Cotton Valley Sand Play
Production Decline Curves
This play has experienced very successful re-frac of old wells, as well as tight-spaced infill drilling. Figure 7 serves as a good production history. It shows the Amoco Brewer Unit 1 Cum versus Time data series, representing a typical well in the trend. The well has a higher gas Cum than the current data imply, but most of the trend has long lived wells which are still actively producing. Many of these wells will also have pay zones behind pipe, not yet producing. This well was selected because it is typical, and has had two different pay zones completed.
The declines in all fields are usually hyperbolic, with an Initial Potential of just over 1 million cubic feet of gas per day. They decline quickly in the first year, but stabilize to a flat rate after that, and produce for 15 to 25 years from one zone. All wells in the trend are hydraulically fraced with sand-gel or light sand slick-water fracs. The size of the job is often a function of the gas price – where good commodity prices encourage larger job sizes.
An ineffective frac will often show no flush production and a low Initial Potential. Areas with no natural fractures may show the same results.
Areas with quality rock, where the ultimate recoveries will exceed 1.5 billion cubic feet, may show an exponential dual-leg decline. Some wells may even show several months of increasing production at the start, as the formation damage is cleaned up over time. The occurrence of these is only about 20 percent of the total wells drilled in Texas.
The decline curve history gives clues to the rock quality and rock type. Energy Frontiers Partners has correlated the production histories to rock type.