Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
2001-05-07
2003-04-29
Warden, Jill (Department: 1743)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C166S281000, C166S293000, C166S295000, C166S300000, C507S220000, C507S269000, C507S901000
Reexamination Certificate
active
06555507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved 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 highly permeable zones are often encountered whereby the drilling fluid circulation is lost into the zones 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 and/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 sealing 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 sealing compositions are utilized.
Thus, there is a need for improved compositions and methods of sealing subterranean zones using the compositions that develop ultra high viscosity in a few seconds or minutes and thereafter harden into firm but resilient sealing masses.
SUMMARY OF THE INVENTION
Improved compositions and methods of using the composition for sealing subterranean zones 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, water containing divalent cations and/or water-in-oil emulsions, known in the art as inverted emulsions.
The sealing compositions of this invention are basically comprised of water, an aqueous rubber latex, an organophillic clay, sodium carbonate, an epoxy resin and a hardening agent for the epoxy resin. 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 cations in the water whereby the rubber is precipitated, and the organophillic clay simultaneously reacts with the oil to instantly form an ultra-high viscosity rubbery mass. The viscous rubbery mass remains in the zone to be sealed until the epoxy resin in the composition is hardened by the hardening agent which forms the composition into a firm but resilient sealing mass which retains its shape, has compressive strength and effectively seals the subterranean zone.
The methods of this invention basically comprise the steps of preparing a sealing composition of this invention, introducing the sealing composition into a subterranean zone to be sealed and allowing the sealing composition to form a firm but resilient sealing mass in the subterranean zone.
It is, therefore, a general object of the present invention to provide improved compositions for sealing subterranean zones and methods of using the compositions.
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 and/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, cross-flows and/or underground blow-outs. The compositions are particularly suitable for use in wells containing oil, water containing divalent cations and/or water-in-oil emulsions. When a composition of this invention contacts oil and water containing divalent cations in the well bore, 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 vugs, fractures and other highly permeable zones through which fluid is lost. Upon entering such zones, the highly viscous sealing composition is retained in the zone long enough for the epoxy resin therein to harden which forms a firm but resilient sealing mass which retains its shape, has compressive strength and effectively seals the zone.
The sealing compositions of this invention are self diverting and plug multiple weak zones in a single well treatment. When a well contains a cross-flow or underground blow-out, the 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 also plugged. The resulting 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.
The sealing compositions of the present invention are basically comprised of water, an aqueous rubber latex, an organophillic clay, sodium carbonate, an epoxy resin and a hardening agent for the epoxy resin. The aqueous rubber latex present in the compositions of this invention is caused to destabilize by water in the well bore containing electrolytes 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 chloride and the like during the preparation of the compositions. Sodium hydroxide can also be added to the compositions to prevent precipitation of the latex if the water used to form the compositions contains magnesium compounds or other similar latex destabilizing compounds.
The epoxy resin in the compositions is caused to harden by the hardening agent therein whereby the initially formed high viscosity rubbery sealing mass is converted into a firm but resilient sealing mass which
Chatterji Jiten
Cromwell Roger S.
King Bobby J.
Cross LaToya
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Warden Jill
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