A good solids control program is essential in order to attain the goal of an optimized drilling program. Proper application and utilization of mechanical solids removal equipment enables the driller to maintain the desired drilling fluid properties which in turn makes it possible for the drilling operation to be carried out in an efficient and possible for the drilling operation to be carried out in an efficient and economical manner.

Drilled solids have a direct and pronounced effect on the drilling fluid. Since the drilling fluid is itself so closely related to a wide range of factors which determine both daily and total drilling costs, it is obvious that there exists a strong relationship between the control of drilled solids and the control of drilling costs.

This paper will present methods to calculate the mechanical efficiency of solids control equipment on site during drilling operations and will demonstrate from case histories a method of determining the economic justification for the use of mechanical equipment.

Data presented in this Paper is based on information gained in the field evaluation of various types of solids control equipment, including sophisticated fluids processing systems, under a wide variety of weather, geographic and geologic conditions.

Introduction

The drilling industry as we know it today has evolved through a combination of trial-and-error and technology, of hard work and luck. Through more than a century of development many of the problems encountered by the pioneers in the business have been problems encountered by the pioneers in the business have been solved, or at least made bearable. The technological advances of the drilling industry are on a par with those of virtually any other industry. But there is one serious problem still facing us and it has been a problem since the earliest days. Very simply, that problem is how to get the dirt out of the hole. The removal of drilled solids from drilling fluid, or drilling mud, has been a problem since the introduction of rotary drilling rigs, The early day driller used gravity settling to accomplish solids removal, and earthen pits were a standard part of the drilling site. Drilling mud became more complex, however, part of the drilling site. Drilling mud became more complex, however, and with the use of barite as a weighting agent in the early 1930's the need for better methods of solids removal became apparent. Vibrating screens designed to remove the undesirable drilled solids while salvaging the barite and liquid mud were introduced to the drilling industry. These "shale shakers", as they came to be called, were the first attempt by the drilling industry to use mechanical equipment for more effective and economical solids removal.

During the past half-entry there have been numerous types of solids removal equipment developed and tried in the industry. When judged solely on an engineering evaluation, much of the equipment was found to be satisfactory for applications in the drilling industry. Nevertheless, the equipment was not widely accepted until economics dictated a reassessment of our drilling practices. Solids removal equipment which had been judged to be too costly and too bothersome during an earlier era of relatively inexpensive drilling and minimum regulation is now being seriously considered as a means of reducing total drilling costs and complying with new environmental regulations.

Drilling Fluids

Drilling fluid, whether it be water-base or oil-base mud, can be described simplistically as being a suspension of solids in a liquid medium - -

. Liquid Phase. This may be either water, oil or salt solution. . Solids. These may be described as either additives or contaminants. The additive materials are further differentiated on the basis of their specific gravity. High gravity solids, such as barite, have a specific gravity of 4.2 or more and are used to increase the density of the drilling fluid. Low gravity solids, such as bentonite. have a specific gravity of 2.6 and are used as a viscosifying agent. Drilled solids, also have a specific gravity of 2.6. and are also referred to as low gravity solids. Drilled solids are the most common contaminant found in drilling fluids and they are responsible for the majority of problems associated with drilling fluids. These drilled solids, by their sheer volume, can significantly alter the density of a fluid and both the volume and the size of the drilled solids can drastically affect the viscosity of the drilling fluid.

Over the years, drilling fluids have been developed to the point that they do an excellent job of transporting drill cuttings up the bore and to the surface. However only part of the job has been done when drilled solids reach the surface. At this point the problem becomes that of removing the drilled solids from the drilling fluid. In as much as the volume and type of solids in a drilling fluid directly influence the density and viscosity - - and indeed all the rheological properties of the drilling fluid, it obviously follows that drilled solids greatly influence mud costs, well costs, rates of penetration, hydraulics, possibilities of kicks" and or returns, and an penetration, hydraulics, possibilities of kicks" and or returns, and an almost endless list of both small and large drilling problems. From both an engineering and an economic viewpoint, solids control becomes one of the most important aspects of drilling fluid treatment. It has been estimated that more money is spent annually to control drilled solids and to correct problems created by inadequate solids control measures than is spent on all problems created by inadequate solids control measures than is spent on all other problems encountered in drilling operations.

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