Assessing the influence of diagenesis on reservoir quality: Happy Spraberry Field, Garza County, Texas

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Title: Assessing the influence of diagenesis on reservoir quality: Happy Spraberry Field, Garza County, Texas
Author: Mazingue-Desailly, Vincent Philippe Guillaume
Abstract: In the Permian Basin , strata of Leonardian age typically consist of interbedded carbonates and siliciclastics interpreted to be turbidite deposits . Happy Spraberry Field produces from a 100 -foot thick carbonate section in the Lower Clear Fork Formation (Lower Leonardian ) on the Eastern Shelf of the Midland Basin . Reservoir facies include oolitic - to -skeletal grainstones and packstones , rudstones and in situ Tubiphytes bindstones . Depositional environments vary from open marine reefs to shallow marine oolitic shoal mounds . Best reservoir rocks are found in the oolitic -skeletal packstones . Diagenesis occurred in several phases and includes (1 ) micritization , (2 ) stabilization of skeletal fragments , (3 ) recrystallization of lime mud , (4 ) intense and selective dissolution , (5 ) precipitation of four different stages of calcite cement , (6 ) mechanical compaction , (7 ) late formation of anhydrite and (8 ) saddle dolomite and (9 ) replacement by chalcedony . Oomoldic porosity is the dominant pore type in oolitic grainstones and packstones . Incomplete dissolution of some ooids left ring -shaped structures that indicate ooids were originally bi -mineralic . Bacterial sulfate reduction is suggested by the presence of (1 ) dissolved anhydrite , (2 ) saddle dolomite , (3 ) late -stage coarse -calcite cement and (4 ) small clusters of pyrite . Diagenetic overprinting on depositional porosity is clearly evident in all reservoir facies and is especially important in the less -cemented parts of the oolitic grainstones where partially -dissolved ooids were subjected to mechanical compaction resulting in "eggshell" remnants . Pore filling by late anhydrite is most extensive in zones where dissolution and compaction were intense . Finally , a porosity -permeability model was constructed to present variations in oolitic packstone - rudstone -bindstone reservoir rocks . The poroperm model could not be applied to oolitic grainstone intervals because no consistent trends in the spatial distribution of porosity and permeability were identified . Routine core analysis did not produce any reliable value of water saturation (Sw ) . An attempt to take advantage of wireline log data indicates that the saturation exponent (n ) may be variable in this reservoir .
URI: http : / /hdl .handle .net /1969 .1 /27
Date: 2004-09-30

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Assessing the influence of diagenesis on reservoir quality: Happy Spraberry Field, Garza County, Texas. Available electronically from http : / /hdl .handle .net /1969 .1 /27 .

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