Plugging of High Permeability - Fractured Zones Using Emulsions
Authors: Romero L. , Ziritt J.L. , Marin A. , Rojas F. , Mogollon J.L. , Paz E. Manrique F. 
Published: December 2007

Low crude oil sweep efficiency may be the result of channeling of injected water through high permeability sands in heterogeneous reservoirs. In these cases the efforts have been focused in improving the distribution of injected water in the wellbore through treatments using cements, gelling agents, and other short radius plugging materials. It has been proven that such treatments contribute to a better water distribution in the formation around the wellbore However, they are unlikely to be completely successful because, deeper in the formation, the fluid may divert. Laboratory and field studies have suggested that oil-in-water emulsions can be used to obtain a deeper formation plugging and this results in better sweep efficiency and a greater oil recovery. However, the suitability of this method for fractured formations remains relatively unknown.

This paper presents the second phase of a three-phase study. The first phase consisted at the formulation of a heavy oil-in-water emulsion. Alkaline solutions were used as emulsifier agents. Parameters such as alkaline solution type and concentration, oil/water ratio, and shear rate were optimized in order to obtain a stable emulsion with an average drop diameter of 3 m. The second phase comprises the laboratory evaluation of the plugging effectiveness of the emulsion. The third phase will address the development of a field-pilot test.

In order to accomplish the second phase objective, coreflood experiments were conducted at 80 C, with a confining pressure of 3000 psi and an injection pressure of 1000 psi. Various types of cores were used, including some with a longitudinal fracture.

It was observed that an undesired breakdown of the emulsion generates plugging at the core injection inlet. A flush with an alkaline conditioner is required to minimize the breaking of the emulsion before it enters the cores. This preflush has no effect on the core permeability. Externally produced emulsions injected into the cores after the pre-flush with the alkaline conditioner reduced the permeability up to 80%. No time degradation on the emulsion plug was observed even after 27 PV of water injected.

Introduction

A number of studies has proved that oil-in-water (o/w) emulsion can cause permeability reduction. McAuliffe postulated and tested in parallel cores experiments that o/w emulsions would enter the most permeable layers of the reservoirs, where it is trapped. The trapped emulsion creates enough blockage for the water injected afterwards, resulting in a diversion process the improves the overall oil recovery.

Considering an initial situation where three oil bearing layers (A, B and C) are waterflooded If one of these three layers (A) has higher permeability than the other two, most of the injected water should flow through it sweeping the oil, but leaving the other two layers (B and C) unswept. After the blockage of layer A with an emulsion, layers B and C can be swept, increasing the recovery of oil.

The only field pilot test of this process was conducted in the Midway Sunset field, California.

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