Patent Application
20150239784
This disclosure relates generally to the field of compositions of cement used to seal the annular space between a drilled wellbore and the wall of a pipe of casing set therein. More specifically, the invention relates to compositions for such cement that set more quickly than convention cement and may be used to seal fluid, e.g., gas, leakage into the annular space of previously cemented pipe in a wellbore.
Cement of various compositions is used to seal an annular space between the wall of a drilled wellbore and a pipe or casing inserted into the wellbore. The cement serves, among other purposes, to hydraulically seal the annular space to prevent migration of fluids (oil, water and/or gas) between formations penetrated by the wellbore or migration of such fluids outside the annular space itself. During initial placement of cement, i.e., the “primary” cementing operation, pressure may be applied to the cement in the annular space and/or in the wellbore to enable proper sealing of the annular space during the time within which the cement, originally pumped as a liquid slurry, hardens and can form a hydraulic seal.
There are situations when the cement must be placed in a wellbore or annulus wherein: (1) the wellbore or annulus cannot be closed (sealed to form a pressure containment) after placement of the cement; (2) additional pressure cannot be applied to the sealed wellbore or annulus to force the cement into any leak path for fluids (i.e. cement cannot be ‘squeezed’ into place and held until it sets); (3) additional pressure cannot be applied to hold the cement in place until it sets; (4) additional pressure cannot be applied to increase pressure within the cement to prevent fluid from migrating through the cement before it sets (i.e., to prevent forming a permanent channel through the cement before or during the setting of the cement); and (5) additional pressure methods include pump pressure or increasing hydrostatic pressure within the closed annulus.
One aspect is a cement composition for sealing leaks in a wellbore includes at least one of an alkali and a transition metal oxide and an acid. A method for using the cement composition includes pumping the at least one of an alkali and a transition metal oxide and an acid as separate components into a wellbore so that a setting reaction begins after pumping is initiated.
Other aspects and advantages will be apparent from the description and claims which follow.
The cement may be placed by the above described tremie tube (grout line) method as shown in
Encapsulation of one or both of the reactive components of the fast-setting cement may be used to control reaction rate and/or eliminate the need for a chemical retarder for the reaction. Liquid solutions of the acid or acidic phosphorous-containing component may be emulsified in a non-aqueous phase such as hydrocarbons including natural and synthetic oils and esters or water-insoluble glycols. Solid components such as the alkali and/or transition metal oxides or solid acidic and acidicphosphorous containing compounds may be coated with water-soluble polymers or waxy surfactants to inhibit contact with the other component or formation of a reactive solution with or in water that will cause formation of the fast-setting cement.
Prior to pumping the sealing cement, it is desirable to determining the severity of the flow from the leak(s) and to determine the type of fluid flowing from the leak(s), i.e., gas or liquid such as water, brine or oil. It is also advisable to determine the maximum length needed for the sealing cement plug. It is also desirable to determine the setting time of the cement and the required time for placement. It is also desirable to determine the density of the cement plug that will temporarily slow or stop the flow of fluid from the leaking area until the cement sets. The density of the cement plug may range from 11 to 25 pounds per gallon (ppg).
Having explained a placement method for sealing cement to form a plug such as shown in
The metal oxide may be, for example, magnesium oxide, calcium oxide, aluminum oxide, zinc oxide, zirconium oxide or a magnesium aluminate spinel. A magnesia rich (MgO rich) spinel may be used in some examples. The magnesium oxide content for magnesia rich spinel should be greater than 20 percent (by weight) and preferably between 25 and 40 percent (by weight). The metal oxide can comprise 10 to 100 percent of the solids of the cement slurry and may be between 20 and 100 percent of the total solids and more preferably may be between 30 and 80 percent of the total solids in the slurry.
The metal oxide is preferably calcined or subjected to higher heat treatment to reduce its surface area and reactivity. Example materials include Magox 98 LR (sold by Premier Chemicals), and Magchem 10 (sold by Martin Marietta). A retarder for the cement may be used. For magnesium phosphate or magnesium polyphosphate base cement compositions, a water-soluble borate releasing or generating compound may be used, e.g., boric acid, borax, etc.
High aluminate first component cement may be used as a metal oxide source and reacted with an acidic phosphate or phosphorous acid.
Optionally, a high aluminate first component cement may be mixed with water and an accelerator added to produce a more rapid set. Accelerators for the aqueous high aluminate cement slurry may include lithium salts such as lithium carbonate, lithium chloride, and/or lithium hydroxide, for example.
Optionally, a slurry of high aluminate cement or Portland cement may be suspended in a non-aqueous carrying fluid (such as an oil or ester) and mixed with an accelerator and a water wetting surfactant. Cement reactions occur in water, therefore the setting reactions will not begin until the non-aqueous slurry is mixed with or contacts water. A water-wetting surfactant enhances the absorption of water into the cement slurry to start the setting reactions. Upon contact with water, the slurry viscosity increases and may prevent flow (or washing away of the slurry) until the cement sets.
Most cement slurries and drilling fluids are non-Newtonian fluids having a gel strength selected to suspend solids and have a selected yield point that must be exceeded to initiate flow. The slurry formulations described herein typically have a selected yield point and gel strength to prevent flow of the leaking fluid until the cement sets. Once flow stops, the gel strength of the slurry forms to keep solids in suspension. The gel strength is an electrostatic attraction force. As the gel strength develops and increases, the slurry begins to act more like a solid than a liquid. Therefore the full weight of the slurry is not transmitted to the surrounding pipe or formation in a well. In a wellbore, therefore, the hydrostatic pressure generated by a column of fluid begins to decrease as gel strength develops.
In a leaking well, the fluid flowing through the leak is driven by the pressure of the formation from which it originates. The hydrostatic pressure in the cement and fluid column above the leak must exceed the formation pressure of the fluid being forced through the leak until the cement develops sufficient structural strength to prevent fluid from flowing through it or washing it away from the opening of the leak.
A two component, fast setting cement formulation according to the present disclosure may comprise the following:
Two separate liquid mixtures are prepared. Each mixture may contain one component of the two-component system. The solutions are pumped at a specific volumetric ratio and mixed to form a high density, fast setting cement.
Example Mixture 1 may be composed of the following:
Example Mixture 2 may comprise the following:
These mixtures may be pumped at a volumetric ratio of 4.38:1 (42 gallons of mixture 1 to 9.6 gallons of mixture 2) to produce 51.6 gallons of fast setting cement having a density of 18.4 pounds per gallon when the two mixtures are combined in this volumetric ratio. The hydrostatic pressure from the column of 18.4 pound per gallon cement is used to stop fluid from migrating through the cement slurry until it sets. The xanthan gum polymer is added to the water prior to addition of the magnesium oxide, borax or barium sulphate to suspend solids during mixing. Different particle sizes of the heat-treated magnesium oxide are used to alter viscosity to make a pumpable slurry for equipment and slurry densities required for each application.
Example Mixture 1 is composed of the following:
Example Mixture 2 is composed of the following:
These mixtures may pumped at a volumetric ratio of 1.59:1 (42 gallons of Mixture 1 to 26.4 gallons of Mixture 2) to produce 68.4 gallons of fast setting cement having a density of 16 pounds per gallon when the two mixtures are combined in this volumetric ratio. The hydrostatic pressure from the column of 16 pound per gallon cement is used to stop fluid from migrating through the cement slurry until it sets. The xanthan gum polymer is added to the water prior to addition of the magnesium oxide, borax or barium sulphate to suspend solids during mixing. Different particle sizes of the heat-treated magnesium oxide are used to alter viscosity to make a pumpable slurry for equipment and slurry densities required for each application.
A plugging operation was designed based upon dumping both components (components as described herein above) down into a leaking well from surface for an onshore well. A solution of Noverite K-7058 polyacrylic acid was poured down into the well from the surface. Dry, coarse, granulated MagChem 10-12×40 mesh magnesium oxide was selected to be poured on top of and to fall through the acidic component to react and form a ductile, fast-setting cement in place. The volume of polyacrylic acid and magnesium oxide can be calculate to provide any required cement column length in the well based upon diameters of the wellbore or casings. A solution of ammonium polyphosphate or other phosphorous containing acids and their acidic salts could be used instead of polyacrylic acid.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/063759 | 10/8/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61713655 | Oct 2012 | US |
