Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
2000-09-14
2003-01-21
Schoeppel, Roger (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C106S607000
Reexamination Certificate
active
06508305
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to cement compositions including mixtures of substantially elastic material and cement and, in one application, to methods for cementing using such cement compositions in substantially closed systems, such as the interior of a mold used for producing preformed concrete items.
2. Description of the Related Art
Cement inflatable packers were originally developed to provide isolation in open holes for stimulation treatments and for water shutoff. Today these packers are being used as an integral part of completion operations to, among other things, provide zonal isolation, control gas migration, isolating the junctions of multilateral completions, and for gravel packing. However, the success rate associated with inflatable packer completions has typically been low. This low success rate has been attributed to, among other things, volumetric shrinkage of Portland cement which is typically employed to inflate cement inflatable packers.
A typical inflatable packer has an annular elastomer packer element mounted around a central tubular member. The elastomer packer element is adapted to receive cement slurry or other fluid, such as drilling mud, under pressure in such a way that the packer element is inflated and compressed between the inflation liquid and the wall of a wellbore. During use, such an inflatable packer is typically run into a wellbore on a pipe string and positioned at a selected setting depth within the wellbore. Once inflated by an inflation fluid, such as cement, a valve system is typically provided within the packer in order to isolate the inflation fluid under pressure inside the inflated elastomer packer element. When used to achieve zonal isolation, the trapped inflating pressure of the inflation fluid within the elastomer packer element must be sufficiently high to maintain a positive hydraulic seal between the exterior of the packer element and the borehole wall.
In typical completion operations, Portland cement is used to inflate the element of an inflatable packer. Typically, a Portland cement undergoes a reduction in volume of from about 2% to about 4.5% during curing or hydration. In well cementing applications not involving inflatable packers, this volume loss is often masked or compensated for by the fact that free water, available from subterranean formations, imbibes into the exposed setting cement. This offsets shrinkage and may even cause a slight expansion. However, in a substantially closed system, such as that present within an inflatable packer, this osmotic transfer of water does not occur. As a consequence, shrinkage and dimensional changes of conventional Portland cement upon curing within an elastomer packer element may result in lack of sufficient pressure or strain to maintain a positive seal. This may result in the formation of a microannulus or other zone of communication which permits pressure and/or fluid communication across one or more areas between the inflated packer element and the borehole wall. Therefore, cement dimensional changes within an inflatable packer have often been linked to various completion problems, including interzonal communication and migration of fluids, such as gas. Such problems typically require costly remedial efforts which may or may not be successful.
Other applications in which cement shrinkage and dimensional changes may have adverse effects include cement applications in other substantially closed systems, such as during annular cementing of concentric strings of pipe in a wellbore. Such adverse effects may also result in the formation of a zone of communication which permits pressure and/or fluid communication across one or more areas in the annular space between the strings of pipe, resulting in various completion problems, including interzonal communication and fluid migration. Substantially closed systems and problems associated therewith may also be present in non-wellbore cementing applications as well.
In an effort to control or prevent cement shrinkage, additives have been developed which favor the expansion of cement. Such additives include materials such as salt, hemihydrated calcium sulfate, magnesium (calcium) oxide, and mixtures thereof. These additives typically require an extraneous source of water to effect expansion of the set cement. Therefore, even with these additives, most cement slurries will exhibit shrinkage under conditions where no access to external water is provided, such as those conditions found within an inflatable packer element. Magnesium oxide and magnesium (calcium) oxide additives used in sufficient concentrations with conventional cements may cause expansion without access to external water, but typically produce excess surface mixing viscosities, are difficult to retard under downhole conditions, and may deteriorate (i.e., exhibit cracking, excessive porosity, etc.) due to excessive increases in bulk volume, and/or uncontrolled expansion.
In an attempt to compensate for the lack of external water available to cement in a closed system, greater amounts of expanding agents (typically greater than 10% by weight) have been employed. However, a number of disadvantages are associated with these relatively high levels of expanding agent concentrations. Such disadvantages include shortened thickening times, excessive mixing viscosity, placement problems, downhole rheologies that create high friction during placement, and high cost. Gas generating additives may be employed to impart expansion, however these materials typically generate flammable gases. The effect of such gases on the long term stability of metal and/or sealing elements is unknown.
SUMMARY OF THE INVENTION
Disclosed herein are compositions and methods of cementing therewith. In one embodiment, a composition may include a mixture of hydraulic cement and a substantially elastic material, and a method of cementing may include placing an uncured cement composition in a selected location and allowing the cement composition to cure to form a cured cement composition; wherein the uncured cement composition includes a mixture of hydraulic cement and substantially elastic material. The substantially elastic material may be selected so that at least a portion of the substantially elastic material yields (i.e., deforms or compresses to a volume that is smaller than the volume of the elastic material in its non-compressed state) under conditions existing when the uncured cement composition is placed in the selected location. Such conditions may include, for example, exposure to pressure or other compressional forces present in the selected location when the uncured cement is placed in position. In one embodiment, the cured cement composition may be formulated to exhibit substantially the same to bulk volume upon curing in the absence of external water as the bulk volume of the uncured cement composition (or to exhibit a net shrinkage in bulk volume upon curing in the absence of external water of less than about 1% as compared to the bulk volume of the uncured cement composition).
In another respect, disclosed is a method of cementing within a wellbore, including introducing an uncured cement slurry into a wellbore, and allowing the cement slurry to cure to form a cured cement composition. In this method the uncured cement slurry may include a mixture of hydraulic cement and a particulate material, with the particulate material being substantially elastic under in situ cementing conditions. Furthermore, within the wellbore, at least a portion of the individual particles of the substantially elastic particulate material may each have a respective first volume at in situ wellbore cementing conditions prior to curing of the cement slurry; and may also each have a respective second volume at in situ wellbore cementing conditions after curing of the cement slurry to form the cured cement composition, with the second volume being larger than the first volume so as to at least partially counteract volumetric shrinkage of the cement slurry dur
Brannon Harold D.
Dillenbeck Robert L.
Mueller Dan T.
Stephenson Christopher J.
BJ Services Company
O'Keefe Egan & Peterman, LLP
Schoeppel Roger
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