Ultra low density cementitious slurries for use in cementing of oil and gas wells

Abstract

The storable, low-density, hydraulically-active, cementitious slurry of the invention is suitable for cementing within a subterranean formation for oil or gas wells. The low-density slurry comprises a hydraulically-active cementitious material, a set retarder, a plasticizer, glass or ceramic micro-spheres, and a strengthening agent. Further the slurry is substantially free of a suspension agent. The storable, low-density, hydraulically-active, cementitious slurry is made by adding glass or ceramic micro-spheres to a hydraulically-active cementitious material, adding a strengthening agent to the microsphere containing composition, and mixing the resulting composition with water, a set retarder, and a plasticizer to generate a slurry, wherein the set retarder is present in an amount sufficient to allow storage of the slurry.

Description

[0001] This application claims the benefit of U.S. patent application Ser. No. 10 / 646,147 filed on Aug. 22, 2003.FIELD OF THE INVENTION [0002] This invention relates to ultra low density storable cementitious slurries useful for oil and gas well cementing, as well as to a method of cementing an oil or gas well using such slurries. Such cementitious slurries are further useful in the zonal isolation of subsurface formations. BACKGROUND OF THE INVENTION [0003] Hydraulic cements are cements that set and develop compressive strength due to a hydration reaction, not drying. Thus, hydraulic cements can set under water. Consequently, hydraulic cements are often used for cementing pipes or casings within a well bore of a subterranean formation for the construction of oil, gas and water wells, as well as other purposes, such as remedial squeeze cementing. In the oil and gas industry, successful cementing of well pipe and casing during oil and gas well completion requires cement slurries to e...

AI Technical Summary

Benefits of technology

[0009] The storable, low-density, hydraulically-active, cementitious slurry of the invention is suitable for cementing within a subterranean formation for oil or gas wells. The low-density slurry comprises a hydraulically-active cementitious material, a set retarder, a plasticizer, glass or ceramic micro-spheres, and a strengthening agent. Further the slurry is substantially free of a suspension agent. Use of such slurries in oil or gas wells helps to establish zonal isolation within the cemented wellbore of the subsurface formations.

[0010] The storable slurry of the present invention allows the density of the cement to be pre-determined and accurately measured before the cementitious slurry is shipped to the wellsite. This in turn, can reduce up-front cost for mechanical equipment such as foam generators and associated nitrogen pumps and storage vessels.

[0011] Further, this invention establishes an alternate means to accurately mix and place ultra-low density cement systems without the use of conventional continuous mix cementing equipment or foam and its associated equipment.

[0013] Further, the accurate control of the premixed slurry properties eliminates job uncertainties and leads to a significant improvement in QA / QC.

Problems solved by technology

Conventional mixing equipment is relatively complex and expensive since it must permit the addition of water to dry cement powder, homogenization of the mixture, measurement of its density and, if necessary, recirculation of the mixture.

If cementing solids are not correctly proportioned, the quality of the cement diminishes.

It is sometimes necessary to use a lightweight cement when there is a weak subterranean formation.

This foaming operation can be difficult because additional nitrogen equipment is required and the addition of gas must occur onsite which requires that the density of the slurry be carefully measured before use.

Such methods can be an inaccurate means of cement solids to water ratio verification—when the density of the cement approaches the density of water, making differentiation between cement and water difficult.

However, the difficulty with these disclosures, and other conventional cementing slurries, is that they set quickly and therefore cannot be made in advance of their use.

A delay in the drilling operation delays the cementing job.

If personnel and equipment for cementing idly wait onsite until the drilling ends, a delay can increase the cost of the cementing job.

These patents, however, do not disclose the use of low density slurries in a storable form.