Dravis, Jeffrey J.¹, David Rolling², Joe Casey³, Stewart Sampson⁴
(1) Dravis Geological Services, Houston, TX
(2) Nexen Petroleum USA, Dallas, TX
(3) Hunt Petroleum Corporation, Houston, TX
(4) Mako Offshore, Dallas, TX

ABSTRACT: Refinement of James Limestone Depositional and Diagenetic Models and Play Relationships on the Western Florida Shelf

Nexen Petroleum USA recently drilled two wells (VK 565 #1 and VK 610 #1) along the western margin of the Florida Shelf, in search of lower Cretaceous James Limestone production. Results from these wells, data from Main Pass Block 254, and regional seismic data, refine the carbonate play relationships and controls on reservoir development in this area.
Prospective depositional facies along this part of the Florida Shelf are isolated reef and ooid shoal complexes developed on paleotopographic highs. Core from well VK 610 recovered a reef complex that shoaled into a mature back-reef flat facies. Secondary vuggy and moldic porosity were best developed in foreslope and back-reef debris sheets.
Ooids occur in some wells, confirming the existence of active ooid sands along this leeward margin. Given the influence of easterly trade winds during lower Cretaceous time, such facies are to be expected and may occur even further inboard on the platform, either as isolated shoals or widespread grainstone sheets. Modern-day Caicos Platform, in the windy southern Bahamas, provides guidance for future exploration in this area. Based on Caicos analogs, active ooid sands also could form along the eastern (windward) sides of isolated reef complexes.
Petrography indicates that much of the secondary porosity encountered formed under deeper-burial conditions. Emplacement of sphalerite, fluorite, saddle dolomites, kaolinite, and authigenic quartz implied that hotter diagenetic fluids were moved along faults, perhaps tied to reactivated basement faults. Local structuring, therefore, may be a key control on James Limestone reservoir development in this area.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.