Method and System for Forming a Non-Circular Borehole

Abstract

System and methods for creating shaped, non-circular boreholes in rocks especially for use with geothermal heat pump applications and for increasing wellbore support in applications such as horizontal oil and gas drilling are described. The systems and methods when applied to geothermal heat pumps create an elliptical shaped hole that is optimized for placing heat transfer tubes with a minimum of grout used. The significantly reduced cross-sectional area of the elliptical borehole also increases the overall drilling rate in rock and especially in hard rocks. In horizontal hard-rock drilling, creation of a horizontal non-circular borehole or modification of a circular borehole to a non-circular geometry is used to stabilize the borehole prior to casing insertion, and may also allow the use of lower mud pressures improving drilling rates. The system uses a non-contacting drilling system which in one embodiment uses a supersonic flame jet drilling system with a movable nozzle that swings between pivot points. In a second embodiment the elliptical shaped hole is created by an abrasive fluid or particle bearing-fluid or air jet drill that moves between pivot points. In another embodiment a non-contacting drill can use dual parallel nutating nozzles that create a pair of overlapping circular holes. The non-circular shaped hole is created by either the high temperature flame or water-particle jet or chemically active fluid jet as it removes rock material by erosion, dissolution and or thermal spalling. Modifications of circular boreholes to a generally elliptical shape can also be done using milling or jetting techniques.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Patent Application No. 60 / 786,456, filed Mar. 27, 2006 whose teachings are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]The present invention relates in general to the formation of intentionally non-circular boreholes. These non-circular boreholes may be shaped for optimized use in a specific system or application, such as underground heat exchange systems, or they may be formed as a means to stabilize the borehole during the drilling, casing, and completion or in operation.[0003]Most conventional and non-conventional drilling techniques are designed to produce boreholes that are substantially circular. In some formations, such as hard rocks with primary stresses oriented vertically, circular boreholes are inherently unstable which might be caused by the non-uniform stress conditions in the rock or from a general weakness in the rock. Once a circular hole is produc...

AI Technical Summary

Benefits of technology

"The present invention provides a system and method for creating non-circular boreholes in rocks, such as elliptical or eccentric shaped holes, for the purpose of stabilizing the wellbore and facilitating the installation or operation of a system. These non-circular holes can help prevent breakouts, improve heat exchange, and increase drilling rates. The invention can be used in various applications such as drilling, piping, and cables. The non-circular hole is created using a non-contacting drilling system, such as a supersonic flame jet drilling system or a high velocity air stream with suspended or entrained particulates. The invention provides an improved geometry for heat exchange and reduces the amount of material that must be removed."

Problems solved by technology

Break-out may be particularly severe in significantly horizontal or non-vertical portions of the wellbore.

Breakout can be caused by significant non-uniform stress concentration in the unsupported borehole resulting in localized shear failure at two opposite nodes in a direction normal to the main stress direction.

Once the break-out occurs, the borehole has a more stable geometry but the material generated by the small scale collapse can cause major complications, delays, and expenses in the drilling, casing and completion of wells.

Images