Abstract

In an industry where the technical demands on a drilling fluid are ever increasing, the use of invert emulsion fluids has been seen as a necessity to meet required drilling performance criteria. At the same time there is increasing pressure to comply, and even exceed, the tightening environmental demands on our industry which has made the use and associated waste treatment of these invert fluids complex and costly. A drilling fluid, which has the drilling performance characteristics of an invert emulsion fluid, but can exhibit the benign environmental characteristics of a simple water-based fluid, has long been the goal of fluids development.

This paper describes the development and application of a unique water-based fluid that utilizes a triple inhibition approach to delivering invert emulsion-like drilling performance. Each component of the fluid system has also been designed to ensure compliance with some of the world's most demanding environmental requirements. The resulting fluid is flexible in formulation such that it can be utilized in freshwater on land wells to meet chloride discharge requirements, can be formulated in seawater for shelf wells to meet low toxicity and logistics requirements, and can be formulated in saturated salt water to meet toxicity and performance requirements for deepwater environments.

The applications of this fluid on a global basis will be evaluated, comparing the drilling performance and economics to offset wells which have utilized both conventional water-based fluids and invert emulsion fluids.

Introduction

Invert emulsion drilling fluids, also known as "oil-based muds" (OBM) and synthetic-based muds (SBM), have traditionally always been the fluids of choice when drilling demanding wells that required a fluid that ensured a high degree of wellbore stability, was capable of insuring high rate of penetration (ROP), gave good lubricity and demonstrated the lowest potential for stuck pipe. The development of a water-based drilling fluid which could exhibit similar drilling characteristics tod an invert emulsion drilling fluid has long been seen as the ultimate goal of drilling fluids research and development.

Invert emulsion drilling fluids (OBM) are universally recognized as being the most efficient fluids to drill with due to the absence of contact between the drilled formations and water, and due to the inherent oil wetting and lubricity characteristics of these fluids. The advantages of invert emulsion drilling fluids have been well documented. The major advantages are:

  • Improved wellbore stability

  • High degree of contamination tolerance

  • Improved rate of penetration

  • Low coefficient of friction

  • Thin, lubricated filter cake

  • Low dilution rates and ease of engineering

  • High degree of re-usability

The disadvantages of invert emulsion drilling fluids are typically outweighed by the advantages and have similarly been well documented. The major disadvantages are:

  • Poor environmental characteristics

  • Poor fracture sealing behavior (higher losses)

  • Density sensitive to temperature/pressure

  • Gas solubility

  • High unit cost

  • Logistical issues with bulk fluid transfers

Several water-based drilling fluid systems have been developed over the past decade that have began to close in on the goal of OBM-like drilling performance.[1–9] A few of the more successful WBMs have been:

  • Potassium/salt/glycol fluids

  • Silicate gluids

  • CaCl2/polymer fluids

  • Cationic fluids

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