Method of enhancing drilling fluid performance

Abstract

The present invention relates to methods of drilling a wellbore wherein a drill-in fluid is foamed at the drill tool. A method in accordance with the present invention comprises providing a drill-in fluid comprising an aqueous fluid, a foaming agent, a foam stabilizer, a gas generating chemical and an encapsulated activator; introducing the drill-in fluid downhole into a drill string connected to a drill tool; and allowing the drill-in fluid to exit the drill tool where, upon exiting the drill tool, the encapsulated activator is de-capsulated sufficiently to react with the gas generating chemical such that a gas is generated within the drill-in fluid and thus foams the drill-in fluid.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to methods of enhancing drilling fluid performance. More particularly, the present invention relates to enhancing drilling fluid performance where foam is used as at least part of the drilling fluid.[0003]2. Description of Related Art[0004]Hydrocarbons, such as oil and gas, may be recovered from various types of subsurface geological formations. Such formations typically consist of a porous layer, such as limestone and sands, overlaid by a nonporous layer. Hydrocarbons cannot rise through the nonporous layer, and thus, the porous layer forms a reservoir in which hydrocarbons are able to collect. A well is drilled through the earth until the hydrocarbon bearing formation is reached. Hydrocarbons then are able to flow from the porous formation into the well.[0005]In conventional drilling processes, a drill bit is attached to a series of pipe sections or coiled drilling tubing referred to as t...

AI Technical Summary

Benefits of technology

The present invention provides a method of drilling in a wellbore by generating gas downhole during drilling operations. This is achieved by introducing a drill-in fluid containing an aqueous fluid, a foaming agent, a foam stabilizer, a gas generating chemical, and an encapsulated activator into the drill string. The encapsulated activator is then de-capsulated sufficiently to react with the gas generating chemical and generate gas within the drill-in fluid, resulting in the formation of a foam. This foam can improve the efficiency of drilling operations and facilitate the removal of drill cuttings.

Problems solved by technology

Also when rotary drill tools or drill bits are used, a tremendous amount of heat can be generated as the drill string is rotated and the bit cuts through the earth.

These drilling fluids have traditionally been called drilling mud and the drilling has been conducted in an overbalanced condition; that is, the hydrostatic pressure of drilling fluid in the wellbore exceeds the pressure of hydrocarbons in the formation.

A major consequence of overbalanced drilling operations is that drilling fluid can flow from the wellbore into the formation.

Seepage, and especially lost circulation, in turn may have several deleterious and costly effects.

The amount and cost of drilling fluid required to drill the well, therefore, is increased.

Second, seepage and lost circulation of drilling fluid can carry with it the cuttings and many of the other components in the drilling fluid, which can decrease the permeability of the formation.

Thus, it becomes more difficult for oil to flow from the formation once drilling is completed and production is started.

Decreased permeability also may require acidizing or fracturing the hydrocarbon bearing formation to enhance production from the formation, which will further increases costs.

While drilling mud is suitable for use in a wide variety of hydrocarbon bearing formations, in many formations the hydrostatic pressure of hydrocarbons in the formation is relatively low and many drilling muds are simply too heavy for low pressure formations.

They can significantly overbalance the well, allowing excessive amounts of drilling fluid to flow into the formation.

The problems caused by seepage and lost circulation are exacerbated when a low pressure formation is also relatively fragile, such as fractured limestone formations.

Fragile formations may be excessively fractured by the hydrostatic pressure of drilling fluid flowing into the formation and carry even more materials into the formation that will diminish its permeability.

Seepage and lost circulation materials, in particular, if they are carried into the formation, can cause extensive damage to the formation.

Generally, additives in drill-in fluids have been limited to ones essential for filtration control and cuttings carrying.

Such drill-in fluids may still be too heavy for use in extremely low-pressure, fragile formations without substantial losses.

Both generating foam at the surface and below the surface, by use of separate streams, entail significant cost.

Thus, systems for preparing and circulating foamed drill-in fluids are relatively costly and require more maintenance, control, and logistical support than those required for more traditional suspended solids drilling fluids.

Such problems are exacerbated in offshore drilling operations where maintenance and logistical support are more difficult and costly.

Offshore, however, valuable space on the drilling rig deck is required, or it may be necessary to provide a barge or support boat to accommodate a foam circulation system.

That can add considerable cost to the drilling operation.