초록 ▼

The disclosed invention is a novel drilling fluid additive for use in reducing lost circulation in wellbores and a method for employing the invention additive for reducing such lost circulation. The invention additive is a highly oil absorbent polymer encapsulated by a reaction-preventive protective

The disclosed invention is a novel drilling fluid additive for use in reducing lost circulation in wellbores and a method for employing the invention additive for reducing such lost circulation. The invention additive is a highly oil absorbent polymer encapsulated by a reaction-preventive protective casing to prevent the polymer from expanding by absorbing oil until it is desired to breach the casing. The reaction-preventive protective casing may be a film which will dissolve after a desired time of residence in the borehole or a film or clay which can be ruptured in the formation, releasing the oil absorbent polymer to expand by absorbing oil. The substantially expanded polymer will seal off their zones and fissures, reducing lost circulation.

대표청구항 ▼

A drilling fluid additive for reducing lost circulation of oil based drilling fluids in a borehole penetrating an underground formation, comprising: an oil absorbent polymer which expands upon absorbing oil, said polymer encapsulated by a reaction-preventive protective casing to prevent the polymer

A drilling fluid additive for reducing lost circulation of oil based drilling fluids in a borehole penetrating an underground formation, comprising: an oil absorbent polymer which expands upon absorbing oil, said polymer encapsulated by a reaction-preventive protective casing to prevent the polymer from absorbing oil and expanding until it is desired to breach the casing, said oil absorbent polymer being a cross-linked linear addition polymer containing repeating units of vinylbenzyl alcohol and at least one other alpha, beta-monoethylenically unsaturated monomer different from vinylbenzyl alcohol, wherein the vinylbenzyl alcohol units comprise about 0.5% to about 20% by weight of the linear polymer. A method of reducing lost circulation of oil based drilling fluids in a borehole penetrating an underground formation, comprising: adding an oil absorbent polymer which expands upon absorbing oil to a slug of drilling fluid, said polymer encapsulated with a clay, said polymer added in a quantity of about two to about 250 pounds of encapsulated polymer per barrel of oil based drilling fluid; spotting the slug of drilling fluid and polymer within a lost circulation zone; shearing the clay encapsulation with the circulating jets of the drill bit, permitting the encapsulated polymer to be released from its clay encapsulation and absorb oil and expand to close off the lost circulation zone; and resuming circulation to clear the borehole of undesired compounds.