DRILLING FLUIDS AND THEIR ENVIRONMENTAL MANAGEMENT: CHARACTERISATION OF BASE FLUIDS AND THE INTRODUCTION OF QUALITY CONTROL PROCEDURES

Abstract

Since the early 1990s, a variety of invert emulsion base fluids have been introduced into the drilling fluid market. The chemical composition of these fluids has evolved with the focus on minimising the environmental impact of discharged cuttings that contain adhered drilling fluids.

The trend within Australia and other regions in which drilling fluids are extensively used, is that the life span of these fluids has become increasingly shorter, due to environmental impact pressures from the regulatory authorities in the North Sea and Australia, as well as public perception within these regions.

The Well Construction Department within Woodside Energy Ltd. (WEL) has identified the need to characterise these base fluids in a manner that was both reproducible and definitive. The need was driven by the availability of a large number of commercial base fluids claiming technical and environmental superiority and the requirement for robust quality control systems for the base fluids from production to discharge—a cradle to grave philosophy.

To this end, a study was initiated in 1997 where several drilling fluids were analysed using gas chromatography- mass spectrometry (GC-MS) techniques. From this work, four classifications of invert emulsion, non-water based fluids (NWBF) have been identified. They include low toxicity oil based fluids (LTOBF), enhanced mineral oil based fluids (EMOBF), synthetic based fluids (SBF), and oxygen based fluids (OBF). The definition of these fluids and the rationale for this classification is presented here.

The GC-MS characterisation has provided an insight into the structure of the base fluid, rheological characteristics, quality control/quality assurance, and in the future, the ability to develop a robust link to minimising environmental impact of the discharge.

All of these benefits will aid in developing drilling fluids which achieve the technical objectives of drilling fluids as well as minimising the environmental impact. The quality control procedures for the base fluid also allow an auditable process for benchmarking with input from the regulator, operator, fluid service company and manufacturer.