Page 397 - Practical Well Planning and Drilling Manual
P. 397

Section 3 revised 11/00/bc  1/17/01  12:00 PM  Page 373








                                                                 Drilling Problems  [     ]
                                                                                  3.3.6



                       lating sub is run as a precaution in the drill collars; check that the
                       opening ball will drop through the accelerator and drift the string
                       while running in.
                           For milling, more weight will be needed, though not nearly as
                       much as would be run on a drill bit. The weight on mill may be rec-
                       ommended by the supplier or, as a guideline, run 1000-2000 lbs per
                       inch of mill diameter. When running a mill shoe on a packer picker or
                       washover pipe, less area is milled and so less weight is used. Refer to
                       the recommendations of the supplier for these because the weight will
                       also depend on what is used to dress the mill.
                           For fishing wireline tools, the logging company should provide the
                       correct fishing equipment to run and crossovers to drill collar and
                       drillpipe connections, if nonstandard connections are used.
                           Fishing jars, accelerators, bumper subs, and fishing tools to catch
                       every sized tubular to be used should also be on location, along with
                       the consumables required such as grapples. Normally they will be pro-
                       vided by the drilling contractor.
                           Bowen has a computer program to optimize jar placement, but it is
                       only applicable to Bowen jars. Other vendors have similar programs.



                       3.3.6.  Using Cement to Stabilize the Wellbore


                           Where the wellbore becomes unstable and leads to significant hole
                       enlargement, problems tripping, running casing, and logging will
                       increase well cost. Cement can be used to isolate the unstable forma-
                       tion while drilling ahead, however, this needs to be planned carefully
                       to maximize the chances of success.
                           Do not wait until hole size has become extremely large. It is better
                       to spot cement shortly after drilling through the enlarged zone. This will
                       also reduce the chances of inadvertently sidetracking while drilling
                       through the cement and will allow the cement plug to be set on bottom.
                           Run a 4-arm caliper log to evaluate the failure extent (depth of top
                       and bottom) and to accurately determine cement requirements.
                           Follow the procedure for setting a kickoff plug as described in
                       Section 2.7.5.
                           In extreme conditions (deviated well, long open hole times ahead,
                       etc.), then polypropylene fibers (Dowell D094 or equivalent) can be added.


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