Closed circuit method of circulating a substantially solid free drilling fluid

Abstract

The basic fluid is water, oil or an oil-water mixture. The primary weighting materials are dissolved salts, e.g., sodium chloride, calcium chloride or mixed brines, and in these the calcium or sodium ions inhibit hydration and swelling of drilled solids. When non-cationic fluids are used, an inhibitor is added to prevent such hydration and disintegration--an electrolyte or a cationic surfactant. Any viscosifier added is one having neither a structured viscosity nor gel strength, hydroxyethyl cellulose, for example. When the drilling fluid is pumped to the surface, most of the drilled solids are in their original condition and size and are readily removed and discarded by screening and other available physical means. There is none of the build-up of solids associated with older systems and, hence, no need for discarding, thinning, and make-up.

What is claimed is: 
     
       1. A closed circuit method of circulating a substantially solid free drilling fluid comprising (1) formulating a drilling fluid based on water, including an additive to inhibit drilled solids from disintegrating, water soluble weighting agents and a viscosifier consisting of material having no gel strength and no structured viscosity, (2) pumping said drilling fluid down the wellbore through the drilling string and bit and back up to the surface in the annulus surrounding the bit and drill string, (3) screening the drilling fluid to separate out and discard the coarse particles (4) removing the major portion of sand, silt and other particles from said drilling fluid by .[.settling and decantation.]. .Iadd.mechanical means, .Iaddend.(5) removing solids remaining in said drilling fluid by .[.mechanical means.]. .Iadd.settling and decantation .Iaddend.and, (6) returning the cleaned-up substantially solid free drilling fluid to the wellbore. 
     
     
       2. The closed circuit method according to claim 1 wherein said drilling fluid comprises a brine. 
     
     
       3. The closed circuit method according to claim 2 wherein said brine is a calcium chloride brine. 
     
     
       4. The closed circuit method according to claim 3 wherein a clear supernatant calcium chloride brine is returned to the wellbore in step 6. 
     
     
       5. The closed circuit method according to claim 3 wherein gum or polymer viscosifiers are employed. 
     
     
       6. The closed circuit method according to claim 1 wherein one major portion of any cuttings are removed by shaker screens. 
     
     
       7. The closed circuit method according to claim 6 wherein sand, silt and other particles are removed by desander and centrifuge. 
     
     
       8. The closed circuit method according to claim 1 wherein a clear drilling fluid is returned to the wellbore in step 6. 
     
     
       9. A closed circuit method of circulating a substantially solid free drilling fluid comprising (1) formulating a drilling fluid based on water and containing therein an additive to inhibit drilled solids from disintegrating, water soluble inorganic salt weighting agents and viscosifier having no gel strength and no structured viscosity and comprising hydroxyethyl cellulose, (2) pumping said drilling fluid down the wellbore through the drilling string and bit and back up to the surface in the annulus surrounding the bit and drill string, (3) screening the drilling fluid to separate out and discard the coarse particles, (4 ) removing the major portion of sand, silt and other particles from said drilling fluid by .[.settling and decantation.]. .Iadd.mechanical means, .Iaddend.(5) removing solids remaining in said drilling fluid by .[.mechanical means.]. .Iadd.settling and decantation .Iaddend.and, (6) returning the cleaned-up substantially solid free drilling fluid to the wellbore.