AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Norphlet Aeolian Sand Fairway Established in the Deep Water Gulf of Mexico
(1) Shell Exploration and Production Company, Houston, TX.
(2) Shell International Exploration and Production Inc., Houston, TX.
Exploration for Norphlet aeolian sands in the deepwater Gulf of Mexico saw the first well drilled in Desoto Canyon 269 (Prospect Shiloh). Following this initial Norphlet oil discovery, a second Norphlet exploratory prospect (Vicksburg) was drilled in Desoto Canyon 353; some 15 miles southwest in hopes of establishing a wider aerial extend of a Norphlet erg. The Vicksburg well found an 850-foot thick Norphlet section dominated by aeolian dune and sandsheet facies. Five large-scale depositional intervals are recognized. They are from bottom to top 1) interbedded lacustrine red-brown mudrocks with some silty/sandy units, 2) stacked aeolian sheetsand or sheetflood facies with minor barchan dune deposits, 3 and 4) two sequences of large-scale drying upward barchanoid dunes with both sinuous and strait-crested forms based on the integration of whole core and OBMI log data, 5) mixed coastal sand sheet with some waterlain sabkha facies. The well reached a total depth after drilling 140 feet of Louann salt below the base Norphlet with very little trace of Pine Hill anhydrite. A whole core was taken just below the top Norphlet and recovered 329 feet. The oil-water contact was also cored. Oil was found filled to a level that was near the mid-range structural contact in the pre-drill estimate. Average log porosity for the cored interval is 17% and for the entire aeolian sand sequence, it is 20 percent. Porosity is preserved by the presence of chlorite clays, which coat sand grains. Illite is also found in the sandstone. Solid hydrocarbons appear largely immovable and are so abundant in the oil column, that both porosity and especially permeability are reduced to a point that it is likely non-productive rock. The distributions of solid hydrocarbons exist throughout the oil column and should be discounted for flow. Solid hydrocarbons tend to be found in the porosity of the originally better quality, coarser grained rock.
The structural style of Vicksburg is set in a compressional regime between several thrust faults. Vicksburg is a three-way closure against a thrust fault. The thrust faults formed in late Oxfordian soon after deposition of the Norphlet and Smackover formations. The couplet of Norphlet and Smackover formations broke and rafted into position down the slope of the large paleo-high of the Middle Ground Arch. The Norphlet sand erg appears to be large with favorable structural traps. Solid hydrocarbons in the reservoir remain a concern.