BAKER HUGHES - Drilling Fluids Reference Manual

FLUIDS ENVIRONMENTAL SERVICES
• Does not discharge hydrocarbon waste to the air.
• Is an inexpensive process, relative to many environmental solutions which are not permanent.
Downhole cuttings injection technology is used by many operators to dispose of drilled cuttings at the
rig site. Developing sou nd slurrification and injection meth
ods has played an important role in
expanding the utilization of cuttings re-injection. A clear, concise understanding of what happens
downhole during the cuttings re-injection operation is critical to successfully implementing this
technology and completing a project successfully.
Cuttings Slurrification
Cuttings generated by the drilling operation are removed from the drilling fluid using conventional
solids control equipment, and then transported to the cuttings slurrification system using blowers,
vacuums, screw conveyors, and/or slides. When the cuttings reach the CRI system, they are
transformed (slurrif ied) into pumpable slurry by mixing sea water and/or chemicals with the drilled
cuttings at approximately a two to one ratio.
The finer the grinding of the cuttings, the less chemical is needed and the smaller quantities of slurries
generated per length of hole drilled. While the cuttings/water/chemicals are blended, the cuttings are
reduced to a predetermined particle size distribution/viscosity by grinding and shearing them with
specially modified centrifugal pumps, and possibly mills, into a homogeneous mixture.
The resulting slurry is usually pumped to an additional onboard storage tank prior to either reinjection
back into the formation (as explained below) or for pumping to a stand-by vessel for onward
shipment to a dedicated intra-field injection platform/rig. There it is usually reduced in viscosity and
then re-injected back into the dedicated well and formation.
Injection Theory
Complex modeling techniques have been created to establish fracturing parameters for increased
hydrocarbon production in tight and porous, brittle and ductile formations. These models have
proven to work well as a guide for CRI services.
To utilize the fracture models, an experienced CRI subsurface engineer must temper the fracture
design with cuttings injection experience to adequately judge how the formations are impacted by
injection operations. This is due to CRI consisting of a different set of parameters than those that the
fracture models were designed for. The fracture models for hydrocarbon simulation are designed for:
• High rates of injection to prevent sand-out.
• Injection with specific brittle particles that are large when compared to cuttings slurry
particles
• No distribution of particle size.
• High fluid horsepower at the formation face.
• Short duration pumping.
• Slurry rheological properties that have low fluid loss and are ultimately designed to create the
maximum fracture that can be obtained.
Disposal of cutting slurries is exactly the opposite:
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 14-36