 2003), the effect of wettability (Kovscek et al 1993;Dixit et al 1999), the effect of pore structure on relative permeability and capillary pressure (Jerauld and Salter 1990), three phase flow (Fenwick and Blunt 1998), and ganglion mobilization (Dias and Payatakes 1986a,b).…”

Predictive pore‐scale modeling of two‐phase flow in mixed wet media

“…As has been noted by many authors [Chatzis and Dullien, 1977;Wilkinson and Willemsen, 1983] the coordination number will influence the network model behavior significantly, both in terms of breakthrough and relative permeability. In order to match the coordination number of a given rock sample, which typically is between 3 and 8 [Jerauld and Salter, 1990], it is possible to remove throats at random from a regular lattice [Dixit et al, 1997[Dixit et al, , 1999, hence reducing the connectivity. The pore and throat size distributions will also affect the estimated macroscopic properties.…”

Liquid water transport in a mixed-wet gas diffusion layer of a polymer electrolyte fuel cell

“…Kovscek et al (1993) were the first to propose a pore-network model incorporating the wettability alteration in a porous medium. The wettability alteration model of Kovscek et al (1993) is adopted by many researchers to investigate the effect of mixed wettability on transport properties of a general porous medium (Blunt, 1997(Blunt, , 1998Dixit et al, 1999;Hui and Blunt, 2000;Piri and Blunt, 2002). Valvatne and Blunt (2004) delineated the underlying pore-scale processes governing oil recovery from mixed-wet sandstone.…”