Intriguing names for individual prospects and entire fields are fairly common in the oil patch.
Think Thunder Horse, Gotcha, Ringo, Pony, Bullwinkle…
But as names go, it’s hard to top Victoria’s Secret.
Got your attention, right?
Relax. The name is a reference to Victoria County, Texas – but the moniker no doubt helped lure a number of the Summer NAPE 2008 viewers who clustered around the Brayton Operating Corp. booth at Houston’s George R. Brown Convention Center, where the prospect was on display.
Officially dubbed the Tally Prospect, this is one of the now-familiar examples of the potential big finds lurking in places that have been subjected to long-ago drilling that failed to pan out as the operators envisioned.
Today, readily available sophisticated seismic technology, hi-tech fracturing techniques and other advances can be real game changers when picking over these old areas, often laying bare the secrets that prevented earlier successes.
The Tally story began late in 1963, when Amerada spudded the R.F. Tally #1 well, which was an ultra deep Wilcox test, according to AAPG member David Desenberg, president of the Corpus Christi, Texas-based Brayton.
“The well was designed to test an extremely large faulted, four-way Wilcox closure,” Desenberg said.
“The test was predicated on early 2-D data, perhaps 100 percent, and probably a very substantial gravity anomaly, which combined to suggest the very large structure.”
First Steps
To begin, the Tally well encountered thick sections of Wilcox sands on its way to total depth of 23,885 feet. A logging run revealed a series of well-developed Upper Wilcox sands.
Cores and additional logs were evaluated, and three successful formation tests confirmed the interval from about 14,100 feet to 14,600 feet likely would produce gas/condensate.
After reaching total depth in 1964, the company elected to plug back to the Upper Wilcox “pay sands.”
When the company perforated the lower portion of the apparent pay section (14,370-foot sand), the well flowed dry gas at a rate of 9,000 Mcfg/d – likely convincing Amerada that it had a significant discovery.
But disaster was nigh once the company seemingly determined that the well was tight and required some form of stimulation.
“The well stimulation business was in its infancy in 1964, so options were limited,” Desenberg said. “Amerada chose a form of acid fracturing, apparently without regard to the clay content of the Wilcox – today, it’s generally known that acid tends to destroy permeability in Wilcox sands by swelling the clays, so it’s avoided.”
“Apparently the acid inhibited the permeability of the completion,” Desenberg noted, “and flow rates and pressures probably dropped dramatically with the introduction of the acid, creating tremendous differential pressure at the perforations.
“Not surprisingly, it’s reported that the casing collapsed opposite the perforations,” he said.
Alas, the best portion of the productive interval was lost. A shallower part of the Wilcox section was then sand-fraced and flowed gas, but the non-commercial well was soon plugged and abandoned.
Try, Try Again
In 1980, an Amerada team twinned the R.F. Tally #1, drilling 250 feet northeast of the original well. Armed only with 2-D seismic data and one log for correlation, they failed to find the 14,370-foot sand that caused the collapse in the initial well.
Today, 3-D data and correlations show the second well faulted out the target Wilcox sand, as the geologists had inadvertently moved the well toward the fault given their sparse database.
In January 2000, a partnership that included Brayton drilled the Koehl #1 about one mile northeast of the Amerada wells using 3-D seismic acquired by Brayton that confirmed the suspected large deep-seated Wilcox structure. The well encountered gas-bearing Upper Wilcox sands, but Desenberg noted the hole ultimately was plugged and abandoned – following considerable head-scratching among the partners.
Undaunted, Brayton has since re-processed the 3-D data and revisited the Tally structure, convinced that “a terrific prospect remained,” according to Desenberg.
Helping to bolster this opinion is a similar “re-discovery” field about 30 miles northeast of the Tally Prospect, where Tri-C Resources successfully offset an old Conoco discovery drilled in 1986. Since the “re-discovery” in 2005 in the former one-well Brushy Creek field, the field has been actively developed, producing over 32 Bcfg and 580,000 barrels of condensate thus far.
On the Tally structure, Brayton is going full speed ahead with plans to offset Amerada’s original apparent major discovery, the R.F. Tally #1.
The planned well is slated to kick off late this year or in 2009’s first quarter.
Desenberg emphasized that fracture stimulation technology has greatly improved since the completion of the previous Tally wells, noting they won’t be using acid owing to the specific clay content in the Wilcox sands.
Guarantees are essentially non-existent in this business, but if all goes according to plan, the company is eyeing total prospect reserves in the range of 206 Bcf of natural gas plus liquids, Desenberg noted, with as many as 10 wells expected to go down.