New Developments in the Control of Lost Circulation

Abstract

Abstract Laboratory and field tests were conducted for the purpose of improving techniques for the control of loss of circulation of drilling fluids and to determine some effects of lost circulation materials on drilling fluids and drilling rates. The physical properties of granular materials most suited for use in drilling fluids to seal fractures were found to be angularity, low specific gravity, high compressive strength, low modulus of elasticity and low hardness factor. Results of tests indicate that materials possessing these physical properties and graded in particle size from 30 mesh to 100 mesh, so as to pass through a shale shaker screen, reduce circulation losses to induced fractures. Also, these materials were found to improve the lubricity of drilling fluids. Results of other tests indicate that the cutting action of rotary rock bits is not impaired by the addition of lost circulation materials to the drilling fluids. Mixtures of coarse, granular materials and solid, oil-soluble materials were found satisfactory to prevent loss of drilling fluids to oil-bearing formations without impeding subsequent flow of oil from these formations. Results of field tests show that a slurry of diesel oil-bentonite-cement will plug severe lost circulation zones containing natural fractures and vugs. Introduction Much progress has been made in the control of lost circulation of drilling fluids as a result of improvements in drilling fluids and drilling techniques, and developments of new lost circulation materials and remedial procedures. Nevertheless, lost circulation remains one of the outstanding problems of the drilling industry. In the Gulf Coast area, lost circulation is often controlled at the expense of increased mud chemical and additive costs. In other areas where large openings in formations are encountered, maintaining circulation may involve large expenditures of time and motley. Some aspects of lost circulation which have been given little attention are the effects of conventional lost circulation materials on the properties of drilling fluids and the cutting action of rotary bits, and the hazard of plugging productive formations when combatting lost circulation.