Wells – Processes – Separate steps of fracturing or attacking formation
Utility Patent
1999-02-12
2001-01-02
Suchfield, George (Department: 3672)
Wells
Processes
Separate steps of fracturing or attacking formation
C166S294000, C166S295000, C166S300000, C175S072000, C507S231000, C507S277000, C507S901000
Utility Patent
active
06167967
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved methods of sealing subterranean zones to remedy the uncontrolled flow of fluids into and from the zones.
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 drilling fluid 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 a 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 methods of sealing compositions have been developed and used for combatting lost circulation, crossflow and underground blow-out problems. However, such methods and compositions have often been unsuccessful due to delayed and inadequate viscosity development by the sealing compositions used. Also, the methods of placement of the sealing compositions have been inadequate to cause plugging of all the weak permeable portions of the zones being treated and to prevent bypassing of such portions by the sealing compositions and/or the wash out of the compositions.
Thus, there is a need for improved methods of placing sealing compositions in subterranean zones to remedy lost circulation, crossflow and underground blow-out problems.
SUMMARY OF THE INVENTION
The present invention provides improved methods of sealing subterranean zones which meet the needs described above and overcome the deficiencies of the prior art. The methods are utilized to seal a subterranean zone penetrated by a well bore during the drilling of the well bore to terminate the uncontrolled flow of fluids into and out of the zone by way of permeable portions of the zone. The methods are basically comprised of the steps of preparing a pumpable sealing composition which very rapidly converts into a high viscosity sealing mass upon mixing and reacting with drilling and other fluids in the well bore comprised of water, oil or both. The sealing composition is pumped into the well bore and into the subterranean zone to be sealed through one or more openings at the end of a string of drill pipe contained in the well bore. The sealing composition is pumped at a low flow rate relative to the well bore fluids therein whereby the sealing composition flows through the well bore fluids with a minimum of mixing therewith. As the sealing composition moves through the well bore fluids, portions of the sealing composition are continuously mixed with the well bore fluids and converted to sealing masses which are successively diverted into and seal the weak permeable portions of the zone through which fluids are flowing out of the well bore. The successive sealing of the weak permeable portions of the subterranean zone (the most permeable portions first followed by the less permeable) allows the hydrostatic pressure exerted in the well bore and in the zone being sealed to increase until all of the permeable portions in the zone are sealed.
It is, therefore, a general object of the present invention to provide improved methods of sealing subterranean zones.
A further object of the present invention is the provision of improved methods of sealing a subterranean zone penetrated by a well bore in which drilling fluid is being lost, a crossflow of formation fluids is occurring or formation fluids are flowing into the well bore.
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
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 sealing of the zone often does not take place. In addition to drilling fluid lost circulation zones, zones containing pressurized fluids are often encountered which cause gas, oil or water crossflows that dilute and wash away sealing compositions. Also, underground blow-outs whereby formation fluids flow into the well bore at low to high flow rates and force drilling fluid out of the well bore can take place.
The present invention provides improved methods of sealing subterranean zones penetrated by well bores to prevent the uncontrolled flow of fluids into or out of the zones by way of permeable portions of the zones, e.g., lost drilling fluid circulation, crossflows, underground blow-outs and the like. The methods utilize improved compositions for sealing subterranean zones which rapidly convert into high viscosity sealing masses upon mixing and reacting with drilling fluid and other fluids contained in the well bore comprised of water, oil or both, collectively referred to hereinbelow as “well bore fluids.”
A subterranean zone containing vugs, fractures and other permeable portions through which the uncontrolled flow of fluids takes place is generally encountered during drilling when the well bore is filled with drilling fluid and a string of drill pipe is disposed therein. The drilling must be terminated pending the sealing the zone, i.e., the sealing of the permeable portions of the zone to stop the drilling fluid circulation loss, crossflow, blowout or other problem encountered. In accordance with the methods of this invention, a pumpable sealing composition which rapidly converts into a high viscosity sealing mass upon mixing and reacting with well bore fluids is prepared. As mentioned, the well bore fluids can be drilling fluid or formation fluids contained in the well bore comprised of water, oil or both. Upon mixing with the well bore fluids, the sealing composition rapidly (within a few seconds or minutes) forms a sealing mass having ultra high viscosity.
After its preparation, the sealing composition utilized is pumped through one or more openings at the end of the string of drill pipe into the zone to be sealed at a low flow rate relative to the well bore fluids in the zone. As a result, the sealing composition flows through the well bore fluids with a minimum of mixing therewith whereby portions of the sealing composition are continuously converted to sealing masses as the sealing composition flows through the zone to be sealed. The sealing masses are first successively diverted into any permeable portions of the zone through which fluids are flowing out of the zone. That is, the sealing masses flow into and seal the most permeable portions of the zone first followed by the least permeable portions through which fluids are exiting the zone. As the outflow permeable portions of the zone are sealed, the hydrostatic pressure exerted on the zone is increased. Once all of the permeable portions through which fluid is exiting the zone have been sealed, the hydrostatic pressure is increased to the point where the inflow of fluids to the zone (if a crossflow or blowout is being experienced) is terminated and reversed, i.e., well bore fluids are caused to flow out of the permeable portions of the zone through which formation fluids were previously flowing in the zone. This, in t
Halliburton Energy Service,s Inc.
Roddy Craig W.
Suchfield George
LandOfFree
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