New Drilling Fluid Technology Mineral Oil Mud
Authors: Bennett R.B. 
Published: December 2007

The use of a paraffinic-based mineral oil, in place of the conventionally used diesel oil, as the continuous phase of an oil-based drilling and spotting fluid is a relatively new concept to the drilling fluid technology of the petroleum industry. petroleum industry. Mineral-oil-based fluids possess the same characteristics but also have definite advantages over diesel-oil-based drilling and spotting fluids. These characteristics and advantages are shown by laboratory evaluations, laboratory toxicity studies, and field case histories. Laboratory toxicity tests have been conducted in both the U.S. and the U.K. Results show that mineral-oil-based fluids are considerably less toxic than diesel-oil-based fluids. Tests also indicate that oil retention characteristics of mineral-oil-based fluids are lower than diesel-oil-based fluids. Government agencies in both the U.S. and the U.K. have consented to the use of this particular mineral-oil-based fluid offshore without a particular mineral-oil-based fluid offshore without a cuttings washer as long as a water spray and flume-type oil recovery system are used. This approval is made by the U.S. Mineral Management Services (MMS) on a well-by-well basis and is independent from area to area.

Introduction

The use of oils as the continuous phase of drilling fluids is not new to the drilling fluids industry. History tells us that the first use of oil-based fluids was for their productivity applications. The first commercial oil-based fluid productivity applications. The first commercial oil-based fluid was introduced in 1942. 2 This fluid was considered a "true oil-based fluid" since it did not rely on the emulsified water as an integral component of the system. These systems were followed with the development of oil-based fluids whereby emulsified water played an integral part in providing both weight suspension and fluid-loss characteristics for the system. These oil-based fluids were called "invert emulsions. "3

Over the years both the so-called true oil-based fluids and the invert emulsions have been so refined that it is very difficult to separate the two on the basis of performance characteristics or field applications. The latest performance characteristics or field applications. The latest advance with respect to conventional diesel-oil-based fluids is the so-called "relaxed filtrate" or, more appropriately, low-viscosity/low-colloid oil-based fluids.

With advances in technology, refinement in formulation, utilization of proper application, and improvement of cost effectiveness, the use of diesel-oil-based fluids has increased over the past decade. The only drawback with use of diesel-oil-based fluids is their environmental impact; had they been environmentally safe, the advent of mineral-oil-based fluids might not have come to pass.

Mineral-oil-based fluids possess all the characteristics of conventional diesel-oil-based fluids without the associated environmental problems. The first mineral-oil-based fluid was designed as a spotting fluid for differentially stuck pipe and was commercially introduced to the market in late 1975. The first use of mineral-oil-based fluid as a drilling fluid was in 1980. Since then, mineral-oil-based fluids have been used in the Louisiana/Texas gulf coast, the North Sea, and the Far East.

Composition

Mineral-oil-based fluids are invert emulsion drilling and spotting fluids. They consist of a specially refined paraffinic-based oil phase, emulsifiers, dispersants, paraffinic-based oil phase, emulsifiers, dispersants, organophilic clays, calcium oxide or hydroxide, high-temperature stabilizer, and water. Mineral-oil-based drilling fluids can be considered to be low-viscosity/ low-colloid oil-based fluid. The collodial solids content is maintained at as low a concentration as possible. The high-temperature/high-pressure (HTHP) fluid-loss characteristics can be controlled to offer either a high filtrate (1.2 to 2.4 cu in. [20 to 40 cm3]) or an extremely low filtrate (0.12 to 0.92 cu in. [2 to 15 cm3]).

Several mineral oils on the market can be used in the formulation of mineral-oil-based fluids. However, note that not all mineral oils are acceptable for use as the continuous oil phase. The viscosity, pour point, and aromatic content are all factors to be considered. The importance of viscosity and pour-point characteristics is obvious, since the resulting mineral-oil-based fluid's viscosity and pour points are prime considerations for acceptance as a functional drilling or spotting fluid. The aromatic content is important for two reasons. First, it is thought that the aromatic fraction is the basis for which mineral oil is environmentally accepted over diesel oil. Secondly, because less-toxic emulsifiers are used, mineral oils with essentially no aromatic fractions will not make suitable or stable drilling fluids.

The emulsifiers and dispersants used in mineral-oil-based fluids are selected on the basis of toxicity. Most conventional diesel-oil-based fluid emulsifiers and dispersants will function well in mineral-oil-based fluids. However, many of these emulsifiers and dispersants are either very toxic or their respective carrying agents are very toxic. The emulsifiers and dispersants used in this mineral-oil-based fluid consist of a fatty acid amide, tall oil fatty acid, calcium sulfonate, and a modified imidazoline. All have relatively low toxicity ratings.

JPT

P. 975