The successful completion of an oil well depends to a considerable
extent on the properties of the drilling fluid. The cost of the drilling fluid
itself is relatively small in comparison to the overall cost of drilling a
well, but the choice of the right fluid and maintenance of its properties while
drilling profoundly influence the total well costs. Drilling mud, the fluid
mixture used in rotary drilling, is as important to petroleum resource
development as blood is to the  human
body. Important conditions that drilling mud affects include the cleaning of
cuttings from the wellbore, controlling subsurface pressures, reducing
reactivity and instability  of the
formation, and reducing fluid loss into the formation2.

Water was the first drilling fluid, and its usage is documented back to
the ancient Egyptian and Chinese cultures and simple rotary tool drilling. A
few patents in the 1800s further mention the use of a drilling fluid in early
rotary drilling designs. Ancient rotary water well drilling would have made mud
as the water mixed with natural clay deposits, and observations on its superior
ability to clean the hole versus water alone were probably noted. The petroleum
drilling in Corsicana, Texas (the 1890s), and Spindle top, Texas (1901),
indicate the use of natural drilling mud (drilling mud from the local clays)
was an established part of rotary drilling by this time2.

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Technical descriptions of the U.S. Bureau of Mines in 1913 and 1914 were
the beginning of a long history of the science and engineering of drilling mud
usage. The first major changes to drilling mud occurred in the 1920s with the
addition of weighting materials (barite, iron oxides) and usage of mined
bentonite clays. This gave birth to the rise of first commercial drilling mud
companies such as NL Baroid. The 1930s was the true beginning of engineered
drilling mud in response to deeper and more difficult drilling conditions. Oil
companies developed major research programs in mud design during this time
frame. Major geologic and borehole conditions that required new mud designs
included over pressured formations, unstable heaving shales, and hydrocarbon
traps along salt dome flanks2.

After World War II, training of field personnel for better mud
management became common as did mud engineers. Another major factor in mud
design began in the 1970s when new environmental regulations began defining
what was chemically acceptable in coastal and offshore mud disposal. This
initiated various studies and publications concerning mud chemistry and
toxicity from the 1970s onward, and also gave rise to some mud modifications
where mud/cuttings discharges were allowed2.

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. 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”2.

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

With advances in technology, refinement in the
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 the 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 pass2.

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 East2.

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