Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
1997-03-14
2001-07-10
Kelly, C. H. (Department: 1721)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C507S221000
Reexamination Certificate
active
06258757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved water based compositions for sealing subterranean zones and methods of utilizing the compositions.
2. Description of the Prior Art
In the drilling, of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures and other thief zones are often encountered whereby the drilling fluid circulation is lost and drilling operations must be terminated while remedial steps are taken. Also, when a subterranean zone is penetrated containing fluids under pressure which exceeds the hydrostatic pressure exerted on the zone by the drilling fluid, formation fluid crossflows and/or underground blow-outs can and often do occur.
Heretofore, a variety of compositions have been developed and used for combatting lost circulation, crossflow and underground blow-out problems. However, such compositions have often been unsuccessful due to delayed and inadequate viscosity development by the compositions. For example, a variety of compositions containing hydraulic cement or the like have been used in attempts to stop lost circulation. The lost circulation is usually the result of encountering weak subterranean zones that contain natural fractures or are fractured by drilling fluid pressures and rapidly break down. When a cement or other slow setting composition is squeezed into the zone, the delay in developing high viscosity allows the cement composition to be diluted and displaced into the zone whereby it bypasses the fractures and vugs causing the lost circulation. The same type of problem often occurs when crosslinked hydrated gels and other similar plugging compositions are utilized.
Thus, there is a need for improved compositions and methods for sealing subterranean zones that develop ultra high viscosity in a few seconds or minutes instead of the longer times heretofore required for sealing compositions to reach plugging viscosity.
SUMMARY OF THE INVENTION
Improved water based compositions for sealing subterranean zones and methods of using the compositions are provided which overcome the deficiencies of the prior art and meet the needs described above. The compositions and methods are particularly suitable for sealing subterranean zones containing oil based drilling fluids, e.g., water in oil emulsions, known as inverted emulsions. The compositions are basically comprised of water, an aqueous rubber latex, an organophillic clay and sodium carbonate. The compositions can also include one or more latex stabilizers, dispersing agents, biopolymers, defoaming agents, foaming agents, emulsion breakers, fillers, rubber vulcanizing agents and the like.
When the sealing compositions of this invention contact oil and water containing divalent cations in the well bore, the rubber latex is destabilized by the divalent cation in the water whereby the rubber is precipitated and the organophillic clays simultaneously react with the oil to instantly form an ultra high viscosity rubbery mass.
The methods of the invention comprise the steps of preparing a sealing composition of this invention and then introducing it into the subterranean zone to be sealed.
It is, therefore, a general object of the present invention to provide improved water based compositions for sealing subterranean zones and methods.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
As mentioned above, in the drilling of wells, subterranean zones are often encountered which contain high incidences of natural vugs and fractures. As a result, drilling fluid circulation is often lost which requires the termination of the drilling and the implementation of remedial procedures which are often of long duration and high cost. Such remedial procedures have heretofore involved the placement of hardenable compositions such as Portland cement compositions or crosslinked stiff gels and the like in the lost circulation zone. However, as mentioned above, because such compositions require considerable time to harden or gel, successful plugging of the zone often does not take place. In addition to drilling fluid lost circulation zones, zones containing pressurized fluids can be encountered which cause gas, oil or water crossflows that dilute and wash away sealing compositions. Also, underground blow-outs at low to high formation fluid flow rates can take place.
The present invention provides improved compositions for sealing subterranean zones and terminating the loss of drilling fluid, crossflows and/or underground blow-outs. The compositions are particularly suitable for use in wells containing oil based drilling fluids, e.g., water in oil emulsions and the like. When a composition of this invention contacts an oil based drilling fluid it instantly forms a resilient rubbery mass having ultra high viscosity. As the sealing mass is displaced through the well bore, it enters and seals thief zones such as vugs and fractures through which fluid is lost. A flexible seal is obtained by a combination of extrusion pressure and friction pressure. The sealing compositions are self diverting and plug multiple weak zones in a single well treatment. When a well contains a crossflow or underground blow-out, the high viscosity sealing compositions plug all the lower pressure weak zones penetrated by the well bore and as the pressure in the well bore is increased, the crossflow or blow-out zone is plugged. The resultant sealed well bore achieved by the sealing compositions of this invention can hold higher drill-ahead drilling fluid weights and produce a wedging effect in plugged fractures that increases the integrity of the entire formation or zone.
Depending upon the particular type of subterranean zone to be plugged, the high viscosity sealing compositions of this invention can range from a soft rubbery consistency to a semi-hard rubber consistency (vulcanized) and when required, to a very hard consistency (cement or other hardenable material added). The portion of the sealing composition left in the well bore after sealing one or more zones therein remains movable to divert to other zones above or below the sealed zones. The rubbery mass is not diluted or washed away by crossflows as are most prior art compositions.
The sealing compositions of the present invention are basically comprised of water, an aqueous rubber latex, an organophillic clay and sodium carbonate. The aqueous rubber latex present in the compositions of this invention is caused to destabilize by water in the well bore containing electrolyte such as calcium chloride whereby the rubber is precipitated. The organophillic clay simultaneously reacts with oil in the well bore to form a high viscosity rubbery sealing mass. The sodium carbonate in the compositions functions to stabilize the rubber latex and prevent precipitation when the latex is mixed with water which contains calcium compounds during the preparation of the compositions. Sodium hydroxide can also be added to prevent precipitation if the water used to form the compositions contains magnesium or other latex destabilizing compounds.
The water in the sealing compositions which is in addition to the water contained in the aqueous latex, is included in the compositions to make the compositions pumpable. The water can be from any source provided it does not contain the above mentioned compounds that adversely affect the rubber latex or other components in the compositions. However, fresh water is preferred. Generally, the additional water is present in an amount in the range of from about 6% to about 50% by weight of the compositions, m
Felio Archie J.
Heathman James F.
Sweatman Ronald E.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Kelly C. H.
Roddy Craig W.
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