Bend Conglomerate Research Articles

Integrated study of seismic and well data for porosity estimation using multi-attribute transforms: a case study of Boonsville Field, Fort Worth Basin, Texas, USA

This study represents part of a research project focused on the Runaway Surface (MFS53), which is one of the reservoir levels in the Boonsville Field of the Fort Worth Basin in north central Texas, USA. This reservoir system is a subunit of the Bend Conglomerate section, which is a productive series of gas reservoirs deposited during the Middle Pennsylvanian fluvio-deltaic environment. This paper adopts an integrated approach to the seismic and well log data, using a combination of geostatistical and multi-attribute regression transform methods. The main focus of the research is to accurately predict the porosity distribution of the Runaway Formation away from the well locations. The input data consists of 32 wells (of which six wells contain porosity logs) together with a 3D seismic volume of Boonsville Field. The 3D seismic volume was inverted to obtain the acoustic impedance cube of the study area. Secondly, six multi-attribute data slices were extracted from both surface seismic and inverted acoustic impedance volumes. Subsequently, the porosity distribution of a selected reservoir level was estimated over the full extent of the study area using both acoustic impedance alone, and multi-attributes. Initially, the multi-attribute transform algorithm was trained using the well log data. The porosity at each well location was averaged over a particular depth zone of interest, and then compared with six extracted attribute slices averaged over the same depth window. In order to select the appropriate number of attributes for analysis, a cross-validation process was followed. The results of this cross-validation process and the training of the multi-attribute transforms were applied to the extracted attribute slices in order to produce the final porosity map of the Runaway Formation. The cross-plot between the seismically derived porosity and the well porosity values showed that accuracy of porosity prediction was increased from 75 %, when using a single attribute (acoustic impedance (AI)), to 90 % when multiple attributes are used. Additionally, when the actual well-derived porosities were overlaid onto the final predicted porosity maps from both techniques, a significant amount of mismatching was observed on the porosity map derived from AI alone, whereas the predicted porosity with the multi-attribute regression transform was a close match to the actual well-derived porosities. Beside this, the subsurface geology (i.e., karst collapse features) were not clear in the porosity map deduced from AI. Based on these cross-correlation results, the porosity map derived from multi-attribute regression transform was selected. The high level of correlation (90 %) with the actual and derived porosity indicates that the seismic multi-attributes were reliably transformed to the reservoir porosity log. The derived porosity map for the Runaway Formation indicates high lithological variation within the reservoir level with a porosity generally varying between 2 and 32 %. The western portion of the Runaway Formation is highly porous and can be considered for future exploration purposes. Although this study retains a certain level of uncertainty, which can be attributed to the well and seismic data used, due to data limitations, uncertainty analysis was not included in the current study, but this should be considered in future studies so as to improve the porosity prediction.

Reservoir systems of the Pennsylvanian lower Atoka Group (Bend Conglomerate), northern Fort Worth Basin, Texas: High-resolution facies distribution, structural controls on sedimentation, and production trends

This study defines the depositional systems of mature lower Atoka Group reservoirs, structural influence on their sedimentation, and sand-transport patterns at a higher degree of resolution and over a significantly larger part of the play area than previously conducted. The reservoir systems are characterized by pronounced variations in depositional style, even between stratigraphically adjacent systems. They represent a variety of on-shelf siliciclastic depositional facies, including gravelly braided river, fluvial-dominated delta, and low-sinuosity incised river deposits. Penecontemporaneous, high-angle, basement-rooted reverse faults and genetically associated folds of the Mineral Wells–Newark East fault system exerted direct control on the orientation of complex fluvial-channel and delta-distributary sand-transport pathways and the geometry of deltaic depocenters. Multiple contemporaneous source areas, including the Ouachita fold belt to the southeast, the Muenster arch to the northeast, and the south flank of the Red River arch, also contributed to the complexity of sandstone trends in the lower Atoka play area. Bubble maps of normalized per-well first-year production and total cumulative production allow qualitative conclusions regarding geologic controls on production distribution. Most wells with optimal gas production occur within two northwest-trending production fairways that coincide with primary sandstone trends of one or more reservoir systems. Highest per-well oil production exists where lower Atoka reservoir facies occur above oil-prone Barnett Shale source rocks (vitrinite reflectance 1.1% Ro) in the western and northwestern parts of the study area. Widespread fault-bounded, karst-produced sag structures that extend vertically from the source rocks through the lower Atoka Group most likely served as hydrocarbon-migration conduits and formed traps for both oil and gas.

Use of 3D digital analogues as templates in reservoir modelling

Geological analogues may be used to rigorously interpret three-dimensional (3D) subsurface reservoir geometry by combining the capabilities of graphics workstations with digital outcrop data collection. Digital data from sedimentary environments and outcropping geological formations are interpreted in a 3D viewing environment to construct 3D templates of analogues for reservoir bodies. These 3D geometries and associated scaling parameters are then available to build 3D digital hypotheses concerning subsurface reservoir geometries. Two examples serve to illustrate this approach. Data from a modern fluvial system in the USA are used to construct digital templates. Interpretation of this dataset enables the relationship between 3D external geometries of sedimentary units to be rigorously defined and related to internal sedimentary structures. The location of gas-filled reservoir compartments in the Carboniferous Bend Conglomerate reservoirs of the Boonsville Field in North Texas are then interpreted using such analogue-derived digital templates.

Use of 3D digital analogues as templates in reservoir modelling

Geological analogues may be used to rigorously interpret three-dimensional (3D) subsurface reservoir geometry by combining the capabilities of graphics workstations with digital outcrop data collection. Digital data from sedimentary environments and outcropping geological formations are interpreted in a 3D viewing environment to construct 3D templates of analogues for reservoir bodies. These 3D geometries and associated scaling parameters are then available to build 3D digital hypotheses concerning subsurface reservoir geometries. Two examples serve to illustrate this approach. Data from a modern fluvial system in the USA are used to construct digital templates. Interpretation of this dataset enables the relationship between 3D external geometries of sedimentary units to be rigorously defined and related to internal sedimentary structures. The location of gas-filled reservoir compartments in the Carboniferous Bend Conglomerate reservoirs of the Boonsville Field in North Texas are then interpreted using such analogue-derived digital templates.

On: “3-D seismic imaging and seismic attribute analysis of genetic sequences deposited in low‐ accommodation conditions” (B. A. Hardage, D. L. Carr, D.E. Lancaster, J. L. Simmons Jr., D. S. Hamilton, R. Y. Elphick, K. L. Oliver, and R. A. Johns, GEOPHYSICS, 61, 1351–1362)

The paper deals with the results of a multidisciplinary study of the Bend Conglomerate (Middle Pennsylvanian fluvio‐deltaic clastics) in a portion of Boonsville gas field in the Fort Worth Basin of North‐Central Texas, especially with those related to the Caddo sequence, at the top of the Bend Conglomerate. The purpose of the study was “to determine how modern geophysical, geological, and engineering techniques could be combined to understand the mechanisms by which fluvio‐deltaic depositional processes create reservoir compartmentalization in a low‐ to moderate‐accommodation basin.” According to Hardage et al. (1996), complexly arranged key chronostratigraphic surfaces are major controls on compartmentalization and architecture of reservoirs. These key chronostratigraphic surfaces are flooding surfaces, maximum flooding surfaces, and erosion surfaces.

3-D seismic imaging and seismic attribute analysis of genetic sequences deposited in low‐accommodation conditions

A multidisciplinary team, composed of stratigraphers, petrophysicists, reservoir engineers, and geophysicists, studied a portion of Boonsville gas field in the Fort Worth Basin of North‐Central Texas to determine how modern geophysical, geological, and engineering techniques could be combined to understand the mechanisms by which fluvio‐deltaic depositional processes create reservoir compartmentalization in a low‐ to moderate‐accommodation basin. An extensive database involving well logs, cores, production, and pressure data from 200‐plus wells, [Formula: see text] [Formula: see text] of 3-D seismic data, vertical seismic profiles (VSPs), and checkshots was assembled to support this investigation. The reservoir system we studied was the Bend Conglomerate, a productive series of gas reservoirs composed of Middle Pennsylvanian fluvio‐deltaic clastics 900 to 1300 ft (275 to 400 m) thick in our project area. We were particularly interested in this reservoir system because evidence suggested that many of the sequences in this stratigraphic interval were deposited in low‐accommodation conditions (that is, in an environment where there was limited vertical space available for sediment accumulation), and our objective was to investigate how fluvio‐deltaic reservoirs were compartmentalized by low‐accommodation depositional processes. Using an extensive well log database (200 plus wells) and a core‐calibrated calculation of rock facies derived from these logs, we divided the Bend Conglomerate interval into ten genetic sequences, with each sequence being approximately 100 ft (30 m) thick. We then used local VSP and checkshot control to transform log‐measured depths of each sequence boundary to seismic two‐way time coordinates and identified narrow seismic data windows encompassing each sequence across the [Formula: see text] [Formula: see text] 3-D seismic grid. A series of seismic attributes was calculated in these carefully defined data windows to determine which attributes were reliable indicators of the presence of productive reservoir facies and which attributes could, therefore, reveal distinct reservoir compartments and potentially show where infield wells should be drilled to reach previously uncontacted gas reservoirs. Our best success was the seismic attribute correlations we found in the Upper and Lower Caddo sequences, at the top of the Bend Conglomerate. These sequences were deposited in a low‐accommodation setting, relative to other Boonsville sequences, and we found that reflection amplitude and instantaneous frequency, respectively, were reliable indicators of the areal distribution of reservoir facies in these low‐accommodation sequences.

Boonsville 3-D data set

The Bureau of Economic Geology at The University of Texas at Austin is making a 3-D seismic data set publicly available as part of the technology transfer activities of the Secondary Gas Recovery (SGR) program funded by the Gas Research Institute and the U.S. Department of Energy. The data are a significant part of the total data base amassed during a two‐year study of the Bend Conglomerate reservoir system in Boonsville Field in north‐central Texas.

Surface-Bounded ReservoIr Compartmentalization in the Caddo Conglomerate, Boonsville (Bend Conglomerate) Gas Field, Fort Worth Basin, Texas: ABSTRACT

Interpretation of cores and logs from 222 wells and a 26 mi[sup 2] 3-D seismic survey in the Boonsville (Bend Conglomerate) Gas Field indicates the Caddo Conglomerate zone (Atoka) contains two reservoir sandstone bodies which are physically separated by a key chronostratigraphic erosion surface. The oil-productive Lower Caddo sandstone represents a southward-prograding, strike-oriented highstand delta system. Downdip wells have encountered both oil and gas in a younger valley-fill sandstone complex comprising the Upper Caddo lowstand systems tract. Abandoned delta-platform limestones at the top of the Lower Caddo highstand tract were truncated during lowstand valley incision prior to Upper Caddo sandstone deposition. The limestones do not occur above the sharp-based, blocky to upward-fining Upper Caddo valley-fill sandstones, and underlying Lower Caddo sandstones typically display upward-coarsening, progradational patterns. Significant gas reserves in Upper Caddo wells located structurally downdip to the Lower Caddo oil accumulation indicate the two units are hydraulically separate reservoir compartments. Both reservoir compartments have been successfully imaged using 3-D seismic attributes analysis, confirming the original, log-based interpretation and providing a powerful infill drilling and reservoir management tool.

High-Resolution Reservoir Characterization of Midcontinent Sandstones Using Wireline Resistivity Imaging, Boonsville (Bend Conglomerate) Gas Field, Fort Worth Basin, Texas: ABSTRACT

In the absence of abundant core data, Formation MicroScanner* (FMS) and Fullbore Formation Microlmager* (FMI) wireline logs from 3 wells in Boonsville Field provided continuous geologic information in a 1000-foot thick, Pennsylvanian (Atoka) interval. Cores provided the most detailed sequence-stratigraphic information, but only 358 ft of core from 4 wells was available to evaluate the 30 mi[sup 2] project area. The FMS and FMI logs thus served as continuous, oriented [open quote]virtual cores[close quote] that expanded our stratigraphic database and improved our interpretations, which included the identification of key chronostratigraphic surfaces, lithofacies, sedimentary structures, faults, and fractures. Paleocurrents inferred from the FMS and FMI images suggest that most Bend Conglomerate sandstones are lowstand valley-fill deposits derived from the Muenster and Red River Uplifts, rather than Ouachita-derived deltas. Combined analysis of cores and wireline resistivity imaging technology enabled the development of a fine-scale, sequence-stratigraphic framework which formed the basis for correlation and mapping of the major Bend Conglomerate reservoir zones, and helped us to identify compartmentalization mechanisms within these complex reservoirs.

Early Pennsylvanian Wrenching Along the Red River-Matador Arch: Formation of a Pull-Apart Basin, Depocenter for Atokan to Lower Des Moines (Bend) Clastics, Cottle County, Texas: ABSTRACT

Early Pennsylvanian wrenching along the Red River-Matador Arch (Tectonic Zone) created a braided series of en echelon faults and folds with associated pop-up structures and pull-apart basins. Local extension, or overstepping, in Southeast Cottle County, Texas, has produced the deepest pull-apart basin along the arch with over 10,000` of structural relief. The emerging Wichita-Amarillo Uplift, to the north, provided an abundant sediment source, which prograded rapidly southward as an alluvial fan-braided river complex. Exposure of basement rocks and lower Paleozoic sediments along the Red River-Matador Arch, also contributed to the basin fill. Syntectonic sedimentation led to the accumulation of over 6000` of Bend (Atoka-lower Des Moines) sediments within the basin. Deposition was dominated initially by alluvial fan to fluvial siliciclastics. As basin subsidence was further amplified by sediment loading, accommodation exceeded sedimentation capturing a large segment of the southward prograding Wichita-Amarillo derived clastic wedge. Encroachment of the late Atoka to lower Des Moines epeiric sea promoted further evolution of depositional environments to fan deltas, marine dominated clastics and, later, localized carbonate development. Type III kerogen rich organic shales produced abundant gas prone source rocks. The extreme depth of the basin combined with the local geothermal gradient provided for significant hydrocarbonmore » generation. By early 1988 new well control helped revise previous stratigraphic correlation demonstrating a rapidly expanding lower Des Moines to Atokan section. The drilling of the Gunn Oil Company-Brothers No. 1 to a total depth of 10,301` in the Mississippian Chappel Limestone, encountered 2025` of Bend sediments, with 279` of gross Bend Conglomerate (162` of net pay). The Brothers No. 1 was potentialled on 11/19/89 with a CAOF of 6.0 MMCFD and filed as the field discovery for the Broken Bone (Bend Conglomerate) field.« less

Sedimentology and Permeability Architecture of Atokan Valley-Fill Natural Gas Reservoirs, Boonsville Field, North-Central Texas: ABSTRACT

ABSTRACT The Boonsville gas field in Jack and Wise Counties comprises numerous thin (10-20 ft) conglomeratic sandstone reservoirs within an approximately 1,000-ft-thick section of Atokan strata. Reservoir sandstone bodies commonly overlie sequence-boundary unconformities and exhibit overall upward-fining grain-size trends. Many represent incised valley-fill deposits that accumulated during postunconformity base-level rise. This stratal architecture is repeated at several levels throughout the Bend Conglomerate, suggesting that sediment accumulation occurred in a moderate- to low-accommodation setting and that base level fluctuated frequently. The reservoir units were deposited by low-sinuosity fluvial processes, causing a hierarchy of bed forms and grain-avalanche bar-front processes to produce complex grain-size variations. Permeability distribution is primarily controlled by depositional factors but may also be affected by secondary porosity created by the selective dissolution of chert clasts. High-permeability zones (-2.8 darcys) are characterized by macroscopic vugs composed of clast-shaped moldic voids (-5 mm in diameter). Tight (low-permeability) zones are heavily cemented by silica, calcite, dolomite, and ankerite and siderite cements. Minipermeameter, x-radiograph, and petrographic studies and facies analysis conducted on cores from two Bend Conglomerate reservoirs (Threshold Development Company, I. G. Yates 33, and OXY U.S.A. Sealy C 2) illustrate the hierarchy of sedimentological and diagenetic controls on permeability architecture. End_of_Record - Last_Page 758-------

Factors Controlling the Distribution of Reservoir Quality in the Pennsylvanian Bend Conglomerate Fan-Delta System

Chert conglomerates, and associated sediments, of the Bend Conglomerate in Taylor Draw field, Upton Co., Texas, were deposited in a series of fan deltas that prograded into an open-marine system. The distribution of reservoir quality in these deposits is facies controlled. Permeabilities range from near zero to 30,000 md. Low-permeability conglomerates contain either a mud matrix or abundant calcite fossil fragments. The calcite grains serve as nucleation sites for calcite cementation and, through dissolution, as a source of calcite cement. High-permeability, sandy (chert and quartz) conglomerates have no mud matrix or calcite grains. Some of them are cemented with a thin rim of chalcedony, while others have no cement and show strong pressure solution at grain contacts. They are commonly friable and are recovered as loose gravels in the core barrel. The mineralogy of matrix gains is related to the distribution of the depositional facies within the fan delta. The low-permeability conglomerates were deposited in the subaerial to subaqueous distal fan-delta complex where calcareous marine organisms or mud were mixed with the conglomerate. The high-permeability conglomerates were deposited as thick channel-gravels in the subaerial proximal and mid-fan sections of the fan deltas. Depositional facies within the fan-delta complex controlled themore » distribution of calcite grains in the matrix and hence reservoir quality. The fossiliferous conglomerates became tightly cemented with calcite during burial, whereas the nonfossiliferous conglomerates remained permeable. Facies maps of the fan-delta complex therefore can be used to delineate high-permeability conglomeratic reservoirs.« less

Developments in North Texas in 1957

Exploratory and development drilling decreased during 1957 but the success ratio increased to 22% and 68%, respectively. Crude production decreased to 75,433,784 bbls. The Boonsville (Bend conglomerate gas) field was created as a 251,000-acre field in Jack and Wise counties.