The purpose of this article is to explain the options under the DCA Wrangler Decline Parameters menu.



Decline Parameters Menu

The Parameters menu is used to adjust the parameters and thresholds of the decline algorithm.

OptionDescription
DeclinePressing the Decline button will generate declines for the wells that are currently marked.
ResetReset will reset all parameter in the submenus to the DCA Wrangler defaults.
SubmenusSubmenus are drop-down menus that allow for user adjustment of each parameter.

Oil, Gas, Water, GOR, Yield, WOR, Forecast, Normalize, Fluid Limits, and Type Curve submenus are more fully described below. 



Stream Submenus

The Oil, Gas, Water, GOR, Yield, and WOR submenus are used to select the decline algorithm for the streams. The algorithm's parameter thresholds are also set in these submenus.

IMPORTANT NOTE: The submenus for Oil, Gas, and Water are the same. The submenus for GOR, Yield, and WOR are the same.

OptionDescription
DropdownThe drop-down will select the decline algorithm for the stream.

See below for the options:

NoneNo decline for this stream will be produced.
Modified Arps (Auto)
A Modified Arps Hyperbolic decline algorithm will produce the stream's decline. This option will allow the user to select a range of parameters (defined below). This option is normally used for declining multiple wells with the same range of parameters. Only available with Oil, Gas, Water
Modified Arps
A Modified Arps Hyperbolic decline algorithm will produce the stream's decline. This option will allow the user to select specific parameters (defined below). This option is used for declining a single well. Only available with Oil, Gas, Water
Linear Piecewise (Auto)
A Linear Piecewise decline algorithm will produce the stream's decline. This option will allow the user to select a range of parameters (defined below). This option is normally used for declining multiple wells with the same range of parameters. Available for all streams.
Linear Piecewise 
A Linear Piecewise decline algorithm will produce the stream's decline. This option will allow the user to select specific parameters (defined below). This option is used for declining a single well. Available for all streams.

Modified Arps (Auto)

QiRange for Qi (Initial Rate) value. If less than or equal to 2, takes the percent of global maximum rate, else takes the absolute rate values.
DeRange for initial decline parameter, De.
BRange for constraining the B1 value.
Low B2 - High B2The Range for constraining the B2 values (Multi-Segment Decline)
Low Time 2 - High Time 2 (Days)The Range in days for the B2 Factor (Multi-Segment Decline)
Low B3 - High B3
The Range for constraining the B3 values  (Multi-Segment Decline)
Low Time 3 - High Time 3 (Days)
The Range in days for the B3 Factor  (Multi-Segment Decline)
DminRange for limiting decline rate Dmin (D lim). Set as both numbers to same to enforce a hard limit.

Modified Arps


QiQi (Initial Rate) value. If less than or equal to 2, takes the percent of global maximum rate, else takes the absolute rate values.
DeInitial decline parameter, De.
Bfactor value.
DminLimiting decline rate Dmin (D lim).
B2 (1/month)B2 Factor value  (Multi-Segment Decline)
Time 2 (Days)The range in days for B2 factor (Multi-Segment Decline)
B3 (1/month)B3 Factor value  (Multi-Segment Decline)
Time 3 (Days)The range in days for B3 factor (Multi-Segment Decline)

Linear Piecewise (Auto)

ScaleLinear or Log10.
No. SegmentsNumber of segments to be used in the continuous Linear Piecewise model.
Initial RateRange for Initial Rate. If less than or equal to 2, takes the percent of the average rate for the initial period, else takes the absolute rate values.
Segment Time (days)Range for guessing the length of the linear segment in days.
Segment Change (%)Range for guessing the change in slope of the model when switching.
Outlier SDStandard deviation (from mean data fit) for declaring data points as outliers.
Initial PeriodDefines the initial period starting from the peak production rate for primary fluid.
Final DeclineLimiting decline rate Dmin (D lim).

Linear Piecewise

ScaleLinear or Log10.
No. SegmentsNumber of segments to be used in the continuous Linear Piecewise
Time (days)Absolute days from start as Comma Separated Values. This defines the length of each segment.
Value (units)Rate for the stream at each end of the segment as Comma Separated Values. This defines the rate of each segment's end.
Final DeclineLimiting decline rate Dmin (D lim).



Forecast Submenu

Forecast parameters determine the length of the decline and if the decline will use a previous output to anchor against.

The DCA Wrangler uses declines stored in the database to “anchor” the autocasting engine.  Using anchoring, the engine will attempt to “update” the previously stored forecast using new data since the model was saved.  In updating, the engine will employ the Eliot Tie method, which:

  • Ties the updated forecast to the most recent data (changing Qi and start date)
  • Adjusts effective decline to handle the latest data
  • Does not change b-factor

If the change in data is too great (5%), the engine will honor the previous forecast decline rather than the data.

OptionDescription
YearsNumber of years the decline algorithm will forecast past the last date of production.
AnchorDetermines if the decline to be run will be anchored on previous results if they exist in the project. To Anchor, previous results must be saved as Official (using Save) to the Petro.ai Engine and then pulled back into the DCA Wrangler via the Sync Button.

Options: Latest Official, Models, or None

Latest Official
Anchor on Latest Official declines that have been synced with the project from Petro.ai.
ModelsIf other models have been brought into the project using the Sync button, the user can anchor on those models.

None
Do not Anchor on previous forecasts.

Minimum Production History Data PointsSet a minimum production history data points.
Example: If the minimum is set to 3, any wells that have less than 3 production data points, the screen below will show.



Normalize Submenu

When creating and comparing type wells, it is important to normalize the production data against a common differing property associated with the well or its location. DCA Wrangler can normalize by linearly scaling individual well history based on a normalization column and value.

Option
Description
Main FluidThe Main Fluid for the well.

Options: Auto, Oil, Gas

AutoDetermines the Main Fluid based on GOR Threshold parameter, set below.
OilSelects Oil as the Main Fluid.
GasSelects Gas as the Main Fluid.
NormalizeDetermines where normalization for the decline curve will begin.

Options: Start, Local Peak, Global Peak, Manual 

Start
Decline Curve will begin at the start of production history.
Local Peak
Decline Curve will begin at the last local maximum. If the Well has more than 10 years of production, the DCA Wrangler will try an End of Life fit for the Decline Curve.
Global Peak
Decline Curve will begin at the global maximum.
Manual
Decline Curve will begin at the user-defined date in Start Date
Start DateWhen the Normalize option Manual is selected, this date will be the Start Date of the decline curve.
GOR ThreshThreshold as a percentage for declaring the Gas as Main Fluid.
Target ValueValue to use in normalization against a normalization column.



Fluid Limits Submenu

Fluid Limits are economic thresholds that will end a decline if the decline curve forecast moves outside of the specified range. 

Option
Description
OilRange of limits for Oil (bbls) stream.
GasRange of limits for Gas (mcf) stream.
GORRange of limits for GOR stream.
Oil TTDRange of limits for Oil TTD (cumulative bbls) stream.
Gas TTDRange of limits for Gas TTD (cumulative mcf) stream.


IMPORTANT NOTE: TTD is Total To Date.


Type Curve Submenu

A type well is a pseudo-well that is usually created by averaging the production rate from many wells. Its intended use is to determine the production rate that can be expected from a new well(s) based on the performance of analogous wells. It may also be used as a benchmark to provide confidence in individual well forecasts for a group of similar wells. These use cases make Type Wells necessary for portfolio management, play inventory ranking, budgeting and forecasting processes, and business case analyses.

DCA Wrangler offers a Type Curve mode to create an average, P10, P50 and P90 type wells for a given group of wells. We use the following formula to create the average Type well for a given group of wells.

Option
Description
Min Well CountSets the cut off on the type curve fit based on well count.  When Min Well Count is less than 1, it is taken as the fraction of the total wells for each group (e.g. 0.43 = 43% of the wells in the group).
Days BinThe number of days to the bin for type curve aggregation of Avg, P10, P50, P90.
Start DateStart Date of the Type Curve.
All Group NameName for the Type Curve Group if no other Group options have been specified.

For additional information on RAI DCA Wrangler documentation, click here