ABSTRACT

Hydrocarbon production at Midale Field is primarily from two intervals in the upper part of the Red River Formation. The heterogeneous transitional zone between the "C" laminated and "C" burrowed interval comprises the stratigraphically highest productive unit in the Red River Formation. A complex facies mosaic characterizes this shallow subtidal to low intertidal environment that includes low relief calcimicrobe and stromatoporoid buildups and associated sand aprons, tidal channels, grain flats, and lagoons. Grain-supported rock types commonly exhibit a relict interparticle pore system that is typically solution-enhanced. Buildups are characterized by vuggy and moldic pores, along with varying amounts of microporosity, predominantly concentrated within algal material. This facies is one of the most heterogeneous facies in the Red River Formation and rapid lateral facies changes are anticipated in this interval. Porosity and permeability are anticipated to vary accordingly. Reservoir units in the stratigraphically lower "D" interval include both the biodetrital mud mound and restricted shelf facies of the upper part of this interval. Generally, the best reservoir characteristics correspond to the restricted shelf facies tract, which consists predominantly of thick, extensive, homogeneous beds of sparsely fossiliferous, burrowed to bioturbated, dolomite mudstones, wackestones and minor packstones that are characterized by predominantly microintercrystalline and abundant vuggy and other secondary dissolution pore types. The reservoir potential of the entire upper part of the "D" interval at Midale Field is somewhat unique as compared to this interval in many other Red River fields in that both the restricted shelf deposits equivalent to the lower, middle, and upper "D" 0 units and the cycle capping burrowed wacke/packstone beds of individual biodetrital mud mound cycles are extensively dolomitized and have good reservoir potential.