Abstract

There are numerous water shut-off techniques available. One of these is to permanently seal watered-out zones with rigid, polymer gelants. This method can be very effective for near-wellbore water flow problems provided the gelant only enters the watered-out interval and does not damage nearby productive pay. Gelant placement can frequently be controlled using mechanical devices such as packers and bridge plugs. However, many times, gelant may still enter productive pay through flow paths outside the casing. For such cases, mechanical isolation within the well may not suffice - especially if crossflow between zones is high. In this paper we discuss a specialized gelant placement technique, referred to as dual injection, that can be used to address these types of water control problems. Dual injection can be implemented several ways. We discuss some of these, as well as a completely new dual injection system.

Introduction

Numerous techniques exist for solving water production problems. These range from simple mechanical means such as bridge plugs and casing patches, to more elaborate schemes involving downhole separation, dual production, and horizontal drilling. Injection of polymer gelants is also a widespread practice.

Polymer gelants can be deployed a variety of ways. By far the most pervasive is to pump down the existing production tubing without any zonal selectivity (viz., "bullheading"). This procedure is operationally attractive because it is easy to implement and treatment costs are comparatively low. However, gelant is distributed among all perforated zones. This is undesirable because many gelants - particularly those intended for near-wellbore applications - will indiscriminately and permanently damage all porous media when gelation or setting occurs.

Mechanical isolation of perforated intervals with packers and bridge plugs, or sand/calcium carbonate fill is preferred over bullheading. Often however, flow can still occur between perforated intervals through flow paths outside the casing. In such cases, mechanical isolation may not suffice. In this paper we will discuss a specialized placement technique, referred to as dual injection, that can be used to address water control problems in such cases.

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