Middle Shale Research Articles

Investigation of Wellbore Instability in Southern Rumaila Oil Field

This study aims to address the issue by providing valuable insights into the factors contributing to the wellbore instability and proposing effective measures to mitigate the problem in the southern part of the Rumaila oil field. A comprehensive one-dimensional mechanical earth model (1D MEM) was developed by utilizing various logs data from 4 wells across the south part of this field, including gamma ray, bit size, caliper, bulk density, and sonic compression and shear logs. The model was validated with laboratory tests, including Brazilin and Triaxial tests, as well as repeated formation tests. To analyze the wellbore stability, three different failure criteria, namely Mohr-Coulomb, Mogi-Coulomb, and Modified lade, were employed. The results indicated that the Mogi-Coulomb criterion was the most accurate failure criterion in predicting rock failure. Wellbore instability problems had been observed across the shale sections throughout the Rumaila oil field, particularly through Tanuma, Khasib, top and bottom of Ahmadi, Nahr Umr, and Upper Shale members and Middle Shale members of Zubair formations. The 1D MEM results indicated that Shaly formations exhibited low stiffness rocks (low Young's Modulus (YME)), low rock strength, and high Poisson's ratio (PR), suggesting potential challenges related to wellbore instability in the Tanuma, top and bottom of Ahmadi, Nahr-Umr, and Zubair formations. A sensitivity analysis was performed to determine the safest mud weight and the optimum well trajectory for future drilling operations. According to the updated mud window of this field in 2023, the pressure in the Mishrif and Zubair formations was reinforced by injection wells, as it was noted that the pressure behavior shifted from depletion (2000 Psi). Based on the findings of this study, the good inclination of (0-25°) can be drilled with the mud weight of 1.24-1.26 sg, while the good inclination of (25-40°) can be drilled with the mud weight of 1.28-1.30 sg in all directions (i.e., all azimuths). The stress regime in most of the formations was found to be a strike-slip to a normal fault regime. The findings of this study can significantly benefit the oil industry and enhance overall productivity.

Reservoir characteristics and pore fluid evaluation of Shan 23 Submember transitional shale, eastern Ordos Basin, China: Insights from NMR experiments

The Lower Permian Shanxi Formation in the Eastern Ordos Basin is a set of transitional shale, and it is also a key target for shale gas exploration in China. Three sets of organic-rich transitional shale intervals (Lower shale, Middle shale and Upper shale) developed in Shan 23 Submember of Shanxi Formation. Based on TOC test, X-diffraction, porosity, in-situ gas content experiment and NMR experiments with gradient centrifugation and drying temperature, the reservoir characteristics and pore fluid distribution of the three sets of organic-rich transitional shale are studied. The results show that: 1) The Middle and Lower shales have higher TOC content, brittleness index and gas content, reflecting better reservoir quality, while the Upper shales have lower gas content and fracturing ability. The total gas content of shale in the Middle and Lower shales is high, and the lost gas and desorbed gas account for 80% of the total gas content. 2) The Middle shale has the highest movable water content (32.58%), while the Lower shale has the highest capillary bound water content (57.52%). In general, the capillary bound water content of marine-continental transitional shale in the Shan 23 Submember of the study area is high, ranging from 39.96% to 57.52%. 3) Based on pore fluid flow capacity, shale pores are divided into movable pores, bound pores and immovable pores. The Middle shale and the Lower shale have high movable pores, with the porosity ratio up to 27%, and the lower limit of exploitable pore size is 10 nm. The movable pore content of upper shale is 25%, and the lower limit of pore size is 12.6 nm. It is suggested that the Lower and Middle shales have more development potential under the associated development technology.

Radiological Risk Parameters of the Phosphorite Deposits, Gebel Qulu El Sabaya: Natural Radioactivity and Geochemical Characteristics

This study investigates the distribution of natural radioactivity and geological, geochemical, and environmental risk assessments of phosphorite deposits to determine their suitability for international applications (such as phosphoric acid and phosphatic fertilizers). The examined Late Cretaceous phosphorite deposits belong to the Duwi Formation, which is well exposed on the southern scarp boundary at the central part of Abu Tartur Plateau, Gebel Qulu El Sabaya, East Dakhla Oasis. This formation is classified into lower phosphorite, middle shale, and upper phosphorite members. The lower phosphorite ranges in thickness from 2 to 3.5 m and mainly comprises apatite (possibly francolite), dolomite, calcite, quartz, hematite, anhydrite, and kaolinite. They contain an average concentration of CaO (38.35 wt.%), P2O5 (24.92 wt.%), SiO2 (7.19 wt.%), Fe2O3 (4.18 wt.%), MgO (3.99 wt.%), F (1.59 wt.%), Al2O3 (1.84 wt.%), Na2O (1.33 wt.%), and K2O (0.22 wt.%). Natural radioactivity and radiological parameters were investigated for fifteen samples of phosphorites using a NaI (Tl) scintillation detector. Absorbed dose rates, outdoor and indoor annual effective dose, radium equivalent activity, external and internal hazard, and excess cancer risk values are higher than the recommended levels, reflecting that exposure to these deposits for a long time may lead to health risks to human organs.

The role of geochemical and coal petrographic analyses to determine the depositional sets of Visean coal and shale sequence in Um Thora-Abu Hish area, Central Sinai, Egypt

The Visean time at the Sinai Peninsula is characterized by the deposition of two conformable formations of a siliciclastic (Abu-Thora) resting upon a calcareous (Um-Bogma). The Abu-Thora Formation (Fm) is informally divided into three rock units that comprise a lower and upper sandstone sandwiched with a middle coal and shale sequence. A combination of paleoenvironmental indices and ratios from petrographic and geochemical analyses of the middle sequence succeed to build up the depositional paleoenvironment and may apply to any other coal and shale sequence, especially in coal mine regions. Geochemical analysis reveals that the studied shale strata are not homogenous and can be subdivided into four units from the base to the top. The lower shale unit at the base is 4m in thickness and composed of kaolinite-rich shale (10–77%; nacrite mineral). The second is the middle shale unit of 5.10m in thickness composed of Fe-shale (Fe2O3; 2.04–16.45 wt%). The third is the coal unit of 0.55m in thickness comprising coal seam, and the fourth is the upper shale unit of 6m in thickness composed of wacke (SiO2; 71.63–72.83 wt%). X-ray diffraction (XRD), x-ray fluorescence (XRF) plus mineralogical analyses are applied on the first, second, and fourth units of almost pure shale, whilst the third unit of almost pure coal is subjected to a petrographic analysis instead to illustrate the depositional site and type of vegetation where coal was formed. The palaeoclimatology based on parameters of CIW, C-value, Rb/Sr, and Sr/Cu refers to the deposition of shale initiated at a warm-humid and then to a hot semi-arid climate. The precursor rock of the studied shale is a basaltic and intermediate igneous rock. The shale is of mature components subjected to intense weathering processes based on CIA and ICV of 91.71 and 0.34, respectively. Furthermore, discriminant functions F-1 and F-2 reveal the shale components came also from quartzose sediments that promoted a multi-source origin that was gathered from both preexisting mafic and sedimentary provenances. The accumulation and deposition took place at a marine anoxic shale-carbonate of the active continental margin and oceanic island arc tectonic setting. Maceral composition of the coal unit reveals a depositional setting of a coal-forming mire system that occurred at a paralic aquatic margin setting involving a dominated reed herbaceous vegetation in a hydrological water-logged of the limnic marsh.

Rock Type and Pore Throat Radius of Zubair Formation in the W Oil Field: Analysis Utilizing Core and Log Data

The Zubair Formation is a prolific oil reservoir in several southeastern Iraq oil fields. The formation comprises thick sandstones with interbedded shales and siltstones of Lower Cretaceous age (Hauterivian to lower Aptian). The environment of the Zubair Formation consists of fluviodeltaic, deltaic, and marine sandstones. In southern Iraq, the area is subdivided into informal members (oldest to youngest). The Lower Shale, lower sand, middle shale, main pay upper sand, and the upper shale. At the W oilfield, the main pay member is an oil producer. The thickness is of the main reservoir about 100 meters thick. A recent study focused on the Main Pay upper sand, which is divided into three informal units. The upper unit H and lower unit L reservoir units are connected by shale intervals (K unit) that extend throughout the field area laterally. There exist four depositional lithofacies of Zubair Formation fluvial, channel, mouth bar, and prodelta depositional lithofacies. Four Facies were defined according to gamma-ray sandstone, shaly sand, sandy shale, and shale Facies. The Zubair formation has four types of rocks (RRT1, RRT2, RRT3, and RRT4) due to heterogeneity. The RRT1 is characterized by 10%-25% porosities and 10-1000 mD permeability. The RRT2 has a similar porosity range to RRT1, 15%–25%, but an order ofmagnitude lower permeability range from 10-100 mD. RRT3 is considered to have high porosity and low permeability is thought to have great storage but poor flow potential. RRT 3 is characterized by 6%-15% porosities and <10 mD permeability. Meanwhile, RRT4 is considered to have low porosity and low permeability. Various rock types showed in the H unit due to heterogeneity, which composed this unit. The K unit unveiled RRT4 due to shale Facies. The rocks types common of unit L are RRT1 and RRT2 where the L unit mostly ranged from sandstone to shaly sand Facies.

Carbon isotope chemostratigraphy of a Gondwanan Ediacaran–Cambrian transition, Soltanieh Mountains, northern Iran

Mixed siliciclastic-carbonate rocks of the Kahar and overlying Soltanieh formations from Chopoghlu, in the Soltanieh Mountains, northern Iran, preserve an expanded stratigraphic record of Ediacaran to lower Cambrian life and environments. To date, regional placement of the Ediacaran-Cambrian boundary has been based on biostratigraphy, with contrasting views of its stratigraphic position. Here we present a high-resolution carbon isotope chemostratigraphic record to provide an independent assessment of correlation to other successions worldwide. Facies analysis indicates that Kahar siliciclastic sediments accumulated in fluvial to tidal environments, with thin microbial carbonates in tidally influenced facies. The overlying Soltanieh Formation records peritidal carbonate deposition followed by significant deepening and deposition of interlaminated mudstones and thin sandstones. δ13C values for Kahar carbonates, with a maximum age of about 550 Ma, lie within a narrow range of 0 to −2‰, save for a moderate positive excursion near the top of the formation. Above this, carbonates of the Lower Dolomite Member, Soltanieh Formation, show consistently negative δ13C values. The overlying Middle Dolomite, Middle Shale and basal part of the Upper Dolomite members feature high amplitude δ13C variations, which rise to values as high as 4‰ towards the top. Considering the integrated chemostratigraphic and paleontological records, Chopoghlu deposition appears to have begun during the late Ediacaran Period. The stratigraphically variable δ13C record of Soltanieh carbonates closely resembles lowermost Cambrian successions elsewhere, supporting placement of the E-C boundary near the top of the Lower Dolomite Member (LDM) and a Terreneuvian age for overlying Soltanieh beds. This is consistent with the presence of Protohertzina sp. and Hyolithellus sp. in or just above uppermost LDM carbonates and the lowermost occurrence of Treptichnus pedum above this. Together, bio- and chemostratigraphy help to integrate the Chopoghlu section into the global record of biospheric change as the Phanerozoic Eon began.

Generation potential, distribution area and maturity of the Barents-Kara Sea source rocks

Identification of the source rock potential and distribution area is the most important stage of the basin analysis and oil, and gas reserves assessment. Based on analysis of the large geochemical and geological data base of the Petroleum geology department of the Lomonosov Moscow State University and integration of different-scale information (pyrolysis results and regional palaeogeographic maps), generation potential, distribution area and maturity of the main source rock intervals of the Barents-Kara Sea shelf are reconstructed. These source rocks wide distribute on the Barents-Kara Sea shelf and are characterized by lateral variability of generation potential and type of organic matter depending on paleogeography. During regional transgressions in Late Devonian, Early Permian, Middle Triassic and Late Jurassic, deposited source rocks with marine organic matter and excellent generation potential. However in the regression periods, during the short-term transgressions, formed Lower Carboniferous, Upper Permian, Induan, Olenekian and Late Triassic source rocks with mixed and terrestrial organic matter and good potential. Upper Devonian shales contain up to 20.6% (average – 3%) of marine organic matter, have an excellent potential and is predicted on the Eastern-Barents megabasin. Upper Devonian source rocks are in the oil window on the steps, platforms and monoclines, while are overmature in the basins. Lower Permian shale-carbonate source rock is enriched with marine organic matter (up to 4%, average – 1.4%) and has a good end excellent potential. Lower Permian source rocks distribute over the entire Barents shelf and also in the North-Kara basin (Akhmatov Fm). These rocks enter the gas window in the Barents Sea shelf, the oil window on the highs and platforms and are immature in the North-Kara basin. Middle Triassic shales contain up to 11.2% of organic matter, there is a significant lateral variability of the features: an excellent generation potential and marine organic matter on the western Barents Sea and poor potential and terrestrial organic matter in the eastern Barents Sea. Middle Triassic source rocks are in the oil window; in the depocenters it generates gas. Upper Jurassic black shales are enriched with marine and mixed organic matter (up to 27,9%, average – 7.3%) and have an excellent potential. On the most Barents-Kara Sea shelf, Upper Jurassic source rock are immature, but are in the oil window in the South-Kara basin and in the deepest parts of the Barents Sea shelf.

Architectural analysis of an Early Cambrian braided-river system on the north Gondwana margin: The lower sandstone of the Lalun Formation in the Shirgesht area, central Iran

The Lalun Formation (Early Cimmerian), up to 867 m thick, was studied in the Shirgesht area, Central Iran. It was laid down across the northern edge of Gondwana, where fluvial sandstones were covered by marine shales, carbonates and sandstones. The Lower Sandstone unit of the formation is dominated by sand-rich braided river deposits (97%) with a general scarcity of fine-grained deposits (3%), and the unit consists nine lithofacies (Se, Spb, Sm, Sp, St, Sh, Sr, Fl and Fm). Common sedimentary structures in the succession include planar and trough cross-bedded, plane-laminated and ripple cross-laminated sandstone, and mudcracks in laminated and structureless mudstone. Architectural elements are defined as channel forms and fills (CHs and CHm), sheet sandstone bodies (SB, DA, and LS) and mudstone bodies (FF). The Early Cambrian fluvial system was operating in a non-vegetated setting, and it is probable that the major flooding of the system took place on a seasonal basis. Six orders of surfaces are identified in the outcrops. The highest order surface (sixth-order) includes the lower contact of the Lalun Formation (Lower Sandstone), which was laid down on the Zaigun Formation, and the upper contact of the Lower Sandstone with estuarine deposits of the Middle Shale, denoting a marine transgression. The paleoflow direction is consistent with the reconstructed position of the Lalun Formation during the Cambrian and indicates that sediment was transported eastward to northeastward in the northern part of the Gondwana margin. The petrographic analysis suggests craton interior and transitional continental sources under seasonal humid conditions, consistent with the reconstructed position of Iran along the northeast margin of the Arabian Shield.

Ammonoids and nautiloids from the earliest Spathian Paris Biota and other early Spathian localities in southeastern Idaho, USA

Intensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval beds within the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoid and nautiloid assemblages. These new occurrences overall indicate that the lower boundary of the Tirolites beds, classically used as a regional marker for the base of the early Spathian, and therefore the regional Smithian/Spathian boundary, must be shifted downward into the Lower Shale unit and coeval beds. Regarding ammonoids, one new genus (Caribouceras) and two new species (Cariboucerasslugense and Albanitesamericanus) are described. In addition, the regional temporal distribution of Bajarunia, Tirolites, Columbites, and Coscaites is refined, based on a fourth sampled site containing a newly reported occurrence of the early Spathian Columbites fauna in coeval beds of the Middle Shale unit. As a complement to ammonoids, changes observed in nautiloid dominance are also shown to facilitate correlation with high-latitude basins such as Siberia during this short time interval, and they also highlight the major successive environmental fluctuations that took place during the late Smithian–early Spathian transition.

The Early Ordovician Middle Shale Member (Am3) of the Amdeh Formation and further evidence of conodont faunas from the Sultanate of Oman

AbstractThe Middle Shale Member of the Amdeh Formation is interpreted to be of Early Ordovician age based on its trace fossils, stratigraphic context and a newly discovered fauna of conodonts. The member abruptly overlies the Lower Quartzite Member, which may be Early Cambrian, and passes gradationally-upward into the Upper Quartzite Member, which is probably Early–Middle Ordovician. The 542.5 m thick Middle Shale Member can be divided into two parts: a shaly lower part, and a sandy upper part that contains an influx of heavy minerals. Bioturbation by marine trace fossils is one of the most obvious characteristics of the member. The shales and sandstones are interpreted to be ofCruzianaandSkolithosichnofacies and represent shallow-marine shelf, shoreface, beach and coastal deposits. Sparse shelly fossils occur in the sandy upper part, principally bivalves, inarticulate brachiopods, ostracods and conodonts. The small assemblage of conodonts includes elements interpreted to be Tremadocian (Tetraprioniodus,Drepanoistodus,Drepanodus,Scolopodus, ?Tropodus,SemiacontiodusandTeridontus), and others which may be Floian or ancestral forms of Floian taxa (Balognathidae gen. et sp. indet. A & B and aff.Erraticodon). No acritarchs have been recovered, probably due to high temperatures experienced during burial to >6 km. It is likely that the Middle Shale Member is the seaward equivalent of the Mabrouk and Barakat formations, and an outcrop gamma-ray log supports such a correlation. The trace fossils, sedimentology, conodont fauna and the general lack of macrofossils are in keeping with the regional Tremadocian–Floian of the Arabian margin of Gondwana.

Devonian shallow marine ostracods from central Japan

AbstractThirteen ostracod species including two new species, Clavofabellina fukujiensis n. sp. and Bythocypris wangi n. sp., are reported from the Middle Shale Member of the Fukuji Formation, Devonian of central Japan. The ostracods demonstrate species‐links with South China, indicating that the Hida‐Gaien Terrane of central Japan shared biogeographical affinities with the shallow marine faunas of the South China paleocontinent during the Early Devonian.

Geochemical and organic petrological study of bituminous sediments from Dahomey Basin, SW Nigeria

Abstract The Dahomey Basin, SW Nigeria, hosts a 3000-m-thick sedimentary succession of Cretaceous and Cenozoic age, of which the Turonian-Maastrichtian Afowo Formation includes sandstones, arkoses, shales, shelly limestones, unconsolidated sand, clay and most importantly, bituminous (tar) sand strata. Eighteen samples were picked up from outcrops exposed by streams and channels, and were examined applying sedimentological, mineralogical, petrographical, geochemical (inorganic and organic) and radiological techniques with the aim of assessing the origin and the thermal maturity of the organic facies. The samples represent mostly coarse-grained sands and subordinately shales, referred usually as ‘tar sands’; they consist of mainly quartz and kaolinite, with variable amounts of mixed clay layers of illite-montmorillonite, mica and pyrite, probably derived from weathering of the Migmatite Gneiss Complex exposed to the north of the basin; this can also explain the relative enrichment in the natural radionuclides 40K, 238U, 226Ra and 232Th for some samples, although the radioactivity falls within the range for world values for soils. The clastic material of Afowo Formation was deposited in a rather oxic shallow marine environment. The particulate organic matter of the bituminous sediments comprises solid hydrocarbons, coalified (huminite) and partially oxidized (inertinite) remnants of terrestrial plants, and minor amounts of both terrestrial and marine liptinite macerals. The random reflectance values of the indigenous huminite population ranges between 0.40 and 0.45% pointing to an immature stage for oil generation. The respective reflectance of the migrabitumens ranges from 0.49 to 0.59% corresponding to vitrinite equivalent reflectance values of 0.70–0.76% falling well within the oil window. This study concludes that the hydrocarbons contained in the Afowo Formation are upwards migrating from parts of the basin where Afowo Formation has subsided at depths corresponding well within the oil window; the source rock corresponds to the middle shale horizon, whereas the sandy horizons act as migration paths and/or reservoirs.

Multistage dolomitization in the Qal'eh Dokhtar Formation (Middle‐Upper Jurassic), Central Iran: petrographic and geochemical evidence

The late Jurassic Qal'eh Dokhtar Formation lithologically comprises three parts, from bottom to top, a lower sandstone unit, middle shale unit and an upper carbonate unit, which extend in a N–S direction over a wide area to the east of the Shotori Range and west of the Lut Block (Central Iran). This succession was deposited on a mixed carbonate–siliciclastic ramp. Carbonate rocks of the Qal'eh Dokhtar Formation vary from undolomitized, to partly dolomitized, to completely dolomitized. Field observations from two measured sections (the type section, 955 m thick, and the Sorond section, 639 m thick), combined with detailed petrographic and geochemical analyses, revealed the diverse types of dolomite in this formation. Five types of replacement dolomite and one type of dolomite cement were distinguished. Replacement dolomites (RD) consist of: (1) fine crystalline planar‐s (RD1); (2) medium crystalline planar‐s (RD2); (3) medium crystalline planar‐e (RD3); (4) coarse crystalline planar‐s (RD4); and (5) coarse crystalline planar‐e (RD5). Coarse crystalline planar dolomite cements (DC) were observed in low abundance and filling dissolution voids and fractures. Variation in dolomite types is mainly related to early to late diagenetic processes leading to changes in composition of the dolomitizing fluids. Replacement dolomites are non‐stoichiometric (Ca43‐56–Mg34‐45) with Sr, Mn and Fe concentrations of 41–138 ppm, 168–919 ppm and 5000–21000 ppm, respectively. These dolomites are characterized by δ18O values ranging from 0.0 to –11.8 ‰ VPDB and δ13C values of +1.1 to +3.2 ‰ VPDB. These values are depleted in δ18O relative to the postulated values for late Jurassic dolomites precipitated in equilibrium with seawater, while δ13C values are within the range of Jurassic seawater dolomite values. Fluid inclusion data of RD4, RD5 and DC yield homogenization temperatures of 72 to 118 °C. Based on petrographic, fluid inclusion microthermometric data and geochemical results, the replacement dolomites in the Qal'eh Dokhtar Formation are interpreted to have formed in the subsurface at shallow to intermediate burial depths. These dolomites were then recrystallized at increased burial depths and temperatures. Seawater was the major source of Mg2+ for early diagenetic dolomite (DR1), while Mg2+ for late diagenetic dolomites was provided from diagenesis of clay minerals in shales and mechanical compaction of mudstone in the Qal'eh Dokhtar Formation. The dolomite cement is postdated by coarsely crystalline mosaic calcite cement indicating that diagenetic fluids eventually became undersaturated with respect to dolomite and oversaturated with respect to calcite. Copyright © 2016 John Wiley & Sons, Ltd.

Freshwater molluscan fauna from the Florissant Formation, Colorado: paleohydrologic reconstruction of a latest Eocene lake

The freshwater molluscan assemblage from the uppermost Eocene Florissant Formation (34.07 ± 0.10 Ma), Colorado, USA, provides a reliable proxy in reconstructing past ecology and environmental characteristics of ancient Lake Florissant. In particular, stable-isotope analyses of aragonitic shell material contribute to our understanding of the paleohydrologic history of this ancient lake. Re-examination of molluscan taxonomy in the middle shale and caprock conglomerate (informal) units produces three sphaeriid bivalves (family Sphaeriidae, genus Sphaerium) and two pulmonate gastropod genera (family Planorbidae, genus Gyraulus; and family Lymnaeidae, genus Lymnaea). The middle-shale assemblage, representing quiet-lake deposition, is dominated by pulmonate gastropods; the shell material in all specimens in this unit has been replaced by silica. The caprock conglomerate assemblage, representing redeposition by a debris flow, is dominated by bivalves; specimens within the caprock conglomerate unit are aragonite, interpreted to be biogenic (original). Carbon and oxygen isotope analyses of the aragonite show a strong covariance (all molluscan data: r = 0.83; sphaeriids: r = 0.76) with consistent grouping (δ13C: 0‰ to −5.5‰, δ18O: +2‰ to −5‰) from all families. This result indicates that ancient Lake Florissant was “closed” and that evaporation had a stronger effect on isotopic values than precipitation, for the duration of the sampled interval. This finding is in agreement with our current understanding of how the sediments of the Florissant Formation were deposited within a lake that formed because of a paleoriver being dammed by debris flows.

A comprehensive approach to sweet-spot mapping for hydraulic fracturing and CO2 huff-n-puff injection in Chattanooga shale formation

Devonian-Mississippian Chattanooga shale plays in North America are categorized as unconventional reserves with potential hydrocarbon resource accumulations. Unlike Chattanooga shale in the Appalachian region, less effort has been dedicated to its correspondent in the Ozark region. The ultra-tight nature of the formation causes fast decline of the production and small recovery factors. However, application of CO2 huff-n-puff can potentially improve the recovery of oil when the complex shale oil resource is fully understood. This would eventually lead to the development of a map which delineates sweet-spots. Therefore, the characterization of these reservoirs is an essential step to fully understand the associated complexities of the reservoir as well as to evaluate the economic viability of their exploitation. Thus this paper presents a fully integrated characterization at multiple scales (petrophysical, geophysical and geological evaluation, geomechanical and geochemical analysis) of the black shale sequence in Sumner County, Kansas. Multi-scale dataset for this regional characterization is obtained from laboratory measured petrophysical parameters, well-log measurements as well as seismic data. Therefore, this paper presents a comprehensive approach to reservoir characterization which would eventually lead to fully understanding the resource play as well as accurately identifying sweet spots for well placement and improved hydrocarbon recovery.Chattanooga shale in Sumner County has an average TOC of ∼2.26 wt. % in the middle shale member with additional organic porosity of 5% and a vitrinite reflectance (Ro %) of 0.62. It is classified as a shale oil resource with OOIP of 4 MMbbl. Petrophysical correlations developed at wellbore vicinity were trained with artificial neural networks (ANNs) and correlated with seismic to provide lateral distribution of such properties farther from the wellbore. Moreover, due to the heavy reliance of unconventional shale plays on fracture network for improved flow conditions, fracture models were developed based on the mineral-brittleness as well as the fracture toughness. Consequently, a complete study based on compositional numerical simulation was conducted to analyze the potential of CO2 as an EOR technique, together with an evaluation of the impact of reservoir and fracture parameters in the well productivity potential. Subsequently, an economic optimization process was also formulated to obtain the best gas injection design for the highest Net Present Value (NPV). The cumulative oil was notably observed to increase by the use of the optimum injection design. Moreover, the huff-n-puff injection of CO2 proved to be a viable option by increasing the final oil recovery from 10% to 53% of the OOIP in the SRV region using optimal parameters.

Optimization of Upper Burgan Reservoir Multilateral Well With Inflow-Control Device

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 175227, “Optimize Development Strategy of Upper Burgan Reservoir Through Multilateral Well With Inflow-Control Device in Raudhatain Field, North Kuwait,” by Sankar Chowdhuri, Peter Cameron, Tarek A. Gawwad, Mohammad R. Madar, Siddhartha Sankar Sharma, Moute’a Dughaim AlMutairi, Vijay Shankar Rajagopalan, Suresh Chellappan, and Moudi Fahad Al-Ajmi, Kuwait Oil Company, prepared for the 2015 SPE Kuwait Oil & Gas Show and Conference, Mishref, Kuwait, 11–14 October. The paper has not been peer reviewed. In coning situations, such as in the production of oil reservoirs with a bottom aquifer, multilateral wells reduce the coning effect and, hence, prove to be more cost-effective. This paper discusses the first multilateral well with a Level-4 junction combined with an inflow-control device (ICD) planned, designed, and drilled in the Upper Burgan reservoir of Raudhatain field, north Kuwait. The paper covers the main challenges of well placement during geosteering to ensure the best quality of reservoir rock in structurally and depositionally complex settings with smart-completion design. Introduction The Raudhatain oilfield structure is one of several developed along a prominent anticlinal ridge that plunges gently north of Kuwait. These individual highs, in which the principal oil accumulations of the area are localized, tend to be of large areal extent and substantial structural relief. The Raudhatain structure exhibits a quasiradial pattern of small normal faults of limited throw. This geometry suggests a primary origin by uplift. The Raudhatain structure is a faulted anticlinal dome with 65 to 90 ft of topographical relief. The 3D seismic has defined the major faulting in the northern part of Raudhatain as northwest trending, whereas in the southwestern part of the field the faults trend northwest. Fault throws are highly variable and range from less than 30 ft to as much as 150 ft. Stratigraphy of Upper Burgan Reservoir The Burgan formation is a major reservoir unit. It unconformably overlies the carbonate Shuaiba formation and underlies the Mauddud carbonates with locally unconformable contact. The thickness of Burgan is approximately 950 ft of soft, clean, porous, well-sorted quartz sandstones of littoral to possibly deltaic aspect, interbedded with siltstones and dark shales. The Burgan formation at Raudhatain has been divided informally into three members, termed the Upper Sand, Middle Shale, and Lower Sand.

Source and Reservoir Rock Potential of Tertiary Units in the Kozaklı Basin, Central Anatolia, Turkey

The authors present the hydrocarbon source rock potential and reservoir properties of the Eocene Formations in the Central Anatolian Kozaklı Basin. Potential source and reservoir rocks in the Kozaklı basin include transgressive-regressive bank carbonates, fore-bank, deep-marine shales and sandstones, and coal and bituminous facies. The organic geochemical data of the Middle Eocene shales (Sarılar Formation) show that inadequate to marginal source rock qualities, and marginally mature to overmature characteristics, resulting from heat flow regime of the studied area. Alemli Member of the İncik Formation is good to excellent according to TOC wt% and immature to mature source rock from Tmax values. Sedimentological features and age data indicate that the Uzunlu Formation was deposited under the control of antecedent topography. Reservoir properties of the Uzunlu Formation and Keklicek member indicate that the carbonate unit is not adequate for reservoir rock. However, siliciclastics of the Sarılar Formation could be reservoir potential due to its high porosity and permeability values.

Cambrian Trace Fossil Zoophycos from the Czech Republic

Abstract Lobate and helical ichnofossils attributable to Zoophycos found in Middle Cambrian shales of the Palác Hill in the Železné Hory Mountains (eastern Bohemia) represent the oldest occurrence of this ichnogenus. Such a complex Zoophycos became frequent during the Mesozoic but has been never recorded in strata older than the Ordovician. As such, they represent the oldest occurrence of helical Zoophycos. Besides Zoophycos isp. there is also a 15 cm thick sandy siltstone layer which is strongly bioturbated by Planolites isp., which seems unusual in a Lower Cambrian ichno-association.

Taphonomy of Anomalocaris from Middle Cambrian Shales of the Southwestern United States

Taphonomy of <i>Anomalocaris</i> from Middle Cambrian Shales of the Southwestern United States

A New Snakefly from the Eocene Green River Formation (Raphidioptera: Raphidiidae)

Agulla protomaculata, new species (Raphidiidae: Raphidiinae), is described and figured from a series of males and females preserved as fine compressions in middle Eocene shale from the Green River Formation of Colorado. The specimens are exquisitely preserved, complete with integumental color patterns. The species is compared with other Tertiary snakeflies.