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It’s now been shown that the “sweet” aspect of an identified sweet spot can change – not only stratigraphically, but also laterally within the zone itself.
Field analogs allow a better characterization of fracture networks to constrain naturally fractured reservoir models. In analogs, the origin, nature, geometry, and other attributes of fracture networks can be determined and can be related to the reservoir through the geodynamic history. In this article, we aim to determine the sedimentary and diagenetic controls on fracture patterns and the genetic correlation of fracture and diagenesis with tectonic and burial history. We targeted two outcrops of Barremian carbonates located on both limbs of the Nerthe anticline (southeastern France). We analyzed fracture patterns and rock facies as well as the tectonic, diagenetic, and burial history of both sites. Fracture patterns are determined from geometric, kinematic, and diagenetic criteria based on field and lab measurements. Fracture sequences are defined based on crosscutting and abutting relationships and compared with geodynamic history and subsidence curves. This analysis shows that fractures are organized in two close-to-perpendicular joint sets (i.e., mode I). Fracture average spacing is 50 cm (20 in.). Fracture size neither depends on fracture orientation nor is controlled by bed thickness. Neither mechanical stratigraphy nor fracture stratigraphy is observed at outcrop scale. Comparing fracture sequences and subsidence curves shows that fractures existed prior to folding and formed during early burial. Consequently, the Nerthe fold induced by the Pyrenean compression did not result in any new fracture initiation on the limbs of this fold. We assume that the studied Urgonian carbonates underwent early diagenesis, which conferred early brittle properties to the host rock.
The Marcellus Shale is considered to be the largest unconventional shale-gas resource in the United States. Two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content. The fracture attributes reflect the geomechanical properties of the rocks, which are partly related to rock mineralogy. The natural gas content of a shale reservoir rock is strongly linked to organic matter content, measured by total organic carbon (TOC). A mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition, rock geomechanical properties, and TOC content. Core, log, and seismic data were used to build a three-dimensional (3-D) mudrock lithofacies model from core to wells and, finally, to regional scale. An artificial neural network was used for lithofacies prediction. Eight petrophysical parameters derived from conventional logs were determined as critical inputs. Advanced logs, such as pulsed neutron spectroscopy, with log-determined mineral composition and TOC data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies. Sequential indicator simulation performed well for 3-D modeling of Marcellus Shale lithofacies. The interplay of dilution by terrigenous detritus, organic matter productivity, and organic matter preservation and decomposition affected the distribution of Marcellus Shale lithofacies distribution, which may be attributed to water depth and the distance to shoreline. The trend of normalized average gas production rate from horizontal wells supported our approach to modeling Marcellus Shale lithofacies. The proposed 3-D modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies.
Size fractions (<4 and 0.4–1.0 μ) of Brent Group sandstones from the northern North Sea contain mostly illite-smectite mixed layers with kaolinite, whereas the same size fractions of Fulmar Formation sandstones from the south-central North Sea consist of illite-smectite mixed layers with minor chlorite. Transmission electron microscope observations show elongated illite laths or agglomerates consisting of small laths when larger individual laths are lacking. The K-Ar data of the fractions less than 0.4 μm of Brent Group samples plot on two arrays in a 40Ar/36Ar vs. 40K/36Ar diagram that have isochron characteristics with ages of 76.5 ± 4.2 and 40.0 ± 1.5 Ma, and initial 40Ar/36Ar ratios of 253 ± 16 and 301 ± 18, respectively. For the Fulmar Formation samples, the data points of the fractions less than 0.2 and less than 0.4 μ also fit two isochrons with ages of 76.6 ± 1.4 and 47.9 ± 0.5 Ma and initial 40Ar/36Ar ratios of 359 ± 52 and 304 ± 2, respectively. Some of the coarser 0.4–1.0-μ fractions also plot on the two isochrons, but most plot above indicating the presence of detrital components more than 0.4 μ. The almost identical ages obtained from illite-type crystals of sandstones with different deposition ages that are located about 600 km (373 mi) apart record two simultaneous illitization episodes. These events were not induced by local burial conditions, but are related to episodic pressure and/or temperature increases in the studied reservoirs, probably induced by hydrocarbon injection. This interpretation is indirectly supported by notably different K-Ar illite ages from cores of a nearby reservoir at hydrostatic pressure. Illite is not as well crystallized as expected for potential crystallization temperatures above 160°C measured by fluid-inclusion determinations. In both the northern and south-central North Sea, the two illite generations remain unaffected after crystallization despite continued burial, suggesting notably higher crystallization temperatures than those estimated from geothermal gradients. No recent illite crystallization or alteration is recorded in the K-Ar ages, despite a dramatic regional acceleration of the subsidence in the southern North Sea. ±
Pore-volume reduction of sediments by plastic deformation during compaction and by cementation of grains has been evaluated for different proportions of ductile and hard grains. We represent the compaction behavior of grains with a purely geometric model, which uses the cooperative rearrangement algorithm to produce dense, random packings of partly interpenetrating spheres. We varied the fraction of grains assumed to be ductile and the radius of the rigid core of the ductile grains. The predicted relationship between the fraction of ductile grains in the sediment and the porosity after compaction agrees well with previously published experimental data in the literature. The radius of the rigid core of the ductile grains is an effective way to represent different kinds of ductile material, ranging from brittle (rigid radius 0.9) to extremely ductile (rigid radius 0.7). We simulated quartz cementation in our compacted rock by adding isopachous cement. Cement thickness was reduced on the smaller grains and increased on the larger grains to account for presumed export of pressure-dissolved material from finer grained regions and the import of material into coarser grained regions. These simulations yield descriptions of pore-scale geometry resulting from processes common in sandstones. Modeled pore geometry provides insight into transport properties of such rocks. For example, the models predict, to within a factor of five, the permeability of samples of tight-gas sandstones having little intragranular porosity.
Exploration for oil and gas in Saskatchewan was initiated in 1888 with the spudding of a 472-meter (1,548.5 feet) well near the settlement of Belle Plaine some 32 kilometers (20 miles) west of Regina.
Coming to a field near you – new technology that will reshape the oil and gas industry. When? Maybe sooner than you think.
Using diverse geologic and geophysical data from recent exploration and development, and experimental results of analysis of gas content, gas capacity, and gas composition, this article discusses how geologic, structural, and hydrological factors determine the heterogeneous distribution of gas in the Weibei coalbed methane (CBM) field. The coal rank of the Pennsylvanian no. 5 coal seam is mainly low-volatile bituminous and semianthracite. The total gas content is 2.69 to 16.15 m3/t (95.00–570.33 scf/t), and gas saturation is 26.0% to 93.2%. Burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity, but also the quality and quantity of thermogenic gas generated from the coal. Gas composition indicates that the CBM is dry and of dominantly thermogenic origin. The thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area. Three gas accumulation models are identified: (1) gas diffusion and long-distance migration of thermogenic gases to no-flow boundaries for sorption and minor conventional trapping, (2) hydrodynamic trapping of gas in structural lows, and (3) gas loss by hydrodynamic flushing. The first two models are applicable for the formation of two CBM enrichment areas in blocks B3 and B4, whereas the last model explains extremely low gas content and gas saturation in block B5. The variable gas content, saturation, and accumulation characteristics are mainly controlled by these gas accumulation models.
Sequence stratigraphy and coal cycles based on accommodation trends were investigated in the coal-bearing Lower Cretaceous Mannville Group in the Lloydminster heavy oil field, eastern Alberta. The study area is in a low accommodation setting on the cratonic margin of the Western Canada sedimentary basin. Geophysical log correlation of coal seams, shoreface facies, and the identification of incised valleys has produced a sequence-stratigraphic framework for petrographic data from 3 cored and 115 geophysical-logged wells. Maceral analysis, telovitrinite reflectance, and fluorescence measurements were taken from a total of 206 samples. Three terrestrial depositional environments were interpreted from the petrographic data: ombrotrophic mire coal, limnotelmatic mire coal, and carbonaceous shale horizons. Accommodation-based coal (wetting- and drying-upward) cycles represent trends in depositional environment shifts, and these cycles were used to investigate the development and preservation of the coal seams across the study area. The low-accommodation strata are characterized by a high-frequency occurrence of significant surfaces, coal seam splitting, paleosol, and incised-valley development. Three sequence boundary unconformities are identified in only 20 m (66 ft) of strata. Coal cycle correlations illustrate that each coal seam in this study area was not produced by a single peat-accumulation episode but as an amalgamation of a series of depositional events. Complex relations between the Cummings and Lloydminster coal seams are caused by the lateral fragmentation of strata resulting from the removal of sediment by subaerial erosion or periods of nondeposition. Syndepositional faulting of the underlying basement rock changed local accommodation space and increased the complexity of the coal cycle development. This study represents a low-accommodation example from a spectrum of stratigraphic studies that have been used to establish a terrestrial sequence-stratigraphic model. The frequency of changes in coal seam quality is an important control on methane distribution within coalbed methane reservoirs and resource calculations in coal mining. A depositional model based on the coal cycle correlations, as shown by this study, can provide coal quality prediction for coalbed methane exploration, reservoir completions, and coal mining.
The fact that velocity models based on seismic reflection surveys commonly do not consider the near-surface geology necessitates filling the gap between the top of a velocity model and the surface of the Earth. In this study, we present a new workflow to build a shallow geologic model based exclusively on borehole data and corroborated by laboratory measurements. The study area is in Chemery (France), located at the southwestern border of the Paris Basin, where a large amount of borehole data is publicly available. The workflow starts with identifying lithologic interfaces in the boreholes and interpolating them between the boreholes. The three-dimensional (3-D) geometry of the lithologies then allows interpretation of the position, orientation, and offset of fault planes. Given the importance of the fault interpretation in the modeling process, a combination of different approaches is used to obtain the most reasonable structural framework. After creating a 3-D grid, the resulting 3-D structural model is populated with upscaled velocity logs from the boreholes, yielding the final near-surface P-wave velocity model. To better constrain the velocity model, we conducted laboratory measurements of P- and S-wave velocities in dry and water-saturated conditions on all lithologies in the model. The laboratory data were used to populate the 3-D near-surface model with VP/VS ratio values. The presented workflow accounts for one-dimensional borehole data and is much more iterative and time-consuming than workflows based on two-dimensional seismic sections. Nevertheless, the workflow results in a robust 3-D near-surface model allowing for structural interpretations and revealing the 3-D seismic velocity field.
Join us for AAPG Orphan, Abandoned, Idle and Marginal Wells Conference 2025. This workshop will focus on orphan, abandoned, idle, and marginal wells and the business opportunities and technology associated with plugging and repurposing wells, reducing methane emissions, protecting water supplies, and extending the lives of marginal wells.
Everyone in Houston lives within a few miles of a bayou. Some people think of them as permanent, but the bayous are constantly changing, especially during high water events like Hurricane Harvey. This trip is a 2.5 mile walk down a section of Buffalo Bayou where we will look at the archives of past storms and discuss what to do for future storms.
This introduction to methane monitoring, measurement, and quantification is for all those who would like to understand the requirements and regulations regarding methane emissions and to be able to design a measurement and monitoring solution, complete with the appropriate types of technologies, techniques, and safety protocols.
Subsurface risk and uncertainty are recognized as very important considerations in petroleum geoscience. And even when volume estimates are relatively accurate, the reservoir characteristics that determine well placement and performance can remain highly uncertain. In analyzing results and work practices, three aspects of uncertainty are reviewed here.
Request a visit from Kurt W. Rudolph!
Physics is an essential component of geophysics but there is much that physics cannot know or address.
Request a visit from John Castagna!
For well over a century there have been conflicting indications of the strength of the crust and of faults and what controls them. Much of our ignorance comes quite naturally from the general inaccessibility of the crust to measurement--in contrast with our understanding of the atmosphere, which is much more accessible to observation as well as more rapidly changing. Crustal strength is best understood in deforming sedimentary basins where the petroleum industry has made great contributions, particularly in deforming petroleum basins because of the practical need to predict. In this talk we take a broad look at key issues in crustal strength and deformation and what we can learn from boreholes, earthquakes, active fault systems, and toy models.
Request a visit from John Suppe!
In comparison with the known boundary conditions that promote salt deformation and flow in sedimentary basins, the processes involved with the mobilization of clay-rich detrital sediments are far less well established. This talk will use seismic examples in different tectonic settings to document the variety of shale geometries that can be formed under brittle and ductile deformations.
Request a visit from Juan I. Soto!
The Betic hinterland, in the westernmost Mediterranean, constitutes a unique example of a stack of metamorphic units. Using a three-dimensional model for the crustal structure of the Betics-Rif area this talk will address the role of crustal flow simultaneously to upper-crustal low-angle faulting in the origin and evolution of the topography.
Climate change is not only happening in the atmosphere but also in the anthroposphere; in some ways the former could drive or exacerbate the latter, with extreme weather excursions and extreme excursions from societal norms occurring all over the earth. Accomplishing geoscience for a common goal – whether that is for successful business activities, resource assessment for public planning, mitigating the impacts of geological hazards, or for the sheer love of furthering knowledge and understanding – can and should be done by a workforce that is equitably developed and supported. Difficulty arises when the value of institutional programs to increase equity and diversity is not realized.
Request a visit from Sherilyn Williams-Stroud!
President Biden has laid out a bold and ambitious goal of achieving net-zero carbon emissions in the United States by 2050. The pathway to that target includes cutting total greenhouse gas emissions in half by 2030 and eliminating them entirely from the nation’s electricity sector by 2035. The Office of Fossil Energy and Carbon Management will play an important role in the transition to net-zero carbon emissions by reducing the environmental impacts of fossil energy production and use – and helping decarbonize other hard-to abate sectors.
Request a visit from Jennifer Wilcox!
Three-dimensional (3D) seismic-reflection surveys provide one of the most important data types for understanding subsurface depositional systems. Quantitative analysis is commonly restricted to geophysical interpretation of elastic properties of rocks in the subsurface. Wide availability of 3D seismic-reflection data and integration provide opportunities for quantitative analysis of subsurface stratigraphic sequences. Here, we integrate traditional seismic-stratigraphic interpretation with quantitative geomorphologic analysis and numerical modeling to explore new insights into submarine-channel evolution.
Request a visit from Jacob Covault!
Paleozoic North America has experienced multiple mountain building events, from Ordovician to Permian, on all margins of the continent. These have had a profound effect on the resulting complex basins and their associated petroleum systems. Subsequent uplift, erosion and overprinting of these ancient systems impedes the direct observation of their tectonic history. However, the basin sedimentary records are more complete, and provide additional insights into the timing and style of the mountain building events. In this study, we employ ~90 1D basin models, ~30 inverse flexural models, isopachs, and paleogeographic maps to better understand the Paleozoic history of North America.
Engineering of wind farms, development of carbon sequestration projects in shelfal waters, the proliferation of communication cables that connect the world, all of these things suggest that it is time to re-examine what we know about shelf processes both updip-to-downdip and along shoreline, and the influence of shelf processes on erosion and transport of sediments.
Request a visit from Lesli Wood!
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