Header Data
The following header data is entered on the Calculations worksheet:
• Well name
• Date of estimate
• Depth unit – “ft” or “m” • Currency – “$”, “£” or “NOK”
• Grnd L/mud line/KOP MD – The measured depth at which the days/10k KPI calculation starts
• Correlation – “ON” (apply correlation coefficients) or “OFF” (set all correlations to zero).
Basic Cost Data
Three cost items not directly associated with well operations can be entered explicitly:
• Planning – One distribution for the number of days required to plan the well, and another for the daily charge for this planning effort (= number of planning engineers x daily charge per engineer).
• Reporting – As for planning.
• External Studies and Costs – A description and cost distribution for each engineering study, survey, inspection, audit, peer review etc. that will be charged to the well.
The all-in daily spread rate applicable during any well operation is the sum of the “Rig Only Rate”, all the “Rig/Operation Support Services” rates and the “Special Day Rate”. The last of these is operation-specific (see below). The others are input here: • Rig Only Rate – A distribution for the daily rig hire charge
• Rig/Operation Support Services – A description and distribution for each service normally incurred throughout the well operations. This will include personnel and office overheads, logistics support and basic rig services.
• Uncertainty in Fixed Costs – A percentage (positive or negative) applied to all fixed costs in the well. Must account for uncertainty in fixed costs scope (what will you buy) and price (inflation, foreign exchange, tax and duty, contract terms).
Time and Cost Data
Well time is partitioned into four “activity sets”: • Preparation – Activities undertaken before spud.
• Dry Hole Drilling – From spud to end of logging at final TD.
• Completion – From end of logging to the point at which the well is ready for handover to production or suspension activities commence.
• Post-Completion – Production or suspension activities.
The purpose of this division is to allow the workbook to calculate KPIs for Dry Hole Drilling and for Completion. More detailed definitions are available from the Drilling and Completions Performance Team.
Each block of data is divided into productive operations (ie productive time), non- specific NPT, waiting on weather NPT and risk-specific NPT.
Productive Operations
Each operation is characterised by: • A short text description
• Start and end depths – Used in calculation of hole section time and for
constructing the drilling time-depth and cost-depth curves. These data need only be entered for drilled intervals and should be left blank for all other operations. • Probability of occurrence – Some productive operations, such as data acquisition
or installing a contingency drilling liner may have a probability of less than 1. • Range of performance – Defined as a distribution (see above)
• Unit of performance – Either a direct unit (eg. “days”) or an ROP-type unit (eg. “ft/hr”). If an ROP-type unit is selected, start and end depths for the operation must also be input.
• Fixed cost (tangibles) – A one-off cost, in thousands, which is not time dependent (eg. tubulars).
• Fixed cost (intangibles) – A one-off cost, in thousands, which is not time dependent (eg. drill bits).
• Special day rate – The difference between the total daily rate for time-related costs during the operation and the basic spread rate (the sum of the rig only rate and all the itemized rig/operation support services rates). A negative number represents a reduction on the basic spread rate.
• Bit depth – Used for calculating the time-depth and cost-depth curves, and the Days/10k KPI. Only required if the depth calculated from the operations data is incorrect.
Completeness and consistency of the data entered for each operation is indicated in the Data Check column. Several checks are made, but the list is not comprehensive. Risk-specific NPT
These events are described by the same data as productive operations (except that bit depth is not entered). If the event can only occur during a particular
“susceptible” operation, this can be chosen from a pull-down menu. As an example, the NPT event “stuck logging tools” might have a susceptible operation of “TD logging”. Note that:
• The probability that the NPT event occurs during the well is unaffected whether or not a susceptible operation is chosen (and whether or not the chosen susceptible operation occurs).
• If no susceptible operation is chosen (as might be the case for “equipment failure”), the NPT event will occur at a random time, with the specified probability. • Any special day rate entered for the susceptible operation will not be applied
automatically to the NPT event. The special day rate must be entered for the NPT event as well.
Non-specific NPT and Waiting on Weather
Non-specific NPT is input as a percentage of total time for that activity set (eg. dry hole drilling) excluding risk-specific NPT and WoW. Weather downtime may be input in the same way, or as risk-specific NPT. See page 38 for more details.
If the input range of %non-specific NPT (or %WoW) includes large values (more than 20%), the relationship between the range mean and the final mean well NPT is changed. Ref 1 explains why and how.
Correlation Coefficients
The SWE uses Correlation (p138) to model the tendency for more very good wells and very poor wells to be drilled than would be the case if performance was a truly random process.
The random input variables which drive the SWE time and cost model are divided into ten groups. The variables are correlated together within groups, with each group being statistically independent. The default pair-wise correlation coefficient for each group is shown below.
*Non-specific NPT and occurrence and duration of risk-specific NPT events (not WoW). Groups of Correlated Input Variables and their Coefficients.
These correlation coefficients are somewhat speculative, but generally produce realistic results. In the interests of standardisation and assurance, users should seek advice from EPT before changing them. Random inputs not listed in the table, such as Rig Daily Rate and Well Planning Costs, are sampled independently. Further features of the SWE’s correlation feature:
Group of Variables Description Default
Coefficient
Rig/Op Services Daily rig rate and all rig/operation support services 0.8
Preparation PT Duration of planned preparation operations 0.8
Preparation NPT* 0.5
Dry Hole Drilling PT Duration of planned dry hole drilling operations 0.8
Dry Hole Drilling NPT* 0.5
Completion PT Duration of planned completion operations 0.8
Completion NPT* 0.5
Post-Completion PT Duration of planned post-completion operations 0.8
Post-completion NPT* 0.5
Waiting on Weather WoW% during preparation, drilling,
completion and post-completion 1.0
Other Inputs Including planning, reporting and fixed costs 0.0
• It can be turned OFF on the Calculations Sheet. This is useful for testing its effects.
• The calculations are included in Excel formulas, which avoids the drawbacks of Crystal Ball’s in-built correlation feature (p141).