Patent EA-002832-B1 (EA)
Title: Method and fluid for drilling or servicing a well, method of decreasing the lost circulation potential
Inventor: BROOKEY TOMMY F
IPC: E21B21/00
Filed: 1999-07-12
Abstract: 1. A method for drilling and servicing a well, the method comprises circulating a drilling fluid in a borehole, the drilling fluid comprising an aqueous liquid having dispersed therein a polymer which increases the low shear rate viscosity of the fluid to the extent that the shear thinning index of the fluid is at least about 10 and the low shear rate viscosity is at least 10,000 centipoise, which comprises adding to the fluid a surfactant and an agent increasing a thermal stability and thereafter generating aphrons in the fluid. 2. The method of Claim 1 wherein the aphrons are generated by circulating the fluid down the drill pipe and through the openings in the bit whereby the aphrons are generated by the pressure drop as the fluid exits the drill bit and contacts the formation being drilled. 3. The method of Claim 1 wherein the aphron content is less than about 15% of the fluid. 4. The method of Claim 1 wherein the surfactant provides an average percent expansion of a sand bed of at least about 50% when evaluated according to the following test procedure: to a low temperature, low pressure API filtration cell, the cylindrical body of which is made from Plexiglas of thickness 1.27 centimeters is added 200 grams of sand having a particle size in the range from 297 μm to 210 μm; this provides a sand bed depth of 2.1 centimeters; no filter paper is used in the cell; 350 cc of the fluid to be tested is slowly added to the cell, the cell assembled, and 689.5 kN/m<2> nitrogen pressure applied; the pressure is released after the nitrogen blows through the bed for 30 seconds; upon releasing the pressure the sand bed will expand in volume/height as the bubbles in the sand bed expand; the expansion is not even, and an average increase in height of the bed as measured at the cell wall and at the center of the sand bed is obtained; wherein the test fluid comprises 4.285 kg/m<3> of well hydrated xanthan gum in water and 2.857 kg/m<3> of the surfactant to be tested. 5. The method of one of Claims 1 to 4 wherein the surfactant is injected into the drilling fluid under pressure. 6. The method of one of Claims 1 to 4 wherein the polymer is a biopolymer. 7. The method of one of Claims 1 to 4 wherein the agent increasing a thermal stability comprises an oligosaccharide mixture composed of pentosans and/or hexosans containing from one to about 10 combined sugar units selected from the group consisting of arabinose, mannose, galactose, glucose, xylose, cellobiose, and mixtures thereof. 8. The method of Claim 1 wherein the solution is recyclable. 9. The method of Claim 1 wherein the polymer provides the low shear rate viscosity is at least 40,000 centipoise. 10. A well drilling and servicing fluid in particular for circulating in a borehole comprising; an aqueous liquid, a polymer which increases the low shear rate viscosity of the fluid to the extent that the shear thinning index of the fluid is at least 10, a surface active foaming agent, increasing the thermal stability, and aphrones wherein the low shear rate viscosity of the fluid is at least 10,000 centipoise. 11. The fluid of Claim 10 wherein the polymer is a biopolymer. 12. The fluid of Claim 10 wherein the agent increasing a thermal stability comprises an oligosaccharide mixture composed of pentosans and/or hexosans containing from one to about 10 combined sugar units selected from the group consisting of arabinose, mannose, galactose, glucose, xylose, cellobiose, and mixtures thereof. 13. The fluid of Claim 10 wherein the oligosaccharide mixture is the water soluble portion of thermally hydrolyzed lignocellulose. 14. The fluid of Claim 10 wherein the aphron content is less than about 15% of the fluid. 15. The fluid of Claim 10 wherein the solution is recyclable. 16. The fluid of Claim 10 wherein the polymer provides the low shear rate viscosity is at least 40,000 centipoise. 17. A method for preventing the loss of circulation comprising drilling or servicing a well in a subterranean formation containing lost circulation zones or depleted, low pressure reservoirs wherein a well drilling or servicing fluid is circulated within the wellbore by using as the well drilling or servicing fluid the fluid of any of Claims 10 to 13. 18. The method of preventing the loss of circulation of Claim 17 wherein the surfactant provides an average percent expansion of a sand bed of at least about 50% when evaluated according to the following test procedure: to a low temperature, low pressure API filtration cell (API Recommended Practice 13 B-1), the cylindrical body of which is made from Plexiglas of thickness 1.27 centimeters is added 200 grams of sand having a particle size in the range from 297 μm to 210 μm; this provides a sand bed depth of 2.1 centimeters; no filter paper is used in the cell; 350 cc of the fluid to be tested is slowly added to the cell, the cell assembled, and 689.5 kN/m<2> nitrogen pressure applied; the pressure is released after the nitrogen blows through the bed for 30 seconds; upon releasing the pressure the sand bed will expand in volume/height as the bubbles in the sand bed expand; the expansion is not even, and an average increase in height of the bed as measured at the cell wall and at the center of the sand bed is obtained; wherein the test fluid comprises 4.285 kg/m<3> of well hydrated xanthan gum in water and 2.857 kg/m<3> of the surfactant to be tested.