Abstract

Kansas Hugoton Gas Field is one of the largest gas fields in North America, with cumulative production over 21 TCFG and years of remaining productive life. The Early Permian Chase Group that contains the reservoir system of Hugoton Field is a deceptively simple vertical alternation of reservoir-prone carbonates/clastics with seal-prone terrestrial clastics. These cycles are easily correlated over thousands of square miles.

Ongoing evaluations from this mature field are helping to define the true geologic complexity of the Chase reservoir (rock and fluid) system in order to support optimizing reservoir management by providing opportunities to increase production and decrease costs. The distribution of reservoir-quality carbonates is difficult to predict because of heterogeneity due to deposition on an epeiric platform (with more random distribution of facies) as opposed to a ramp (with shoreline-parallel facies belts). Vertical facies patterns vary almost randomly across the field, although reservoir-prone clastics, along the west and north field edges, tend to follow paleoshoreline trends.

Key diagenetic processes affecting reservoir characteristics of the Chase Group are a) pan-evaporative dolomitization, b) near-surface leaching of limestones, c) near-surface calcite rim cementation, d) burial-induced chemical compaction of fine-grained carbonates, e) burial leaching of dolomites, and f) late cementation by dolomite and anhydrite. The best reservoir rocks in Hugoton Field are those deposited as grain-supported textures. Exposure to late leaching fluids significantly enhanced reservoir characteristics in dolomites and mixed dolo-clastics.