Abstract

Injecting oilfield waste into suitable receiving formations is an effective and environmentally acceptable method to dispose of drilling and production waste including cuttings, drilling fluids, produced water, emulsions and other produced waste. Traditionally, solid waste is degraded to less than 300 microns and suspended as water-based slurry containing 20% solid matter. Rheological properties are controlled so that the slurry can be injected, typically using triplex pumps, under high pressure (1000 to 5000 psi) through a casing annulus or tubular into hydraulic fractures. At locations, where injection pressures are within limits and the disposal well and domain may cope, or be benefitted with higher rates of injection, increases in the rate of disposal is beneficial to operations due to the increased efficiency allowing faster ROP's or faster evacuation of waste storage devices.

This paper discusses the suitability and application of multistage centrifugal pumps for drilling waste injection and provides some data obtained during real time waste injection operations using multistage centrifugal pumps in parallel installation with traditionally used triplex pumps. Wear data in conjunction with engineering economic evaluation will be discussed. Slurry viscosity and particle size data will be presented to show the effect of pump shear on slurry properties and the implications for waste injection.

A multistage centrifugal pump proved capable of pumping waste slurry continuously at relatively high rates for a limited trial period of time. A multistage centrifugal pump provides a continuous flow without the pulsation normally associated with using a reciprocating plunger-style pump and the need to have such pulsation dampened. Laboratory testing and real-time subsurface injection data at an offshore installation indicates that multistage horizontal centrifugal pumps may offer some benefits compared to traditional reciprocating triplex plunger pumps. Some operations requiring relatively high flow rates with flow media containing solids may benefit from implementation of this style pump providing the net power requirement and equivalent downhole pressure requirement are within the pump design range, and there is available footprint at the location.

Oilfield waste can be disposed of in an environmentally responsible manner under zero-discharge conditions with the performance of the pump ensuring operational reliability and injection assurance. Operations on a global scale may benefit from this new application for multistage pumps. Decreased downtime together with slurry stability and controlled injection assures operational performance and cost effectiveness, enabling oilfield waste to be disposed in a safe, controlled and environmentally responsible manner.

Introduction

Since it was first tried in the mid-1980s in the Gulf of Mexico, waste injection (WI) has developed into a strong segment of environmentally responsible drilling waste management operations. Waste management system hierarchy favors waste reduction through reuse-and-recycle rather than disposal to mitigate environmental burden with associated long-term implications and waste ownership burden. Compared to surface disposal, WI uses subsurface injection and permanent placement of disposed materials into hydraulically fractured receiving stratum or adequate formation downhole. Such operations performed by qualified and experienced operators have been proven on multiple locations around the world to be secure and compliant with zero-discharge demands on land and offshore.

Although the injection of cuttings and other drilling wastes into suitable formations may not be applicable for every drilling operation in every region (Guo and Nagel 2009), it may be considered not only viable, but the preferred option in environmentally sensitive, remote or otherwise challenging locations. Examples are found in the North Sea, where other drilling waste disposal options are cost prohibitive or noncompliant with regulatory requirements implemented in a region.

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