Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-08-26
2002-11-12
Wood, Elizabeth D. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S639000, C106S692000, C106S696000, C106S737000, C106S772000, C106S788000, C106S726000, C106S727000, C106S730000, C106S732000, C106S780000, C106S819000, C106S820000, C106S823000, C507S103000, C507S129000, C507S135000, C507S136000, C507S139000, C507S140000, C507S906000
Reexamination Certificate
active
06478868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to early-enhanced strength foamed and non-foamed cement compositions that can be utilized in a variety of applications.
2. Description of the Prior Art
Hydraulic cement compositions, both foamed and non-foamed, are commonly utilized in surface construction applications as well as in the construction of oil, gas and water wells. For example, in the construction of wells, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing and liners 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 surfaces of a pipe string 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 exterior surfaces of 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 carrying out primary cementing, the foamed or non-foamed cement compositions utilized must have adequate pumping time before placement and relatively short set times after placement within which the cement compositions attain high compressive strengths. If a well cement composition is slow to set, pressurized formation fluids can flow into and through the cement composition before and after it sets. Also, in well construction, it is important that the cement composition used sets and attains compressive strength as quickly as possible in order to prevent long drilling rig down time and the high costs associated therewith. Similar situations exist in surface construction projects.
Heretofore, inorganic salts such as calcium chloride, sodium chloride and the like have been used as set accelerators and compressive strength enhancers in cement compositions. However, in very low temperature applications, such salts are relatively ineffective in providing accelerated set times and enhanced compressive strengths. Also, the heretofore used inorganic salts must often be used in high concentrations as a result of low temperature conditions to produce enhanced compressive strengths. The high concentrations drastically reduce the placement or pumping times of the cement compositions that are often too short for placing the compositions in the required locations. When set-retarding agents are utilized to increase the placement or pumping times of the compositions, the enhanced compressive strength development of the cement compositions is also lost. Another disadvantage associated with the use of chloride salts is that suchksalts can cause steel pipe or steel structural members in contact with cement compositions containing the salts to rapidly corrode.
Thus, there are continuing needs for improved early-enhanced strength cement compositions for use in surface construction projects and in the construction of wells.
SUMMARY OF THE INVENTION
The present invention provides improved early-enhanced strength cement compositions and methods that meet the above-described needs and overcome the deficiencies of the prior art. The improved early-enhanced strength cement compositions of this invention are basically comprised of a hydraulic cement, water present in an amount sufficient to form a slurry and hydrophobic silica powder present in the compositions in an amount sufficient to provide early and enhanced compressive strength to the compositions. The hydrophobic silica is preferably present in the cement compositions in an amount in the range of from about 0.3% to about 5% by weight of cement in the compositions.
If the time between when a cement composition of this invention is formed and when the composition sets is too short to place the composition in a desired location, a known set-retarding additive can be added to the composition to increase the placement time without affecting the enhanced compressive strength development of the cement composition.
The present invention also provides lightweight cement compositions, i.e., non-foamed cement compositions that have low densities, but provide high compressive strengths for cementing subterranean zones having low fracture gradients or for use in the construction industry generally.
The methods of this invention for cementing a construction zone are basically comprised of the following steps. A cement composition is formed comprised of hydraulic cement, water present in an amount sufficient to form a slurry and hydrophobic silica powder. The composition is placed in the construction zone, and then allowed to set into a hard impermeable mass therein.
It is, therefore, a general object of the present invention to provide improved early-enhanced strength cement compositions 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
The phrase “early-enhanced strength cement composition” is used herein to mean a cement composition that has an accelerated set time and also has enhanced compressive strength after setting. Prior to this invention, inorganic salts such as calcium chloride, sodium chloride and the like have been used in cement compositions as set accelerators and compressive strength enhancers. However, in low temperature applications, i.e., applications wherein the cement temperature is in the range of from about 40° F. to about 70° F., such salts are relatively ineffective in providing an early set or enhanced compressive strength to a cement composition. Also, such inorganic salts must often be used in high concentrations whereby they decrease the placement or pumping time, i.e., the time between cement composition preparation and when the cement composition sets, to a time period so short that the composition can not be placed or pumped into a desired location. Further, when chloride salts are utilized in cement compositions, they often cause corrosion to steel members in contact with the set cement compositions containing the salts.
The improved early-enhanced strength cement compositions of this invention attain early-enhanced compressive strengths over a broad temperature range including at the low temperatures often encountered in offshore wells and in many surface construction projects, i.e., temperatures in the overall range of from about 40° F. to about 130° F. Another novel beneficial characteristic of the cement compositions of this invention is that when longer placement or pumping times are required, a set-retarding agent can be utilized without affecting the enhanced compressive strengths attained by the compositions.
As mentioned, the early-enhanced strength cement compositions of this invention can be foamed or non-foamed. The non-foamed cement compositions are basically comprised of a hydraulic cement, water present in an amount sufficient to form a slurry and hydrophobic silica powder to provide early and enhanced compressive strength to the cement compositions and/or to provide lightweight to the cement compositions. The foamed cement compositions are the same as the non-foamed compositions except that they further include a gas present in an amount sufficient to form a foam and a mixture of foaming and foam stabilizing surfactants present in an effective amount.
A variety of hydraulic cements can be utilized in the foamed and non-foamed compositions including, but not limited to, those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, pozzolana cements, gypsum cements, high aluminum content cements and high alkalinity Cements. Portland cements are generally preferred for use in the construction of oil, gas and water wells. P
Crook Ronald J.
Fitzgerald Russell M.
Gray Dennis W.
Reddy Baireddy R.
Traxel Brent E.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Wood Elizabeth D.
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