Abstract: A stabilized fracturing fluid and a method of stabilizing a fracturing fluid containing at least one of guar gum and its derivatives is disclosed, wherein at least one stabilizing compound selected from the thiol derivatives of heterocyclic compounds is added to the fracturing fluid. This method of stabilization prevents degradation of the fracturing fluid, i.e., reduction in its rheological properties at high temperatures and permits smooth practice of the fracturing operation.

Abstract: A process for producing a modified hydroxyethyl cellulose comprising the steps of:allowing hydroxyethyl cellulose to be swollen in a solvent; andmixing the hydroxyethyl cellulose swollen in the solvent, with a 2-mercapto benzimidazole compound having the formula (I): ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 independently represent hydrogen, methyl, or ethyl, and X is hydrogen, an alkali metal, an alkaline earth metal, or ammonium.

Abstract: A stabilized fracturing fluid and a method of stabilizing a fracturing fluid containing at least one of guar gum and a derivative thereof is disclosed, comprising adding at least one stabilizing compound selected from 2-mercaptobenzimidazole and 2-mercaptobenzothiazole compounds to the fracturing fluid. This stabilization prevents degradation of the fracturing fluid, i.e., reduction in its rheological properties at high temperatures and permits smoothly carrying out the fracturing operation.

Abstract: A completion and workover fluid which comprises an aqueous liquid medium containing hydroxyethyl cellulose, an inorganic salt selected from the group consisting of calcium chloride, calcium bromide and zinc bromide, and a component selected from the group consisting of the following components:(1) thiol derivatives of heterocyclic compounds;(2) thioamide derivatives;(3) at least one compound selected from the group consisting of thiuram disulfide compounds, thiuram monosulfide compounds and dithiocarbamate compounds;(4) benzothiazole; and(5) a copper compound and an iodine compound in combination.

Abstract: A completion and workover fluid is described, containing a soluble salt, a hydroxyethyl cellulose and at least one compound selected from 2-mercaptobenzimidazole compounds, 2-mercaptobenzothiazole compounds, 2-mercaptothiazoline and 2-thioimidazolidone.

Abstract: A drilling fluid is described, consisting essentially of sodium carboxymethyl cellulose, bentonite, water, and at least one compound selected from 2-mercaptobenzimidazole compounds, 2-mercaptobenzothiazole compounds, 2-mercaptothiazoline and 2-thioimidazolidone.

Abstract: Equipment for dissolving polyacrylamide powder to obtain an aqueous solution thereof for enhanced oil recovery comprisesfirst and second powder storage tanks for storing polyacrylamide powder under nitrogen atmosphere;a gas conveyor unit for carrying the polyacrylamide powder from the first storage tank to the second storage tank by nitrogen gas flow;a constant powder supply unit for receiving the polyacrylamide powder from the second storage tank, metering the powder, and sending the metered powder toa powder dispersion unit for dispersing in water the polyacrylamide powder.A first liquid supply unit sends the dispersion or solution of polyacrylamide powder obtained from the powder dispersion unit to a dissolution tank for completing dissolution of the polyacrylamide;and a second liquid supply unit transfers the polyacrylamide solution from the dissolution tank to a solution storage tank for storing the polyacrylamide solution.