Abstract

Produced water is routinely re-injected into many producing or disposal formations as a portion of ongoing operations. The inherent success of these operations is conditional on the ability to successfully inject the required volume of water in an economic fashion below the fracture gradient pressure of the formation under consideration. Many issues affect the success of a potential injection project, including well placement, geometry, and inherent formation quality and relative permeability characteristics. In addition to these factors, poor injection or disposal water quality can compromise the effective injectivity of even high quality sandstone or carbonate formations, resulting in economic failures and the need for costly workovers and recompletions on a regular basis to facilitate injection operations. This paper reviews the state of the art in diagnosing and evaluating injection water quality, and determining the effect of various potential contaminants such as suspended solids, corrosion products, skim/carryover oil and grease, scales, precipitates, emulsions, oil wet hydrocarbon agglomerates, and numerous other phenomena that can result in the degradation of injectivity. Screening criteria are presented, which review the process of analyzing the quality of a given injection or disposal formation, and the associated injection and disposal water. Suggestions for improving water quality, when required, are provided.

Introduction

Water injection has been used worldwide as a means of pressure maintenance for improving recovery of hydrocarbons, as well as to dispose of unwanted produced water from oil and gas wells in an environmentally responsible fashion. Conditional to the success of this process is the ability to inject the required volume of water into the porous formation of interest at a pressure; in most cases, under the fracture pressure gradient of the reservoir (toaintain good conformance of the injected water within the target formation).

A number of reservoir issues can obviously impact the ability to inject into the formation of interest, including inherent permeability, relative permeability effects associated with initial immobile fluid saturations, stress-induced issues, etc.(1) Mechanical formation damage issues associated with fines migration may also be problematic(2).

In many cases, even if formation character and reservoir parameters are favourable, injection rates are compromised due to quality problems with the injected water. The purpose of this paper is to review common water quality problems, describe how they may impact potential injectivity in a water injection /disposal well, and then indicate screening and design criteria for acceptable water quality evaluation purposes.

Injection Water Sources

Water that is injected into porous formations for waterflood or disposal purposes can be sourced from a number of locations. The source of the water, its temperature and pressure path during production and injection operations, compatibility issues between blended waters, and possible seasonal variations in the water quality are all issues which may affect the overall quality of the injected water from a damage/impaired injectivity perspective.

Common sources of injection/disposal water include:

  • Produced formation water(s)

  • Surface water sources (lakes, rivers, ocean, etc.)

  • Shallow groundwater (potable)

  • Deeper "wet" formations which act as water sources

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