Abstract

A unique diverting aid has been successfully used to reduce the incidence of acidizing into water in limestone and dolomite reservoirs. Proper application of this diverting aid has allowed excellent stimulation of hydro-carbon bearing formations previously only receiving very limited stimulation.

Results of field tests over a period of two years will allow those interested the opportunity to evaluate the economics of this material. Some advantages appear to be minimal stimulation of water zones, maintained production and reduced GORs.

Introduction

Almost since acidizing was introduced by Herman Frausch in 1896, people in the oil patch have been trying to get acid to open up only hydrocarbon bearing zones.

Most carbonate reservoirs, where acid is commonly used to stimulate. have either a natural water drive or a water flood drive. Production of water is costly, and lifting, corrosion, treater (water knock out) and re-injection costs are rapidly increasing. Water production in a carbonate reservoir so has a tendency to leach out the formation and further increase the problem. Acidizing only hydrocarbon bearing zones allows increased production of that valuable energy source without increased production of water.

The objective of this paper is to describe a procedure of selectively acidizing only hydrocarbon bearing zones.

THEORY

The theory of acidizing only hydrocarbon bearing zones is an excellent one. [Jut how does one apply it in the field.

There are several methods that can be used to stimulate only known hydrocarbon bearing zones. The approach that has been used for this process here is to place a blocking material in the formation that sets up only in water. This prevents the acid from entering the water bearing zones.

Some material requirements are listed below.

  1. The material to be pumped into the formation should have as low a viscosity as possible. This will allow penetration of even low permeability sections.

  2. The material has to be able to set up quick enough when it comes in contact with water so that it does not set up several metres from the well bore leaving the well bore area exposed to acid.

  3. The material cannot act up instantly, when it contacts water, as it would plug only the well bore and perforations, thus giving no protection in that first one half metre to one metre around the wellbore.

  4. The material cannot remain in the hydro carbon bearing zone. It must break down to permit production of the hydrocarbons.

MATERIAL DESCRIPTION

The generic description of the base product is a blend of oxyalkylatcd alkylphenols and fatty amine salts in a solvent blend of isopropyl alcohol and other hydrocarbon solvents.

The physical description of the base product is a concentrated, hydrocarbon soluble, cationic surfactant.

The base product is mixed with a clean, dry hydrocarbon, such as diesel; at a ratio of 5% to 40% by volume. This field mix functions by forming a gelatinous mass. When it comes in contact with formation or fresh water.

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