Methodolgy and apparatus for programmable robotic rotary mill cutting of multiple nested tubulars

Abstract

A methodology and apparatus for cutting shape(s) or profile(s) through well tubular(s), or for completely circumferentially severing a well through multiple tubulars, including all tubing, pipe, casing, liners, cement, other material encountered in tubular annuli. This rigless apparatus utilizes a computer-controlled, downhole robotic three-axis rotary mill to effectively generate a shape(s) or profile(s) through, or to completely sever in a 360 degree horizontal plane wells with multiple, nested strings of tubulars. This is useful for well abandonment and decommissioning where complete severance is necessitated and explosives are prohibited, or in situations requiring a precise window or other shape to be cut through a single tubular or plurality of tubulars.

Description

REFERENCE TO RELATED APPLICATION[0001]This application claims priority under 35 U.S.C. § 119 to application No. 61 / 131,874, filed Jun. 14, 2008, entitled “Rotary milling casing cutter,” which is hereby fully incorporated by reference.BACKGROUND OF THE INVENTION[0002]When oil and gas wells are no longer commercially viable, they must be abandoned in accord with government regulations. Abandonment requires that the installed tubulars, including all strings of tubing, pipe, casing or liners that comprise the multiple, nested tubulars of the well must be severed below the surface or the mud line and removed. Using explosive shape charges to sever multiple, nested tubulars in order to remove them has negative environmental impacts, and regulators worldwide are limiting the use of explosives. Therefore, a need exists for effective alternatives to the use of explosives for tubular severance in well abandonment.[0003]Mechanical blade cutting and abrasive waterjet cutting have been implement...

AI Technical Summary

Benefits of technology

[0013]This invention provides methodology and apparatus for efficiently severing all installed multiple, nested strings of tubulars, either concentric or eccentric, as well as cement or other material in the annuli between the tubulars, in a single trip into a well bore. This invention overcomes the difficulties encountered by prior art mechanical blade cutters by the rotary mill cutter machining through metal tubulars and other encountered material even if the nested tubulars and cement are not installed concentrically.

[0014]The invention utilizes a computer-controlled robotic downhole rotary mill to effectively generate a shape(s) or profile(s) through, or completely sever in a 360 degree horizontal circumferential plane, all installed tubing, pipe, casing and liners as well as cement or other material encountered in the annuli between the tubulars. This process occurs under programmable robotic, computerized control, making extensive use of digital sensor data to enable algorithmic, robotic actuation of the downhole assembly and robotic rotary mill cutter.

[0015]With this invention, for the purposes of complete severance of multiple, nested tubulars, the beginning and end points of the cut are immaterial as the robotic rotary mill cutter generates a wide swath or void. The severed casing will drop vertically at the surface platform, providing visual verification of the severance. The length, and therefore the reach of the spindle, is designed to extend beyond the outermost casing with any number of additional tubulars inside this outermost casing being extremely eccentrically positioned, even with each tubular abutting each successively nested tubular. This solves the cutting “reach” problems that are encountered with abrasive waterjet cutting when the waterjet has difficulty cutting through the thickest, most widely spaced mass of the eccentrically positioned tubulars and cement. The precision, programmable computer-controlled, sensor-actuated rotary milling process will take much less time to complete severance than mechanical blade cutters or abrasive waterjet cutting. The extremely precise, actively adjusted rotary milling, profile generation process greatly limits vibration and impact, preventing the impact breakage that plagues mechanical blade cutters encountering non-concentric, multiple, nested tubulars. Furthermore, this invention's capability of being deployed and completing the severance in one trip downhole provides a significant advantage over prior art.

Problems solved by technology

When oil and gas wells are no longer commercially viable, they must be abandoned in accord with government regulations.

Using explosive shape charges to sever multiple, nested tubulars in order to remove them has negative environmental impacts, and regulators worldwide are limiting the use of explosives.

Rotary drive systems are both cumbersome and expensive to have at the work site.

An example of the prior art is disclosed in U.S. Pat. No. 5,150,755, which is deficient in that its mechanical blade cutters may break when they encounter non-concentric tubulars, defeating its aim of severing multiple strings of tubulars in a single trip.

Another deficiency is the limitation on the number of nested tubulars that may be severed by this mechanical blade cutter.

There is no claimed capability of severing a greater number of tubulars, for example, five, nested tubulars, and certainly not in the event that such multiple, nested tubulars were to be non-concentrically positioned.

Thus these fundamental problems of prior art in mechanical blade cutting persist.

The mechanical blade cutter trip back into the wellbore to the previous tubular cut location for additional cutting is compromised because the length of the work string varies due to temperature changes or occasionally human error in marking or counting work string joints.

Non-concentric, multiple, nested tubulars present serious difficulties for mechanical blade cutters.

The prior art utilizing abrasive waterjet cutters also experiences difficulties and failures to make cuts through multiple, nested tubulars.

However, the prior art in abrasive waterjet cutters for casing severance often results in spiraling cuts with narrow kerfs in which the end point of the attempted circumferential cut fails to meet the beginning point of the cut after the cutting tool has made a full 360 degree turn.

In other words, the cut does not maintain an accurate horizontal plane throughout the 360 degree turn, and complete severance fails to be achieved.

Another problem encountered by prior and current art abrasive waterjet cutting is the inability to cut all the way through the thicker, more widely spaced mass of non-concentrically positioned tubulars.

A further disadvantage of traditional abrasive waterjet cutting is that in order to successfully cut multiple, nested tubulars downhole, air is required to be pumped into the well bore to the area where the cutting is to take place, allowing the abrasive waterjet tool to function in air and not be impeded by water or wellbore fluid.

The presence of fluid in the cutting environment greatly limits the effectiveness of prior art abrasive waterjet cutting.

This method of verification is time-consuming and expensive.

However, these milling methods do not completely sever multiple, nested non-concentric tubulars for well abandonment.

This prior art does not permit 360 degree circumferential severance of multiple, nested tubulars and is not suited for the purpose of well abandonment.

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