Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2001-09-21
2002-04-09
Tsay, Frank S. (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C166S295000, C523S130000
Reexamination Certificate
active
06367549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and compositions for sealing pipe strings in well bores, and more particularly, to such methods and compositions wherein the well bores penetrate formations which readily fracture at low hydrostatic pressures.
2. Description of the Prior Art
Sealing compositions are commonly utilized in oil, gas and water well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior of a string of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
In some well locations, the subterranean zones or formations into or through which wells are drilled have high permeabilities and low compressive and tensile strengths. As a result, the resistances of the zones or formations to shear are low and they have very low fracture gradients. When a well fluid such as a hydraulic cement composition is introduced into a well bore penetrating such a subterranean zone or formation, the hydrostatic pressure exerted on the walls of the well bore can exceed the fracture gradient of the zone or formation and cause fractures to be formed in the zone or formation into which the cement composition is lost. While light weight cement compositions have been developed and used, i.e., non-foamed cement compositions having densities as low as about 10 pounds per gallon, subterranean zones or formations are still encountered which have fracture gradients too low for even the light weight cement compositions to be utilized without the formation of fractures and the occurrence of lost circulation problems.
Thus, there are needs for improved methods and ultra-low density sealing compositions for sealing pipes such as casings and liners in well bores which penetrate zones or formations having very low fracture gradients.
SUMMARY OF THE INVENTION
The present invention provides methods and ultra-low density sealing compositions for sealing pipe in well bores penetrating zones or formations having low fracture gradients which meet the needs described above and overcome the deficiencies of the prior art. The methods of this invention basically comprise the steps of providing a hardenable ultra-low density sealing composition comprised of an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, an optional organosilane bonding agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition density in a range of from about 5 to about 8.5 pounds per gallon. The sealing composition is placed into the annulus between a pipe and the walls of the well bore and the sealing composition is then allowed to harden. Upon hardening, the sealing composition eliminates the permeability of the zone or formation, increases its strength and resistance to failure and seals the exterior surface of the pipe to the walls of the well bore.
An ultra-low density sealing composition of this invention is basically comprised of an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition having an ultra-low density in the range of from about 5 to 8.5 pounds per gallon. The ultra-low density sealing compositions can also include an organosilane bonding agent.
It is, therefore, a general object of the present invention to provide methods and ultra-low density sealing compositions for sealing pipe in well bores.
Other and further objects, features and advantages of the present inventions 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, oil, gas and water wells are often drilled into subterranean zones or formations having high permeabilities and low resistances to failure. When conventional well sealing fluids enter such zones or formations by way of the well bores penetrating them, the fracture gradients of the zones or formations can often be exceeded. As a result, fractures are formed in the zones or formations and the sealing fluids are lost therein. In many cases, the fracture gradients of the formations are so low that wells drilled into the formations cannot be completed and must be abandoned. The term “fracture gradient” is used herein to mean the hydraulic pressure per unit of depth required to be exerted on a subterranean formation to cause fractures therein.
By the present invention, methods and ultra-low density sealing compositions are provided for sealing pipes in well bores penetrating zones or formations which readily fracture at low hydrostatic pressures e.g., hydrostatic pressures as low as 10 pounds per gallon. The methods of this invention for sealing a pipe in a well bore penetrating a zone or formation which readily fractures at low hydrostatic pressures is basically comprised of providing a hardenable ultra-low density sealing composition comprising an epoxide containing liquid, a hardening agent for hardening the epoxide containing liquid, an optional hardening accelerating agent, a light weight filler and hollow glass microspheres present in an amount sufficient to produce a sealing composition density in the range of from about 5 to about 8.5 pounds per gallon. The sealing composition is placed into the annulus between the exterior surfaces of the pipe and the walls of the well bore and the sealing composition is allowed to harden therein. As mentioned above, the sealing compositions of this invention can optionally include an organosilane bonding agent to increase the ability of the sealing composition to provide a strong bond to the pipe and to the walls of the well bore.
A variety of hardenable epoxide containing liquids can be utilized in accordance with this invention. Examples of preferred such hardenable epoxide containing liquids include, but are not limited to the diglycidyl ether of 1,4-butanediol, the diglycidyl ether of neopentyl glycol, the diglycidyl ether of cyclohexanedimethanol and mixtures thereof. Of these, the diglycidyl ether of cyclohexanedimethanol is the most preferred.
A suitable epoxide containing liquid comprised of the diglycidyl ether of 1,4-butanediol is commercially available from the Shell Chemical Company under the trade name “HELOXY®67”. This epoxide containing liquid has a viscosity at 25° C. in the range of from about 13 to about 18 centipoises, a molecular weight of 202 and a 1-gram equivalent of epoxide per about 120 to about 130 grams of the liquid. A suitable diglycidyl ether of neopentyl glycol is commercially available from Shell Chemical Company under the trade name “HELOXY®68”. This epoxide containing liquid has a viscosity at 25° C. in the range of from about 13 to about 18 centipoises, a molecular weight of 216 and a 1-gram equivalent of epoxide per about 130 to about 140 grams of the liquid. A suitable diglycidyl ether of cyclohexanedimethanol is commercially available from Shell Chemical Company under the trade name “HELOXY®107”. This epoxide containing liquid has a viscosity at 25° C. in the range of from about 55 to about 75 centipoises, a molecular weight of 256 and a 1-gram equivalent of epoxide per about 155 to about 165 grams of the liquid.
A variety of hardening agents can also be utilized in the sealing composit
Chatterji Jiten
Cromwell Roger S.
Crook Ronald J.
Gray Dennis W.
King Bobby J.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Tsay Frank S.
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