Abstract

Foam is widely used in oil and gas recovery operations as a mobility control and profile correction agent. A brief list of foam applications includes acid diversion during matrix stimulation, gas blocking, hydraulic fracturing and clean-up of contaminated subsoil. In order to meet the growing demand of more difficult foam applications a deep insight on the dynamic of foam flow in a porous media is crucial to design a successful treatment. This paper is concerned with the foam flow behavior for acid diversion application taking into account the oil presence in the treated zone.

We report an experimental study based on core-flood experiments performed with the aid of X-ray computed tomography (CT) imaging technique, using Bentheimer sandstone and N2 foam. During the experiment, the residual oil condition was first established by performing drainage process followed with gravity stable water flooding to mimic the initial fluid distribution of the treated zone. Then, N2 was injected at a constant flow rate into the porous media saturated with surfactant solution.

A series of longitudinal CT images were taken at different time intervals and pressure drop over the core was also monitored. The experiments were analyzed in terms of qualitative description of CT images, in situ liquid saturation profiles and pressure drop evolution along the core.

The experimental results indicate although foam breakthrough in the presence of oil occurs earlier than in absence of oil; however, foam generation continues, so that the liquid phase is displaced by foam flow in the treated region.

Introduction

Near-wellbore formation damaged is due to several mechanisms, including fines migration, paraffin and asphaltene deposition as well as drilling and completion fluids. The pore are plugged by particles and the permeability is reduced resulting in skin ranging from 10 to 300 [Williams 1979; Kotlar et.al. 2003].

Matrix acidizing is a method used to stimulate wells, for improving their inflow performance. The acid treatment consists in injecting a limited amount of a cid into the formation to dissolve minerals and return permeability of matrix [Williams 1979; King 1986]. The formation consists often of layers with different porosities, permeabilities and rock types. When acid is injected it naturally flows into the most-permeable, least damaged layers, and leaves the less-permeable, most damaged layers untreated.

Foam is used during matrix acidizing for diverting acid from the high-permeable layers into the less-permeable layers [Burman 1986; Thomas et.al 1998]. The goal of such a foam diversion process is to reduce the flow of acid into layers where less is needed and thereby divert it into layers more need of stimulation [Burman et.al. 1986; Nguyen et.al. 2009; Kibodeaux et.al. 1994].

Foam is a dispersion of gas in a continuous liquid phase, stabilized by surfactant. It is a highly efficient acid diversion agent for matrix stimulation operations. It is inherently non-damaging and low cost, allowing easily recursive treatments in case of an unsuccessful operation [Burman 1986; Parlar et.al. 1995].

Foam has been widely used in different oil and gas recovery operation, but the dynamic of foam flow behavior are not as well understood. Many studies of foam flow in porous media have been reported in the literature [Nguyen et.al. 2009; Kibodeaux et.al. 1994; Kam et.al. 2003; Farshbaf Zinati et.al. 2007]. However, studies of foam for acid diversion in the presence of oil are scarce.

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