BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
Applications
The principal application for low molecular weight water-soluble glycols is in the drilling of
reactive shales. Wellbore stability is improved over conventional water-based drilling fluids
because of the ability of the glycol to “cloud-out” within the shale matrix and form a physical
barrier to reduce filtrate invasion into the shale matrix. This mechanism of minimizing water
invasion into the matrix reduces pore pressure transmission into the shale and improves the
strength and stability of the wellbore. The AQUA-DRILL system was the first water-based
drilling fluid that was specifically designed to reduce pore pressure transmission into shales. Pore
pressure transmission reduction is considered to be the primary wellbore stability mechanism of
emulsion-based drilling fluids.
The higher initial make-up cost of the glycol-base fluid is often entirely offset by reduced dilution
costs. In less reactive areas, the benefits of reduced dilution can also be realized, making the fluid
viable across a wide range of applications. Selection of the correct glycol allows partially
saturated or salt-saturated fluids to be formulated. This extends the potential use of these fluids
into wells where salts will be encountered. Return permeability figures obtained by several
operators on glycol fluids indicate no detrimental effects (and perhaps even some beneficial
effects) in using glycols across reservoir sections. This is particularly true at higher glycol
concentrations (5% to 10% by volume).
AQUA-DRILL System
The AQUA-DRILL system uses glycols to stabilize shales by reducing pore pressure
transmission into the shale matrix and was the first-generation high-performance water-based
mud system for Baker Hughes Drilling Fluids. AQUA-DRILL is a non-toxic, non-sheening
system that eliminates the potential environmental disadvantages associated with oil/synthetic
base fluids.
The Core System
The “core” AQUA-DRILL system is comprised of the following products.
Water Soluble Glycol
• AQUA-COL TM – a low molecular weight glycol ether for increasing the inhibitive
properties of fresh water and low salinity water-base fluids when drilling reactive shales.
• AQUA-COL B - a low molecular weight glycol ether providing enhanced shale
stabilization when using higher salt concentrations in water-base fluids.
• AQUA-COL TM D – a low molecular weight glycol ether providing enhanced shale
stabilization when using higher salt concentrations in water-base fluids.
• AQUA-COL TM S – a low molecular weight polyglycol ether providing enhanced shale
stabilization when using higher salt concentrations in water-base fluids (up to saturation).
Polymeric Shale Inhibitor
• AQUA-SEAL TM – a proprietary polymer to aid in preventing hydration and dispersion of
drill cuttings, and for delivering filtration control.
• NEW-DRILL ® – a partially hydrolyzed polyacrylamide (PHPA) polymer that provides
cuttings encapsulation and helps reduce dispersion of cuttings.
Reference Manual
Baker Hughes Drilling Fluids
3-70 Revised 2006