Shale Beds Research Articles

Investigating deep geological reservoirs using seismic reflection and well logs, Tawila oil field, Yemen: Implications for structural setting and reservoir properties

Seismic reflection data were used to evaluate the deep geological structures in Tawila oil field, Masila rift basin, Yemen. A combined set of 2D seismic profiles and geophysical well logs were used to produce structural mapping at the top of the clastic Qishn reservoir and the several overlying and underlying horizons. We have investigated the distribution of reservoir fluids in relation to the identified structures. The seismic horizons with their intersecting faults have been determined to be very important in the hydrocarbon distribution. Two key fault systems have been identified to control the hydrocarbon entrapment in the study area: major, deep, E–W normal faulting that affected the northern area, which caused extensive structural deformation, and a much shallower ENE–WSW fault system to south. The shale type and distribution and the basic reservoir properties, were enhanced through analysing the logging data using the standard clastic models. The reservoir is composed of three clastic compartments (S1, S2 and S3) which are separated by thin shale beds. No hydrocarbons were found in the S1 top unit which had considerable shale volume of a dispersed shale type. Considerable to good hydrocarbon content up to 57% and 61%, associated with a structural uplift, was identified in front of the S2 and S3 units, respectively. A dispersed/laminated shale model was assigned for these two units with a laminated style priority. The hydrocarbon entrapment in the study area was caused by the sealing characteristics of the overlying layers as well as the juxtaposition of the reservoir against other seal rocks. The distribution maps show an increase in hydrocarbon saturation toward the west, north and northeast which coincided with areas of low seismic-derived properties of velocity, acoustic impedance and negative reflection coefficient. An elongated structural horst of good hydrocarbon potentiality was identified in the upthrow of the major fault. This prospective structural high is a key to explore hydrocarbons in nearby areas and other basins of similar geologic characteristics.

Response analysis of shale bedding structure to ultrasonic characteristics and its application

Abstract Based on the wave theory, different bedding structure models for shales in Lower Silurian Longmaxi Formation of southeastern Chongqing area were established, numerical simulations of responses of different bedding structures of shale to ultrasonic wave were carried out by using the second order in time and fourth order in space grid finite difference method, based on the grey system theory, sensitive factors of acoustic parameters of bedding structure were selected, and the dynamic mechanical parameter model of bedded shale was established, which was verified by the ultrasonic transmission experiment results on core down Well ZY1 and YY1 and the logging data of Well ZY2. The results show that: (1) The correlation coefficient between analog and experimental waveforms is greater than 80%, indicating that the numerical simulation method can effectively simulate ultrasonic transmission experiment. (2) Acoustic velocity is a conventional sensitive factor used to characterize shale bedding structure, whereas the attenuation coefficient is sensitive to the change of bedding thickness, with correlation coefficient of 0.89, therefore, using the normalized results of attenuation coefficient to comprehensively describe the shale bedding can make the results more accurate. (3) The correlation between the dynamic and static parameters calculated by the model is better than that of the traditional model; and the predicted values of rock mechanics obtained by using the model and logging data inversion are in good agreement with the experimental values. The research results lay the foundation for further accurate prediction of rock mechanic parameters using sonic logging data.

Modeling and field-testing of fracturing fluid back-flow after acid fracturing in unconventional reservoirs

When the oil shale reservoir completes acid fracturing, the back-flow of fracturing fluid program is needed. In this paper, a three-dimensional model is established and the finite element analysis software is used to simulate the feasibility of gas lift back fracturing fluid in Fuyu oil shale formation after acid fracturing. The results show that when the injection pressure of FK-1 well is 8.5 MPa, the fracturing fluid can be effectively displaced. Fracturing fluid is discharged along the fracture into FK-2 well, and a few fracturing fluids overflow the pyrolysis zone along the direction of oil shale bedding. Then the experiment is carried out to verify the accuracy of numerical simulation. What's more, it is also verified that the connectivity of oil shale reservoir meets the needs of oil shale in-situ pyrolysis process.

Contribution to Gas Production from Minor Coal Seams and Adjacent Shales: Numerical Modelling Results for the Mannville Coal Measures, South Central Alberta

The contribution to production of the gas stored within the coal and shale beds adjacent to the main coal seam in the Mannville Group, in which a lateral is drilled, was investigated through a series of numerical simulations. The results indicate that the added gas from the minor coal seams, with interbedded shales with no gas, results in 1.4 times (×) more produced gas and 3.0× more produced water after 25 years of production than when only the main Mannville coal seam is considered. Including gas in the shales results in 1.7× more produced gas and 2.5× more produced water after 25 years of production than when only the main coal seam is considered. The produced gas recovered from the shales exceeds the produced gas recovered from the coals after ~8.5 years, resulting in 2.1× more produced shale gas than coal gas after 25 years of production. Over half (56%) of the produced coal gas after 25 years of production is recovered from the main coal seam while a quarter (22%) is recovered from the L1 seam, which is the thickest and nearest minor coal seam to the horizontal wellbore located in the main seam. The results from the numerical simulations provide insights that are not intuitive or otherwise predictable in developing complex reservoirs. Although the results are specifically for the Mannville producing fairway, undoubtedly the production from minor coal seams and interbedded gas shales should be considered in other producing and potential coal gas reservoirs to identify higher producible reserves and optimize drilling and completions strategies.

Water-rock interaction of the Jilh and Tawil aquifers in the Wadi Sirhan Basin, NW Saudi Arabia

A total of 79 groundwater samples from the Upper Silurian-Lower Devonian Tawil and Triassic Jilh aquifers in NW Saudi Arabia were analysed for hydrochemical and strontium isotopic composition. A sequential extraction and 87Sr/86Sr analysis were conducted on 32 cutting samples from the groundwater host rocks and the underlying shale bed. The chemical composition of the groundwater was distinct from that of the host rock lithologies in terms of elemental abundance (i.e., Na+ was dominant in the groundwater and K and Ca were the main constituents of the aquifer units). Principal component analysis (PCA) of water samples showed a positive loading of Na+ and negative loadings of Ca2+ and SO42-. The replacement of gypsiferous waters by Na+-rich waters is suggested by this ion exchange. The shale rock samples showed Na to be the dominant chemical constituent. 87Sr/86Sr ratios of the groundwater (0.707673-0.711577) and host rock samples (0.707930-0.712477) suggest that groundwater inherits the Sr signature of the rock from the exchangeable, carbonate, and the oxides phase, reflecting reducing conditions in Tawil aquifer. The elevated groundwater 87Sr/86Sr ratios were found in deeper sections of the aquifers, which coincided with the radiogenic 87Sr/86Sr of the deeper aquifer lithologies and the underlying shale bed.

Mineralogical and Geochemical Studies of Oil Shale Deposits in the Cretaceous/Paleogene succession at Quseir Area, Egypt

Cretaceous/Paleogene succession in Quseir area represents one of the most important economic sedimentary rocks, which contain phosphate and oil shale beds. Oil shale samples selected from nine mines around Quseir area were subjected to mineralogical, petrographical and geochemical analyses. As raveled by X-ray diffraction analysis, the oil shale samples are composed of calcite, quartz, dolomite, smectite, kaolinite, gypsum and pyrite. The petrographical investigation of the studied oil shales indicates the dominance of two microfacies: calcareous foraminiferal claystone and Calci-mudstone. The EDX results of oil shale samples show that the pyrite found as framboidal-disseminated particles in smectite. The high ratio of the sulfur and organic carbon contents in the selected mines indicate highly reducing environment. Five mines (El-Nakheil, Abu Tundub, Abu Tundub Bahree, El Beida and Hammadat) are markedly rich in organic content and can be considered as good to excellent source rock.

Organic Geochemistry and Source Rock Potential of Naokelekan Formation in Selected Wells, North Iraq

In this study, organic geochemical characteristics and potential of Upper Oxfordian–Lower Kimmeridgian aged bituminous shale beds in Naokelekan formation (North Iraq) were investigated by using TOC and pyrolysis analyses. The Total Organic Carbon (TOC) contents for the studied samples varying between from 0.46-21.33%, average 7.06% and Taq Taq-1 well as good hydrocarbon potential (0.85-1.66 %, with average of 1.06%), whereas Jk-1 well can be rated as an very good hydrocarbon potential from 1.04-4.16 %, with average of 2.15 %. The low Hydrogen Index (HI = 24-605 mg HC/g TOC) for Bj-1 well, (HI = 147-673 mg HC/g TOC) in the Jk-1 well while in Taq Taq-1 well (HI = 9-48 mg HC/g TOC) indicate that kerogen type for the vast majority of the studied samples is Type II/I for Bj-1 well and Type IV with few samples, Type of I and II kerogens in the Taq Taq-1 and Jk-1 well. Consequently most of the organic matter of Bj-1 and Jk-1 well tends to generate petrol, even though a small portion of them exhibit a tendency to generate gas. While all samples of Taq Taq-1 well tends to generate gas. The studied bituminous rock samples characterized by low Tmax (434-602 °C) for Bj-1,Taq Taq-1 (344-429 °C) and (419-602 °C) for Jk-1 well. These values show, in terms of potential of hydrocarbon generation, that the studied samples have a source rock potential of organic matter from immature to over mature. Additionally, the S1 hydrocarbon type values indicate no external contribution of migrated hydrocarbons to the bituminous rocks of the studied area.

Experimental study on shale fracturing assisted by low-temperature freezing

Under the cold impact of liquid nitrogen, the shale suffers from the significant freezing damage, which provides the possibility of liquid nitrogen fracturing. Moreover, shale fracturing assisted by liquid nitrogen can effectively reduce reservoir pollution. In this paper, the hydraulic fracturing experiments of natural shale samples frozen by liquid nitrogen were carried out to investigate the factors affecting the crack propagation of shale after low temperature fracturing. The results show that a large number of cracks or macropores form inside the natural shale sample after freezing treatment by liquid nitrogen. The fracture pressure of the shale decreases with increasing impact time at the beginning of the immersion time, and remains substantially stable after an immersion of 2 hours. When the freezing time increases, the crack initiation time increases accordingly. After low temperature impact, the fracture pressure of shale decreases with the increase of stress difference, but the cracking times vary with the stress with obvious regularity. It is easier to form main fracture with larger displacement on the premise of well-developed shale bedding.

Effective stress characteristics in shale and its effect on shale gas productivity

Research of effective stress characteristics on the productivity of shale gas has a great significance. The samples of the black shale and bedding shale at the Lower Silurian Longmaxi Formation in Sichuan Basin are selected. Microscopic pore structure characteristics are described by scanning electron microscopy, and the effective stress coefficient is measured by the cross-plotting method. The experimental results show that the effective stress coefficient of black shale is 0.29 on average and the bedding shale is 0.71. There are micro-fractures in bedding shale; thus pore pressure has a more significant influence on bedding shale than black shale. Fitting the relationship between effective stress and permeability by an exponential function, and the calculated stress sensitivity constants of black shale and bedding shale are 0.268 MPa−1 and 0.355 MPa−1, respectively. Recovery model of the fractured horizontal well was established according to experimental results involving effect of geological stress and flow scale, and the abandoned pressure approach was used to evaluate the recovery. The results show that the geological stress greatly influences the reservoir with developed micro-fractures, the production pressure should be adequately controlled for the high production well. The fractured block size and micro-fractures in the fractured block of the construction area have a significant influence on gas recovery; then for the reservoirs with small amount of micro-fractures and large fractured blocks, wellbore pressure should be controlled to improve the recovery.

Bedrock erosion and changes in bed sediment lithology in response to an extreme flood event: The 2013 Colorado Front Range flood

In this study, we use before and after flood observations of bed sediment lithology to determine how the lithological composition of bed sediment changes in response to an extreme flood event and use the post-flood measurements and observations to estimate values of critical shear stresses needed to erode shale bedrock and protective bank vegetation in the study streams. We present results from measurements of bed sediment lithology taken after the 2013 Colorado Front Range flood and compare these results with the same measurements taken before the flood. These two data sets provide a unique opportunity to determine how bed sediment lithology changes following an extreme flood event and allows insight into sources of channel bed sediment. After the flood, bed sediment lithology shifted distinctly towards the lithological distribution of the total catchment. Before the flood, bed sediment in most locations was primarily composed of granitic material, while after the flood, the streams were more likely to have metamorphic, volcanic, or sedimentary rocks in the bed sediment, reflecting more input from more non-local hillslopes compared to before the flood. Our post-flood measurements and observations allowed us to estimate threshold critical shear stress for the plucking of shale bedrock (212 Pa) and the removal of large cottonwood trees (364 Pa) in downstream sections of the study streams. Bank vegetation plays a critical role in protecting bedrock banks from lateral erosion, such that only the largest flood events can remove vegetation and expose bedrock on channel banks to potential erosion. We found that this large flood event plucked shale bedrock from both the channel bed and banks and that the shale bed sediment then quickly breaks down and is transported away by small flows. As such, this data set allowed us to make conclusions about the effect of large flood events on the long-term evolution of lateral and vertical erosion in bedrock rivers.

Source-rock evaluation and depositional environment of black shales in the Triassic Yanchang Formation, southern Ordos Basin, north-central China

A recent drilling operation in the Triassic Yanchang Formation (Tongchuan District of the Ordos Basin, north-central China) reached a black shale bed with an average in-situ gas content of 1.11 g/ml. Subsequent total organic carbon (TOC) content measurements and rock-eval analysis showed that the black shale section was generally classified as excellent source rock, with TOC contents commonly over 12% and an average genetic potential reaching 90 mg HC/g rock. The black shale samples of the Yanchang Formation contain kerogen of types I and II1, indicating the presence of oil source rocks, and the Tmax values range from 438 to 442 °C, which indicate a maturity stage in the early oil window. To reconstruct the depositional environment of the black shales with high TOC contents, various geochemical elements and their ratios were analyzed, yielding a number of interesting results: (i) the paleoclimate indexes CIA, CIW and C-values range from 50 to 72 (mean 65), 56 to 85 (mean 75), and 0.8 to 2.6 (mean 1.5), respectively, indicating humid conditions during the sedimentation period of the black shales; (ii) the redox conditions during the sedimentation of the black shales were dysoxic to anoxic as evidenced by the cross-plot of V/Cr vs. V/(V + Ni); (iii) the water column environment was a deep, fresh-water lake, further confirming the moist paleoclimate and reducing environment; and (iv) the high TOC contents of the black shales are attributed to inputs from hydrothermal fluids as evidenced by the samples falling into or near to the hydrothermal area of the Ni/Cr vs. Ti plot and the Ti vs. V plot.

A FACIOLOGIA DO GRUPO PASSA DOIS NO RIO GRANDE DO SUL

The study of geological sections in the outcropping area of the Passa Dois Group in Rio Grande do Sul, complemented with the study of cores from drillings for coal, showed the relations in the State, which are related bellow. 1) The Passa Dois Group is constituted by the Irati and Estrada Nova Formations; the Rio do Rasto Formations is lacking. 2) The thickness of the group is about 100 m. 3) The contact with the subjacent formation is characterized by the occurrence of limestone concretions immersed in a grey silty shale, very similar to the Palermo Formation. 4) The Irati Formation has two facies. One characterized by the occurrence of two beds of pyrobituminous shale associated with fossiliferous limestone lenses. These two beds are intercalated with a grey silty shale with concoidal fracture, and with yellowish limestone concretions immersed in it. This facies, when present, occupies the lower part of the formation and was called Tiaraju facies. The second facies, partially synchronous with the first one, is constituted by grey silty shales with limestone concretions and West of Pantano Grande, is cut by oblique veins of silica. Toward the east it is predominantly siltic, showing cross-lamination. This facies ends the Irati deposition in the State and was called Valente facies. 5) The Estrada Nova Formation also has two lithologic facies, one being pellitic; the other, sandy, which, when present, occupies the top. The pellitic facies was called Caveiras facies and is characterized by the development of pink and red colours alternating with grey. The sandy facies, also reddish, is characterized by lenticular bodies of very fine sandstone, by occurrences of limestone lenses with irregular shapes, and also by large limestone concretions. This facies was called Armada facies. 6) The upper limit of the group was set on the contact of the above mentioned lithologies with a pink medium sanstone, with planar and channal cross stratifications, and with intraformational conglomerates.

Numerical Study of Fracture Network Evolution during Nitrogen Fracturing Processes in Shale Reservoirs

This paper develops a numerical model to study fracture network evolution during the nitrogen fracturing process in shale reservoirs. This model considers the differences of incompressible and compressible fluids, shear and tensile failure modes, shale heterogeneity, and the strength and permeability of both shale matrix and bedding planes through the coupling of mechanical-seepage-damage during fracturing fluid injection. The results show that nitrogen fracturing has a lower breakdown pressure and larger seepage zone than hydraulic fracturing under the same injection pressure. Tensile failure was identified as the major reason for the initiation and propagation of fractures. Ignoring the effect of bedding planes, the fracture initiation pressure, breakdown pressure, and fracturing effectiveness reached their maxima when the stress ratio is 1. Under the same strength ratio, the propagation path of the fractures was controlled by the stronger effect that was casused by the bedding angle and stress ratio. With increasing the strength ratio, the fracture number and shearing of the bedding plane increased significantly and the failure pattern changed from tensile-only mode to tensile-shear mode. These analyses indicated that the fracture network of bedding shale was typically induced by the combined impacts of stress ratio, bedding angle and strength ratio.

Test and analysis on the permeability of induced fractures in shale reservoirs

In order to improve the effectiveness of shale gas stimulated reservoir volume (SRV), it is necessary to evaluate and study the permeability of different types of induced fractures in shale and its influential factors. In this paper, the mineral composition characteristics, reservoir pore and fracture characteristics of shale were investigated, and the permeability of three types of induced fractures in shale (i.e., in-situ closed type, shear self-propped type and single-layer propped type) was tested. Besides, the effects of fracture type, fracture surface roughness, carbonate content, shale bedding and confining pressure on the permeability of induced fractures in shale reservoirs were studied systematically. The following research results were obtained. First, the permeability–pressure relationship of in-situ closed fracture is in accordance with the Walsh theory. The permeability decreases with the increase of confining pressure and it is in the range of 0.13–16.75 mD. In-situ closed fracture plays the same role in increasing the productivity of shale gas reservoirs with or without proppant filling or dislocation. Second, compared with in-situ closed fracture permeability, the shear self-propped fracture permeability is 1–2 orders of magnitude (7.53–88.48 mD) higher, and single-layer propped fracture permeability is 2–3 orders of magnitude (9.98–771.82 mD) higher. Third, the larger the fracture surface roughness, the higher the fracture permeability. And there is a better positive correlation between the fractal dimension and the fracture permeability. Fourth, the permeability–pressure relationship of shear self-propped fracture and single-layer propped fracture is, to some extent, deviated from the Walsh theory, which reflects the influence of self-propped point crushing, proppant embedding and crushing. In conclusion, the experimental results can be used as the reference for the selection of shale fracturing technologies and the optimization of parameters.

Organo-mineralogical insights of shale gas reservoir of Ib-River Mand-Raigarh Basin, India

In the present study, Permian shale beds of Ib-River Mand-Raigarh Basin have been evaluated for insights of depositional conditions, organic, clay and mineral composition allied to shale matrix. The shale core samples were obtained during exploratory drilling and analysed for the properties like proximate, petrography, Rock-Eval, Total organic content (TOC), X-ray diffraction (XRD) and X-ray fluorescence (XRF). The values of vitrinite content and TOC varies from 2.00 to 16.20 (vol%) and 1.88–6.99 wt % with an average value of 10.34 (vol%) and 3.75 (wt.%) respectively, suggesting fair to excellent source rock potential of shale for gas. Whereas, results of the Rock-Eval pyrolysis indicated fair to very good source rock potential (S1: 0.04–0.22 and S2: 0.57–39.45). The indicator of thermal maturity parameters like Tmax (423–470 ᵒC) and VRo (0.64–0.96%), counsels moderately matured shales. The plot of hydrogen index (HI) vs oxygen index (OI), Tmax vs HI and TOC vs HI illustrated the presence of type II and III kerogen in studied shales. The uniformity in carbon conversion elucidates negligible effects of intrusive and basin tectonics on shale reservoir which is validated from the passive stable tectonic setting of Ib-River Mand-Raigarh basin which favours deposition of organic matter. The high percentage of quartz (26.30–57.60 vol%) signifying the resistive nature of SiO2 towards erosion and weathering. However, the negligible or typical absence of K-feldspar and a large percentage of kaolinite (16.80–53.30 vol%) attributed to the strong weathering process. Consequently, the instantaneous reduction condition supported the preservation and transformation of organic matter.The paper focuses on the significance of various essential parameters like depositional conditions, organic richness, the degree of maturation, clay types and mineral constituents on the gas genesis and storage. The parameters interpreted through facies and evolution history of the basin to evaluate the prospects of shale gas resource development in Ib-River Mand-Raigarh Basin, India.

Phosphatized tungsten-metabolizing coccoid microbes interpreted from oil shale of an Eocene lake, Green River Formation, Utah, USA.

Microscopic globular structures have been observed in some beds of oil shale from eastern Utah. These beds comprise carbonate-dominated mud that is interlaminated with variably thick and continuous organic-rich layers. Collectively they are enriched in phosphorus, REEs, and actinides. The beds are considered of lacustrine origin and assigned to the Eocene Green River Formation. The globules themselves are of microcrystalline carbonate fluorapatite (μCFA), often contain concentric internal structures, and usually group together in clusters of up to 80, possibly more. Detailed SEM and microprobe analyses have revealed tungsten (W) to be almost exclusively associated with the globular clusters found within the more organic-rich laminae, often at concentrations of over 200ppm, two orders of magnitude above shale standards. The globular structures are present in freshly cut sections where they occasionally grade into a μCFA matrix cement. This, together with the draping of the clusters by stringers of organic matter that would have accumulated in the Eocene lake, confirms that the structures are not a contaminant. The limited range of sizes and globular shapes is consistent with the morphology of coccoidal bacteria: Concentric internal structures may represent remnants of the nucleoid and cell wall. Paired concentric structures may indicate cell division (reproduction) processes were occurring until mineralization. The phosphate mineralization itself may have been promoted by release of phosphate from the stressed cells, bringing porewaters to supersaturation, or by the cells acting as nucleation sites. The recording of trace amounts of W almost exclusively in globular clusters preserved in the most organic-rich stringers (anoxia prone) further suggests facultative use of W-enzymes in a microbial metabolism. Combined, their context, morphology, and indication of biogenic process are strong evidence that the structures are fossilized (phosphatized) microbes, possibly sulfate-reducing bacteria, or methanogenic archaea.

Evaluation of gas resource potentiality, geochemical and mineralogical characteristics of Permian shale beds of Latehar-Auranga Coalfield, India

The shale beds associated with Permian coal-bearing Barakar Formation of the Latehar-Auranga coalfield (north Koel Valley), India have been investigated for the hydrocarbon prospects and their critical reservoir properties. The shale core samples were collected from boreholes drilled in three different blocks like Gowa, Jagaldaga and Banhardih. The shale core samples are examined for in-situ gas content, desorbed gas composition, geochemical, Rock-Eval, scanning electron microscopy (SEM), X-ray diffraction (XRD), high pressure CH4 adsorption isotherm, porosity and permeability aspects. The shales are rich in carbonaceous and silty materials with alternate bands of intercalations; suggesting deposition of the sediments and organic matters by slow or wavering river currents under the reducing environment. The van Krevelen diagram of H/C and O/C atomic ratio of the shales has demonstrated type III/IV kerogens; specifying that organic matters transformed from the fluvio-terrestrial depositional conditions to the diagenesis and catagenesis stages and placed in wet to dry gas window (H/C ratio < 0.5). The values of in-situ gas, lost gas, desorbed gas and residual gas contents are ranging from 1.06–7.02, 0.21–0.98, 0.35–4.16 and 0.42–2.45 cc/g, respectively. The Langmuir volume (VL) is varying between 5.6 and 0.9 cc/g, when values of VL compared to the in-situ gas revealed low to moderate gas saturation (26.86–73.75%) of the shale beds. The negative trend of Langmuir pressure (PL) with depth suggests affinity of CH4 to the shale pore surfaces. The plot of lower hydrocarbons ratios like (C2/C1) × 1000 and (C3/C1) × 1000 shows the dry thermal origin of desorbed gas. The Rock-Eval pyrolysis constituents like S1, S2, S3, PI, Tmax, TOC, HI, OI and Calc. VRo% varies from 0.11–0.47, 3.45–28.34 mg HC/g, 0.11–0.89 mg CO2/g, 0.00–0.07, 414–456 °C, 1.28–16.26 wt%, 39.54–821.45 mg HC/g TOC, 1.52–20.00 mg CO2/g TOC and 0.29–1.05% respectively.The plots of hydrogen index (39.54–821.45 mg HC/g TOC) with calculated VRo (0.29–1.05%) and Tmax (414–456 °C) are signifying types I, II, III and IV kerogen in the shales prone to generate oil, wet and dry gas placed in immature to mature regions. The positive linear correlation of the VL with kaolinite and illite contents suggests that mainly clays contribute to the formation of shale matrix. The SEM images show six types of pore: i) lenticular open pores along the fissility, ii) altered pores due to weathering, iii) intergranular pores, iv) intermingled pores between crystal lattices, v) partially filled pores associated with clays and minerals, and vi) evolved pores by cracking of the organic compounds. The values of porosity and permeability have been measured under reservoir simulated confining pressure, and are ranging from 0.87–8.18% and 0.08–1.45 mD, respectively. This shows poor connectivity between the pores and fracture mechanisms controlled by the clay and minerals. It is summarized that the studied shales of Latehar-Auranga Coalfield have a low to moderate gas potential, based on their in-situ gas, TOC content (1.28–16.26 wt%), sorption capacity, Tmax values and thermal maturity. Moreover, the significant residual volume, low porosity and low permeability are the most critical properties for shale gas resource development at the Latehar-Auranga coalfield.

Binding of heavy metals by oxidised kerogen in (palaeo)weathered black shales

Sub-aerial weathering of black shales drives the gradual leaching of sulphur- and organic-bound heavy metal elements, which are usually abundant in these rocks due to depositional conditions. The formation of oxygen functional groups in kerogen, however, can lead to an opposing mechanism - metal adsorption and binding, similar to a process common in soils. An increase in cation exchange capacity (CEC) measured previously using metal complexes on black shales oxidised under laboratory conditions implies that the same phenomenon may occur in a naturally oxidised black shale. This idea was tested on a unique, well-developed and -preserved Permian palaeoweathering profile containing two neighbouring but diverse black shales from the Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland).In the studied black shale beds, the oxygen groups formed in kerogen in the partially-weathered zone were found to be responsible for significant changes in adsorption properties measured using hexamminecobalt(III) and Cu(II)‑triethylenetetramine cations, which are common probes for CEC. Compared to a pristine part of black shales, the partially weathered zone was depleted of total organic carbon (TOC), sulphur, and sulphur- and organic-bound metals, and highly enriched in Cu, which is generally present in low levels in the nascent shales.In the partially weathered zone, where TOC content is reduced, apparent CEC values surpass the CECs predicted from the contents and structures of clay minerals, and correlate linearly with the content of oxygen groups developed during weathering. The adsorption properties of carboxyl groups in the oxidised kerogen are suggested as being responsible for the syn- or post-weathering enrichment in Cu caused by the remobilisation of older Cu-sulphide ores present in the area. As opposed to natural weathering, aggressive oxidation, e.g. under laboratory conditions produces a high proportion of cross-linked oxygen groups that do not participate in metal cation adsorption. The CEC values of artificially oxidised samples reached a limit corresponding to those of naturally oxidised shales.

Exploration History of Messla Oil Field, Sirt Basin, North Central Libya

The exploration history in Libya started in the western part of Libya near the border to Algeria by Esso Company one of the Seven Sisters hopefully that the oil accumulation will extend from El Hasi El Masoudi in Algeria. The first well drilled (Wildcat) was Al Atshan well. There were only oil shows in this well. It was plugged and abandoned. Then Esso Oil Company was given a concession in Sirt Basin in the early fifties by the Libyan Ministry of Petroleum. The exploration history in Messla Oil Field started by drilling the wildcat HH1-65. The field was discovered in 1971 and was located in the southeastern part of the Sirt Basin approximately 40 km northwest of the supergiant Sarir Oil Field. Although in an early stage of development, the field is estimated to contain approximately 3.25 billion bbl. of original oil-in-place. The field was a seismically defined stratigraphic accumulation located on the east-dipping flank of a broad Precambrian basement high. The reservoir is in the Lower Cretaceous fluvial Sarir Sandstone, which wedges out westward on the basement and is truncated by a basin-wide unconformity at the base of the capping Upper Cretaceous marine shales (considered to be the source rocks) and by the seal Busat Formation (Anhydrite Cap). The reservoir consists of two sandstone units separated by a continuous shale bed (Red Shale). Porosity values average 17% and the permeability 500 md. The oil column averages approximately 90 ft, and is productive from an average depth of 8,800 ft, Over 200 km2. Early 1978 production is in excess of 100,000 bbl/d of 40° API oil with a cumulative production of 45 million bbl.

Thermal controls of lamprophyre sill on hydrocarbon generation outlook of shale beds in Raniganj basin, India

The present work highlights the role of lamprophyre sill on the potential of hydrocarbon generation of shale beds. Here, the authors had systematically collected seven shales for detailed investigations of thermal impact provided by lamprophyre sill both along the dip and opposite to the dip directions of the shale beds. Proximate, ultimate, Rock Eval pyrolysis, organo-petrographic, vitrinite reflectance, Fourier Transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and X-ray diffraction (XRD) analyses were performed. Authors have also introduced new parameters like index of aliphaticity (IAL), index of aromaticity (IAR) and index for hydrocarbon generation (IHG) for precise quantification of FTIR spectra of shales, which in turn helpful in indicating the influence of thermal aureole on shale beds. The results indicate more distinct thermal alterations in the heat-affected shales collected along the dip direction of the shale beds owing to more pronounced and extensive thermal impact of lamprophyre sill in the dip direction. The estimated vitrinite reflectance (EVRo) and mean random vitrinite reflectance (VRo) show maximum difference in the heat-affected shales. Low genetic potential (GP), IHG indicate poor potential for heataffected shales along the dip due to intense thermal influence. In contrast, the fairly-affected shales collected opposite to the dip of the bed have higher GP, IHG and hence considered to be excellent source material. The mesopores present in the fairly-affected shales held good amount of hydrocarbons and thus suitable for hydrocarbon exploration and exploitation. The igneous intrusion improves the overall the general maturity of the area although at the expense of the reduction of the hydrocarbon generation potential of the proximal samples.