The facies, environments of deposition and cyclicity of the Yates Formation, North Ward-Estes field, Ward County, Texas

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Johnson, Ronnie Delane
Texas A&M University
geology.; Major geology.
thesis / dissertation description
The Yates Formation is part of the Artesia Group, a sequence of interbedded carbonates, clastics and evaporates that was deposited across the back-reef shelves of the Permian basin in Late Permian (Upper Guadalupian) time. The Artesia Group is the shelfal equivalent of the shelf-marginal Capitan and Goat Seep Reefs and deep-basinal Delaware Mountain Group. This study is based on the description of seven cores and twenty-two well logs from North Ward-Estes field along the western margin of the Central Basin Platform. The Yates Formation consists of sub-arkosic sandstones and siltstones and dolomitic mudstones and wackestones. It has sharp contacts with the carbonates of the underlying Seven Rivers Formation and evaporite-rich beds of the underlying Tansill Formation. Five facies are distinguished in the Yates Formation and its bounding surfaces on the basis of their lithologies and stratification. Three elastic facies (Facies 1, 2, and 3) were deposited in fluvial, deltaic, eolian and sabkha environments. One carbonates facies (Facies 4) was deposited in a shallow subtidal environments and one evaporate facies (Facies 5) was deposited in a sabkha environment. The stratigraphy of the Yates Formation was determined by the correlation of cores and well log data strike and dip profiles through the field. Two sequences and ten to twelve parasequences are recognized within the Yates Formation. Each sequence consists of basal lowstand incised valley fill (IVF), which is overlain by a Transgressive Systems Tract (TST') and Highstand Systems Tract (HST). The two sequences which have slightly wavy sheet geometries in the strike direction and thin in the landward direction, marking two long-term cycles of relative sea level fall and subsequent rise in the field area.Reservoir properties of the Yates Formation were determined by the use of core plug data for porosity and permeability measurements. This physical data, along with measured data from well logs, was then correlated to identify the quality, lateral extent and continuity of the elastic reservoirs in this formation. Facies 1 is identified as the best reservoir rock and Facies 3 is identified as the poorest. Facies 2 has intermediate quality.