GOM3 News - February 2013

Decline Curve Analysis

Decline Curve Analysis
Decline curve analysis is now available for every completion in the Gulf of Mexico, accessible by clicking on a completion with the Hotlink tool (the red exclamation point) in ArcGIS. The analysis is also available in the Feature Reports/Charts/Logs button in GOMsmart. The tool fits the oil and gas production to each of the Arps equations: exponential, cumulative, and hyperbolic/harmonic. For gas, the P/Z chart is also used when sufficient pressure data is available. Production data is gathered from every completion if a single interval contains multiple completions. Since it is not uncommon for wells in decline to go through several regimes over time, the tool automatically finds these structural changes and begins analysis at the latest regime to increase the accuracy of predictions. As is common, the curves for the exponential and hyperbolic models are fit in semi-log space. Typically these are simply back transformed, but our curves use a bias correcting factor commonly known (yet rarely used) in statistics literature. Once the curves are fit, production is forecasted and prediction intervals around the remaining resources are calculated based on the statistical strength of the decline curve.

MI623 Decline Curve
Users have several options to enhance the analysis. First, users must specify a production rate limit for oil and gas. This is given as barrels per day for oil, Mcf per day for gas, and psi for the P/Z method. The decline curve is forecasted into the future until reaching these limits. Likewise, users can specify a maximum water cut and water to gas ratio to limit the forecast. Finally the date at which to begin analysis can be entered. While the tool defaults to begin analysis at the latest regime, users may have specific knowledge of a well and choose a date to begin analysis.

Decline Curve Options
Output is given in one of three ways. Charts will show the plots for each model as well as the associated estimates and some statistical information. Reports will contain engineering information, the production history, more statistical information and the plot of the model that fits the data best. Advanced users can also download the data into a single CSV that can be opened with Excel. As always we welcome feedback on the analysis or the input/output for the tool itself.

Modifications to load Wells and Leases

Originally a checkbox on the Wells dialog would load wells with velocity surveys. This has been expanded to a list of options including those wells with paleo information, with directional surveys, those that have produced and horizontal wells. Wells Dialog

When loading leases, a new option sets the end date range for the past leases. Because a particular block can be leased multiple times through the years, this option limits the number of leases shown.
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