The need for characterization of the Germania unit has emerged as a first step in the review, understanding and enhancement of the production practices applicable within the unit and the trend area in general. Petrophysical characterization of the Germania Spraberry units requires a unique approach for a number of reasons ?? limited core data, lack of modern log data and absence of directed studies within the unit. In the absence of the afore mentioned resources, an approach that will rely heavily on previous petrophysical work carried out in the neighboring ET O??Daniel unit (6.2 miles away), and normalization of the old log data prior to conventional interpretation techniques will be used. A log-based rock model has been able to guide successfully the prediction of pay and non-pay intervals within the ET O??Daniel unit, and will be useful if found applicable within the Germania unit. A novel multiple regression technique utilizing non-parametric transformations to achieve better correlations in predicting a dependent variable (permeability) from multiple independent variables (rock type, shale volume and porosity) will also be investigated in this study. A log data base includes digitized formats of gamma ray, cased hole neutron, limited resistivity and neutron/density/sonic porosity logs over a considerable wide area.

The need for characterization of the Germania unit has emerged as a first step in the review, understanding and enhancement of the production practices applicable within the unit and the trend area in general. Petrophysical characterization of the Germania Spraberry units requires a unique approach for a number of reasons ?? limited core data, lack of modern log data and absence of directed studies within the unit. In the absence of the afore mentioned resources, an approach that will rely heavily on previous petrophysical work carried out in the neighboring ET O??Daniel unit (6.2 miles away), and normalization of the old log data prior to conventional interpretation techniques will be used. A log-based rock model has been able to guide successfully the prediction of pay and non-pay intervals within the ET O??Daniel unit, and will be useful if found applicable within the Germania unit. A novel multiple regression technique utilizing non-parametric transformations to achieve better correlations in predicting a dependent variable (permeability) from multiple independent variables (rock type, shale volume and porosity) will also be investigated in this study. A log data base includes digitized formats of gamma ray, cased hole neutron, limited resistivity and neutron/density/sonic porosity logs over a considerable wide area.

The Germania Unit is located in Midland County, 12 miles east of Midland, Texas and is part of the Spraberry Formation in the Midland Basin which is one of the largest known oil reservoirs in the world bearing between 8.9 billion barrels and 10.5 billion barrels of oil originally in place. The field is considered geologically complex since it comprises typically low porosity, low permeability fine sandstones, and siltstones that are interbedded with shaly non-reservoir rocks. Natural fractures existing over a regional area have long been known to dominate all aspects of performance in the Spraberry Trend Area. Two stages of depletion have taken place over 46 years of production: Primary production under solution gas drive and secondary recovery via water injection through two different injection patterns. The cumulative production and injection in Germania as of July 2003 were 3.24 million barrels and 3.44 million barrels respectively and the production level is 470 BOPD through 64 active wells with an average rate per well of 7.3 BOPD and average water cut of 60 percent. This performance is considered very low and along with the low amount of water injected, waterflood recovery has never been thoroughly understood. In this research, production and injection data were analyzed and integrated to optimize the reservoir management strategies for Germania Spraberry Unit. This study addresses reservoir characterization and monitoring of the waterflood project with the aim of proposing alternatives development, taking into account current and future conditions of the reservoir. Consequently, this project will be performed to provide a significant reservoir characterization in an uncharacterized area of Spraberry and evaluate the performance of the waterflooding to provide facts, information and knowledge to obtain the maximum economic recovery from this reservoir and finally understand waterflood management in Spraberry. Thus, this research describes the reservoir, and comprises the performance of the reservoir under waterflooding, and controlled surveillance to improve field performance. This research should serve as a guide for future work in reservoir simulation and reservoir management and can be used to evaluate various scenarios for additional development as well as to optimize the operating practices in the field. The results indicate that under the current conditions, a total of 1.410 million barrels of oil can be produced in the next 20 years through the 64 active wells and suggest that the unit can be successfully flooded with the current injection rate of 1600 BWPD and pattern consisting of 6 injection wells aligned about 36 degrees respect to the major fracture orientation. This incremental is based in both extrapolations and numerical simulation studies conducted in Spraberry.

The Germania Unit is located in Midland County, 12 miles east of Midland, Texas and is part of the Spraberry Formation in the Midland Basin which is one of the largest known oil reservoirs in the world bearing between 8.9 billion barrels and 10.5 billion barrels of oil originally in place. The field is considered geologically complex since it comprises typically low porosity, low permeability fine sandstones, and siltstones that are interbedded with shaly non-reservoir rocks. Natural fractures existing over a regional area have long been known to dominate all aspects of performance in the Spraberry Trend Area. Two stages of depletion have taken place over 46 years of production: Primary production under solution gas drive and secondary recovery via water injection through two different injection patterns. The cumulative production and injection in Germania as of July 2003 were 3.24 million barrels and 3.44 million barrels respectively and the production level is 470 BOPD through 64 active wells with an average rate per well of 7.3 BOPD and average water cut of 60 percent. This performance is considered very low and along with the low amount of water injected, waterflood recovery has never been thoroughly understood. In this research, production and injection data were analyzed and integrated to optimize the reservoir management strategies for Germania Spraberry Unit. This study addresses reservoir characterization and monitoring of the waterflood project with the aim of proposing alternatives development, taking into account current and future conditions of the reservoir. Consequently, this project will be performed to provide a significant reservoir characterization in an uncharacterized area of Spraberry and evaluate the performance of the waterflooding to provide facts, information and knowledge to obtain the maximum economic recovery from this reservoir and finally understand waterflood management in Spraberry. Thus, this research describes the reservoir, and comprises the performance of the reservoir under waterflooding, and controlled surveillance to improve field performance. This research should serve as a guide for future work in reservoir simulation and reservoir management and can be used to evaluate various scenarios for additional development as well as to optimize the operating practices in the field. The results indicate that under the current conditions, a total of 1.410 million barrels of oil can be produced in the next 20 years through the 64 active wells and suggest that the unit can be successfully flooded with the current injection rate of 1600 BWPD and pattern consisting of 6 injection wells aligned about 36 degrees respect to the major fracture orientation. This incremental is based in both extrapolations and numerical simulation studies conducted in Spraberry.

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.

The Permian (Leonardian) aged Upper Spraberry Formation found in the Happy Field of Garza Co. TX, contains one of the best examples of a reservoir composed of resedimented carbonates in a deep-water slope-basin setting, with numerous whole core of wells with full suites of electric logs, high resolution 3D seismic coverage, and 20+ years worth of production data. Sequence stratrigraphic analysis from seismic data combined the lithologic analysis from outcrop analog, core, and well log data helps identify that the Happy Field is located within the transgressive systems tract of the fifth composite sequence in the Leonardian. The reservoir is composed of discrete allochthonous ooid and skeletal grains transported downslope via hyperconcentrated density flows sourced from a re-entrant in the shelf margin and deposited in a long-lived topographic depression at the toe-of-slope. Vertical heterogeneity due to layers of shaley silt punctuated by successive flows of oolitic and skeletal grains along with lateral heterogeneity created by younger flows of material create reservoir compartmentalization which can impede efficient development. Core-calibrated electric log correlations aids in the mapping of isolated compartments which helps with efficient development planning for the field. / text

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.