Hummocky Cross-stratified Sandstone Research Articles

Facies and stratigraphy of the basal Ediacaran cap carbonate, Naukluft Mountains, Namibia

The termination of the Marinoan Snowball Earth glaciation constitutes a dramatic interval of climate change. This field study seeks to investigate this climate transition by characterizing the basal-Ediacaran cap carbonate succession of the Tsabisis Formation overlying the Blässkranz Formation glacial deposits exposed in the Naukluft Mountains of Namibia by using sedimentologic and stratigraphic field observations supplemented by chemostratigraphic analyses. Measured sections and lateral bed/unit tracing delineate stratigraphic stacking patterns and regional facies changes. In downdip areas Marinoan diamictite transitions upward into dolostone intermixed with sandstone and extrabasinal clasts that is gradually overlain by fine grained laminated dolostone. Updip localities show the diamictite is overlain by intercalated sandstones, gravels, and shales before an abrupt change to laminated dolostone of the cap carbonate. A succession of stromatolites, which become strongly elongate upward, prograde into the laminated dolostone in the updip localities. The stromatolites are overlain by laminated dolostone that grades upward into rhythmite with intercalations of shale. Near the top of the cap, rhythmites may be reworked into tabular intraclast conglomerate, locally intercalated with hummocky cross stratified sandstone, which passes upward into the shale and limestone members of the Tsabisis Formation. The Tsabisis Formation is overlain by the Noab Formation, dominated by sedimentary breccia, laminated dolostone, and sandstone. The lateral and vertical distribution of facies indicate a retreat of the shoreline and glacially sourced siliciclastics near the base of the cap carbonate, a shallowing succession to fair-weather wave base at the top of the stromatolite facies, and a second shallowing succession to storm wave base near the top of the cap carbonate. Maximum flooding occurred soon after the initiation of carbonate deposition and two sequence boundaries mark higher stratigraphic levels within the cap carbonate. The depositional patterns of the Tsabisis Formation cap carbonate resemble that of other Precambrian mixed carbonate-siliciclastic platforms and shows multiple base-level fluctuations that could be attributed to a range of mechanisms. Some of the base-level changes may have been directly coupled to events driven by deglaciation but distinguishing these from conventional controls on accommodation space in the rock record is challenging and multiple depositional models are feasible.

3D geo-cellular static virtual outcrop model and its implications for reservoir petro-physical characteristics and heterogeneities

Geostatistical data plays a vibrant role for surface-based reservoir modeling through outcrop analogues, which is used to understand three-dimensional (3D) variability of petrophysical properties. The main purpose of this study is to improvise the surface-based 3D geo-modeling to demonstrate petrophysical characteristics and heterogeneities of Sandakan reservoirs, NW Borneo. We used point cloud data from Light Detection and Ranging (LiDAR) to build high-resolution virtual outcrop modeling (VOM) onto which we mapped 6 different lithofacies. Porosity and permeability of core plugs were measured to determine the average variance of petrophysical properties for each lithofacies. By utilizing the integration of VOMs analogues and petrophysical properties in Petrel™, we demonstrated the distribution and associations of all lithofacies in pseudo wells that have inherent thin beds heterogeneities in 3D geo-cellular model. The results concluded that the heterogeneity of thin beds in lithofacies is dependent on porosity and permeability with input dataset. According to the final model, cross-bedding sandstone (CBS), hummocky cross-stratified sandstone (HCSS) and trough cross-bedding sandstone (TCBS) show good reservoir quality due to high porosity ranging from: 25.6% to 20.4% and, 19.3%–14.5%, and permeability ranging from: 74.03 mD to 66.84 mD and, 64.86 mD to 21.01 mD. In contrast, massive to weak laminae sandstone (MWLS) and bioturbated sandstone (BS) show fair to poor reservoir quality, caused baffling of surrounding mud sediments in the reservoir lithofacies. Results also revealed that LiDAR based VOM with petrophysical properties can significantly reduce the risk and minimize the cost of reservoir modeling in petroleum industry.

Reservoir characterization of fairways in a tight light oil play of the Upper Cretaceous Cardium Formation, west Pembina, Alberta, Canada

Shallow-marine reservoirs of the Upper Cretaceous Cardium Formation contain one of the largest light oil accumulations in Canada, which have been exploited since the 1950s. Since 2008, multistage fractured horizontal wells have revived this play. This study presents a reservoir characterization of the offshore to shoreface unconventional reservoirs of the Cardium Formation in the halo play along the western margin of the legacy Pembina oil pool in central Alberta. Although permeability of these facies is too low to achieve economic production from vertical wells, they were the main carrier beds forming the migration pathway for charging the updip conventional reservoirs in the Pembina field. Three reservoir facies are present in the west Pembina study area: bioturbated muddy sandstones, interbedded sandstones and mudstones, and hummocky cross-stratified sandstones. Shoreface sandstones are relatively thin in the halo play area; thus, significant production in the horizontal wells is attributed to the thin sandstone beds and bioturbated muddy sandstone reservoir facies. To characterize these unconventional, heterogenous reservoirs, traditional reservoir evaluation techniques are integrated with computerized tomography scanning to better evaluate reservoir properties and flow pathways. Cutoffs of 90 gamma-ray API units, 6% porosity, and 0.075-md permeability were used to create a series of reservoir property maps. These detailed maps show the most prospective area of the halo play is a 4-km (2.5-mi)-wide zone immediately to the west of the legacy west Pembina Pool boundary. This lateral heterogeneity with narrow sweet spot fairways explains the significant production variability in these shallow-marine reservoirs.

Sedimentology, petrography, and deposition of the Upper Cretaceous Codell Sandstone in the Denver Basin

We integrate new and previous stratigraphic and petrographic data for the mid-Turonian Codell Sandstone to interpret its provenance, depositional characteristics, and environments. Our focus is on sedimentologic, X-ray diffraction, and X-ray fluorescence analyses of cores and thin sections spread throughout the Denver Basin, augmented by interpretation and correlation of well logs, isopach maps, outcrops, and provenance data. Although we treat the Codell as a single mappable unit, it actually consists of two geographically disjunct sandstone packages separated by a southwest-northeast-trending gap, the NoCoZo, short for No Codell Zone. The Codell is everywhere capped by a significant unconformity and across much of the northern Denver Basin rests unconformably on the underlying shales of the Carlile Shale. In the southern Denver Basin, the Codell commonly contains two parasequences, each of which becomes less muddy upward. Biostratigraphic and geochonologic data suggest that the unit represents deposition over a relatively brief time, spanning ~0.4 Ma from ~91.7 to ~91.3 Ma. The Codell is predominantly a thin (<50 ft) sheet-like package of pervasively bioturbated coarse siltstone and very fine-grained sandstone dominated by quartz and chert grains 50 to 100 μm in diameter. The unit is more phosphatic than the underlying members of the Carlile Shale, and its grain size coarsens to medium-grained in the northern part of the basin. An unusual aspect of the Codell across our study area is the generally excellent grain sorting despite the presence of an intermixed clay matrix. This duality of well sorted grains in a detrital clay matrix is due to the bioturbation that dominates the unit. Such burrowing created a textural inversion that obscures most of the unit’s primary sedimentary structures, except for thin intervals dominated by interlaminated silty shale and very fine sandstone. A relatively widespread and unburrowed example of this bedded facies is preserved in a thin (<10 ft) interval that extends across most of the northern Denver Basin where it is informally called the middle Codell bedded to laminated lithofacies. Sparse beds with hummocky or swaley cross-stratified and ripple cross-laminated fine-grained sandstone are present locally in this bedded facies. We hypothesize that Codell sediments were derived from a major deltaic source extending into the Western Interior Seaway from northwestern Wyoming, and that the Codell was deposited and reworked southward on the relatively flat floor of the Seaway by waxing and waning shelf currents as well as storms and waves. Codell sediments were spread across an area of more than 100,000 mi2 in this epeiric shelf system that spans eastern Colorado, southeastern Wyoming, western Kansas, parts of Nebraska and beyond.

Timing of Bellerophontoid (Gastropoda) Demise in the Early Triassic of South Primorye, Russian Far East

The stratigraphic distribution and modes of occurrence of Early Triassic Bellerophontoidea (Gastropoda) are studied at seven sections in South Primorye, Russian Far East, where depositional environments ranging from nonmarine, shoreface, to distal basin plain settings are recorded. Warthia zakharovi and Dicellonema abrekensis are abundant in Induan (Griesbachian and Dienerian) fine- to medium-grained, hummocky cross-stratified (HCS) sandstone beds occasionally intercalated with wavy-mudstone layers, whereas they are absent in coarser-grained cross-stratified successions. This observation suggests that bellerophontoids inhabited a lower shoreface environment above the storm wave base and possibly an inner shelf environment as well during this particular stage. Olenekian (Smithian and Spathian) bellerophontoids have not been found in the storm-induced sandstone beds, but W. zakharovi occurs in the lower Smithian sandstone beds of distal turbidites intercalated in the laminated mudstone. This mode of occurrence strongly suggests that W. zakharovi inhabited a deeper environment than lower shoreface, most probably an inner shelf environment, and after death, its shells were transported from their habitat to the basin-floor by sediment gravity flow. Bellerophontoids have not been found in middle Smithian and younger strata in South Primorye, and the timing of this disappearance is synchronous with other areas of the world. Bellerophontoids were distributed over wide-ranging areas from the equator to the high latitudes during Induan time, but they disappeared from the lower latitude areas and the shallower marine environments of middle latitude South Primorye during the early Smithian, before eventually becoming extinct during middle Smithian time. Such a step-by-step demise strongly implies that the severe global warming and related harmful events that occurred during the Smithian may have had a serious effect on bellerophontoids. The extinction of Bellerophontoidea before the beginning of the late Smithian suggests that the group may have been more sensitive to global warming and related harmful events than other organisms.

Lithofacies characteristics and depositional environment interpretations of the Middle Jurassic Fort Member rocks, Jaisalmer Formation, Western Rajasthan, India

The present study is focused on the identification of lithofacies characteristics and depositional environments for the Middle Jurassic sediments of Fort Member, Jaisalmer Formation, Western Rajasthan (NW India). Three facies associations are documented as tidally influenced fluvial, tidal/inter-tidal flat and wave-dominated shoreface facies deposits. Facies association-1 contains matrix-supported clasts, planar and flaser cross-stratified sandstone, interbedded sandstone and horizontal laminated sandstones; indicative of tidally influenced fluvial deposits. Facies association-2 characterized by herringbone cross-stratified sandstones, horizontal laminated sandstones, planar and trough cross-stratified sandstones, the alternate band of sandstone and shale, mud-crack sandstone developed on a tidal/inter tidally influence deposits. Facies association-3 consists of wave-dominated shoreface facies association consisting of wavy and lenticular beds, interference ripples, horizontal laminated sandstone, small scale planar cross-stratified sandstone, trough, and hummocky cross-stratified sandstone as well as fossiliferous limestone. Palaeoflow patterns from unipolar to bipolar indicate a change from tidal influence fluvial to marine depositional environments. The overall lateral and vertical distribution of lithofacies shows that the depositional environment was tidal-dominated fluvial channel to the marine realm.

Gyrophyllites cristinae isp. nov. from Lower Ordovician Shallow-Marine Deposits of Northwest Argentina

The lower Paleozoic marine siliciclastic succession of the Central Andean Basin, northwestern Argentina, provides a valuable record of the onset of the Great Ordovician Biodiversification Event in western Gondwana. A new ichnospecies of rosette trace fossil, Gyrophyllites cristinae, is documented from lower and upper Tremadocian (Tr1 and Tr2) deposits of this basin. It is characterized by five to six non-overlapping petaloid lobes and can be easily differentiated from the other four formally defined ichnospecies. Gyrophyllites cristinae occurs at the top of hummocky cross-stratified sandstone regularly interbedded with mudstone. These deposits are interpreted as reflecting the alternation of high-energy storm events and low-energy fair-weather conditions immediately below the fair-weather wave base, representing deposition in offshore transition environments. Gyrophyllites has been traditionally interpreted as the product of worms of uncertain taxonomic affinity that mined the sediment in search for food (fodinichnia). The occurrence of Gyrophyllites cristinae in these Ordovician deposits records post-storm colonization. Storms may have increased oxygenation and supplied fresh organic detritus that were exploited by worm-like, surface detritus- or shallow deposit-feeders exploring the uppermost silt-rich fine-grained sediments.

Sedimentology and oceanography of Early Ordovician ironstone, Bell Island, Newfoundland: Ferruginous seawater and upwelling in the Rheic Ocean

The Bell Island and Wabana groups together comprise a ca. 150-m-thick succession of interbedded clastic and chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin of the Rheic Ocean. Lithofacies stacking patterns indicate that deposition occurred during a marine transgression with superimposed small-scale sea level fluctuations producing at least six parasequences. Parasequences containing ironstone are 10 to 20-m-thick and composed of hummocky cross-stratified sandstone interbedded with organic-rich mudstone and phosphatic Fe-silicate-bearing siltstone, which is overlain by hematitic granular ironstone capped by an erosive flooding surface.This lithofacies association is interpreted to record the deposition of upwelling-related ironstone on a storm-dominated shelf. The close relationship between Fe-silicates and phosphorite typical of upwelling systems suggests that Fe was delivered from deep, anoxic, nutrient-rich seawater that also stimulated high surface productivities. The result was the precipitation of authigenic sedimentary apatite in anoxic organic-rich sediments that accumulated near the upwelling front. The gradual advection of Fe-rich waters away from the upwelling front, initiated precipitation of Fe-silicate coated grains and cements in suboxic pore-waters. Iron pumped into shallower environments through advection and Fe-redox cycling is interpreted to have precipitated Fe-(oxyhydr)oxide grains in sediment of the oxygenated middle shelf. These coated grains were subsequently concentrated by fairweather and storm currents on the shoreface to create granular economic Fe deposits.We challenge conventional models of Paleozoic ironstone deposition that rely on a continental source of Fe by proposing a hydrothermal source that supplied Fe2+ to the shelf through upwelling. It also highlights the potential connection between the delivery of anoxic, ferruginous seawater to the margins of the Rheic Ocean and the Early Ordovician extinctions that punctuated the beginning of the Great Ordovician Biodiversification Event.

Amazon fluid mud impact on tide- and wave-dominated Pliocene lobes of the Orinoco Delta

The modern Orinoco Delta is a major sink for the world's largest alongshore (littoral) mud dispersal system; it receives some 108 tons/yr from the Amazon river delta. The influence of these huge volumes of Amazon mud on the paleo-Orinoco Delta succession is now investigated for the first time. Abundant fluid-mud deposits are preserved in outcrops from the Pliocene Orinoco Delta deposits (Lower Morne L'Enfer, Manzanilla and Mayaro formations on Trinidad) with different styles in tide-dominated, in tide-dominated and wave-influenced, and in storm wave-dominated delta lobes. Fluid-mud deposits in sandy parasequences (10–20 m thick) of the Lower Morne L'Enfer Formation change from thin layers amalgamating to form mud bedsets (up to 4 cm) or draping across ripple laminae in the lower part, to thick layers (up to 10 cm) occasionally with deformed and load structures at their top, in the upper part. The Manzanilla Formation parasequences (30–40 m thick) exhibit coarsening-to-fining-upward (CUFU) facies successions with fluid-mud deposits located mainly in the middle to upper parts of the parasequences, near the transition between the CU and FU parts of the units. Most of the fluid-mud layers are interbedded with bi-directional, current rippled-sandstones, whereas minor mud layers are associated with erosion-based sandstones with small-scale swaley strata and bi-directional symmetrical ripples. The Mayaro Formation parasequences (5–15 m thick) are characterized by alternating fluid-mud intervals and sets of hummocky cross-stratified sandstones (HCS) passing upward into amalgamated swaley cross-stratified (SCS) sandstones. The fluid-mud intervals have flat or irregular tops occasionally overlain by amalgamated SCS sandstones with fluid-mud clasts.Very thick (1–1.5 m) fluid-mud intervals occur in places in both tide- and wave-dominated strata and these are probably large muddy bedforms similar to mud banks that migrate currently along the modern Amazon-Orinoco coast. The outcrop analysis strongly suggests that the fluid-mud banks, as they approached the Orinoco delta-front area, were handled differently depending on whether the delta-front lobes were wave- or tide-dominated. Tide-dominated delta lobes tended to trap the muds near the shoreline and on the subaqueous delta-front platform in water depth < 10 m with only minor volumes escaping offshore. In contrast, storm wave-dominated delta lobes had a more dynamic impact on the approaching mudbanks. Mud accumulated in the shallow water tend to be eroded and re-deposited into deeper water near the storm wave base (15–50 m water depth).The volumes of Pliocene Amazon mud transported along the innermost shelf and arriving on the Orinoco Delta were likely influenced by high-amplitude, Pliocene glacio-eustatic sea level fluctuations. During sea-level fall and lowstand periods, increased volumes of Amazon mud would have bypassed to the deep water and thus decreased mud volumes drifted and became incorporated in the Orinoco delta front. In contrast, sea-level rise and highstand periods would have promoted increased volumes of Amazon mud both on the shelf and onto the Orinoco, similar to the Holocene and modern muddy system.

Oligocene storm-induced lacustrine deposits in the Yaxi Area of the Jiuxi Basin, northeastern margin of the Tibetan Plateau

Storm-induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow. Thin-bedded sandstone, siltstone, and interlayered mudstone deposits of the Oligocene Jianquanzi Member in the Yaxi Area of the Jiuxi Basin along the northeastern margin of the Tibetan Plateau were formed by shallow lacustrine storm-generated flows. Petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub-mature to immature. Based on investigation of drill cores, six storm-deposit lithofacies are identified, including massive or graded sandstone, parallel and trough cross-bedded sandstones, hummocky cross-stratified sandstone, wave-rippled sandstone and siltstone, massive or horizontal bedded mudstone, and structurally deformed sandstone and mudstone. In a vertical succession, these lithofacies occur as three fining-upward lithofacies associations, each of which represents different architectural elements (and depositional processes) of proximal to distal storm deposits. The relatively coarse proximal architectural element is formed by strong density flows and unidirectional-dominated combined flows; the transitional architectural element is dominated by unidirectional- and oscillatory-dominated combined flows to pure oscillatory flows, resembling Tb-e divisions of the classic Bouma sequence; the relatively fine distal architectural element is dominated by unidirectional-dominated combined flows with a very weak oscillatory flow component. The origin of storms responsible for these deposits is attributed to Asian winter monsoons associated with the paleoclimatic and paleogeographic setting.

Facies Distribution and Petrophysical Properties of Shoreface-Offshore Transition Environment in Sandakan Formation, NE Sabah Basin

Newly exposed outcrop of Miocene shallow marine sandstone in Sandakan Formation, allows characterization of the facies distribution and petrophysical properties of shoreface to offshore transition environment. Six facies are defined: (1) Poorly bioturbated Hummocky Cross Stratified (HCS) sandstone (F1), (2) Moderately bioturbated HCS sandstone (F2), (3) Well bioturbated HCS sandstone (F3), (4) Poorly bioturbated Swaley Cross Stratified (SCS) sandstone (F4), (5) Interbedded HCS sandstone with sand-silt mudstone, (6) Heterolithic mudstone. The sedimentary successions were deposited in upper to lower shoreface, and offshore transition environment. Facies F3, F4 and F5 shows good reservoir quality with good porosity and fair permeability values from 20% to 21% and 14 mD to 33 mD respectively. While Facies F1 exhibits poor reservoir quality with low permeability values 3.13 mD.

An ichnological-assemblage approach to reservoir heterogeneity assessment in bioturbated strata: Insights from the Lower Cretaceous Viking Formation, Alberta, Canada

Facies-scale trends in porosity and permeability are commonly mapped for reservoir models and flow simulation; however, these trends are too broad to capture bed and bed-set heterogeneity, and there is a need to up-scale detailed, bed-scale observations, especially in low-permeability reservoir intervals. Here we utilize sedimentology and ichnology at the bed- and bedset-scale to constrain the range of porosity and permeability that can be expected within facies of the Lower Cretaceous Viking Formation of south-central, Alberta, Canada.Three main facies were recognized, representing deposition from the middle shoreface to the upper offshore. Amalgamated, hummocky cross-stratified sandstone facies (Facies SHCS) consist of alternations between intensely bioturbated beds and sparsely bioturbated/laminated beds. Trace fossil assemblages in bioturbated beds of Facies SHCS are attributable to the archetypal Skolithos Ichnofacies, and are morphologically characterized by vertical, sand-filled shafts (VSS). Bioturbated beds show poor reservoir properties (max: 10% porosity, mean: 85.1 mD) compared to laminated beds (max 20% porosity, mean: 186 mD). Bioturbated muddy sandstone facies (Facies SB) represent trace fossil assemblages primarily attributable to the proximal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur in varying proportions, namely sediment-churning assemblages (SC), horizontal sand-filled tube assemblages (HSF), VSS assemblages, and mud-filled, lined, or with spreiten (MLS) assemblages. Ichnological assemblages containing horizontal (max: 30% porosity, mean: 1.28 mD) or vertical sand-filled burrows (max: 10% porosity, mean: 2.2 mD) generally have better reservoir properties than laminated beds (max: 20% porosity, mean: 0.98 mD). Conversely, ichnological assemblages that consist of muddy trace fossils have lower porosity and permeability (max 10% porosity, mean: 0.89 mD). Highly bioturbated, sediment churned fabrics have only slightly higher porosity and permeability overall (max: 15% porosity, mean: 1.29 mD). Bioturbated sandy mudstone facies (Facies MB) contain ichnofossils representing an archetypal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur throughout Facies MB that are similar to Facies SB; SC, HSF, VSS, and MLS assemblages. The SC (max: 15% porosity, mean: 21.67 mD), HSF (max: 20% porosity, mean: 3.79 mD), and VSS (max: 25% porosity, mean: 7.35 mD) ichnological assemblages have similar or slightly lower values than the laminated beds (max: 20% porosity, mean: 10.7 mD). However, MLS assemblages have substantially lower reservoir quality (max: 10% porosity, mean: 0.66 mD).Our results indicate that the most likely occurrence of good reservoir characteristics in bioturbated strata exists in sand-filled ichnological assemblages. This is especially true within the muddy upper offshore to lower shoreface, where vertically-oriented trace fossils can interconnect otherwise hydraulically isolated laminated sandstone beds; this improves vertical fluid transmission. The results of this work largely corroborate previous findings about ichnological impacts on reservoir properties. Unlike previous studies, however, we demonstrate that the characteristics of the ichnological assemblage, such as burrow form and the nature of burrow fill, also play an important role in determining reservoir characteristics. It follows that not all bioturbated intervals (attributed to the same facies) should be treated equally. When upscaling bed-scale observations to the reservoir, a range of possible permeability-porosity values can be tested for model sensitivity and to help determine an appropriate representative elementary volume.

Fractures system within Qusaiba shale outcrop and its relationship to the lithological properties, Qasim area, Central Saudi Arabia

The basal Qusaiba hot shale member of Qalibah Formation is considered to be an important source rock in the Paleozoic petroleum system of Saudi Arabia and an exploration target for tight shale as one of the Unconventional resources of petroleum. This work has been carried out to understand the fractures network of Qusaiba shale member in outcrops located to the west of Qusayba' village in Al-Qasim area, Central Saudi Arabia. The main objective of this study is to understand the distribution of natural fractures over different lithological units. Description data sheets were used for the detailed lithological description of Qusaiba shale member on two outcrops. Spot-7 and Landsat ETM+ satellite images were used for lineament mapping and analyses on a regional scale in a GIS environment. Fractures characterization in outcrop-scale was conducted by using linear scanline method. Qusaiba shale member in the study area consists of 5 main lithofacies, divided based on their sedimentary structures and petrographical properties, from base to top in the outcrops, the lithofacies are; fissile shale, very fine-grained micaceous siltstone, bioturbated mudstone, very fine to fine-grained hummocky cross-stratified sandstone, and fine to medium-grained low/high angle cross-stratified sandstone lithofacies. Lineaments interpretation of the Spot-7 and Landsat ETM+ satellite images showed two major directions in the study area; 320° that could be related to Najd fault system and 20° that could be related to the extensional activities which took place after Amar collision. Fractures are much denser in the fissile shale and mudstone lithofacies than sandstones lithofacies, and average spacing is smaller in the fissile shale and mudstone lithofacies than sandstones lithofacies. Lineaments and large-scale fractures are Non-Stratabound fractures and they deal with the area as one big mechanical unit, but small-scale fractures are Stratabound fractures that propose different mechanical units within Qusaiba shale member in the study area. The fractures network in the study area has a wide range of properties related to fractures density, length, spacing, height, and termination degree. The conceptual multi-scale model divides the fractures in the study area into 4 orders depending on the available data that have been observed from satellite images and field. The multi-scale fractures model that was generated in this study could help to understand the distribution of stratigraphically controlled fractures when integrated with flow simulation models. Overall, this work could have a significant contribution to tight shale exploration plans in the subsurface by providing some knowledge about the fractures mechanical behavior of the lower part of Qusaiba shale member of Qalibah Formation.

Quadlateral Success Story in a Heavy-Oil Reservoir

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 180433, “Quadlateral Success Story in a Heavy-Oil Reservoir,” by E. Livingston, D. Lee, M. Werner, B. Tejo, K. Wibisono, and S. Redman, ConocoPhillips, and D. Callis and C. Bostick, Baker Hughes, prepared for the 2016 SPE Western Regional Meeting, Anchorage, 23–26 May. The paper has not been peer reviewed. This paper documents the success story of the first quadlateral completion for an Alaskan operator by use of stacked, rotatable, Technical Advancement for Multilaterals Level-3 junction systems. This well is also the first in the world in which the junction system is stacked more than twice in a single well. This quadlateral completion design is the product of targeting multiple formation layers from a single wellbore by use of openhole horizontals with slotted liners. The rotatable, multilateral junction system accommodates the increased number of laterals necessary for continued economic exploitation of the West Sak heavy oil reservoir. Introduction The West Sak in the Kuparuk River Unit Drillsite 1D area is a 300-ft-thick Upper Cretaceous shallow marine sequence comprising very-fine-grained single and amalgamated hummocky cross-stratified sandstone beds. The initial 1997 West Sak development drilling in this area consisted of all vertical producers. The thinner A4, A3, and A2 sands were targeted along with the D and B sands. These wells had fracpack completions for sand control and were supported by vertical water injectors. With the start of horizontal multilateral drilling in 2000, the focus shifted to the thicker D- and B-sand targets using sand-exclusion wire-wrapped screens. In 2004, the completion strategy changed from sand exclusion to sand management, for development to remain economically viable. The 1E and 1J projects used slotted liners and targeted the D, B, and, in some areas, the A sands from a single wellbore by use of dual- and trilateral completions.

Facies analysis of the Semanggol Formation, South Kedah, Malaysia: A possible Permian–Triassic boundary section

Although the Permian–Triassic Semanggol Formation is widely distributed in northwestern Peninsula Malaysia and is made of various lithofacies, its sedimentology and possible relation with the Permian–Triassic boundary (PTB) were not considered before. In this study, detailed facies analysis was conducted for two sections of the Semanggol Formation at the Bukit Kukus and Baling areas, South Kedah to clarify its sedimentology and relation to the PTB. Four facies from the Permian part of the Semanggol Formation that were identified at the Bukit Kukus section include laminated black mudstone, interbedded mudstone and sandstone, volcanogenic sediments, and bedded chert. In Baling area, the Triassic part of the formation is classified into three members. The lower member comprises of claystone and bedded chert facies, while the middle member is composed of sandstone and claystone interbeds (rhythmite). On the other hand, the upper member is grouped into two main units. The lower unit is mainly claystone and includes two facies: the varve-like laminated silt and clay and massive black claystone. The upper unit is composed of various sandstone lithofacies ranging from hummocky cross stratified (HCS) sandstone to thinly laminated sandstone to burrowed sandstone facies. The HCS sandstones occur as two units of fine-grained poorly sorted sandstone with clay lenses as flaser structure and are separated by a hard iron crust. They also show coarse grains of lag deposits at their bases. The laminated black mudstone at the lowermost part of the Semanggol Formation represents a reducing and quite conditions, which is most probably below the fairweather wave base in offshore environment that changed upwards into a fining upward sequence of tide environment. Abundance of chert beds in the volcanogenic sediments suggests the deposition of tuffs and volcanic ashes in deep marine setting which continues to form the Permian pelagic bedded chert and claystone. The bedded chert in the lower member of the Triassic section suggests its formation in deep marine conditions. The rhythmic sandstone and claystone interbeds of the middle member are suggestive for its formation as a distal fan of a turbidite sequence. Lithology and primary sedimentary structure of the upper member suggest its deposition in environments range from deep marine represented by the varve-like laminated silt and clay to subtidal environment corresponds to the massive black claystone to coastal environment represented by the hummocky sandstone units and reaches the maximum regression at the hiatus surface. Another cycle of transgression can be indicated from the second hummocky unit with transgressive lag deposits that develops to relatively deeper conditions as indicated from the formation of relatively thick laminated sandstone and bioturbated massive sandstone facies that represent tidal and subtidal environment, respectively. Late Permian lithological variation from the radiolarian chert into early Triassic claystone probably resulted from a decrease in productivity of radiolarians and might represent a PTB in the Semanggol Formation. Volcanogenic sediments in the studied section can be used as an evidence for volcanic activities at the end of the Permian, which is probably connected to the nearby volcanic ash layers in the eastern China, the ultimate cause of the PTB in this area. Black mudstone in the Permian part of the studied section may be interrelated to the Latest Permian Anoxia that started to build in the deep ocean well before the event on shallow shelves.

Ichnological characteristics and variability of Miocene deposits in the Cenozoic Niger Delta: Examples from cores in the Coastal Swamp and Offshore depobelts

This work examines ichnological attributes and variability of core samples from four wells (1–4) within the Coastal Swamp and shallow Offshore depobelts in the Niger Delta basin. The cores consist of facies interpreted as mainly shoreface deposits. These deposits are in successions and well-developed. The shoreface successions are divided up into a lower, middle and upper shoreface. The lower shoreface lies within fair weather wave base. The ichnofossils assemblages characteristically represent a diverse and abundant Cruziana ichnofacies. The middle shoreface contains swaly and lesser hummocky cross-stratified sandstones with an ichnofossil assemblage dominated by the Skolithos ichnofacies. The upper shoreface is dominated by planar and trough cross-beddings. Ichnofossils are fairly abundant and consist of deeply penetrating structures of the Skolithos ichnofacies. These facies reveal a wide range of variability, mostly limited to the lower and middle shoreface intervals. This variability appears to be determined by relative storm dominance and the episodic character of associated storm bed deposition. The successions are grouped into three: (1) high energy shorefaces consist entirely of stacked storm beds with moderate bioturbation, (2) moderate energy shorefaces comprises stacked laminated to burrowed intervals, recording recurrent erosive storm bed emplacement, followed by opportunistic colonization, and normally overprinted by resident fair-weather burrowing, and (3) low energy shorefaces ordinarily exhibit intense bioturbation with low preservation of storm beds. Discrimination between lower and middle shoreface deposits is mainly based on the resident fair-weather ichnofossil assemblage; under increased energy settings. In addition, based on storm intensity, relative water depth, storm frequency and shoreline character, the nature of coexistent lower and middle shoreface facies can differ significantly along strike. In some cases, the lower and middle shoreface differentiation was difficult.

Onshore Sandstone Facies Characteristics and Reservoir Quality of Nyalau Formation, Sarawak, East Malaysia: An Analogue to Subsurface Reservoir Quality Evaluation

Shallow marine sandstones are substantial hydrocarbon reservoirs located around the globe and in Southeast Asia. Understanding the internal characteristics, distribution, geometry and lateral extent of these sandstones are essential parts of successful exploration and production strategy. This study presents the first detailed work on reservoir sandstone facies including textural characteristics of shallow marine sandstones (well-exposed outcrops) of the Nyalau Formation (Oligocene–Middle Miocene), Bintulu area, Sarawak, East Malaysia. This formation is the onshore equivalent of the offshore cycles II and III. We examined five different major types of sandstone facies on the basis of sedimentological characteristics, grain size distribution, porosity (ϕ) and permeability (k). The analyzed sandstone facies are: (1) hummocky cross-stratified sandstones (ϕ = 32.07 %, k = 20.78 md; thickness from 1 to 2 m); (2) herringbone cross-bedded sandstones (ϕ = 31.31 %, k = 7.7 m; thickness from 1 to 10 m); (3) trough cross-bedded sandstones (ϕ = 35.80 %, k = 5.97 md; thickness from 0.5 to 1 m); (4) wavy- to flaser-bedded sandstones (ϕ = 19.84 %, k = 2.31 md; thickness from 0.5 to 3.5 m); and (5) bioturbated sandstones (ϕ = 8.21 %, k = 3.46 md; thickness from 1 to 2 m). By integrating these parameters, we observed that the best reservoir quality sandstones are hummocky cross-stratified sandstone and herringbone cross-bedded sandstone, because they have better porosity–permeability than that of other sandstone facies, despite having similar grain distribution with probability curves having steep trends and almost same grain size, roundness and sorting. Upon comparing the different facies, inferences can be made that porosity–permeability is distributed randomly. We conclude that there exist heterogeneities within different sandstone facies which may apply to the reservoir properties in the subsurface.

Black shale in late Jurassic Jhuran Formation of Kutch: Possible indicator of oceanic anoxic event?

This paper reports the results of sedimentary facies analysis and organic geochemical investigations of the middle Member of the Jurassic Jhuran Formation of Kutch which is conspicuous by the occurrence of organic-rich shales. Five lithofacies have been identified for lower part of the Middle Member, e.g. Facies A: Black shale, Facies B: Black shale with siltstone inter-bedding, Facies C: shale and siltstone alternations with minor sandstones, Facies D: siltstone-sandstone alternations and Facies E: plane laminated and hummocky cross-stratified sandstone. The average TOC content of the shales decreases from facies A (av. TOC- 3.4%), to facies D (av. 0.6%) through facies B (av. 1.75%) and facies C (av. 1.34%). The Facies E comprises dominantly of hummocky cross-stratified sandstones. The facies study indicates storm-influenced, shallow marine depositional conditions. Organic geochemical study of shale samples collected from several outcrops from Bhuj to Zara suggests a mixture of type III and type IV kerogen, supplied from higher plant sources. Although most organic matters are mildly matured (av. Tmax c. 427°C), some of the samples reflect overheating related to extrusion of Deccan basalt (av. Tmax c. 604°C). V, Ni, and Co concentrations are indicative of anoxic condition within the depositional settings. The Ni/Co ratio (av. 2.5) and V/(V+Ni) ratio (av. 0.82) as well as size of pyrite framboids (7 to 20 micron), advocates intermittent anoxic and sulfidic conditions in the depositional setting. Black shales within the Jhuran Formation possibly suggest intermittent anoxia related to late Jurassic Oceanic anoxic event (OAE). Detailed investigations are needed to explain the factors causing anoxia in shallow marine conditions.

Facies Relationships and Stratigraphic Architecture of Distal, Mixed Tide- and Wave-Influenced Deltaic Deposits: Lower Sego Sandstone, Western Colorado, U.S.A

Abstract The facies characteristics and stratigraphic architectures of ancient mixed, wave- and tide-influenced deltas are poorly documented, despite the abundance of analogous modern shorelines. This paper presents the first facies analysis and stratigraphic-architectural characterization of the distal part of the Cretaceous lower Sego Sandstone (Book Cliffs, Colorado, U.S.A.), whose correlative proximal part is arguably the most comprehensively documented example of ancient deltaic strata that exhibit evidence for the activity of tides and waves. The distal lower Sego Sandstone consists of tide-dominated and wave-dominated deposits arranged within four regressive–transgressive tongues bounded by flooding surfaces. The proximal part of each regressive–transgressive tongue contains tide- dominated sandstones that sharply to erosionally overlie, and laterally interfinger with, wave-dominated deposits in the distal part of the tongue. Tide-dominated sandstones are fine to medium grained, and comprise wavy bedded and cross-bedded sandstones with abundant mud drapes, reactivation surfaces, and bidirectional, ebb- and flood-tide-directed paleocurrents. They define active tidal distributary channel-fill and nonchannelized tidal-bar deposits of similar lithologic character, which represent the proximal part of the delta front. Abandoned tidal distributary channel fills comprise intensely bioturbated mudstones. The outer, paleoseaward parts of tidal bars contain direct evidence for mixed tide and wave influence in the form of hummocky cross-stratified, very fine-grained sandstone beds intercalated with cross-bedded, fine- to medium-grained sandstones containing tidal indicators. These deposits locally pass paleoseaward into low-angle and hummocky cross-stratified sandstones with grain size and texture similar to tidal-bar deposits, implying reworking by storm waves. Wave-dominated deposits consist of coarsening-upward successions of mudstone and hummocky cross-stratified sandstone beds that represent the distal part of the delta front. Localized rhythmic variations in the wavelength of hummocky cross-stratification in some deposits may record tidal modulation of water depth and storm-wave velocities. These facies components and their architectural arrangement suggest that tides and waves operated together throughout deposition of the “lower Sego Delta,” but that tide-dominated and wave-dominated deposits were spatially partitioned into the proximal and distal parts of each regressive–transgressive tongue. Thus, tides and waves were effective in transporting and reworking sediment in different water-depth ranges and at different geographic locations. Mixed tide- and wave-influenced deposits are generally preserved only at the down-dip pinchout of regressive–transgressive tongues, because they are removed by tidal scour during delta progradation in more proximal locations. The spatial partitioning of time-equivalent tide-dominated and wave-dominated deposits is readily explained in a single depositional model, which requires the interpretation of neither sequence boundaries nor temporal changes in process regime across the sharp-to-erosional juxtaposition of tide-dominated sandstones above wave-dominated deposits in a regressive–transgressive tongue.

Constraints on the Statherian evolution of the intraplate rifting in a Paleo-Mesoproterozoic paleocontinent: New stratigraphic and geochronology record from the eastern São Francisco craton

An integrated approach of stratigraphic analysis and U–Pb age dating reveals some information on the tectono-sedimentary evolution of the Statherian cover of the São Francisco craton in the so-called Espinhaço basin (Atlantic shield in eastern Brazil). Here, continental sedimentation patterns, such as alluvial fan, braided-plain and lacustrine facies associations, with associated volcanic rocks are documented in two superposed basin fill-successions, which are defined as the Algodão and Sapiranga Synthems and grouped in the Botuporã Supersynthem. Both studied units consist mainly of conglomerates and cross-bedded sandstones and minor amounts of mudstones, sedimentary breccias, volcanic lava beds and volcaniclastic rocks, which were deposited in a rift basin – the Botuporã rift – during two syn-rifting phases. The Algodão Synthem represents the first rifting phase. The basal synsedimentary conglomerates of this unit were deposited mainly by subaerial debris flows, most likely along and near a rift border fault. The framework of this rock consists of only crystalline rock clasts from the basement and no fragments of volcanic rocks. Detrital zircon grains that were extracted from this facies show ages older than 2.05Ga. The remainder of the section is dominated by fluvial sandy lithofacies with minor conglomerate lenses and sandstone–mudstone heterolithic lithofacies, which represent distal, waning-flood deposits in a lacustrine environment. The upper section also contains hummocky cross-stratified sandstone lithofacies, which are related to a storm-influenced deposition. On top of the Algodão succession, the volcanic rocks were dated at 1775±7Ma, which was interpreted as the near final age of the first rift-phase. Representing the second rift-phase, the Sapiranga Synthem shows similar sedimentation patterns to the Algodão Synthem. The Sapiranga Synthem rests directly on the volcanic rocks of the Algodão Synthem, and its basal conglomerates (which are most likely also related to a master fault) contain voluminous clasts of volcanic rocks, sandstones and crystalline rocks. The detrital zircon grains that were extracted from this facies show ages of 1741±14 and 1766Ma as well older than 2.05 Ga. The volcanic rocks on the upper succession of the Sapiranga Synthem record ages of 1740±10Ma, which finalized the Botuporã rift evolution. A preliminary geochemical study of volcanic rocks from the Botuporã Supersynthem showed that these rocks are alkaline rocks with high K2O/Na2O ratios, which belong to an ultrapotassic suite. The low concentrations of MgO wt.% suggest a felsic ultrapotassic character. The Botuporã Supersynthem is unconformably covered by a volcano-sedimentary rift-succession of EoCalymmian age — the Pajeú Synthem, which represents the second rifting stage of the Espinhaço basin. Several Statherian-related volcano-sedimentary sequences and anorogenic granitoids occur dispersed in the São Francisco block, which requires a regional geologic model to explain the extensional and magmatism process during this time. We used the last Columbia paleocontinental reconstruction to constrain these processes by relating them to far-field continental extensional and magmatic record as part of a silicic LIP, which was triggered by the convection-driven tectonic-plate motion on the western border of the Atlantica block inside of the Columbia supercontinent.