ABSTRACT
Computer software is used extensively to increase productivity and
reduce man’s hours of labour. This work presents the development of a
solids control software (SOLCON) which is designed for real time mud
system management and quick performance of routine rig computations:
determination of total solids and low gravity solids content; mud
property and density control requiring optimal ejection rate into the
mixing pit; volume of mud and amount of barite, bentonite and additives
to be added during the upgrading process of the mud. This software has
the ability to evaluate the need for dilution depending on the maximum
allowable drilled solids, viscosity and recommended total solids in the
drilling fluid.
Finally, this software provides the atmosphere to control drilled
solids as quickly as possible with all the necessary parameters.
CHAPTER ONE
FORMULATION OF THE PROBLEM
1.1 Introduction
Drilling fluid was introduced into the rotary drilling technology as
means of transporting the drilled solids to the surface. Other function
of the drilling fluids are controlling subsurface pressure, lubricating
the drill string, cleaning the bottom of the hole, aiding in formation
evaluation protecting formation productivity and aiding formation
stability (Moore, 1986). One major function of the rig circulation
system is the removal of drilled solids from the drilling mud before
recirculation because of the adverse effects the drilled solids have on
the drilling rate. One way of reducing drilling cost is the maximization
of drilled solids removal from the drilling fluid (Field, 1972).
For sometimes now the industry has battled with various
unsatisfactory solutions to the problem of solids control. These
included the following:
1. A piecemeal, temporary and very expensive way to reduce
solids content is by discarding part of the system and rebuilding
volume with added solids, water and chemical additives.
2. The use of „inhibitors‟ such as lime and polymers to
reduce the contribution of drilled solids to mud. Generally, these
materials only delays the time when a mud must be discarded.
3. A benefit more apparent than real way is the use „thinners‟. Thinners can reduce
the gel strength and the yield point of the mud (Nelson, 1970).
There are direct and indirect costs associated with drilled solids.
The direct cost involves dilution and discarding of the excess volume of
mud. The indirect cost is connected to the increase mud weight
resulting from the presence of drilled solids in the drilling fluid.
This may results in pressure differential between the drilling fluid and
the formation fluid and hence reduction in rate of penetration. A
reduction in hole cleaning ability as result of an increase in plastic
viscosity may also lead to reduction in rate of penetration and
generation of finer cuttings (Wells, 1976). Low rate of penetration
increases rig time and in tend increase the cost of drilling. In order
to maintain a low specific gravity of solids in the drilling fluid,
about one- quarter of the volume of the drilling fluid containing the
drilled solids is removed.
The three basic way to control the concentration of drilled solids in
drilling fluids are; removal of solids, adding solids or their
equivalent and treating solids chemically. Soluble solids and clay is
added to increase yield point, gel strength, plastic viscosity and
decrease filtration rate with minimum weight increase. To increase the
density of the mud, barite is added with minimum effect on the mud
properties and solid volume.
It is necessary to control the concentration of the drilled solids in
the drilling fluid before returning it in to the drill pit. The more
effectively the solids are mechanically removed the less dilution and
hence the lesser the chemical treatment required (Moore, 1986).