Waste Minimization for Land-Based Drilling Operations
Authors: Thurber Neal E. 
Published: December 2007

This paper discusses engineering variables that should be addressed to minimize waste-toxicity and -generation while drilling land-based wells. Proper balance of these variables provides both operational and environmental benefits.

Introduction

Increasing public awareness of environmental issues has focused attention on methods to improve the environmental performance of land-based drilling operations. Waste minimization, a concept that may be used to accomplish this goal, motivates waste generators to minimize waste volumes and/or waste toxicity before disposal. This paper describes effective techniques for waste minimization, emphasizing the reduction of drilling-related waste toxicity and volumes.

The higher level of environmental performance achieved by the reduction of waste toxicity and volumes involves further operational benefits of potential cost savings from reduced drilling-fluid dilution requirements, waste-disposal costs, reserve-pit construction, and reclamation costs.

Drilling-Waste Characterization

Drilling waste comprises about 2% of the U.S. E&P waste stream.1 API estimated that 62% of drilling fluids are freshwater based, 24% salt based, 6% oil based, and the remainder of various compositions.1 Both the U.S. Environmental Protection Agency (EPA) and API studied the drilling-waste stream extensively and identified arsenic, benzene, sodium, cadmium, chromium VI, boron, and chloride as the constituents that pose the greatest human health and environmental risks.2 Other constituents, such as barium, lead, and pentachlorophenol, were identified; however, low concentrations and mobility considerations suggested low risks. Drilling-waste densities can vary widely, from about 8.5 to 16 lbm/gal [1018 to 1916 kg/m3]. Drilled cuttings may be generated at rates as high as 38 ton/hr [9.58 kg/s].

The drilling-waste stream principally includes drilled cuttings, excess or spent drilling fluid, rig wash, precipitation that enters the reserve pit, water from such rig activities as pump lubrication, and wastes from cementing operations.1

In addition, time plays a significant role in drilling-waste generation; deeper or slower drilling operations tend to create greater variability in waste-stream quantity and complexity. The operational role and chemical composition of drilling fluids are covered in Ref. 3.

Drilling-Fluid Waste Minimization

Toxicity Reduction.

Data from the EPA and API indicate that water-based drilling wastes typically exhibit low toxicity.1,2 Several constituents of concern were identified, however, and may be traced to either drilling-fluid additives or on-site waste-management practices. The constituents often can be reduced or eliminated by substituting different additives that do not contain any constituents of concern.

Table 1 lists several generic drilling-fluid additives, the constituents of concern, and possible substitutes.4 The waste-minimization practice of toxicity reduction may be accomplished by not using additives with a toxic or hazardous constituent. Therefore, the drilling-fluid vendor should be consulted before a drilling project so that less toxic or less hazardous drilling-fluid additives may be chosen. For example, polymer additives, such as polyacrylamides, are suggested to replace chrome-based fluid-thinning additives.

As shown by Bray5 in Gulf of Mexico operations, substantial progress in drilling-fluid toxicity reduction has been brought about by the EPA Region VI requirements for bioassay testing of drilling fluids and an LC50 of 30,000 ppm or greater for discharge. Careful screening and product substitution by Bray resulted in fluid LC50's that commonly approach 1 million ppm. Fig. 1 shows a typical additive screening, while Figs. 2 and 3 how overall progress in reducing fluid toxicity on a per-well basis.

While bioassay testing of every drilling-fluid additive with every potentially exposed organism is not feasible, drilling-fluid vendors have sufficient data to identify additives of concern and to recommend those with the least toxicity. Once these additives have been selected, additional additives should be used only when their effect on the waste stream has been determined. Careful additive selection also reduces the demand for existing toxic additives, which in turn can reduce the pollution associated with the toxic product's manufacture and its mismanagement during transportation and storage.

Toxicity Reduction.

Data from the EPA and API indicate that water-based drilling wastes typically exhibit low toxicity.1,2 Several constituents of concern were identified, however, and may be traced to either drilling-fluid additives or on-site waste-management practices. The constituents often can be reduced or eliminated by substituting different additives that do not contain any constituents of concern.

Table 1 lists several generic drilling-fluid additives, the constituents of concern, and possible substitutes.4 The waste-minimization practice of toxicity reduction may be accomplished by not using additives with a toxic or hazardous constituent. Therefore, the drilling-fluid vendor should be consulted before a drilling project so that less toxic or less hazardous drilling-fluid additives may be chosen. For example, polymer additives, such as polyacrylamides, are suggested to replace chrome-based fluid-thinning additives.

As shown by Bray5 in Gulf of Mexico operations, substantial progress in drilling-fluid toxicity reduction has been brought about by the EPA Region VI requirements for bioassay testing of drilling fluids and an LC50 of 30,000 ppm or greater for discharge. Careful screening and product substitution by Bray resulted in fluid LC50's that commonly approach 1 million ppm. Fig. 1 shows a typical additive screening, while Figs. 2 and 3 how overall progress in reducing fluid toxicity on a per-well basis.

While bioassay testing of every drilling-fluid additive with every potentially exposed organism is not feasible, drilling-fluid vendors have sufficient data to identify additives of concern and to recommend those with the least toxicity. Once these additives have been selected, additional additives should be used only when their effect on the waste stream has been determined. Careful additive selection also reduces the demand for existing toxic additives, which in turn can reduce the pollution associated with the toxic product's manufacture and its mismanagement during transportation and storage.