tuscaloosa

Aug 06
An Allure Lingers
Tuscaloosa Maturing Gracefully
By LOUISE S. DURHAM
EXPLORER Corespondent You ain’t seen nuthin ‘til you’ve seen the Tuscaloosa.

Sound familiar?

If so, it’s because this was probably the most popular talk making the rounds of the professional meeting circuit in the late 1970s.

The deep expensive wells coming on stream in rapid succession in south-central Louisiana’s Tuscaloosa Trend were gas condensate behemoths -- suitable symbols of those heady times in the industry.

Fortunes were made.

Then, seemingly without warning, fortunes were lost when those folks who had bet everything but their children on the play got caught in the downdraft of plunging oil and gas prices that triggered the infamous 1980s oil industry depression.

Today, the Trend’s several big-name fields, such as Judge Digby, Port Hudson, Morganza and others, continue to kick out impressive amounts of hydrocarbons. Production is from the Lower Cretaceous Tuscaloosa sands, principally the Lower Tuscaloosa Massive Sand facies.

As the longtime undisputed kingpin of the play, Amoco held a controlling interest in the majority of the better fields in the heart of the Trend. In fact, the play’s longevity is due in large part to an aggressive redevelopment program Amoco initiated in 1994.

BP assumed the mantle of lead operator in the play via its purchase of Amoco, and its current inventory includes 46 producing wells in six fields in the vicinity of Baton Rouge, La. The company plans to maintain a two-rig program in the Trend for 10 years.

According to BP’s onshore South Louisiana fact sheet, flowing tubing pressures exceeding 12,000 PSI and bottomhole temperatures reaching 370 degrees are the norm for the deep sand producers. Average well depth exceeds 21,000 feet.

Port Hudson Field is the crown jewel of the Trend. Since discovery in 1977, the field has produced a staggering 761.3 billion-plus cubic feet of natural gas and 85.8 million-plus barrels of condensate. BP currently operates 13 wells there.

“Port Hudson is different than every other deep Lower Tuscaloosa Field,” said Steve Walkinshaw, president of Vision Exploration. “It’s salt cored and very rich in condensate, while the remainder of the Trend is dry.”

Despite the mega-production, exploration in recent years has been -- and continues to be -- spotty at best.

“There’s not a lot of new things happening,” said Remy Williams, consulting geologist and long-time Trend player. “It’s kind of the same-old, same-old.”

Walkinshaw concurred.

“When it comes to exploring in the Trend, it’s very quiet,” he said. “A lot of people are optimizing reserves, and I can’t blame them.

“Vision is not the only one exploring, but small independents don’t have the resources to shoot 100-square-mile 3-Ds,” he said. “We’re using 2-D data and well control to generate prospects.

“There are not a lot of people who understand the Trend,” Walkinshaw noted. “These are Cretaceous reservoirs, and there aren’t a lot of geologists still in the profession who have worked this trend and understand the clay content and the sand distribution and the regional picture -- that’s why you see some of the best gas wells being completed in known fields.

“But the presumption there are no new fields is incorrect,” he added. “There are plenty of additional targets to drill -- and the Tuscaloosa is not just deep.”

Knowing Where to Look
In fact, production has occurred from the A and B sand units, which occur higher in the section and differ considerably from the Massive Sand.

The A and B sands can be as much as 9-10 percent chlorite as well as kaolinite, according to Walkinshaw. The chlorite lowers the log resistivity reading for productive intervals compared to the chlorite-free Massive Sand, which exhibits higher resistivity numbers.

“One must be very careful and experienced in working the logs in the area,” Walkinshaw said. “If you start in the deep part of the Trend -- which mainly produces from the Massive Sand -- and move northward where you get on the shelf area in the Florida parishes part of the Trend, you’ll have trouble understanding the need to make the transition from looking for high resistivity pay in the Massive Sand to low resistivity pay in the A and B sands in these parishes.

“Also, you typically have stratigraphic traps in the A and B in the Florida parishes that are productive,” Walkinshaw added, “and not structural traps as in the Massive Sand.”

New Players
Vision’s efforts to interest companies in exploring jointly and acquiring 3-D seismic surveys attracted a company that is not only new in the Tuscaloosa play but new to Louisiana as well.

Publicly-traded California Oil & Gas Corp., which is headquartered in Calgary, Canada, signed a Letter of Intent (LOI) to take a 40 percent interest in a Vision prospect targeting objectives below an older field that has produced 28 million barrels of oil from Tertiary formations.

Both the overpressured fractured Lower Chalk and the underlying Lower Tuscaloosa Massive Sand have been tested on the structure of interest and proved to be hydrocarbon bearing, according to a company news release in June.

Modern-day completion techniques weren’t available when these targets were drilled to depths of 13,000 and 16,000 feet, respectively. The technology that was used failed to bring the wells on production.

The prospect agreement between the two companies includes acquiring a “state of the art” 3-D survey up to 35 square miles over the structure of interest. A well that initially went down in 1982 will be re-drilled.

This early well encountered what appears to be significant gas volumes in the Lower Tuscaloosa Massive Sand unit, according to California Oil & Gas, but mechanical failure caused it to be abandoned after testing gas.

California Oil & Gas also signed an LOI to participate in certain Louisiana activity with publicly traded Daybreak Oil & Gas -- a small, relatively new company headquartered in Spokane, Wash.

The agreement is for California Oil & Gas to have a 15 percent working interest participation in a well to be drilled to test sands at depths of 10,000-11,000 feet in a prospect in St. Landry Parish. The objective reportedly is an unexploited Tertiary formation in a unitized field of more than 4,500 acres.

Still, the Tuscaloosa has captured the company’s attention as well.

“Daybreak and partners put a basal Tuscaloosa well on production at 8,200 feet in Tensas Parish early this year,” said company president Bob Martin.


http://www.aapg.org/explorer/2006/08aug/tuscaloosa.cfm