Browsing by Subject "Reservoir quality"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Characterization and prediction of reservoir quality in chlorite-coated sandstones : evidence from the Late Cretaceous Lower Tuscaloosa Formation at Cranfield Field, Mississippi, U.S.A.(2013-05) Kordi, Masoumeh; Fisher, W. L. (William Lawrence), 1932-; Hovorka, Susan D. (Susan Davis)The effectiveness of CO₂ injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework. The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction. During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume. The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis. In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial.Item Depositional environment, diagenesis and reservoir quality of the middle Bakken member in the Williston Basin, North Dakota(2016-08) Ayhan, Oguzhan; Fisher, W. L. (Williams Lawrence), 1932-; Hammes, Ursula; Kerans, CharlesThe Upper Devonian-Lower Mississippian Bakken Formation in the Williston Basin is an important source rock for oil production in North America. The Bakken Formation is comprised of three units: Upper and Lower Bakken black shales and Middle Bakken Member. Upper and Lower Bakken shales are high quality source rocks which source reservoirs in the Middle Bakken, Upper Three Forks and lower Lodgepole Formations. The Middle Bakken Member, consisting of predominantly gray, silty and sandy dolostone, is under investigation in this study. The goals of this study are to determine the regional distribution of lithofacies and depositional environments of the Middle Bakken Member and explain diagenetic sequence and reservoir quality parameters in the Williston Basin. The reservoir quality of the Middle Bakken Member is mainly influenced by mineralogical composition and cementation resulting in low porosity and permeability and linked to lithofacies distribution in the basin. Dolomitization is pervasive throughout the unit, and also occurs as dolomite cement. Moreover, cementation occurred including quartz overgrowths, K-felspar, clay cement and pyrite as both cement and nodules. Not only dolomitization but also pyrite cementation plays an important role in reducing pore space in the reservoir. The pore types that were identified are intergranular, intragranular, fracture and moldic pores. Secondary intragranular porosity generally resulted from dissolution of biogenic fragments and dissolution of other unstable minerals including feldspar and dolomite. In this study, five lithofacies and one sandy interval within lithofacies C were described throughout the North Dakota portion of the Williston basin. The sandy interval in Lithofacies C was interpreted as bars or channel fills, which differentiates this study from previous studies in terms of core description. N-S, W-E, NE-SW, NW-SE oriented cross-sections drawn via cores suggest that the lithofacies of the Middle Bakken Member pinch out towards the edges. However, the anticlines in the basin affect their thickness distributions. Sandy interval in Lithofacies C reaches its thickest succession in the center of the basin. Lithofacies C and D consist of up to 80% of dolomite although the other lithofacies consist of relatively lower dolomite (up to 65%). While well logs indicate 4-8% of porosity, point-counting results show up to 5% of porosity. The sequence of diagenetic events in the North Dakota portion of the Williston Basin is from youngest to oldest: micritization, mechanical and chemical compaction, calcite cementation, dolomitization, pyrite cementation, microcrystalline quartz cementation, syntaxial calcite overgrowth, quartz overgrowth, K-Feldspar overgrowth, dolomite dissolution, feldspar dissolution, dedolomitization, fracturing, anhydrite cementation and hydrocarbon migration.Item Depositional environment, sequence stratigraphy, and reservoir quality of the Tonkawa Sandstone in the western Anadarko Basin, Hemphill, Lipscomb and Roberts Counties, Texas(2015-05) Tussey, Logan Brien; Fisher, W. L. (William Lawrence), 1932-; Ambrose, William A.; Cutright, Bruce LThe Anadarko Basin contains some of the most prolific hydrocarbon reserves in all of North America. A recent USGS publication estimated undiscovered resources across the basin to be 495 million barrels of oil (MMBO), 27 trillion cubic feet of natural gas (TCFG), and 410 million barrels of natural gas liquids (MMBNGL). Pennsylvanian age sandstones contribute substantially to total estimated reserves within the basin. The focus of this study is the late Pennsylvanian Tonkawa Sandstone, the lowermost unit of the Douglas Group, Virgilian Series. Through the integration of core analysis, subsurface mapping, petrographic analysis, and porosity and permeability data, this study presents a detailed analysis of the Tonkawa Sandstone across approximately 1,400 mi² (3,630 km²) in the western Anadarko Basin. The Tonkawa Sandstone is comprised of three high-order transgressive-regressive sequences within one larger, lower-order sequence. Sandstone-body distribution varies greatly, depending upon depositional environments and their associated facies. The Tonkawa Sandstone was deposited in deltaic and estuarine environments with a source area to the northeast. The HST-2 interval, the oldest sandstone-rich sequence in the Tonkawa Sandstone, was deposited in a deltaic environment with a mixed wave and tide-dominated energy regime. The younger HST-3 interval was deposited in a tide-dominated deltaic environment. The youngest interval, TST-3, was deposited in a mixed wave and tide-dominated transgressive estuarine environment. The Tonkawa Sandstone is a sublitharenite to litharenite. Widespread quartz overgrowths minimize variation in reservoir quality among facies. However, more proximal facies display better reservoir quality. Detailed characterization of Pennsylvanian formations such as the Tonkawa Sandstone contributes greatly to the understanding of similar formations within the Anadarko Basin, and other foreland and cratonic basins worldwide.Item Regional character of the lower Tuscaloosa formation depositional systems and trends in reservoir quality(2012-12) Woolf, Kurtus Steven; Wood, Lesli J.For decades the Upper Cretaceous Lower Tuscaloosa Formation of the U.S. Gulf Coast has been considered an onshore hydrocarbon play with no equivalent offshore deposits. A better understanding of the Lower Tuscaloosa sequence stratigraphic and paleogeographic framework, source-to-sink depositional environments, magnitude of fluvial systems, regional trends in reservoir quality, and structural influences on its deposition along with newly acquired data from offshore wells has changed this decades-long paradigm of the Lower Tuscaloosa as simply an onshore play. The mid-Cenomanian unconformity, underlying the Lower Tuscaloosa, formed an extensive regional network of incised valleys. This incision and accompanying low accommodation allowed for sediment bypass and deposition of over 330 m thick gravity-driven sand-rich deposits over 400 km from their equivalent shelf edge. Subsequently a transgressive systems tract comprised of four fluvial sequences in the Lower Tuscaloosa Massive sand and an overlying estuarine sequence (Stringer sand) filled the incised valleys. Both wave- and tide-dominated deltaic facies of the Lower Tuscaloosa are located at the mouths of incised valleys proximal to the shelf edge. Deltaic and estuarine depositional environments were interpreted from impoverished trace fossil suites of the Cruziana Ichnofacies and detailed sedimentological observations. The location and trend of valleys are controlled by basement structures. Lower Tuscaloosa rivers were 3.8m – 7.8m deep and 145m – 721m wide comparable to the Siwalik Group outcrop and the modern Missouri River. These systems were capable of transporting large amounts of sediment indicating the Lower Tuscaloosa was capable of transporting large amounts of sediments to the shelf edge for resedimentation into the deep offshore. Anomalously high porosity (>25%) and permeability (>1200md) in the Lower Tuscaloosa at stratigraphic depths below 20,000 ft. are influenced by chlorite coating the detrital grains. Chlorite coatings block quartz nucleation sites inhibiting quartz cementation. Chlorite coats in the Lower Tuscaloosa are controlled by the presence and abundance of volcanic rock fragments supplying the ions needed for the formation of chlorite. Chlorite decrease to the east in sediments derived from the Appalachian Mountains. An increase in chlorite in westward samples correlates with an increase of volcanic rock fragments derived from the Ouachita Mountains.Item Stratigraphic relationships between the Webber Sandstone and the Maroon Formation, Northwestern Colorado, US(2006-08) Van Berkel, Diego Jose, 1959-; Fisher, W.L. (William Lawrence), 1932-; Milliken, K.L.The study of interbedded eolian and fluvial deposits, their inherent heterogeneities, and the impact on reservoir quality are the main subject of this research. The analysis of more than 2000 feet of core from four wells along with petrophysical data from 50 wells in the Rangely oil field, northwestern Colorado, allowed the characterization of textural and diagenetic parameters which ultimately control the reservoir quality. Compositional and compactional parameters were determined for the reservoir lithologies of both facies. Dune deposits lithology include subarkosic sandstones, arkose and lithic arkose sandstones. They have an architectural assemblage of F70M1C17P12 and major grain ratios of Q77F16R7. Fluvial channel deposits show an assemblage of F79M3C14P4 with a major grain ratio of Q64F23R13. Textural and compositional parameters clearly show that eolian dune sandstones are more mature texturally than their fluvial counterparts. These textural differences influenced the path of porosity loss processes and controlled the performance and quality of the reservoir. Quantification of compactional parameters as Intergranular Volume (IGV), Compactional Porosity Loss (COPL), Cementational Porosity Loss (CEPL) and Index of Compaction (Icomp) enable the determination of the best reservoir facies. IGV values for eolian dune deposits average 26.7%, with COPL and CEPL averaging 24.8%, 11.1% and 0.69, respectively. Sand sheet sandstones show average values of 25.4%, 26% and 14% with an Index of Compaction (Icomp) in the order of 0.6 Average values for fluvial deposits regarding the same porosity loss and compactional parameters result in an IGV=16.8%, COPL=33.3%, CEPL=9.4 and Icomp=0.8 The vertical pattern and relative proportions of eolian and fluvial facies allowed the subdivision in two intervals designated informally as Upper and Lower Weber. At a reservoir scale the thickness and spatial distribution of contrasting eolian and fluvial textures as well as their locally relative proportions ultimately determined the zones of better quality in the area of Rangely Field. A steady thickening trend of eolian deposits is observed in the informal Upper Weber. Conversely, a thinning and regular thinning trend is apparent in fluvial facies. Lack of data in the north and northwestern zones prevented a determination of spatial trends for the Lower Weber.