BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
ALPLEX
Overview
ALPLEX is a dry aluminum complex, highly soluble in all water-base drilling fluids, designed to
stabilize shales via a mechanism of reducing pore pressure transmission. Although some base
exchange occurs, ALPLEX contains certain derivatives which are designed to form humic acid
complexes that contribute to shale stabilization by complexation on basal hydroxides on the
octahedral/tetrahedral sheets of formation clays (depending upon the clay type). The humic acid,
by virtue of its chemistry will act as a dispersant and develops a needed low fluid viscosity
without compromising the inhibitive/stabilization characteristics of the system.
The main mechanism of shale stabilization is driven by the chemical interaction of the high pH
filtrate with low pH connate (pores and fractures) water. This reduction of the mud filtrate pH
will cause the aluminum hydroxide to precipitate in the shale pores and micro-fractures. Basically
the tetrahydroxyl aluminate, Al(OH) 4¯, that is present in the higher pH filtrate of an ALPLEX
system will precipitate into an insoluble aluminum hydroxides Al(OH) 3 when exposed to lower
pH connate water. This crystalline form of aluminum hydroxide blocks the filtrate invasion
(reduction in pore pressure transmission) into the shale pores and micro-fractures, thus enhancing
the shale strength by preventing it from swelling and/or disintegrating.
The alkalinity (pH) of the system should be managed using caustic soda, not ALPLEX. In
freshwater systems, ALPLEX can be added directly through the mixing hopper. To increase its
performance in salt water systems, the ALPLEX should be pre-solubilized in fresh water before
adding it to the system. The pH of the freshwater should be increased to pH 10.5, using caustic
soda, before adding ALPLEX to make the slurry.
ALPLEX increases shale inhibition in all water-based mud systems using freshwater, seawater,
sodium chloride and other salts.
Application Guidelines
Basic Formulation
This basic formulation can be used in wells with bottom hole temperatures not exceeding 300°F.
For higher BHT, special formulations may be required.
Table 3-27 Basic Formulation for ALPLEX Systems
Water
Fresh to saturated NaCl
MILGEL, lbm/bbl 5 - 15
NEW-DRILL, lbm/bbl 1 - 3
BIO-LOSE, lbm/bbl 2 - 3
XAN-PLEX D, lbm/bbl
As needed for desired yield point
Caustic Soda, lbm/bbl As needed for pH 10.5
ALPLEX, lbm/bbl
1 - 6 depending on shale reactivity
Mixing Procedure
Freshwater System
ALPLEX can be added directly to the circulating system through the hopper. To achieve
maximum effectiveness, the water should be treated for any possible hardness.
Reference Manual
Baker Hughes Drilling Fluids
3-88 Revised 2006