Depositional and Diagenetic Controls on Porosity Permeability and Oil Production in McFarland/Magutex (Queen) Reservoirs, Andrews County, West Texas

HOLTZ, MARK H., Bureau of Economic Geology, Austin, TX

The McFarland/Magutex Queen reservoir complex lies along the northeastern edge of the Central basin platform in the west Texas Permian basin and produces oil from the Permian (middle Guadalupian) Queen Formation. Current production from this complex totals 42 million stock-tank barrels (MMSTB) of an estimated 219 MMSTB of original oil in place, with an estimated 90 MMSTB of remaining mobile oil (RMO).

The gross pay interval contains two parasequences consisting of progradational, 30-ft-thick, upward-shoaling facies packages. Facies include shoreface, mixed tidal channel and intertidal flat, and supratidal. Elongate shoreface facies are characterized by poorly consolidated, massive to thinly laminated sandstones. Sinuous tidal-channel facies consist of point-bar deposits and cross-cut shoreface and intertidal facies. The intertidal flat facies are characterized by root traces, algal laminations, and flaser bedding. The supratidal facies, which act as permeability barriers, are characterized by algal-laminated dolostone and nodular, laminated, and massive anhydrite containing halite and gypsum pseudomorphs. Highest production and the largest amount of the 90 MMSTB of RMO is associate with the shoreface and tidal-channel facies. Bulk pore volume storage capacity and permeability are also highest within these two facies.

Sandstones are arkosic, containing anhydrite and dolomite cements. Accessory minerals are clays, authigenic feldspar, and dolomite. Porosity and permeability and their interrelationship are controlled by the relative amounts of cements and accessory minerals. Three main pore types are recognized: interparticle, moldic and intraconstituent, and micropores. Interparticle porosity is greatest in the shoreface and tidal-channel facies, where smaller bulk volumes of cement exist. Moldic and intraconstituent porosity is associated with leached feldspars and anhydrite cement dissolution. Microporosity is associated with syndepositional, grain-coating corrensite, dissolution-enhanced feldspar cleavage planes, and authigenic multifaceted dolomite. Microporosity derived from clays and dolomite s formed preferentially in tidal-channel and intertidal flat facies.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)