Apparatus for wellbore communication

Abstract

Methods and apparatus for communicating between surface equipment and downhole equipment. One embodiment of the invention provides a wellhead assembly that allows electrical power and signals to pass into and out of the well during drilling operations, without removing the valve structure above the wellhead. Another embodiment of the invention provides an electromagnetic casing antenna system for two-way communication with downhole tools. Another embodiment of the invention provides an antenna module for a resistivity sub that effectively controls and seals the primary / secondary interface gap.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims benefit of U.S. provisional patent application Ser. No. 60 / 485,816, filed Jul. 9, 2003, which is herein incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention generally relates to methods and apparatus for use in oil and gas wellbores. More particularly, the invention relates to methods and apparatus for communicating between surface equipment and downhole equipment. [0004] 2. Description of the Related Art [0005] Oil and gas wells typically begin by drilling a borehole in the earth to some predetermined depth adjacent a hydrocarbon-bearing formation. Drilling is accomplished utilizing a drill bit which is mounted on the end of a drill support member, commonly known as a drill string. The drill string is often rotated by a top drive or a rotary table on a surface platform or rig. Alternatively, the drill bit may be rotated by a downhole motor mounted at...

AI Technical Summary

Benefits of technology

Enables time and cost savings by allowing continuous monitoring of downhole tools, improves two-way communication with downhole tools by reducing signal attenuation, and reduces manufacturing costs for resistivity subs by allowing more flexible tolerance ranges.

Problems solved by technology

While drilling with weighted fluid provides a safe way to operate, there are disadvantages, like the expense of the mud and the damage to formations if the column of mud becomes so heavy that the mud enters the formations adjacent the wellbore.

Underbalanced drilling involves the formation of a wellbore in a state wherein any wellbore fluid provides a pressure lower than the natural pressure of formation fluids.

A significant difference between conventional overbalanced drilling and underbalanced drilling is that in the latter fluid pressure in the well acts on the drill string.

Consequently, when the drill string is inserted into the well or removed from the well, the drill string tends to be thrown out of the well due to fluid pressure acting on it from the bottom.

As the formation and completion of an underbalanced or near underbalanced well continues, it is often necessary to insert a string of tools into the wellbore that cannot be inserted through a rotating drilling head or blow out preventer due to their shape and relatively large outer diameter.

While lubricators are effective in controlling pressure, some strings of tools are too long for use with a lubricator.

However, there does not exist a system that allows passage of the electrical power and signals through the wellhead assembly during drilling operations.

Another problem encountered by many prior art downhole measurement systems is that these conventional systems lack reliable data communication to and from control units located on a surface.

For example, conventional measurement while drilling (MWD) tools utilize mud pulse telemetry which works fine with incompressible drilling fluids such as a water-based or an oil-based mud; however, mud pulse telemetry does not work with gasified fluids or gases typically used in underbalanced drilling.

However, EM telemetry suffers from signal attenuation as it travels through layers of different types of formations in the earth's lithosphere.

However, both of these techniques have their own problems and complexities.

Currently, there is no available means to cost efficiently relay signals from a point within the well to the surface through a traditional control line.

Another communication problem associated with typical drilling systems involves the resistivity subs which contain the antennas for transmitting and receiving electromagnetic signals.

This method is costly to manufacture and can be difficult to service.

Tight manufacturing tolerances typically results in higher costs.

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