Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2002-07-25
2003-02-11
Suchfield, George (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C106S676000, C106S677000, C106S678000, C166S292000, C166S295000, C166S309000
Reexamination Certificate
active
06516883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and low density compositions for cementing pipe in well bores, and more particularly, to such methods and compositions for cementing pipe in well bores penetrating subterranean zones or formations which readily fracture at low hydrostatic pressures.
2. Description of the Prior Art
Hydraulic cement 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 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 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 lightweight cement compositions have been developed and used heretofore, i.e., cement compositions having densities as low as about 12 pounds per gallon, subterranean zones or formations are still encountered which have fracture gradients too low for even the lightweight cement compositions to be utilized without fracturing the formation and the occurrence of lost circulation problems. Also, the lightweight cement compositions utilized heretofore have often not had sufficient compressive, tensile and bond strengths upon setting.
Thus, there are continuing needs for improved methods of cementing pipe in well bores and low density cement compositions which have enhanced compressive, tensile and bond strengths upon setting.
SUMMARY OF THE INVENTION
The present invention provides methods of cementing pipe in well bores and low density cement compositions therefor which meet the needs described above and overcome the deficiencies of the prior art. The methods of this invention for cementing pipe in well bores penetrating subterranean zones or formations which readily fracture at low hydrostatic pressures are comprised of the following steps. A low density cement composition having enhanced compressive, tensile and bond strengths upon setting is provided comprised of a hydraulic cement, sufficient water to form a slurry and hollow glass microspheres which are surface treated with a mixture of organosilane coupling agents present in an amount sufficient to produce a cement composition density in the range of from about 6 to about 12 pounds per gallon. The cement composition is placed into the annulus between the pipe to be cemented and the walls of the well bore and the cement composition is allowed to set therein. Upon setting, the cement composition provides enhanced compressive, tensile and bond strengths and seals the exterior surface of the pipe to the walls of the well bore.
A low density cement composition having enhanced compressive, tensile and bond strengths upon setting of this invention is comprised of a hydraulic cement, sufficient water to form a slurry and hollow glass micro spheres surface treated with a mixture of organosilane coupling agents present in an amount sufficient to produce a cement composition density in the range of from about 6 to about 12 pounds per gallon.
The low density cement compositions of this invention described above can also have densities of about 5 pounds per gallon or below by foaming the compositions.
The 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
Improved methods of cementing pipe in well bores penetrating subterranean zones or formations which readily fracture at low hydrostatic pressures are provided by the present invention. The methods are basically comprised of the following steps. A low density cement composition having enhanced compressive, tensile and bond strengths upon setting is provided. The low density cement composition is comprised of a hydraulic cement, sufficient water to form a slurry, hollow glass microspheres which have been surface treated with a mixture of organosilane coupling agents and optionally, a gas and a mixture of foaming and foam stabilizing surfactants for foaming the cement composition. The microspheres are present in the low density cement composition in an amount sufficient to produce a density in the range of from about 6 to about 12 pounds per gallon and when the composition is foamed, it can have a density of about 5 or below. The cement composition is placed into the annulus between the pipe and the walls of the well bore and the cement composition is allowed to set therein.
Because the cement composition has a low density, i.e., a density such that the hydrostatic pressure of the cement composition exerted in the subterranean zone or formation being cemented is less than the fracture gradient of the subterranean zone or formation, fracturing of the zone or formation does not take place. Also, because the cement composition of this invention has enhanced compressive, tensile and bond strengths upon setting, a strong bond exists between the pipe and the walls of the well bore penetrating the subterranean zone or formation which prevents formation fluids from entering the annulus between the pipe and the well bore. The high overall strength of the cement composition also prevents it from being shattered by contact with the drill bit and drill string when the well is drilled to greater depths.
Examples of hydraulic cements which can be utilized in accordance with the present invention include, but are not limited to, Portland cements, slag cements, pozzolana cements, gypsum cements, aluminous cements, silica cements and alkaline cements. Of these, Portland cement is preferred. The Portland cement can be of ultra fine particle size or standard particle size with the ultra fine particle size being preferred for use in subterranean zones or formations having high permeabilities and which fracture at very low cement hydrostatic pressures.
The water utilized in the cement composition can be fresh water or salt water. The term “salt water” is used herein to mean unsaturated salt solutions or saturated salt solutions including brine and seawater. The water used is generally present in the low density cement composition in an amount in the range of from about 58% to about 160% by weight of the hydraulic cement in the composition.
The hollow glass microspheres utilized in the low density cement compositions are preferably synthetic hollow glass microspheres which are commercially available from the Minnesota, Mining and Manufacturing Co. (“3M™”) under the trade name “SCOTCHLITE™”. These very low density microspheres are formed of a chemically stable soda-lime borosilicate glass composition which is non-porous. The hollow glass microspheres are included in the cement composition of this invention in an amount sufficient to produce a cement composition density in the range of from about 5 to about 12 pounds per gallon. Generally, the hollow glass microspheres are included in the cement composition in an amount of fr
Brenneis Darrel C.
Chatterji Jiten
Cromwell Roger S.
King Bobby J.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Suchfield George
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