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Reservoir characterization of Yates Formation (Permian, Guadalupian), South Ward field, Ward County, Texas
Abstract
The Yates Formation is a prominent hydrocarbon producing unit in the Permian Basin of west Texas. Production is predominantly from very fine grained sandstones and siltstones that are interbedded with carbonates. The producing clastics have northwest-southeast trend in west Texas and roughly an east-west trend in New Mexico. The present work focuses on the Yates reservoirs of South Ward field in west Texas. The main objective of this thesis is to examine the clastic reservoirs at pore scale, facies scale and at field scale. Yates facies include: (1) fine grained yellowish well sorted sandstones with poor cementation; (2) very fine grained, gray, moderately sorted and ripple laminated sandstone; (2a) very fine grained, gray, bioturbated and massive sandstone; (3) very fine grained and silty, reddish silty sandstone, laminated and typically anhydrite cemented; (4) silty to very fine grained, gray with displacive anhydrite nodular cement; (5) siltstone, dark gray to black, compact and laminated, with pyrite and salt pits; (6) dolostones with predominantly mudstones and wackestones. Sandstones are sub-arkosic and differ in matrix and cement composition. Depositional environments of the clastics facies vary from shallow marine to continental, eolian and fluvial. Carbonates are restricted subtidal to supratidal shelf deposits. The facies-dependent reservoir rocks were ranked by reservoir quality from the highest (o = 20-30%; k = 100-250md) to the lowest (o = < 4% to; k = <Imd). Each of these facies is characterized by a particular 0 vs k relationship observed through alinear regression model. Average capillary displacement pressures calculated for the elastic facies 1 and 2 are 12psia and 43psia respectively. These are classed as "good reservoirs"; the same for facies 3 is 148psia, which is classed as "seal facies". Facies 4 through 6 are also fluid barriers. At a field scale, the Yates Formation is divided into two High Frequency Sequences (HFSS) separated by a prominent erosional unconformity. The lower HFS is made up of 10 parasequences; the upper HFS is made up of 7 parasequences. Each parasequence represents an "upward drying" cycle that starts with a "wettest" facies and ends with "driest" facies. The HFSs start with a lower Trangressive Systems Tract (TST) and end with an upper Highstand Systems Tract (HST). There is evidence of Incised Valley Fills (IVFS) at the bases of the TSTS. The Yates is a composite sequence, that was deposited during a sea level fall of 3 rd order scale. Internal cyclicity in the Yates Formation is the result of superimposition of 4 Ih and 5 th eustatic cycles on the 3 rd eustatic cycle. A constant, low subsidence rate was assumed for the entire shelf, during the deposition of Yates Formation.
Description
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Citation
Dronamraju, Sharma (1997). Reservoir characterization of Yates Formation (Permian, Guadalupian), South Ward field, Ward County, Texas. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -D76.
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