BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
.
Table 3-26
Typical Offshore Discharges Figures for Water Base Mud Systems
AQUA-DRILL
0.4 - 0.8 bbls/ft
KCl Polymer
GYPSUM
0.8 - 1.5 bbls/ft
2.0 - 4.0 bbls/ft
Logistics
Most polymer fluids are routinely shipped as premix concentrates from the shore based fluid
plants. The use of AQUA-DRILL and the consequent reductions in fluid volumes have reduced
the volumes required by 40% to 70%. Typically, one or two boat movements replace the previous
four to eight.
Conclusions
The AQUA-DRILL System is a proven inhibitive fluid system. Increasingly demanding
applications will establish the degree to which it can be considered a viable replacement for oilbase
fluids. Relatively high initial make-up costs of the system are offset by reduced dilution
requirements. Overall, a more stable wellbore and reduced chemical discharge to the sea is
achievable. Additional benefits such as improved lubricity and reduced formation damage require
further qualification in the field.
ALPLEX ® – Aluminum-Based Shale Stabilizer
Introduction
Laboratory results and actual field experience have shown that aluminum compounds are viable
additives in water-base fluid systems for reducing pore pressure transmission in shales via a
mechanism similar to that of the PERFORMAX and AQUA-DRILL Systems.
Aluminum Chemistry
Under alkaline (high pH) conditions, aluminum sulfate or aluminum chloride form colloidal
aluminum hydroxide. In addition, free aluminum ions are highly flocculating to clay particles
found in drilling fluid. The high viscosity produced by these salts is unacceptable for drilling
operations. Consequently, a complex reaction with the aluminum ion is needed to reduce its
tendency to precipitate. “Complex” is the general term used for this new structure. Aluminum
salts that have been reacted to form complexes are stable in alkaline environments. The degree of
stability depends upon the complex agent, the fluid pH, and time. ALPLEX is soluble in the form
of an aluminate ion, Al(OH) 4¯, at pH levels above pH 10. ALPLEX becomes insoluble in the
form of aluminum hydroxide, Al(OH) 3 , as pH decreases below pH 10. The pH of the connate
water in shales is typically below pH 10, so the mechanism imparted by ALPLEX in plugging
shale pores and micro fractures is driven by the change in pH from the drilling fluid and the
formation. ALPLEX enters the pores and micro fractures in a soluble form, but then quickly
forms an insoluble aluminum hydroxide precipitate (gel) with pH reduction in the shale matrix.
Effectively, this precipitate acts as a barrier to prevent further fluid invasion (pore pressure
increase) within the shale matrix. The concentration of ALPLEX must be measured using a
Fluoride Selective Electrode (FSE) probe. Material (mass) balance CANNOT be used to
accurately measure the ALPLEX concentration.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-87