BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
time, annular circulating rate, degree of deviation, and mechanical abrasion from the drillstring.
Disintegration can be shear dependent. It is extremely important to remove as many of the drilled
solids as possible on the first circulation.
Low Gravity Solids Concentration
Most fresh water-base drilling fluids use bentonite for viscosity and filtration control. Low density
fresh water drilling fluids may contain approximately two (2) volume % bentonite or about 18
lbs/bbl to achieve desirable properties. As mud density increases, the concentration of bentonite
required decreases. Polymer based fluids may not use bentonite for this purpose by the substitution
of other synthetic materials to achieve similar controls.
Experience has shown that the low gravity solids concentration should be controlled and
maintained at specific levels for optimum fluid performance. Experience with the economics of
solids control has indicated that the specific level for low gravity solids concentration falls between
4 and 6 percent. Since bentonite concentration can be approximately 2 volume %, this leaves room
for only 2 - 4 volume % drill solids.
Various publications have addressed the issue of drilling and mud economics. The subjects of
“dilution” vs. “displacement” have been considered. Since waste disposal has become a major
economic factor in drilling operations today, emphasis has been placed on the proper selection and
operation of mechanical solids control equipment. This has resulted in concentrating the volume of
“dry” drill solids requiring disposal and therefore has minimized the need for building large
volumes of dilution mud to achieve optimum fluid performance.
Dr. Leon Robinson presents an economic analysis that bears repeating. In his article 1 , Robinson
states that since drilling fluid costs vary greatly, a particular well situation needs to be analyzed.
That involves the cost of fluid associated with each barrel of discarded drill solids which can be
calculated. Using the data in Figure 10 - 2, if the drilling fluid target solids is 4 volume % and the
system has a 60% removal efficiency, 9.6 bbl of drilling fluid will be discarded with each barrel of
drilled solids discarded. Assuming a $50/bbl fluid cost, 1000 bbl of drilled solids would require
$480,000 for new drilling fluid.
If the drilling fluid target solids can be increased to 6 volume % and the removal efficiency
increased to 70%, only 4.7 bbl of drilling fluid must be built for each barrel of discarded drill
solids. Again, for a $50/bbl fluid, the same 1000 bbl of drilled solids discarded would cost
$235,000.
1 Robinson, L., How to Optimize Solids Control Economics, Efficiency, Handbook by Derrick Equipment
Co., “Solids Control Manual for Drilling Personnel”.
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-3
REFERENCE MANUAL