[PDF] A Fracture And Texture Analysis Of The Bakken Formation Montana eBook

Author : Eric Joseph Easley
Publisher :
Page : 356 pages
File Size : 49,42 MB
Release : 2014
Category : Bakken Formation
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The Bakken Formation underlies much of eastern Montana, North Dakota and Saskatchewan, with correlative units extending in the subsurface beyond these regions. It is composed of three informal members: an upper shale member, a middle silty limestone/dolostone member, and a lower shale member. The Bakken petroleum system acts as a conventional and unconventional reservoir within the Williston Basin and fractures that occur naturally within the Bakken petroleum system can either help or hinder reservoir characteristics. Unconventional reservoirs, such as the Bakken Formation, rely heavily on fracture enhancement (hydraulic fracturing) to become producible oil plays. Pre-existing fractures and weaknesses open more readily with fracture stimulation than the creation of new fractures, and have been correlated to increased early production in shale plays. To determine the influence of these fractures on the reservoir in the Bakken Formation and its correlative units, fractures in core and outcrop were examined. Clay-rich shales, such as those within the Bakken Formation, display high intrinsic anisotropy, which can be helpful in interpreting seismic profiles. Despite the importance of shale oil reservoirs, the contribution of preferred orientation of minerals to shales is not well constrained. These constituent clay minerals are phyllosilicates that acquire preferred orientation during sedimentation and early diagenesis. Hard X-rays produced from a synchrotron source are effective at extracting orientation distributions of individual mineral components within a shale. Crystallographic preferred orientation can be determined through synchrotron X-ray diffraction and the interpretation of three-dimensional images by using a Rietveld refinement method. This method incorporates a least squares approach to produce a calculated model of the degree of preferred orientation. Samples of the Bakken shales from wells in North Dakota and Montana, and outcrops from southwestern Montana were investigated. Individual phyllosilicate minerals such as illite, smectite, muscovite, and chlorite yield individual orientation patterns. The elastic properties of each shale sample were determined by averaging the calculated properties of each mineral phase over their orientation distributions. The presence of specific clay minerals and degree of anisotropy is highly variable from well to well. A better understanding of shale anisotropy could help improve exploration and production of unconventional shale oil reservoirs.

Author : Zeynep Adiguzel
Publisher :
Page : pages
File Size : 27,12 MB
Release : 2013
Category :
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The Upper Devonian-Lower Mississippian (Late Fammenian-Tournaisian) Bakken Formation in the Williston Basin is one of the largest continuous oil fields in the U.S. The upper and the lower shale members are organic rich source rocks that supplied oil to the middle member, which is reservoir rock. Although the oil-producing Bakken Formation has been intensely studied in the Williston Basin, the lateral relationship between the Bakken Formation and the coeval Sappington Formation in western Montana remains cryptic. This study correlates the Sappington Formation in western Montana with the Bakken Formation in the Williston Basin in northeastern Montana. It clarifies the lateral relationship between these two units, and extent of their members across Montana and, the causes of these thickness variations. This study utilized 675 well logs (mostly gamma ray, caliper, sonic, density, neutron, resistivity logs) to make multiple E-W and N-S cross sections and isopach maps. Also, seven outcrops of the Sappington Formation in southwestern Montana and five Bakken Formation cores in the Williston Basin were tied to the subsurface data. Variations in the distribution of the Bakken/Sappington Formation were caused by eustatic changes and local epeirogenic uplifts. The Bakken/Sappington Formation is thickest in the depressions in southwestern and the northeastern Montana, the Central Montana Trough and the Williston Basin in Montana. The Bakken/Sappington Formation is thin coincident with major structural uplifts that were active during the Late Devonian, such as Yellowstone Park Uplift, Bearpaw Anticline, Scapegoat-Bannatyne Anticline and Nesson Anticline. Devonian strata are difficult to identify in the subsurface of south-central Montana making the Bakken/Sappington correlation problematic in this area. The Lower Bakken/Sappington Member thickness is 15 ft (4.6 m) in northeastern and southwestern Montana. The Lower Bakken/Sappington Member is more continuous in western Montana than the other Bakken/Sappington Members. The Middle Bakken/Sappington Member is thickest (~55 ft; 16.7 m) in the northeastern Williston Basin and in the Central Montana Trough (~50 ft; 15.2 m). The Middle Bakken/Sappington Member was less affected by the tectonics and it is present from northwestern to northeastern Montana, except in far northwestern and central Montana. The Upper Bakken Member (~5-15 ft; 1.5 m-4.6 m) is the most continuous unit in the Williston Basin, as the Bakken Members show onlapping relationship that makes the distribution of each younger member greater. However, the Upper Bakken/Sappington Member is absent west of the Central Montana Trough due to basin inversion and it is also absent in far northwestern and central Montana as a result of the erosion or nondeposition caused by the local uplifts. Transgressions were responsible for the deposition of the upper and the lower black shales in offshore marine environments, whereas the Middle Bakken/Sappington Member was deposited during regression and records multiple offshore marine to tidal environments. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148352

Author : David Nyrup Maldonado
Publisher :
Page : pages
File Size : 17,24 MB
Release : 2012
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The late Devonian-early Mississippian Bakken Formation was deposited in a structural-sedimentary intracratonic basin that extends across a large part of modern day North Dakota, eastern Montana, and the southern portion of Canada's Saskatchewan Province. The deposition of the Bakken Formation occurred during a fascinating period of geologic time that is linked to one of the five major mass extinctions. The occurrences of these mass extinctions are recorded worldwide as organic rich mud rocks similar to the ones found in the Bakken Formation. Collectively, the Bakken Formation consists of a middle dolomitic siltstone that is representative of a transgressive deposit and is bound by regressive organic rich mud rocks deposits that were influenced by rapid flooding events induced by the late Devonian-early Mississippian seaway. Geochemical proxies, total organic carbon and stable isotopic results that were recovered from four cores provide insight into the paleoenvironmental conditions during the deposition of the Bakken Formation. Geochemical analysis and interpretation of sample suites exhibit aggregate mineralogical composition from related shifts in elemental concentrations in weight percent (wt. %) consisting of magnesium (Mg), calcium (Ca), silicon (Si), aluminum (Al) and iron (Fe). The occurrence of chemostratigraphic shifts from concentrations of the Bakken Formation's bulk rock mineralogical composition represent facies changes of sedimentary packages within the middle Bakken and are linked to dolomite, calcite, quartz, pyrite, and clay (mainly illite) content. Furthermore, geochemical proxies of redox sensitive elements expressed as enrichment factors (EF) brought insight into the redox conditions during deposition of the upper and lower Bakken shales across the Williston Basin (e.g., Mo, U, V, Zn, Ni, and Cu). Molybdenum-total organic carbon (Mo -TOC) relationships, established two separate anoxic episodes that are represented by the Bakken shales and also provided insight into the degree of basin restriction the Williston Basin experienced during late-Devonian-early Mississippian time. Observed geochemical Mo -TOC relationships from the Bakken shales display similar trends of basin restriction comparable to modern silled basin analogues, specifically the Cariaco Basin (Algeo et al. 2006). The elemental shifts from Mo -TOC vs. depth profiles, demonstrate that the Bakken shales were deposited under semi-restricted conditions. Furthermore, Mo -TOC relationships also inferred water mass residence times and variable hydrographic mixing from deep basin waters from the Williston Basin. TOC and stable isotopic composition of TOC ([delta]13C) from the Bakken shales were utilized as geochemical proxies to examine the change and distribution of organic matter across the Williston Basin. Lastly, stable isotopic composition of TOC results potentially demonstrate a blend of kerogen source formed from marine organic matter (plankton) and land-plant lipids based on previous studies.

Author : Shashank Khatri
Publisher :
Page : 92 pages
File Size : 30,60 MB
Release : 2017
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The Bakken formation in the Elm Coulee Field of the Williston Basin consists of three members: 1) upper shale member, 2) middle silty dolostone member, and 3) lower shale member. The upper and lower members act as excellent source rocks and the main reservoir is the middle member with an average porosity of 3 to 9% and average permeability of 0.04md. The Bakken oil play in this area is a stratigraphic trap with a pinch-out to the southwest and a diagenetic facies change in the northeast. The main production is interpreted to come from matrix permeability in the field area. However, the first year production trends from the Elm Coulee Field show areas of anomalously high production. This study used 3D seismic data from Crane Field, which is located in the southeastern part of the Elm Coulee Field, to investigate structures which might be responsible for the anomalous production trends at the Elm Coulee Field. We used post stack seismic conditioning and seismic attributes to amplify the structure of the basement. Further investigation revealed the presence of a pop-up structure in the central portion overlying a zone of basement deformation. This zone of deformation was interpreted to be composed of a left lateral wrench faulting system based on a model-driven approach. This study goes on further to map the structure and faults in 3 dimensions using a model driven approach, which reveals that the pop-up structure evolved from an obtuse angle left lateral step over system in the basement. In addition, the presence of this left lateral wrench fault network is interpreted to be related to a regional left lateral strike slip system - the Brockton Froid Fault Zone The fracture network characteristics in the middle member of the Bakken Formation are directly related to the local stresses generated by the interpreted left lateral wrench fault system in the study. There are two fracture sets- NE-SW and NW-SE. The structure and fracture network characteristics help explain the presence of regions of anomalously high EUR [CB1] values in the Elm Coulee Field. The regions of anomalously high EURs in the Elm Coulee Field may be regions where the middle member of the Bakken Formation has increased natural fracturing related to the local stresses induced by left-lateral oblique slip strike slip faults..

Author : Michael E. Beecher
Publisher :
Page : 108 pages
File Size : 26,49 MB
Release : 2013
Category : Electronic dissertations
ISBN : 9781303215544

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The oil-in-place estimate for the Bakken Formation has varied from 10 billion barrels in 1974 to 503 billion barrels in 1999. However, only a small fraction of this estimate is recoverable due to the formation having very low porosity and permeability. Implementation of hydraulic fracture stages along horizontal wells in the Bakken has been productive. Recently, identification of zones where the formation is brittle has been used to improve hydraulic fracture stimulation efficiency in an effort to improve production.