Cotton Valley Lime (Oolitic Shoal) Play
Production Characteristics
The Cotton Valley Lime along the east flank of the East Texas Basin is characterized by outstanding statistical numbers, including an average Cum of over 3.2 BCFGE (at P62) and average EUR of over 4 BCFGE. The median (P50) Cum is 2.1 BCFGE. A P10 Cum, or lowest 10% of performers, lies at over 100 MMCFGE, with the bottom quarter of all wells yielding at least 750 MMCFGE, which is nearly economic at current prices and drilling and completion costs. The P75 Cum, or best quartile of wells, is over 5 BCFGE, and the best well should produce over 20 BCFGE. These numbers are displayed in Figure 1, a probability distribution plot for this area.
Figure 2 shows a log-log plot of practical IP (Best Monthly Cum) versus Cum, and clearly shows a power-law fit to the data, typical of many fractured lime plays.
Figure 3 demonstrates the play history in a graphical sense, and lists some of the more important statistics. On the left is the date, with the first wells drilled in the late 1960s and most developed in the 1970s having little or no stimulation. In the late 70s and early 80s, acid fracing gave the play a boost (as well as good product prices), but drilling died until 1992, when infill drilling at Gilmer Field and gelled-sand fracing began to take off. The statistics reveal that pre-1992 wells had practical Initial Potentials of 1,300 MCFGPD, declined at 29%, perforated an average 105 feet, and have an average Cum of 2.6 BCFGE. In contrast, the post-1992 completions have practical Initial Potentials of 2,700 MCFGPD, declines of 21%, perforated an average 155 feet, and have already Cumed 2.5 BCFGE in a much shorter timeframe. These numbers can be explained by looking at a few decline curves and some simple petrophysics.
Figure 19 demonstrates the corresponding production response after the re-completion.