Abstract

Historically, operators have very often experienced the problem of ensuring uniform displacement of the reservoir fluid by injection water. The result of poor displacement is early breakthrough to the producing well, with a subsequent reduction in the percentage of recoverable oil.

A non-polymer delayed gelling system has been developed and field tested in order to solve this problem. The characteristics of the system are very low water-like viscosities during injection, non-shear sensitivity, and a controllable gelling time.

These properties permit a deep penetration of the gel into the formation, thereby extending the profile modification further into the reservoir, and thus improving the efficiency of the treatment. A further application for this type of system is in reducing the water/oil ratio in production wells where water coning is a problem.

A field case study showing the effectiveness of this new system is also presented in the paper, with data showing the injection profile before and after the treatment.

Introduction

Many materials and techniques have been used to plug water thief zones in a multi-layered reservoir, Polymer especially polyacrylamides, based techniques (1–8) are largely used because of their relatively low east and their supposed selectivity. i.e., only the water permeability is reduced (9).

These systems are sensitive to traces of oxygen, wellbore shearing and salinity as well as the hardness of field water. Polymers are also subjected to thermal and biological degradation (5). Injectivity of the polymer fluids is poor as they have viscosities many times higher than that of water. They may not preferentially flow into the water channels and may cause placement problems. The success of their field applications are fortuitous.

Many alternative treatment fluid systems having good injectivity have: also been developed. Lignosulfonate gels (10–11) have been shown to be cost effective systems but they require a long time to form gels and arc sensitive to tcmperature and salts. Furfuryl alcohol resins (12) and polyisocyanurate salts (13) cause problems in controlling the in-situ reactions and are not removable once the gels are formed in the zones of interest. A low pH aluminum chloride solution can form a good gel when the pH of the fluid is increased (14); but the dissolution of this chemical in water generates a lot of heat and toxic acid fumes.

The new system overcomes if not all, most of the problems encountered by the systems mentioned above. Field test results show that it is very efficient in pore blocking regardless whether sandstone or fissured limestone formations very simple to mix and pump, and applicable in a wide temperature range (20 to 120 ºC).

GEL FORMATION AND CONTROL
Gel Formation

The system uses only two chemicals; both are readily soluble in any mix water including seawater. The first one is an inorganic salt used as the gelling (or plugging) agent. The second one is the activator which decomposes with time and causes the gel formation. X-ray diffraction and SEM studies showed that the gels formed by this system are extremely fine and homogeneous.

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