Dormant old fields continue to offer lucrative opportunities for operators – particularly those who are up to speed on the latest drilling and completion technologies.
The long-productive Tertiary Wilcox Trend, which extends from south Texas across central Louisiana to the Mississippi border, is one of the latest examples of successful old field rejuvenation.
Newly public Midstates Petroleum Co. has re-entered eight south-central Louisiana Wilcox fields in Beauregard, Allen and Evangeline parishes. The result: significantly revved-up production, via horizontal drilling and multi-stage fracturing.
The Louisiana Wilcox interval measures 3,000 feet to 4,000 feet gross thickness. Depths across the Midstates focus area are 9,000 feet to 17,000 feet.
Among the company’s success stories is the oil-prone Pine Prairie field in Evangeline Parish. Pine Prairie, a piercement salt dome, was discovered in 1908 and developed primarily during World War II.
“In the 1940s all the majors were in there, initially drilling shallow wells and then deeper,” said AAPG member Brad Broekstra, co-founder and senior geological adviser at Midstates. “The dome only covers pieces of about four sections, and they each had only a small piece of the pie. With the land so fractionated it wasn’t worth their while to do a full-scale development of the field.
“Once they began making discoveries in the very lucrative, highly productive fields south of I-10,” Broekstra added, “they got out of Pine Prairie, selling their holdings to small independents – what we call mom ‘n’ pop shops.”
A Second Helping
For the Louisiana novice, I-10 has come to represent the geographic boundary between north and south Louisiana for many folks. In large part, the inhabitants of the southern portion of the Bayou State tend to think of this as a nebulous demarcation.
In general, the small entities latching onto the Pine Prairie production lacked the funds to drill additional wells, opting to let the ongoing production continue until it essentially played out.
“This and other fields lay dormant for perhaps 40 years until we came in early in 1998 and started cobbling together these individual positions to do development,” Broekstra said. “We did this at Pine Prairie, West Gordon, South Bearhead Creek and other Wilcox fields in the trend.
“We commonly targeted fields discovered by majors,” he said. “If they got out before 1973 when we had the oil price spike from $3 to $10, then our presumption was that those fields were probably underdeveloped.”
Midstates drilled its first well in the trend in 2006 at Pine Prairie, which harbors more than 30 productive horizons. The Miocene test well encountered 240 feet of pay at a depth of 2,400 feet.
The company’s initial Wilcox horizontal well went down in early 2012 and was followed by four others, with three completions to date and one still drilling.
Broekstra noted that they also have re-entered a number of old wells where the existing casing was large enough to allow them to sidetrack and drill another 2,000 feet to reach the Wilcox.
Success is evident when comparing production increases in the target fields since the program commenced. In Pine Prairie, for example, produced volumes have soared from slightly more than 400,000 barrels in 2006 to 1.2 million in 2011.
Back in the day, the operators did no fracture stimulations and also had downspacing limitations along with other hindrances to development.
“The well log analysis in the Wilcox is challenged at best,” Broekstra commented. “The petrophysics make it difficult to tell what’s pay and what isn’t.
“To overcome that, we’re drilling in known productive fields doing multi-stage fracturing, and we’re able to commingle the Wilcox sand production,” he said. “The old-timers would perf and produce one sand until it was uneconomic and then pop the next zone; they couldn’t commingle because of the state regulations, which have now been relaxed.”
Midstates is utilizing extensive 3-D data with the intent to use 3-D for development throughout the program. The company is shooting 265 square miles of 3-D, with the goal eventually to cover each of its fields. A part of this is already complete and in hand.
Less (Complexity) Is Good
There’s a good geologic reason why horizontal wells will lead the way in this current stage of development.
The upper, middle and lower Wilcox sands are comprised of significant clay and shale content and have been classified as “dirty sands.” These respond quite well to laterals and fracture stimulation.
Midstates operates 121 wells in the trend, with more than 1,000 prospective locations on its existing acreage.
Broekstra emphasized that the company zeroed in on the onshore upper Gulf Coast early on because it recognized that it is repeatable and there are somewhat predictable investment opportunities.
The sands are laterally extensive, and the geology is relatively simple compared to south of I-10.
“This is not South Louisiana,” Broekstra proclaimed emphatically. “The geology is far less complex.
“There are large three-way and four-way anticlines, and some of the structures are 5,000 acres,” he noted. “That’s as big as an OCS block, and maybe three wells were drilled on them until we got there.
“Also, these tend to be depletion drive reservoirs.
“South of I-10, the reservoirs are more compartmentalized, more complex and typically waterdrive,” he noted. “We call them ‘one-offs,’ because there aren’t many offset locations once you make a discovery.
“However, on these 5,000-acre Wilcox structures,” Broeskstra said, “you can drill a whole lot of wells at 40-acre spacing.”