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Pathak M.,University of Utah | Deo M.,University of Utah | Craig J.,Eni Exploration and Production Division | Levey R.,Energy and Geoscience Institute
Society of Petroleum Engineers - SPE/AAPG/SEG Unconventional Resources Technology Conference | Year: 2016

Recent developments in shale technology have revolutionized oil and gas production in the United States. However, there is still a strong requirement for assessing the prospectivity of emerging shale plays, both in the United States and internationally. This paper is an attempt to generalize the results from three major US shale plays: Bakken, Eagle Ford and Niobrara, and to use these to assess the prospectivity of emerging shale plays elsewhere. Porosity, permeability, total organic carbon (TOC) content, thickness, brittleness, composition and maturity of shales are all important in the generation and retention of hydrocarbons. Factors such as depositional environment, uplift and burial, proximity to porous media, presence of natural factures, and reservoir pressure distribution over geologic time all also affect the ability of shales to retain hydrocarbons and be economically productive reservoirs. As an example, in the Eagle Ford Shale, regional overpressure has been generated through disequilibrium compaction as a result of rapid burial from the Late Cretaceous to the Palaeogene. Post-burial uplift is least in the Central Eagle Ford and the generated over pressure is, therefore, best preserved there. Overpressured shale reservoirs usually have high free gas contents. This is critical for high fluid flow rates from shales. Across the Karnes Trough in the northeast of the play, there is a good seal to the Eagle Ford Formation and, hence, good production, despite the fact that the production from the overlying Austin Chalk reservoir is poor in this area. Thus, the potential of a particular shale reservoir to produce hydrocarbons could be generalized into a "retention" factor. The geologic features that control the retention and production of hydrocarbons in these three shale plays are compared and analyzed. An attempt is made to correlate these factors and their contributions over geologic time scales in order to estimate hydrocarbon in-place in each. The results obtained from the study of these three major shale plays are generalized to provide insights into the relationships between geologic features, retention and production trends for shale plays. 'Retention' factor charts are prepared to provide a quick assessment of the prospectivity of emerging shale resources plays. Copyright 2014, Unconventional Resources Technology Conference (URTeC).

Hardwick C.L.,Utah Geological Survey | Allis R.,Utah Geological Survey | Wannamaker P.E.,Energy and Geoscience Institute
Transactions - Geothermal Resources Council | Year: 2015

Magnetotelluric (MT) data are an integral part of geothermal resource exploration throughout the world. The Black Rock Desert (BRD), Utah, may be unique, with large datasets of MT soundings and gravity measurements in combination with oil exploration wells extending to 5 km depth possessing a variety of geophysical logs, and proven high heat flow in the central part of an underlying basin (temperatures exceeding 240°C at 3 m depth). Wireline geophysical data indicate basin fill signatures of 1 to 10 ohm-m and bedrock signatures of 10 to over 1000 ohm-m. Throughout the BRD, are large variations in lithology and, consequently, resistivity. Massive salt sections, when emplaced in clay-rich basin fill, show resistivities on the order of 100 ohm-m. The upper portions of the ID, 2D, and 3D resistivity models have reasonable agreement with the wireline data, whereas in the central part of the basin, the deeper portions of the wells and the models have disparities that are an order of magnitude different. Possibly the most striking difference is the bottom of the Pavant Butte well where temperatures reach 240°C and in-situ resistivities are 100 ohm-m, but the modeled resistivities are an order of magnitude lower (<10 ohm-m). Possible explanations for this difference are the existence of aligned conductive fracture networks deep within the bedrock with a small fraction of crustal fluids in the pore space or differences in the averaging scale of MT data versus downhole wireline data. While emergent signatures of a deeply rooted system are more than likely detected with MT soundings, the signature of our specific target (stratigraphic reservoir) remains elusive. © Copyright (2015) by Geothermal Resources Council All rights reserved.

Allen J.L.,Energy and Geoscience Institute | Allen J.L.,University of Utah | Johnson C.L.,University of Utah
Sedimentology | Year: 2011

Marginal marine deposits of the John Henry Member, Upper Cretaceous Straight Cliffs Formation, were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits. Complete transgressive-regressive cycles, comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies, are distinguished based on their internal facies architecture and bounding surfaces. Two main types of boundaries occur between the transgressive and regressive portions of each cycle: (i) surfaces that record the maximum regression and onset of transgression (bounding surface A); and (ii) surfaces that place deeper facies on top of shallower facies (bounding surface B). The base of a transgressive facies (bounding surface A) is defined by a process change from wave-dominated to tide-dominated facies, or a coaly/shelly interval indicating a shift from a regressive to a transgressive regime. The surface recording such a process change can be erosional or non-erosive and conformable. A shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces (bounding surface B). These two main bounding surfaces and their subtypes generate three distinct transgressive-regressive cycle architectures: (i) tabular, shoaling-upward marine parasequences that are bounded by flooding surfaces; (ii) transgressive and regressive unit wedges that thin basinward and landward, respectively; and (iii) tabular, transgressive lagoonal shales with intervening regressive coaly intervals. The preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive-regressive cycles. Acknowledging variation in transgressive-regressive cycles, and recognizing transgressive successions that correlate to flooding surfaces basinward, are both critical to achieving an accurate sequence stratigraphic interpretation of high-frequency cycles. © 2011 The Authors.

Zhou J.,University of Utah | Huang H.,Idaho National Laboratory | Deo M.,University of Utah | Jiang S.,Energy and Geoscience Institute
Society of Petroleum Engineers - Unconventional Resources Technology Conference, URTeC 2015 | Year: 2015

Because of the low permeability in shale plays, closely spaced hydraulic fractures and multilateral horizontal wells are generally required to improve production. Therefore, understanding the potential fracture interaction and stress evolution is critical in optimizing fracture/well design and completion strategy in multi-stage horizontal wells. In this paper, a novel fully coupled reservoir flow and geomechanics model based on the dual-lattice system is developed to simulate multiple non-planar fractures propagation. The numerical model from Discrete Element Method (DEM) is used to simulate the mechanics of fracture propagations and interactions, while a conjugate irregular lattice network is generated to represent fluid flow in both fractures and formation. The fluid flow in the formation is controlled by Darcy's law, but within fractures it is simulated by using cubic law for laminar flow through parallel plates. Initiation, growth and coalescence of the microcracks will lead to the generation of macroscopic fractures, which is explicitly mimicked by failure and removal of bonds between particles from the discrete element network. We investigate the fracture propagation path in both homogeneous and heterogeneous reservoirs using the simulator developed. Stress shadow caused by the transverse fracture will change the orientation of principal stress in the fracture neighborhood, which may inhibit or alter the growth direction of nearby fracture clusters. However, the initial in-situ stress anisotropy often helps overcome this phenomenon. Under large in-situ stress anisotropy, the hydraulic fractures are more likely to propagate in a direction that is perpendicular to the minimum horizontal stress. Under small in-situ stress anisotropy, there is a greater chance for fractures from nearby clusters to merge with each other. Then, we examine the differences in fracture geometry caused by fracturing in cemented or uncemented wellbore. Moreover, the impact of intrinsic reservoir heterogeneity caused by the rock fabric and mineralogy on fracture nucleation and propagation paths is examined through a three-layered reservoir. Finally, we apply the method to a realistic heterogeneous dataset. Copyright 2015, Unconventional Resources Technology Conference.

Megson D.,University of Plymouth | Brown T.A.,University of Plymouth | Johnson G.W.,Energy and Geoscience Institute | O'Sullivan G.,Mount Royal College, Calgary | And 6 more authors.
Chemosphere | Year: 2014

PCB signatures can be used for source identification, exposure studies, age dating and bio-monitoring. This study uses comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-ToFMS) to produce a PCB signature comprised of over 80 PCBs for individual Leach's storm petrels (Oceanodroma leucorhoa). The Leach's storm petrel is a relatively small, elusive, understudied pelagic bird, which only returns to remote islands under darkness during the breeding season. Samples were obtained from 25 Leach's storm petrels found dead in Canada and the UK following storm events in 2006 and 2009. Tissue samples were extracted and analysed by GCxGC-ToFMS and results showed that 83 PCB congeners were present in >60% of samples. An assessment of the PCB signature in four different tissue types showed that it did not vary greatly in samples obtained from the gut, heart, liver and stomach. Multivariate statistical analysis identified a distinctive PCB signature in birds from Canada and Europe which was used to identify the regional provenance and transatlantic movement of individual birds. The findings showcase the ability of GCxGC-ToFMS to provide the high quality congener specific analysis that is necessary for PCB fingerprinting, as well as highlighting the potential of PCB signatures for use in ecological studies of movement, foraging and behaviour. © 2014 Elsevier Ltd.

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