Patent EA-005149-B1 (EA)
Title: Shear-sensitive plugging fluid for plugging and method for plugging a subterranean formation zone
Inventor: MABERRY JACK
IPC: C09K8/575
Filed: 2002-07-19
Abstract: 1. A plugging fluid for plugging a subterranean formation zone surrounding a drill hole essentially consisting of an emulsion comprising a dispersed aqueous phase containing an aqueous base and a continuous hydrophobic phase containing a polymer consisting of a grafted cellulose ether derivative, a surfactant and a crosslinking activator of the polymer. 2. The plugging fluid of claim1, wherein the polymer is a grafted hydroxyalkylcellulose polymer derivative graft polymer. 3. The plugging fluid of claim 2, wherein the polymer is 2-hydroxyethyl cellulose grafted with vinyl phosphonic acid. 4. The plugging fluid of claim 3, wherein the ratio of 2-hydroxyethyl cellulose to vinyl phosphonic acid monomers in the graft polymer ranges from about 5% to about 20%. 5. The plugging fluid of claim 1, wherein the crosslinking activator of the polymer are selected from the groups consisting of compounds providing iron III, boron, titanium IV, zirconium IV, aluminum III and antimony V ions; compounds containing divalent calcium and magnesium ions, amines, acetates, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium acetate, ammonia, ammonia generating compounds, chelating agents, sodium gluconate, sorbitol, and glycerol and mixture thereof. 6. The plugging fluid of claim 5, wherein the crosslinking activator comprises an admixture consisting of magnesium oxide, sodium carbonate, hydroxyethylethylene-diaminetriacetic acid, and sodium tetraborate. 7. The plugging fluid of claim1, wherein the oil is present in a concentration of from about 5 to about 70 wt%, and the water is in a concentration of from about 30 to about 95 wt%. 8. A plugging fluid comprising from about 10 to 25 wt% of diesel oil, 0.1 to 3 wt% of a polyamide derivative, 0.1 to 5 wt% of a 2-hydroxyethylcellulose grafted with vinyl phosphonic acid, 70 to 90 wt% of fresh water, 0.5 to 1.5 wt% of magnesium oxide, 0.5 to 1 wt% of sodium carbonate, 0.1 to 1 wt% of sodium tetraborate pentahydrate and 0.1 to 1 wt% of the hydroxyethylethylene-diaminetriacetic acid. 9. A method of preparing a plugging fluid comprising the steps of dissolving a surfactant into an oil, adding a polymer consisting of a grafted cellulose ether derivative and a crosslinking additive of the polymer to prepare a pre-mix and blending this pre-mix with water. 10. A method of sealing a lost circulation zone in a wellbore comprising the step of pumping a plugging fluid consisting of an emulsion comprising a dispersed aqueous phase containing an aqueous base and a continuous hydrophobic phase containing a polymer consisting of a grafted cellulose ether derivative, a surfactant and a crosslinking activator of the polymer and initiating the gellation of the plugging fluid by shear forces. 11. The method of claim 10, whereby the shear forces are applied through the drill bit nozzles. 12. The method of claim 10, whereby the polymer is not allowed to significantly hydrate before the initiation of the gellation of the plugging fluid by shear forces. 13. The method of claim 10, wherein the polymer is a grafted hydroxyalkylcellulose polymer derivative graft polymer. 14. The method of claim 12, wherein the polymer is 2-hydroxyethyl cellulose grafted with vinyl phosphonic acid.