Loss of drilling fluid to the formation is one of the costliest problems that drillers face during well construction. Until recently, the primary method used to control losses involved incorporating materials in the fluid or in pills to bridge or plug the loss zone. Current technology enables a more comprehensive -- and more effective -- approach that includes this remediative method but gives greater emphasis to preventing lost circulation.
This multi-element approach focuses on...
• Best drilling practices, including managed pressure drilling, casing/liner drilling and other techniques
• Optimizing hardware configurations
• Use of drilling fluids that inherently inhibit invasion into permeable or fractured zones
• Minimizing the fluid’s equivalent circulating density
• Use of wellbore stability models that model rock and fracture mechanics more accurately
• "Strengthening" the wellbore
Wellbore strengthening encompasses a wide variety of techniques that may be classified as physical, chemical, thermal, and mechanical. Physical techniques include methods to shield the formation from fluid and pressure through deposition of a barrier that behaves in some ways as casing. Chemical techniques involve changes in composition of the rock or pore fluid, thereby altering the fabric and mechanical properties of the rock. Thermal techniques involve increasing or decreasing the temperature of the wellbore by heating or cooling the drilling fluid at the surface. Finally, mechanical techniques involve pressure-stressing the wellbore through hoop stress enhancement (stress caging), to increase the apparent fracture gradient of the rock.
By incorporating these technologies and the lost circulation prevention philosophy in the planning of the well and development of the drilling program, it is now possible and economical to drill wells that previously could not be drilled or that incurred unacceptable levels of non-productive time.
Fred Growcock is currently serving as Global Fluids Specialist for Occidental Oil & Gas Corp (Oxy) in Houston, Texas, where he provides technical support to the company’s worldwide drilling fluid field operations. He began his career as a scientist at Brookhaven and Oak Ridge National Laboratories in the mid-70’s, working on coal liquefaction and gasification and nuclear reactor safety. He then moved to Dowell Schlumberger to develop acidizing corrosion inhibitors and foamed fracturing fluids. Subsequently, he joined Amoco Production Company to carry out drilling fluids R&D, and served as an adjunct professor of chemical engineering at the University of Oklahoma. In 1999 he moved to M-I SWACO, where he worked primarily on development of drilling fluid products and systems, then left in 2011 to join Oxy. Dr. Growcock holds Ph.D. and M.S. degrees in physical chemistry from New Mexico State University, and B.A. and B.S. degrees in chemistry from the University of Texas at Austin. He has written more than 100 papers and holds a dozen patents on corrosion inhibitors, drilling fluid systems, and completion fluid products.