Page 157 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 133

2.1.5
Preliminary Work For the Drilling Program [ ]

2.1.4. Time Estimates

Any estimate will be improved with more detail. Spreadsheets are
invaluable because they allow a great amount of detail, which can then
be totaled, diced in many different ways, and easily updated.
The cost of a well is, of course, intimately related to the time it
takes. In making a time estimate, break down the overall work into
small chunks and give reasonable time estimates, based on local expe-
rience, for each chunk. As the work progresses, the spreadsheet can be
updated by substituting the estimated times for the actual times, which
will update the forecast.
The time estimates will vary depending on the purpose of the esti-
mate. When planning a well, an estimate should give forecasts for
logistics. In this case, the shortest possible time should be estimated for
each operation—it is much easier to allow things to slip than to pull
supply of equipment forward. For cost estimates, use a reasonable
“average” time, not the shortest possible. This will give a different over-
all estimate.
I have created a spreadsheet (planner.xls) that takes a start date,
start time, and times for individual operations, and produces a forecast
for getting things to the rig. This spreadsheet can be downloaded from
my web site at http://www.drillers.com, or you can build your own.
Figure 2-1 is an example of this spreadsheet.

2.1.5. Cost Estimates

Well cost estimates are made at different stages in the planning
process. These will vary by the level of detail possible and therefore by
the level of accuracy. Following are cost estimates that will usually be
needed as the project progresses.
Budget estimate. The accuracy of a budget estimate is ±25%. The
level of information usually given will include approximate location and
water depth, approximate target location and TVD, desired total depth
TVD, and desired completion status. Other information may be includ-
ed. For this type of estimate the best way is to look at the costs of offset
wells and make simple adjustments for depths, rig day rates, etc. Since
little engineering work can be done at this stage, you are making an edu-
cated guess. The spreadsheet discussed below can be used by taking a
previous estimate and revising it for best guess times, rates, and depths.

133