Controlled variable density fluid for wellbore operations

Abstract

Fluid systems may contain elements to provide changes in bulk fluid density in response to various environmental conditions. One environmental driver to the variable density is pressure; other environmental drivers include, but are not limited to, temperature or changes in chemistry. The variable density of the fluid is beneficial for controlling sub-surface pressures within desirable pore pressure and fracture gradient envelopes. The variability of fluid density permits construction and operation of a wellbore with much longer hole sections than when using conventional single gradient fluids.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. provisional application No. 60 / 582,687 filed Jun. 24, 2004.FIELD OF THE INVENTION [0002] The present invention relates to wellbore operations fluids, and more particularly relates, in one embodiment, to wellbore operations fluids having variable density. BACKGROUND OF THE INVENTION [0003] Prior variable density drilling fluids primarily concerned the use of a highly compressible gas (e.g. air or nitrogen) as a free phase in the fluid. Limited, if any, efforts are made during conventional air, mist or foam drilling to control the expandability of the bulk fluid or to adjust or engineer the compressibility of the fluid other than managing the ratio of air or other gas to the fluid. Other proposals to employ a virtual multiple gradient fluid include so-called dual gradient drilling. This method would use two columns of different density fluids. One column would be essentially static, while the sec...

AI Technical Summary

Benefits of technology

[0008] Still another object of the invention is to provide a method of drilling a wellbore with a reusable, variable density fluid that permits construction and operation of a wellbore with longer hole sections than when using conventional single gradient fluids.

[0011] There is additionally provided a method of improving the lift of a produced fluid that involves injecting into the produced fluid at a subsurface point an effective amount of a plurality of elements that change their volume / weight ratio in response to a condition that may be pressure, temperature, and / or chemical composition of the produced fluid to increase the lift thereof.

Problems solved by technology

Limited, if any, efforts are made during conventional air, mist or foam drilling to control the expandability of the bulk fluid or to adjust or engineer the compressibility of the fluid other than managing the ratio of air or other gas to the fluid.

While these density changes are often accounted for during the mathematical modeling of the fluid pressures in the wellbore, the density changes resulting from this behavior is not sufficient to change the design of the wellbore with respect to pore and fracture pressure profiles, as well as position and number of casing strings.

No effort is known to be made to intentionally modify the compressibility (density) of classic drilling fluids.

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