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29 Apr

2nd Edition: Geological Process-Based Forward Modeling AAPG Call For Abstracts Expires in 1 day

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Bulletin Article

Gas saturation and CO2 enhancement potential of coalbed methane reservoirs as a function of depth

The influence of moisture, temperature, coal rank, and differential enthalpy on the methane (CH4) and carbon dioxide (CO2) sorption capacity of coals of different rank has been investigated by using high-pressure sorption isotherms at 303, 318, and 333 K (CH4) and 318, 333, and 348 K (CO2), respectively. The variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding Langmuir parameters in combination with a geothermal gradient of 0.03 K/m and a normal hydrostatic pressure gradient. Taking the gas content corresponding to 100% gas saturation at maximum burial depth as a reference value, the theoretical CH4 saturation after the uplift of the coal seam was computed as a function of depth. According to these calculations, the change in sorption capacity caused by changing pressure, temperature conditions during uplift will lead consistently to high saturation values. Therefore, the commonly observed undersaturation of coal seams is most likely related to dismigration (losses into adjacent formations and atmosphere). Finally, we attempt to identify sweet spots for CO2-enhanced coalbed methane (CO2-ECBM) production. The CO2-ECBM is expected to become less effective with increasing depth because the CO2-to-CH4 sorption capacity ratio decreases with increasing temperature and pressure. Furthermore, CO2-ECBM efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between CO2 and CH4 for low mature coals.

Added on 31 January, 2014

Bulletin Article

Evaluation of hydrocarbon generation and migration in the Molasse fold and thrust belt (Central Eastern Alps, Austria) using structural and thermal basin models

The Molasse Basin represents the northern foreland basin of the Alps. After decades of exploration, it is considered to be mature in terms of hydrocarbon exploration. However, geological evolution and hydrocarbon potential of its imbricated southernmost part (Molasse fold and thrust belt) are still poorly understood. In this study, structural and petroleum systems models are integrated to explore the hydrocarbon potential of the Perwang imbricates in the western part of the Austrian Molasse Basin. The structural model shows that total tectonic shortening in the modeled north–south section is at least 32.3 km (20.1 mi) and provides a realistic input for the petroleum systems model. Formation temperatures show present-day heat flows decreasing toward the south from 60 to 41 mW/m2. Maturity data indicate very low paleoheat flows decreasing southward from 43 to 28 mW/m2. The higher present-day heat flow probably indicates an increase in heat flow during the Pliocene and Pleistocene. Apart from oil generated below the imbricated zone and captured in autochthonous Molasse rocks in the foreland area, oil stains in the Perwang imbricates and oil-source rock correlations argue for a second migration system based on hydrocarbon generation inside the imbricates. This assumption is supported by the models presented in this study. However, the model-derived low transformation ratios (20%) indicate a charge risk. In addition, the success for future exploration strongly depends on the existence of migration conduits along the thrust planes during charge and on potential traps retaining their integrity during recent basin uplift.

Added on 31 January, 2014

Bulletin Article

Electrical and flow properties of highly heterogeneous carbonate rocks

In reservoir engineering, hydrodynamic properties can be estimated from downhole electrical data using heuristic models (e.g., Archie and Kozeny-Carman's equations) relating electrical conductivity to porosity and permeability. Although proven to be predictive for many sandstone reservoirs, the models mostly fail when applied to carbonate reservoirs that generally display extremely complex pore network structures. In this article, we investigate the control of the three-dimensional (3-D) geometry and morphology of the pore network on the electrical and flow properties, comparing core-scale laboratory measurements and 3-D x-ray microtomography image analysis of samples from a Miocene reefal carbonate platform located in Mallorca (Spain). The results show that micrometer- to centimeter-scale heterogeneities strongly influence the measured macroscopic physical parameters that are then used to evaluate the hydrodynamic properties of the rock, and therefore, existing models might not provide accurate descriptions because these heterogeneities occur at scales smaller than those of the integration volume of the borehole geophysical methods. However, associated with specific data processing, 3-D imagery techniques are a useful and probably unique mean to characterize the rock heterogeneity and, thus, the properties variability.

Added on 01 January, 2014

Explorer Article By David Brown

Discoveries Made It a Year to Remember

Discoveries were comparatively sparse, but they persisted steadily throughout the year. Here are some of the more significant discoveries of the past year.

Added on 01 January, 2014

Explorer Article By David Brown

No Elephants, But Plenty of Potential for 2014

A review of major oil and gas discoveries of 2013 shows a down year in terms of quantity—but that’s not the whole story.

Added on 01 January, 2014

Explorer Regions and Sections By Carol McGowen,Jeremy Richardson

It Was a Very Good Year for Europe Region

European Region office is on the move. They are relocating and it is now a good time to look back over the year and reflect on has occurred for 2013.

Added on 01 December, 2013

Explorer Article By Sarah Haviland

New Research Center Planned in Scotland

Edinburgh, Scotland, has a new research center planning to open its doors in 2015. It is the Sir Charles Lyell Centre, named after Britain's 19th century geologist. The uptick of interest in emerging industries of shale oil and gas and deep sea metal mining is just one of the areas of the focus planned for the centre.

Added on 01 December, 2013

Bulletin Article

Controls on CO2 fate and behavior in the Gullfaks oil field (Norway): How hydrogeochemical modeling can help decipher organic-inorganic interactions

Oil degradation in the Gullfaks field led to hydrogeochemical processes that caused high CO2 partial pressure and a massive release of sodium into the formation water. Hydrogeochemical modeling of the inorganic equilibrium reactions of water-rock-gas interactions allows us to quantitatively analyze the pathways and consequences of these complex interconnected reactions. This approach considers interactions among mineral assemblages (anorthite, albite, K-feldspar, quartz, kaolinite, goethite, calcite, dolomite, siderite, dawsonite, and nahcolite), various aqueous solutions, and a multicomponent fixed-pressure gas phase (CO2, CH4, and H2) at 4496-psi (31-mPa) reservoir pressure. The modeling concept is based on the anoxic degradation of crude oil (irreversible conversion of n-alkanes to CO2, CH4, H2, and acetic acid) at oil-water contacts. These water-soluble degradation products are the driving forces for inorganic reactions among mineral assemblages, components dissolved in the formation water, and a coexisting gas at equilibrium conditions. The modeling results quantitatively reproduce the proven alteration of mineral assemblages in the reservoir triggered by oil degradation, showing (1) nearly complete dissolution of plagioclase; (2) stability of K-feldspar; (3) massive precipitation of kaolinite and, to a lesser degree, of Ca-Mg-Fe carbonate; and (4) observed uncommonly high CO2 partial pressure (61 psi [0.42 mPa] at maximum). The evolving composition of coexisting formation water is strongly influenced by the uptake of carbonate carbon from oil degradation and sodium released from dissolving albitic plagioclase. This causes supersaturation with regard to thermodynamically stable dawsonite. The modeling results also indicate that nahcolite may form as a CO2-sequestering sodium carbonate instead of dawsonite, likely controlling CO2 partial pressure.

Added on 30 November, 2013

Bulletin Article

Tectonic versus diagenetic origin of fractures in a naturally fractured carbonate reservoir analog (Nerthe anticline, southeastern France)

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.

Added on 30 November, 2013

Bulletin Article

Episodic and simultaneous illitization in oil-bearing Brent Group and Fulmar Formation sandstones from the northern and southern North Sea based on illite K-Ar dating

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. ±

Added on 30 November, 2013

Field Seminar

Krakow, Poland

Monday, 27 May 2024, 8:00 a.m.–5:30 p.m.

Upper Jurassic Carbonate Depositional System of the Carpathian Foreland – Surface and Subsurface Insight

This one day pre-conference field trip will be focused on the Upper Jurassic deposits formed within the southern part of epicontinental basin of the Carpathian foreland.

Added on 24 October, 2023

Field Seminar

Krakow, Poland

Thursday, 30 May – Friday, 31 May 2024, 8:00 a.m.–5:00 p.m.

Outer Carpathians – Cradle of Petroleum Geology and Oil Industry

Surface seeps of oil and exhalations of methane have been known in the Northern Outer Carpathians for centuries. During this field trip, key localities will be visited, including frontal deformed part of the thrust belt accessible in the world-famous Wieliczka salt mine, and outcrops located within more internal thrust sheets (nappes).

Added on 19 October, 2023

VG Abstract By Keith Gerdes

Tethyan Carbonates - Linking Tropical Seas and Crashing Plates to Some of the Largest Oil and Gas Fields in the World

The carbonate sequences that were deposited in the now exhumed Tethyan Ocean influence many aspects of our lives today, either by supplying the energy that warms our homes and the fuel that powers our cars or providing the stunning landscapes for both winter and summer vacations. They also represent some of the most intensely studied rock formations in the world and have provided geoscientists with a fascinating insight into the turbulent nature of 250 Million years of Earth’s history. By combining studies from the full range of geoscience disciplines this presentation will trace the development of these carbonate sequences from their initial formation on the margins of large ancient continental masses to their present day locations in and around the Greater Mediterranean and Near East region. The first order control on growth patterns and carbonate platform development by the regional plate-tectonic setting, underlying basin architecture and fluctuations in sea level will be illustrated. The organisms that contribute to sequence development will be revealed to be treasure troves of forensic information. Finally, these rock sequences will be shown to contain all the ingredients necessary to form and retain hydrocarbons and the manner in which major post-depositional tectonic events led to the formation of some of the largest hydrocarbon accumulations in the world will be demonstrated.

Request a visit from Keith Gerdes!

Added on 24 August, 2015

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