Water Injection In Algeria - Problems And Solutions
Authors: Khelil C. , Delhoume A. 
Published: December 2007

The majority of oil fields in Africa and the Middle East were discovered in the 1950's. If we take into account the rate of development of these fields, we find that many of them are at the point or just about where secondary recovery or pressure maintenance becomes necessary. For that purpose, water injection is by far the most popular process. At this point we then face a major problem: availability of water. In that part of the world (Africa and the Middle East), the only sources of water available are sea water and, in most of the cases, deep brackish water, which are incompatible, from the standpoint of chemical composition, with formation water. This incompatibility might lead to disastrous scale formation that would properly kill wells and even fields. This problem will be more acute in the case of pattern injection compared with peripheral injection. peripheral injection. In order to proceed with water injection, we are left with two alternatives:water treatment before injection andchemical inhibition of scale formation.

Neither of these alternatives has been fully recognized as an effective and feasible way under prevailing economics to run a trouble-free water injection program with incompatible waters.

This paper is directed toward the engineers who may face the task of designing a water injection program where the only water source available is program where the only water source available is incompatible with formation water.

A research work currently is underway to develop a proper way to evaluate scale inhibitors under actual field conditions, in order to solve the scale formation problem around the wellbore, in the production string, and in the surface installations. production string, and in the surface installations. In the meantime, work is underway to set up a pilot for water treatment before injection.

WATER INJECTION-AN OVERVIEW

Water injection is by far the most popular secondary recovery and pressure maintenance method. Its popularity did build up in the United States and Canada, mainly because of the availability of a water source almost everywhere.

Many factors should be considered to determine the suitability of a given reservoir to waterflooding or pressure maintenance. These factors are important because they influence the economics of a given project. Some of these factors would be reservoir characteristics: rocks properties (permeability, porosity), depth, fluid saturation, etc. Factors other than reservoir characteristics also will have a great influence. In this particular case we are interested in, another factor is the availability of water. When the suitability of a given project is determined, the next important question to be answered is when a given project should be initiated. It ha been recognized that the only way to determine the optimum time to start a waterflood or a pressure maintenance program is to compute recovery, rate, investment, and income for several times of initiation and optimize on the basis of economic criteria that are specific to each company.

AVAILABILITY OF WATER

Most of the oil and gas fields in Algeria are located in the Sahara Desert. Therefore, the availability of a water source in an arid zone becomes an obvious problem, while the need for water injection is obvious for a certain number of reservoirs.

A pressure maintenance program was initiated in 1966 for the Zarzaitine Field near the Lybian border in the southeastern portion of the Illizi Basin in Algeria. The reservoir under consideration is at about 1450 m subsea, with a maximum thickness of about 70 m. It is a saturated reservoir with a gas cap. The original producing mechanism was a combination of solution gas drive, gas-cap expansion, and partial water drive.