ONSHORE ALABAMA NORPHLET TEST UNDER SPOTLIGHT

A.D. Koen
Gulf Coast News Editor

Amerada Hess Corp. and partners are drilling a deep wildcat in southern Baldwin County, Ala., that is expected to expand the focus of Jurassic Norphlet exploration in the southeastern Gulf Coast region.

If Amerada's 21,000 ft 1 Pizzotti 14-6 wildcat finds Norphlet gas, as many observers expect, the prospect could open a major onshore hydrocarbon province and spawn a stampede to spud other Norphlet exploratory wells in southern Alabama.

Amerada spudded the well Aug. 9 and by Aug. 16 had set 13-/8 in. surface casing to 5,200 ft.

CLUES TO SIGNIFICANCE

Companies familiar with the region's geology-including at least one of Amerada's partners in the test-say the Pizzotti prospect was generated on the basis of well log information and 3D seismic data.

As understanding of the Norphlet offshore play has grown with development in Mobile Bay, several companies noticed close correlations of data from onshore wells. Foremost among the clues is a unique signature on dual induction logs of all productive Norphlet wells drilled in the bay that also is found on logs of some deep wells drilled onshore. The key signature is caused by a pyritic zone that likely resulted when gas charged with hydrogen sulfide contacted and reacted with basal limestone overburden.

Another key is the realization among companies developing Norphlet pay in Mobile Bay that productive Norphlet sands occur in parallel series of eolian dunes, each of which functions essentially as a separate reservoir.

Amerada Hess would not comment for this story about similarities between 1 Pizzotti's prospective geology and Mobile Bay Norphlet geology or about the significance of the deep onshore wildcat. But sources familiar with the prospect say it will test a Norphlet sand dune shown by seismic data to be identical in deposition and structure to productive Norphlet formations offshore.

"If the Hess well is successful, it will prove up a major onshore hydrocarbon province," a Point Clear, Ala., consultant said. "If the Pizzotti's dune has gas, all the Norphlet dunes onshore have it. So exploration will just be a matter of picking out sweet spots on the dunes and drilling at about one third of the cost of what companies are spending offshore."

KEY TO PRODUCTIVITY

Available subsurface data indicate the Jurassic Smackover acts as seal and source rock to gas prone Norphlet sands in the Mobile salt subbasin.

Deep Norphlet sand dunes have been identified at many locations in the southeastern U.S. Gulf Coast. Also, Norphlet dunal traps are found across southern Alabama and into Mississippi.

The key to deep Norphlet gas productivity around Mobile Bay is lack of porosity in the shallower Smackover.

"When you don't have porosity in the Smackover, the formation's hydrocarbons charge into the Norphlet and lend themselves to very large Norphlet reserves," said Bruce Martin of Mitchell Energy & Development Corp. Mitchell has a 7,000-8,000 acre leasehold in Baldwin County and hopes to drill an onshore Norphlet test of its own. Martin said some geoscientists have suggested the Norphlet is the main conduit that allows long distance hydrocarbon migration through the area.

"So we look forward to the possibility that gas might have migrated out of the bay and charged these traps directly onshore," he said.

By contrast, on the Smackover platform, in Baldwin County south of the Conecuh arch, the Smackover is porous and capped by the Buckner formation, allowing hydrocarbons to migrate into the upper part of the formation.

"If you can make a Smackover well, you can't make a Norphlet well, because the Smackover not only is charging the Norphlet but it also is a seal," said geologist J. David Barrett, a principal of consultants Key & Barrett, Point Clear. Barrett and Albert W. Key manage Geo Resources Group, one of the 1 Pizzotti partners. With a 13,000 acre leasehold in southern Baldwin County, Geo Resources expects to assemble other onshore Norphlet prospects, pending outcome of 1 Pizzotti.

INDICATORS ONSHORE

Martin, Barrett, and others credit earlier onshore Baldwin County Smackover dry holes by Amoco Corp., Getty Oil Co., and Union Texas Petroleum (UTP) with defining extent of the Mobile salt subbasin that mostly appears to underlie Mobile Bay.

They believe the subbasin is bounded on the west by the Mobile high and on the north by a line connecting the Wiggins anticline and Conecuh arch.

UTP's Chandler 10-5 dry hole encountered about 200 ft of relatively porous Smackover and did not register the pyritic zone that gives the unique log signature at the base of the Smackover.

"That's the northern edge of the basin," Barrett said. "We believe that well is out of the play."

However, logs from Amoco's Amos 32-12 and Getty's Woerner 16-7 dry holes showed tight Smackover strata, pyritic signatures at the base of Smackover, and Norphlet strata that resembled logs from productive Norphlet wells in Mobile Bay. The significance of that was not understood then, Barrett said, because Norphlet productivity had not yet been established in Mobile Bay.

Norphlet reservoir rock penetrated by Amoco's Amos well "is the exact match of the producing reservoir rock offshore," Martin said.

Linear Norphlet sand dune trends can be as long as 50-60 km. But isolated typical dunal highs are described as 3-5 miles long, 1/7-1 mile wide, and 3,000-4,000 acres in areal extent.

"Those are the targets companies want to drill," Barrett said.

Seismic data indicate 1 Pizzotti will encounter an expanded section of Norphlet sand dune similar to dunes productive in the bay. Amerada, Barrett, Martin, and others expect 1 Pizzotti logs to have the key pyritic signature present on logs of offshore Norphlet wells.

Based on his knowledge of existing leaseholds in Baldwin County and the high success rate of wildcat drilling in Mobile Bay, Barrett said the drilling response will be phenomenal if 1 Pizzotti finds Norphlet pay.

"We have had calls from a number of major companies. They're watching this closely," he said. "If the Pizzotti well is successful-and we feel strongly there is a very good chance it will be-it will cause a stampede over here."

Onshore Norphlet dry hole costs are estimated at $3-4 million and completions at $6-7 million. Salt structures underlying Norphlet sand dunes onshore are smaller than in the bay, causing some hesitancy among major companies.

But if the linear dune-interdune Norphlet depositions onshore prove to be as effective traps as offshore, Martin said much exploration is sure to result.

"The 1 Pizzotti is really a test to see if we have some viable traps onshore," he said.

Copyright 1993 Oil & Gas Journal. All Rights Reserved.