Abstract

Produced water reinjection (PWRI) is one of the most usual ways of produced water reuse in mature fields with high water cut. The relationship between water quality and injectivity decline in wells is well known and it is particularly important in mature fields, such as Barrancas, an old field located in Mendoza -Argentina, with more than 40 years of water injection. In this reservoir significant injectivity losses were recorded when fresh water was replaced by produced water in the 90´s.

Formation Damage mechanism is mainly caused by external cake. Particles are principally, iron sulfide, calcium carbonate, and oil droplets.

Water treatment and injection well chemical stimulation are two important contributions to oil lifting cost at Barrancas. The average water quality is quite good between water treatment plant and wells. In spite of this, injection wells require regular acidic and non acidic stimulations to restore injectivity.

To identify the causes, a team effort combining field experience, chemical and bacteriological analysis, laboratory and on site core flooding test was performed.

Through this work, water quality performance between plant and down hole well at the level of perforated zones was analyzed. Oil and solids chemical dispersants were tested during core experiments to avoid fall of injectiviy.

The experimental study has demonstrated that the use of dispersants could help to maintain water quality stability at the level of case perforations. A pilot in a selected group of wells will be implemented. It is likely to be successful.

Down -hole water quality is a critical parameter as well as the on site evaluation tests. Based on the outcome new experiences and down-hole monitoring tool will be developed.

The final goal is to improve water quality stability at the level of formation, prevent injectivity decline and reduce working pressure.

Introduction

The injection of produced water (PWRI) is the main process implemented in YPF SA to recover oil in Argentina. This is one of the most important reasons for high volumes of water produced. This is particularly true when water cut increases with the field maturity.

The PWRI is an attractive option for improving oil recovery, and also to maintain pressure. Another important aspect is that produced water (PW) is an important source of minimizing environmental risks associated with water discharges. (C.J.A. Furtado, et al, 2005).

Furthermore studies have shown that the injection of produced water induces formation damage by external and internal filter cake. These mechanisms cause loss of injectivity especially PWRI matrix. (Bennion, D.B., 2001) Injectivity decline is a complex phenomenon that depends on the quality of water, conditions of injection and reservoir properties.

The water quality required will be mainly a function of permeability and pore throats size distribution. Layers of small thickness and low permeability require better water quality than the corresponding layers with high pemeability. The mechanism and extent of the blockage for a given period of time depends on the formation, type, concentration, composition, shape and size distribution of particles in suspension, in addition the flow rate and injection pressure. (F.A.A. Al-Abduwani et al, 2001)

This content is only available via PDF.
You can access this article if you purchase or spend a download.