Recoverable Natural Gas Reserves from Jurassic Norphlet Formation, Alabama Coastal Waters: ABSTRACT

Abstract

ABSTRACT To date, eleven Norphlet gas fields have been established in offshore Alabama. These fields are part of a deep Jurassic gas trend that extends across southern Mississippi and Alabama into the Gulf of Mexico. Recoverable reserves of 4.9 to 8.1 trillion cubic feet of gas are estimated for the Norphlet formation in Alabama's coastal waters. Proven reserves are estimated to be 3.7 to 4.6 trillion cubic feet of gas, and potential reserves are estimated to be 1.2 to 3.5 trillion cubic feet of gas. The natural gas is trapped in a series of generally east-west trending salt anticlines. The mechanism of structure formation appears to be salt flowage that has formed broad, low-relief anticlines, most of which are faulted and many of which are related to small-scale growth faults. Salt movement is the critical factor in the formation of these petroleum traps. The primary Norphlet reservoir lithofacies are eolian dune and interdune sandstones that range in thickness from 140 to over 600 feet in Alabama's coastal waters. Gas pay can exceed 280 feet in thickness. Porosity is principally secondary developed as a result of decementation and grain dissolution. Jurassic Smackover algal carbonate mudstones were the main source for the Norphlet hydrocarbons. The seal for the gas is the nonpermeable upper portion of the Norphlet Formation. The overlying lower Smackover carbonates are also nonpermeable and may serve as pad of the seal.