Shale Beds Research Articles

Macroinvertebrates of the Capivari marine bed, late Paleozoic glacial Itararé Group, northeast Paraná Basin, Brazil: Paleoenvironmental and paleogeographic implications

A 2-m-thick silty shale bed within the Taciba Formation, Itararé Group, Paraná Basin, State of São Paulo, southeastern Brazil, records marine sedimentation in a siliciclastic-dominated, low-energy, shelf setting, during a short-lived deglacial event. The bed is located 100–150 m below the base of the lower Permian, post-glacial Tatui Formation. The marine assemblage is dominated by rhynchonelliform brachiopods, with subordinate bivalves, gastropods and crinoids, recording the highest phylum-level diversity so far identified within a given fossil-bearing horizon in the uppermost portion of the Itararé Group. Two new species are described, one brachiopod Biconvexiella saopauloensis and one gastropod Peruvispira brasilensis. Additionally, shells of Lyonia rochacamposi, Rhynchopora grossopunctata, Quinquenella rionegrensis, Phestia tepuelensis, Streblopteria aff. S. lagunensis, Limipecten capivariensis, Praeundulomya cf. subelongata and Mourlonia (Woolnoughia)? sp. are identified. Crinoid columns were assigned to øPentaridica sp. (a genus based on elements of the columnal). This is the first systematic description of members of the Eurydesma-Lyonia fauna in the northeastern part of the Paraná Basin, Brazil. The overwhelming majority of brachiopods belong to Biconvexiella saopauloensis, followed by Rhynchopora grossopunctata. The record of Lyonia rochacamposi closely resembles that of the uppermost part of the Taciba Formation in southern Brazil. Hence, the Capivari marine fauna correlates approximately with that of the upper part of the Taciba Formation. Lyonia rochacamposi also indicates correlation with Permian units of the Sauce Grande-Colorado (Argentina), Huab (Hardap shale of the Dwyka Group), Aranos area (Namibia), southwest Africa, and the Carnavon (Western Australia) basins. These correlations support a latest Asselian-earliest Sakmarian age for the fauna.

Passive seismic horizontal to vertical spectral ratio (HVSR) surveying to help define bedrock depth, structure and layering in shallow coal basins

SummaryTrial passive seismic HVSR survey lines were carried out in the north-western part of the Wilga sedimentary basin in Western Australia, which is a small and shallow isolated sub-basin to the Perth Basin, sitting above rifted Archaean granite-gneiss basement rocks. The HVSR survey method was trialled to determine if it could resolve subsurface basin features quickly and cheaply. This trial HVSR survey was carried out as a series of transects along open walking tracks. It was very successful for mapping the general basin architecture by resolving bedrock depth to a maximum depth of close to 200 m along the survey transects, and defining a half-graben structure that forms the faulted eastern boundary of the basin, with the basin depth gently deepening toward the west. The HVSR data are also interpreted to have detected subtle layering within the basin sedimentary sequence to possibly map Permian black shale beds, coal measures and splits sitting below an unconformity of Cretaceous sedimentary cover. The passive seismic HVSR method has potential to be a robust survey method for defining basin architecture in shallow coal basins with poorly indurated basin fill deposits, especially in remote parts of the world with difficult access and limited exploration funds to carry out active seismic surveys.

Shale bedding planes control rock removal behaviors of PDC cutter: Single cutter experiment

Shale bedding planes arise with the complexity of rock removal by the PDC cutters. A series of single cutter experiments were conducted to understand the effects of bedding planes of shale on chip formation behaviors. Six bedding inclinations were taken into account by recording the variation of cutting force, cutting size, topography of debris, and high-speed images. Results demonstrate that the average cutting force highly correlates with bedding inclination where a parabolic relation is observed. The maximum value of cutting force is presented while perpendicular cutting to the bedding plane. Crushing and chipping are approved to be two mechanisms of rock removal of the laminated shale. Particularly, the bedding plane controls the chip formation behaviors. While the cutting force is perpendicular to shale bedding, the crushing dominates the rock removal process in which more powder debris are created. While the cutting force is parallel to shale bedding, the chipping dominates the rock removal and more chunk-like cuttings are generated. Shear cracking along the weak bedding planes promotes chipping that is controlled by the bedding inclination. In summary, the bedding plane attributes to the variation of cutting force response, cutting size distribution, and even rock removal mechanisms.

Effect of Shale Anisotropy on Hydration and Its Implications for Water Uptake

Water uptake induced by fluid–rock interaction plays a significant role in the recovery of flowback water during hydraulic fracturing. However, the existing accounts fail to fully acknowledge the significance of shale anisotropy on water uptake typically under in situ reservoir temperature. Thus we investigated the shale-hydration anisotropy using two sets of shale samples from the Longmaxi Formation in Sichuan Basin, China, which are designated to imbibe water parallel and perpendicular to shale bedding planes. All the samples were immersed in distilled water for one to five days at 80 °C or 120 °C. Furthermore, samples’ topographical and elemental variations before and after hydration were quantified using energy-dispersive spectroscopy–field-emission scanning electron microscopy. Our results show that shale anisotropy and imbibition time strongly affect the width of pre-existing micro-fracture in hydrated samples. For imbibition parallel to lamination, the width of pre-existing micro-fracture initially decreases and leads to crack-healing. Subsequently, the crack surfaces slightly collapse and the micro-fracture width is enlarged. In contrast, imbibition perpendicular to lamination does not generate new micro-fracture. Our results imply that during the flowback process of hydraulic fracturing fluid, the shale permeability parallel to bedding planes likely decreases first then increases, thereby promoting the water uptake.

3D Structural, Facies and Petrophysical Modeling of C Member of Six Hills Formation, Komombo Basin, Upper Egypt

Two main reservoirs are producing in Komombo Basin: the first one belongs to the C Member of the Six Hills Formation, and the second belongs to the Albian/Cenomanian cycle. The C Member reservoir lacks detailed studies. Therefore, a detailed study of this reservoir is needed. 3D geological reservoir modeling of the C Member reservoir can be a pertinent part of an overall strategy for the development of hydrocarbon fields in Komombo Basin. Five boreholes, three vertical seismic profiles and twenty 2D seismic reflection sections are integrated in Petrel™ modeling software for building 3D structural, facies and petrophysical models for the C Member reservoir. The constructed 3D structural model reveals the presence of two normal faults, in NW–SE and NE–SW directions. A detailed petrophysical evaluation was performed for the available wells. The resulted facies/petrophysical parameters are then used as input in the processes of facies and petrophysical modeling. The C Member reservoir exhibits thickness values ranging from about 91.5 to 426.5 m. The constructed 3D facies model of the studied reservoir depicts that the shale beds have the large probability distribution in the study area with the comparison of the sandstone and siltstone beds. The created 3D petrophysical models reveal that the C Member reservoir has a fair reservoir quality. This reservoir exhibits, generally, high water saturation values in most parts of the study area, while the hydrocarbon saturation is restricted to the depocenter of the basin.

Geochemical Studies of Cenozoic Shale Beds of the Western Cis-Caucasian Region

Geochemical parameters of the Cenozoic shale strata of the western Ciscaucasia have been analyzed. Oil source strata were identified in the study. The geochemical characteristics of organic matter (OM) of the Kumian rocks revealed high oil source potential of the rocks. The formation and emigration of hydrocarbons (HCs) were inferred from qualitative and quantitative changes. Sapropelic OM generated large amounts of hydrocarbons in the Kuma Sequence, with the value increasing from the top to the bottom of the profile. Para-autochthonous and migratory bitumoids were registered on the PC3 gradation and well-developed on the MK2 gradation (at a depth of 4.6–5.0 km). A comprehensive study of OM from Khadumian rocks by pyrolysis, bituminology, and chromatography showed that all kerogen types were developed in the rocks, but mixed OM with moderate oil source potential predominated. Maximal organic carbon (Corg) concentrations and genetic potential were observed within the Western Kuban trough, as well as in the strip of outcrops in the Adygei ledge area. The improvement in geochemical parameters in these areas is due to a decrease in the terrigenous component in the crude OM in the same direction.

Oil shale reactor: process analysis and design by CFD

The oil shale pyrolysis process using a moving bed reactor was investigated with a three-dimensional mathematical model considering turbulent and multiphase flow in a porous moving bed, under non-isothermal and reactive conditions. Mass, heat and momentum balances involving chemical reactions of interest were formulated following a Eulerian approach to represent the process behavior. In the present approach, the shale bed was modeled as a porous medium and the advection due to its movement was implemented. Process analysis via CFD enabled the location of the drying, heating, reacting and cooling zones to be identified in the pilot-scale reactor. Moreover, it was possible to analyze in detail the conversion of organic matter to products, according to the reaction mechanism. The effects of heat and mass transfer inside the reactor were assessed through parametric sensitivity analysis, considering five parameters and five response values. The results were analyzed using the response surface method, which established the influence of each variable. The best values obtained for the thermal-energy consumption and the mechanical-energy consumption were 126.16 and 12.39kJ/kg, respectively. Considering the best operational conditions, scaling-up effects were also evaluated to shed light on the technical viability as well to carry out the design and analysis of the process.

Orientation of Paleostress of Raplee Ridge Anticline

During the Laramide Orogeny several major folds were formed in Southern Utah, one of those being the Raplee Ridge anticline. Raplee Ridge is approximately eight miles from Mexican Hat, Utah. The San Juan River cuts through the anticline, exposing the Honaker Trail Formation’s beds of shale and limestone with chert nodules. Accompanying the mountain-scale ductile deformation of the Raplee Ridge anticline are decimeter-scale brittle conjugate fractures in the limestone’s chert nodules. The objective of this study is to compare the orientation of paleostress that formed the Raplee Ridge anticline with the conjugate fractures within the chert nodules to see if the two different styles of deformation could have occurred during the same orogeny.

Organic Matter Type, Maturity, Depositional Environmental Characteristics, and Liquid Hydrocarbon Potential of Late Carboniferous Kozlu Bituminous Coal and Coaly Shale Beds (Zonguldak-Amasra Basin, NW Anatolia, Turkey): An Application of Biomarker Geochemistry

The Upper Carboniferous (Westphalian A) Kozlu Formation consisting chiefly of sandstone, thick coal layers, shale, and conglomerate levels crops out in the Zonguldak-Amasra Basin, NW Anatolia. The Kozlu Formation contains a total of 20 mineable coal layers with the thickness varying from 0.5 to 6 m. The lower level of formation is represented by lacustrine deposits, whereas the upper part is made up of thick flood plain sediments and meandering river deposits bearing laterally continuous coal levels. In this study, coal samples taken from coal layers within the Kozlu Formation at the Kozlu Underground Coal Mining site were evaluated using the data obtained from pyrolysis/total organic matter (TOC), gas chromatography, and gas chromatography–mass spectrometry. The average total organic matter (TOC) value of Kozlu coals is 40.28%. The coals are characterized by relatively high hydrogen index (HI) value (average 262 mg HC/gTOC) and very low oxygen index value (2 mg CO2/gTOC). Pyrolysis data indicate that coals contain dominantly type II and less amount of type III kerogen, and Tmax values range from 454 to 468 °C. In gas chromatographs, the recorded distribution consists predominantly of low-carbon-numbered n-alkanes and subordinately of high-carbon-numbered n-alkanes and the terrigenous/aquatic ratio value is very low (0.05–0.09). Pristane abundance is greater than that of phytane, and Pr/Ph ratios are in the range of 1.11–1.60. The sterane abundances in the Kozlu coals are in the following order: C29 > C28 > C27. Coals have high C19 and C20 tricyclic terpane concentrations and high (C19 + C20)/C30 ratio, high C30* (diahopane) and C29Ts concentrations, and high C30*/C29Ts ratio and low C31R/C30 and C29/C30 hopane ratios. The dibenzothiophene-to-phenanthrene ratio of Kozlu coals is found to be very low (0.04–0.14). Based on the pyrolysis and biomarker data, the Kozlu coals are interpreted as being deposited in a suboxic–oxic continental environment in which there is effective input of clay and dominantly terrestrial (with significant lipid-rich components) and bacterial organic matter. High Tmax values, CPI values close to 1, low moretane/hopane (0.23–0.12), equilibrated 22S/(22S + 22R) homopane (for C32), 20S/(20S + 20R) C29 sterane (0.52–0.54) and TA(I)/TA(I + II) steroid ratios, high ββ/(ββ + αα) sterane (0.51–0.55), C30*/C29Ts, C30*/(C30* + C30H), MPI-3(α/β) (1.24–1.41), and MDR and MA(I)/MA(I + II) steroid are indicative of mature–late mature organic matter. Ro values between 0.9 and 1.25% determined from Tmax (454–468 °C) values indicate “high-volatile bituminous B–medium-volatile bituminous” rank for Kozlu coals. Kozlu coals having HI values (up to 331 mg HC/gTOC) extremely higher than those of classical coals indicates that these coals have significant oil and gas generation potential, and high S1 (average 6.04 mg HC/g rock) and S2 (110.08 mg HC/g rock) values imply that they generate notably high amount of liquid hydrocarbons and still have generation potential.

Shear-tensile fractures in hydraulic fracturing network of layered shale

Understanding hydraulic fractures generation and geometric properties are significant for optimizing hydraulic fracturing treatment design which improves the ultimate production from shale reservoirs. The propagation of the hydraulic fractures is influenced by bedding planes. Simple opening or tensile crack model is not enough to meet the hydraulic fractures generation process, and the fault slipping model which is regarding as the cause of the natural earthquake is also not compatible with the actual physical meaning of fracking induced fractures. Hydraulic fractures consist of not only the opening but also slippage. Acoustic emission monitoring combined with the true triaxial hydraulic experiment provides direct information about the propagation and the geometric parameters of fractures. Moment tensor of acoustic emission is related to the mechanical mechanics of fractures. In this paper, the moment tensor interpretation is based on the shear-tensile crack model, then the orientation and the opening width of the hydraulic fractures are calculated. Computerized tomography scanning figures of the samples give support to the interpretation process. The distributions of hydraulic fractures orientations are different in the two samples with different normal stress applied on the bedding plane. Higher normal stress on the bedding plane led to a more complex fracture orientation. And the opening widths of the fractures in the far area from the wellbore are smaller than the fractures nearby the wellbore. These two parameters quantify the fractures geometric properties and provide information for adjusting the next step of the fracturing process. The findings of this study can help for better understanding of hydraulic fractures generation in the bedding shale. Shear-tensile crack model is supported by actual physical models has good adaptability in explaining the hydraulic fracture propagation process.

Geochemistry and architecture of the host sequence of the massive sulfides in the northern Iberian Pyrite Belt

The northernmost Iberian Pyrite Belt hosts several small felsic volcanogenic massive sulfide orebodies (<15 Mt), except the Aguas Teñidas and Magdalena each with ca. 45 Mt, which are economically important because of their high base and precious metal grades if compared with the bulk of the IPB. They occur aligned in a E-W belt located just south of the major suture that limits the South Portuguese Zone with the Pulo do Lobo Unit. The mineralization is related to a specific felsic volcanic unit that occurs in different tectonically dismembered units, but has a specific geochemical signature and a characteristic hydrothermal alteration. Six principal tectonostratigraphic units can be differentiated: (1) The Lower Felsic Unit is composed of feldspar-quartz-phyric rhyodacite (crypto)-dome complexes, intruded by sills and dykes of similar composition. Pumice and glass-rich breccia beds occur at the top and on the lateral margins of the dome complexes. A major shear zone separates the Lower Felsic Unit from the overlying Volcano-Sedimentary Unit; (2) The Volcano-Sedimentary Unit consists of vesicular basaltic lava and associated mafic epiclastic sandstone and siltstone, intercalated with thin beds of shale. A major tectonic contact marks the upper boundary; (3) The Middle Felsic Unit represents a series of intercalated coherent rhyolite domes with associated volcaniclastic rocks, and polymictic epiclastic sedimentary rocks. They are cut by numerous volcanic dykes and geochemically equivalent sub-volcanic intrusions; (4) The Sedimentary Unit is a highly deformed package of grey siltstone with interlayered shale and fine-grained epiclastic sedimentary rocks; (5) The Upper Felsic Unit is a package of dacitic to rhyolitic dome complexes with similar characteristics to the Lower Felsic Unit. Both the basal and upper contacts of this unit are narrow and high-strain tectonized zones. (6) The uppermost unit, the Andesite Unit, is comprised of andesitic dome complexes rich in hyaloclastite breccias and andesitic volcaniclastic rocks. Massive sulfides are hosted dominantly by the Lower Felsic Unit with only some orebodies related spatially to the Upper Felsic Unit (Lomero Poyatos, San Telmo and El Carpio).Geochemically, the Volcanic Sedimentary Complex is dominated by andesitic to rhyolitic calc-alkaline magmatic rocks with a significant proportion of dacite and andesite. The Lower Felsic and Upper Felsic Units are geochemically identical and probably represent dismembered parts of a single volcanic felsic complex. If that holds true, massive sulfide deposits of the northern IPB are hosted by volcaniclastic rocks located in the hanging wall of a single unit dominated by dacite-rhyolite dome complexes. This volcanic unit is characterized by Zr contents <200 µg/g (ppm) which are significantly lower than those of the more evolved Middle Felsic Unit (200–750 µg/g).Structural analysis and the geochemistry suggest that the volcanic sequence is tectonically imbricated, with the youngest units located at the lowest structural position. The proposed reconstructed stratigraphic sequence comprises an andesitic footwall, overlain by the felsic complexes of the Middle Felsic and Lower-Upper Felsic Units. Thus, the massive sulfide deposits formed toward the top of the whole sequence, and associated with the youngest felsic rocks having a specific geochemistry.

Numerical local upscaling of elastic geomechanical properties for heterogeneous continua

An efficient, numerical local upscaling technique for estimating elastic geomechanical properties in heterogeneous continua is proposed. The upscaled anisotropic elastic properties are solved locally with various boundary conditions and reproduce the anisotropic geomechanical response of fine-scale simulations of sand–shale sequence models with horizontal and inclined shale bedding planes. The algorithm is automated in a parallel program and can be used to determine optimum upscaling ratios in different regions of the reservoir. The successful application of the proposed upscaling method in a field-scale coupled reservoir–geomechanics simulation demonstrates an improvement in overall computational efficiency while maintaining accuracy in the geomechanical response and reservoir performance.

Peri-Gondwanan acritarchs from the Ordovician of the Llanos Orientales Basin, Colombia

There are few publications on the precise age and palaeogeography of the Palaeozoic rocks of Colombia. In the present study the Pluspetrol Paisa-1 well, located in the central part of the Colombian Llanos Orientales Basin, is investigated palynologically, in order to determine the age, the palaeoenvironment and the palaeogeography of the sediments. The lowermost stratigraphical interval of the well (4939–5040′; ∼1505–1536 m) is composed of alternating sandstone and black shale beds, from which a well-preserved assemblage of Ordovician acritarchs has been identified in five samples (cuttings and sidewall cores). The acritarch assemblage contains some diagnostic taxa, including Arbusculidium, Barakella, Coryphidium, Dactylofusa, Striatotheca, and Veryhachium, among others, indicating an Early to Middle Ordovician age. The presence of a few biostratigraphical index species, such as Dactyolofusa velifera or Coryphidium bohemicum, and the absence of others point to a middle Floian age. As the three diagnostic genera (Arbusculidium, Coryphidium, Striatotheca) are present, the assemblage clearly belongs, in terms of palaeobiogeography, to the peri-Gondwanan acritarch province. Our study thus extends the geographical distribution of this province to the north-western part of South America, extending the palaeobiogeographical distribution map of Early to Middle Ordovician acritarchs. A comparison of the palynoflora with models of acritarch distribution in different palaeoenvironments implies a relatively shallow-water environment.

The Cenomanian/Turonian boundary interval deep-sea deposits in the Zagros Basin (SW Iran): Bioevents, carbon isotope record and palaeoceanographic model

The Cenomanian/Turonian (C/T) boundary interval, spanning the upper part of the Sarvak Formation in the Zagros Basin (Izeh Zone), has been studied to determine the timing and the possible cause of biotic turnovers, coinciding with the intense environmental perturbations during the Oceanic Anoxic Event 2 (OAE2). The upper Cenomanian strata in the study section, composed of light-colour marlstone/organic-rich marlstone and shale bedding couplets, record fluctuations in microfossil assemblages and organic carbon contents. We suggest that the organic-poor layers, characterized by high abundance of radiolarians, were deposited during cold periods under surface water eutrophication (upwelling) and ventilated seafloor. In contrast, water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic-rich strata. Continued stratification and also increased runoff and primary productivity during warm intervals of OAE2 led to expansion of oxygen minimum zone (OMZ), which may have caused extinctions of deep followed by intermediate water planktic foraminifera. Such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus Planoheterohelix (“Heterohelix” shift event). The δ13C curve in the study interval reveals the diagnostic features of global C/T boundary carbon isotope record, including three positive peaks (A, B and C) within the Whiteinella archaeocretacea Biozone. These carbon isotope features and the most important bioevents in the study section are stratigraphically listed below: 1- Highest occurrences (HOs) of Th. greenhornensis and Th. deeckei, 2- HO of R. cushmani and δ13C peak A, 3- HO of “G”. bentonensis, 4- Onset of “Heterohelix” shift event, 5- δ13C peak B, 6- δ13C peak C, 7- Filament event, 8- Lowest occurrence (LO) of H. helvetica, and 9- Holywell event.

Криволинейное радиальное течение сжимаемой вязкопластичной нефти со свободной текучестью в однородном пласте

The paper presents a solution to a steady-state hydrodynamic problem dealing with one-dimensional free-surface radial flow of compressible viscoplastic oil in a horizontal homogeneous circular formation. A vertical producing oil well is located in the centre of the formation, penetrating the pay zone fully, with no well casing or perforation present. We used generalised Darcy's law and equations of state for a compressible fluid to determine mass flow rate of the compressible viscoelastic oil and derive equations for current density, oil flow rate, current pressure distribution in the drainage area, and current pressure gradient. The equations take into account oil compressibility and initial pressure gradient. We also determined the time it takes an oil particle to reach the well starting from the current radius vector and from the external boundary. This is the case when the oil deposit lies close to the earth surface. This depth range features no shale beds or interbedded formations. Since subsurface mining is possible with shallow oil deposits, both wells and tunnels may be used for production.

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

Density stratification between freshwater and brine is periodically formed during massive evaporation events, which often associates deposition of organic-rich sediments. Here, we investigated phototrophic communities and nitrogen cycle during the deposition of two organic-rich shale beds of gypsum–shale alternation, representing the initial stage of the Messinian salinity crisis (Vena del Gesso, Northern Apennines, Italy). The structural distributions and the carbon and nitrogen isotopic compositions of geoporphyrins show a common pattern in the two shales, indicating the predominance of a particular phototrophic community under freshwater–brine stratified conditions. The ~6‰ difference in δ13C of total organic carbon between PLG 4 and 5 shales was associated with similar shift in δ13C of the porphyrins derived from chlorophyll c, suggesting that the eukaryotic algae producing chlorophyll c were the major constituent of the phototrophic community. Importantly, these porphyrins show δ15N values (−7.6‰ to −4.7‰) indicative of N2-fixation. We suggest that nitrate-depletion in the photic zone induced the predominance of diazotrophic cyanobacteria, which supplied new nitrogen for the chlorophyll c-producing eukaryotic algae. The large difference in the δ13C values of porphyrins and total organic carbon between PLG 4 and 5 shales are interpreted to reflect the depth of the chemocline, which fluctuates in response to changes in the regional evaporation–precipitation balance. Such variation in the chemocline depth may have dynamically changed the mode of the nitrogen cycle (i.e., nitrification–denitrification–N2-fixation coupling vs. phototrophic assimilation of ammonium) in the density-stratified marginal basins during the Messinian salinity crisis.

Dynamic Crack Initiation Toughness of Shale under Impact Loading

The impact loading of a notched semi-circular bend (NSCB) specimen of outcrop shale in Changning Sichuan was carried out using a split Hopkinson pressure bar (SHPB) to study the effect of shale bedding on the dynamic crack initiation toughness. Three loading configurations were tested: Crack-divider, Crack-splitter and Crack-arrester loading. Bedding plane has a significant effect on the crack initiation of shale. Under the Crack-divider and Crack-splitter modes, shale had lower dynamic crack initiation toughness. The dynamic crack initiation toughness of the shale was affected by the loading rate for all three loading configurations. The correlation between loading rate and dynamic crack initiation toughness was most significant for the Crack-arrester mode, while the Crack-splitter mode was the weakest. When loading was carried out on Crack-arrester, the bedding plane could change the direction of crack growth. In the Crack-splitter mode, only a small impact energy was needed to achieve effective expansion of a crack. The research results provide a theoretical basis for shale cracking.

The forced imbibition model for fracturing fluid into gas shales

Understanding the factors controlling the fracturing fluid leak-off due to forced imbibition during the hydraulic fracturing operations is critical for the accurate assessment of the fracturing fluid invasion depth and the extent of the formation damage in gas shales.Here, we present results of an experimental and a modeling study of the factors controlling fracturing fluid forced imbibition into the organic rich shale gas reservoirs. The main objectives of the study were to: i-) Experimentally investigate the forced imbibition of the brine and the slick water (SW) into the shale; ii-) Develop an analytical model of the fracturing fluid forced imbibition into the shale matrix.The shale samples collected from Silurian Longmaxi (SL) Shale Formation, which is located in Southern Sichuan Basin in China, were used to conduct the forced imbibition experiments. Effects of varying fluid properties (i.e., the viscosity and the surface tension), the direction of the imbibition with respect to the shale bedding plane/lamination, and the fluid pressure across the shale face on the cumulative mass of the imbibed fluid per unit area over time were investigated.A new analytical model of the forced imbibition into a shale rock was developed. The Hagen-Poiseuille law and the capillary tube bundles model were used to describe flow through tortuous capillary. The new model also considered the effects of the fluid pressure across the rock face (i.e., forced imbibition) and the viscous pressure loss in the capillary. Comparison of the model predictions with the experimental results indicated that the effects of the fluid pressure and viscous pressure loss on the imbibed fluid mass are not negligible. The close agreement with the model predictions and experimental results in the direction parallel to shale lamination confirmed that the new model accurately describes the process of fracturing fluid forced imbibition into the shale matrix in the direction parallel to shale bedding plane.The new model could potentially be used for the field scale prediction of the average depth of fluid invasion into the shale matrix in the direction parallel to lamination due to the forced imbibition of the fracturing fluid.

Geochemical attributes, pore structures and fractal characteristics of Barakar shale deposits of Mand-Raigarh Basin, India

Pore structures in the shale matrix are an essential factor affecting the storage capacity of gas of shale beds as well as production performance. Twenty organic-rich shale samples at different depths were collected from Barakar Formation of Mand-Raigarh basin, to examine the pore structure and their fractal characteristic. Fractal dimension was calculated by following FHH theory to investigate the complexity of pore surfaces, storage mechanism and the pore network system. The complex pore system influenced by thermal cracking of organic matter, pore dissolution during geochemical weathering and tectonics of the basins having surface area 5.56–23.94 m2/g (avg. 14.21 m2/g). Whereas, the pore volume determined using the BJH model varying from 0.035 to 0.076 cc/g (avg. 0.053 cc/g). FTIR spectrum demonstrated that significant presence of aliphatic side chains and aromatic carbon structures existing in studied shale influencing the pore volume. It is summarized that pores and matrix of shale are built by complex mixtures of organic and inorganic content. Further, the pores are categorized into organic pores evolved during thermal cracking, inter-granular, intra-granular and inter-crystalline due to the large content of altered clays and minerals showing fissile nature. The SEM-EDX derived facies indicating the involvement of different chemical constituents following the trend of alteration as well as carbon enrichment. The D1 and D2 values obtained through FHH model range from 1.17 to 2.45 and 2.54–2.70, the fractal values particularly D2 are ∼3 demonstrating the pore surfaces and structure of studied shales beds are complex and heterogeneous. This study helps to enhance the exploration and advancement in the shale gas resources from Ib-River of Mand-Raigarh Basin, India.

A SPECTRAL METHOD OF LITHOFACIES DIFFERENTIATION WITHIN A HYDROCARBON RESERVIOR UNIT USING SEISMIC AND WELL DATA FROM TOMBOY FIELD NIGER DELTA

Seismic facies analysis is a key component of Seismic interpretation workflow, as much information on depositional process, environment, reservoir architecture and potential can be determined from the seismic data. This enhances the seismic visibility of subtle stratigraphic features, and prediction of new prospects for drilling due to lateral continuity of sand bodies (the hydrocarbon reservoir) deposited within the sedimentary column. This study presents the results of the application of seismic amplitude inversion and spectral decomposition to differentiate lithofacies within a thin-sand reservoir and show their lateral and vertical continuity using amplitude-derived attributes (rock properties) in the interpretation of 3D seismic and well log data from “TOMBOY” field Niger Delta. A thin-sand reservoir was delineated from lithologic log signatures within the interval 11,135.61-11,210.35ft which corresponds to the time window 2.752 - 2.768secs on the seismic data along an arbitrary line drawn to connect the six wells (01-06) in the field. Crossplot of acoustic impedance against density across the reservoir bed showed three compartments interpreted as gas filled sand, oil filled sand and shale. The interpretation was enhanced via spectral analysis by computing frequency maps of acoustic impedance, density and velocity using discrete Fourier transform (DFT) technique at top (2.752sec) of the reservoir in terms of magnitude, phase and frequency. Phase response for the three attributes (acoustic impedance, density and velocity) showed lateral continuity and discontinuity of sand lithofacies at the various well locations which were not evident on their original amplitude time slice, while frequency response showed bed thickness, with low frequency indicating presence of hydrocarbon or sand rich beddings, while high frequency indicates thin shale beddings. It was observed that the top (2.752sec) of the reservoir for wells 02, 05, 01 and 04 showed low frequency values for the three attributes (acoustic impedance, density and velocity) which indicates potential zones for hydrocarbon production and development in the field, while wells 03 and 06 within the same time slice (2.752sec) showed a higher value in acoustic impedance frequency, density frequency and velocity frequency and suggests the presence of thin shale facies at the top (2.752sec) of the thin-sand reservoir. By defining the lateral and vertical continuity of sand facies within the reservoir bed, hydrocarbon fairways were better defined and knowledge of this can be incorporated into drilling decisions for field development. The results gave enhanced structural disposition of the reservoir bed and more insights into the variation of sand lithofacies with depth. Keywords: Lithofacies, Amplitude inversion, Geologic transform, Seismic attributes, Cross plots and Spectral decomposition. DOI : 10.7176/JEES/9-3-14 Publication date :March 31 st 2019