Supplementary borehole drilling

Details Supplementary borehole drilling Supplementary borehole drilling

1998-07-20

2001-02-06

Neuder, William (Department: 3672)

Wells

Processes

Parallel string or multiple completion well

C166S117500, C166S050000

Reexamination Certificate

active

06182760

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a device and process for drilling at least two supplementary boreholes from an existing well or borehole. More specifically, the invention is concerned with providing a supplementary borehole drilling device and method for recovering additional oil or natural gas from an existing or abandoned production well.
BACKGROUND OF THE INVENTION
As the discovery of new oil fields or other natural resources becomes more difficult, increased emphasis has been placed on maximizing the recovery of natural resources from known sources. For known oil and gas fields, this emphasis has increasingly required additional wellbores to be drilled into less permeable or less productive portions of the field or a producing subterranean formation, e.g., drilling several supplementary or “step out” boreholes at a deviated angle from a nearly-vertical main portion of a conventional production well. Typically, the position and direction of the supplementary boreholes must be carefully controlled since oil or gas recovery from less productive portions of the field may be less tolerant of direction and positional errors when compared to vertical wells drilled into the more productive portions of the field.
Although supplementary boreholes can be drilled using various methods and devices, many supplementary boreholes have been drilled using a conventional whipstock tool and related apparatus. The conventional whipstock tool is typically prepositioned in a main portion of a well prior to drilling a supplementary borehole. A drill string is then run down the well and is diverted radially outward by the whipstock tool to drill a supplementary borehole into a formation of interest. After drilling the supplementary borehole and withdrawing the drill string, the conventional whipstock tool may be repositioned in the well to allow the drilling of a second supplementary borehole from the well. If several supplementary boreholes are drilled into a thin production zone, repositioning may only essentially require rotation of the whipstock tool within the well. One conventional whipstock with an associated tool assembly is an SS-WS packer and whipstock supplied by TIW located in Houston, Tex., USA. Another conventional means for drilling supplementary boreholes from an existing well is a Baker Downhole Drilling System supplied by the Baker Hughes Company, located in Houston, Tex., USA.
The drilling of supplementary boreholes from existing wells located on offshore platforms can be especially desirable. The limited space on a platform may not allow room for another conventional well to be drilled from the same platform and, even if room exists on the platform, another well may interfere with other closely spaced wells at shallow subsurface locations. One or more supplementary boreholes drilled from an existing well may be used to fracture less permeable formation portions near an existing platform well and/or provide an extended conduit within a shallow thin zone, significantly improving the recovery of oil or other resources.
However, the cost of conventionally drilling these supplementary boreholes has limited their use. The limited incremental amount and value of the recoverable natural resource in a less productive formation or a thin production zone can severely limit the acceptable cost of drilling and completing these supplementary boreholes. Additional risks of damaging the existing well can also result from conventional procedures such as repositioning the whipstock within the existing well and running drilling strings through existing well tubulars.
SUMMARY OF THE INVENTION
The present invention provides a method for drilling multiple supplementary boreholes from an existing borehole or well with an inventive whipstock string, the use of which substantially reduces the cost and time of drilling multiple boreholes by avoiding the need to withdraw the drill sting and reposition the whipstock string. In one embodiment, an inventive whipstock string comprises (1) joined conductor or duct sections having spaced-apart separators that form two semicircular, but discontinuous channels in the whipstock string and (2) a whipstock or end duct section that includes dual whipstocks, a load-bearing separator plate between the whipstocks, and two whipstock drilling ports in the end duct section. In a self-aligning embodiment of the invention, protruding separator plate portions and mating alignment slots are used to reliably self-align and position the duct sections during assembly and running of the whipstock string, allowing drilling of the supplementary boreholes to be more reliably directed into the formation of interest.
The process of using the inventive whipstock string reduces the risk of damaging the existing well and comprises running the whipstock string into the existing well, positioning one of the whipstock drilling ports and a whipstock adjacent to a desired kickoff location for a supplementary borehole, running a drilling assembly through one channel within the positioned whipstock string, and drilling outwardly into the formation to form a supplementary borehole portion. After drilling a first supplementary borehole, a second borehole can be drilled using a drilling assembly in a second channel within the positioned whipstock string. The supplementary boreholes allow fluids to be recovered or injected into a previously unused formation or a formation portion previously producing limited amounts of fluids.


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