Splay Facies Research Articles

DETERMINATION OF HYDROCARBON ZONE AND DEPOSITIONAL ENVIRONMENT FACIES IN TALANG AKAR FORMATION, SOUTH SUMATRA BASIN AT "EPURA" FIELD

The EPURA field is one of the oil and gas producing fields in the South Sumatra Basin, where well completion has been carried out in the Talang Akar Formation, and the production test results are interpreted to mean that in wells EP-13, EP-14, EP-15, EP-16, EP-17 and EP-23 contain several reservoir zones that have the potential to contain hydrocarbons. This research with facies interpretation analysis uses data from six wells (wireline, mudlog, RCAL and lithology data), so it is hoped that it can provide more detailed information for the development of an oil and gas field. The analysis carried out is in the form of facies analysis, depositional environment, electrofacies and facies correlation. From the research results, it was found that the Talang Akar Formation has depositional facies in the form of a fluvial, which in this study is the Lower Talang Akar Formation with depositional facies in the form of channel, Crevasse Splay, point bar and flood plain. Based on the analysis results, the Talang Akar Formation is divided into 3 reservoir zones, namely Zone EP-1, EP-2, and EP-3. After going through all stages of petrophysical analysis, it was found that zones with high hydrocarbon potential were found in wells EP-13, EP-23 and EP-16. The wells with low hydrocarbon potential are EP-14, EP-15 and EP-17 wells. The zone of highest hydrocarbon potential in prospect wells is in the EP-1 zone with a Crevasse Splay facies association and has thick sandstone lithology characteristics with medium to fine grain size.

Karakteristik Lapisan Batubara pada Cekungan Bentarsari Terhadap Pola Sebaran Di Daerah Bentar Dan Sekitarnya Kecamatan Salem Kabupaten Brebes

The Kaliglagah Formation in the Bentarsari area, Salem District, Brebes Regency, Central Java Province is included in the Bentarsari Basin. This formation is a coal-bearing formation in the Bentarsari Basin of Late Pliocene age and is composed of layers of claystone, sandstone and coal. The coal seams in this formation were analyzed megascopically to determine the type of characteristics based on taking outcrop profiles in the research area and analyzed using the Horne classification approach, 1978 so that the depositional environment and facies of the formation of the coal seams were found. The results of the two analyzes were then used to determine the characteristics and distribution patterns of the coal seams of the Kaliglagah Formation. Characteristics The coal seam in the study area was deposited in the Crevasse splay facies, in the transitional lower delta plain depositional environment according to Horne, 1978. The distribution pattern of coal with a northwest-southeast trend, the withdrawal of coal distribution obtained three seams, namely a seam with a thickness of 1.21 m at Lp 4 , seam b with a thickness of 0.82 m on Lp 4, on Lp 2 the thickness of the coal seam is 0.03 m on seam b upper, 0.02 m on seam b middle and seam c lower 0.1 m, and 0.04 m on seam b upper and 0.03 m on seam b lower Lp 5 and seam c with a thickness of 1.65 m on seam b upper and seam c lower on Lp 1.

Distribution Characteristics of Quaternary Channel Systems and Their Controlling Factors in the Qiongdongnan Basin, South China Sea

The study of deepwater channels is important for the understanding of the sedimentary evolution mechanism and the sedimentary process of the marginal sea. In 2019, thick pore-filling gas hydrate with high saturation was firstly discovered in the Quaternary sands of the Qiongdongnan Basin (QDNB), which expanded the reservoir types of gas hydrates in the South China Sea. However, the distribution of sand-related channels is not well characterized, which limits the ability to predict sand reservoirs with gas hydrate. Using integrated 2D/3D seismic, multi-beam, well logging, and coring data, the current study documents the distribution characteristics of channel systems in the Quaternary strata and discusses their controlling factors. The integrated analysis shows that the channel-related sedimentary facies include channel-filling facies, levee facies, crevasse splay facies, and lobes facies. A total of six periods of channel systems is identified in the Quaternary strata. There are obvious distribution differences between the Channel 1 and Channel 3 systems when comparing the western, middle, and eastern sections: the channels in the western and eastern sections are mainly dominated by near straight V-shaped channels, while the middle section mainly consists of large braided channels, where channel-levee sedimentary facies developed. Compared with the distribution of the Central Canyon that developed in the Miocene, the Channel 1 and Channel 3 systems in the western section show southward migration since the Miocene. The distribution and evolution of Quaternary channels were likely collectively controlled by seafloor morphology, tectonic movement, sea-level fluctuations, and provenance supply. Tectonic movement controls seafloor morphology, which directly controls the flow of channels and their distribution characteristics; provenance supply determines the scale and sedimentary characteristics of each channel. The periodic changes in sea-level determine the evolution of multi-stage channel systems. This study has implications for the prediction of gas hydrate–bearing sands in the Quaternary QDNB and deepens our understanding of the Quaternary tectonic and sedimentary evolution in the QDNB.

Facies architecture of fluviatile deposits of the Jurassic-Cretaceous Bertangga Formation, Peninsular Malaysia

Bertangga Formation is a part of the Jurassic-Cretaceous non-marine sequences in Thailand and Malaysia. However, its facies analysis and depositional model have not been investigated in detail. Eleven lithofacies have been described in the Bertangga Formation and combined five facies associations including channel, point bar, floodplain, crevasse splay and swamp facies associations. Channel deposits are stacked bodies of fining upward sequences with prevalent erosional bases, formed by vertical aggradation and avulsion of channels. Point bar sands comprise cross bedded sandstone bodies formed in upper flow regime and possible lateral accretion surfaces. Crevasse splay deposits form sheets of fine-to-medium-grained sandstone. Floodplain sediments are composed of motteled grey mudstone. Swamp depositional environment is characterized by an association of coal, carbonaceous shale and siltstone. Facies analysis allows reconstruction of the depositional environment of the Bertangga Formation as a meandering fluvial system. Facies association also shows the increasingly distal and fine-grained trend from west to east of the studied area, which suggests possible eastward paleo-flow direction of the river. The existence of kaolinite in all samples indicates weathering of felsic rocks under acidic conditions. In the same time, the presence of smectite in the eastern part of the study area may suggest a contribution of mafic and/or volcanic rocks to the source of sediments in this area.

The influence of stratigraphy and facies distribution on reservoir quality and production performance in the Triassic Skagerrak Formation of the UK and Norwegian Central North Sea

Abstract Stratigraphy, depositional facies and proximal-distal position within a depositional system are identified as controls on reservoir quality and dynamic reservoir performance in the Triassic, fluvial-dominated, Skagerrak Formation reservoirs of the UK and Norwegian Central North Sea. Core sedimentological analysis from across the basin links decreasing trends of channel facies proportion and channel package thickness with increasing floodplain and splay facies proportions and their respective package thicknesses. These trends are considered to represent the proximal to distal transitions of distributive fluvial systems. Depositional facies are shown to strongly control static and theoretical dynamic reservoir quality using porosity–permeability cross-plots and stratigraphically modified Lorenz plots using conventional core plug data. This linkage of stratigraphy, depositional system position, facies proportions and package thicknesses with static and theoretical dynamic reservoir performance is used to predict pressure-depletion profiles in various settings of Triassic reservoirs of the Central North Sea beyond major areas of well and field control in UK Quads 22 and 30.

The São Jerônimo da Serra Site, Rio do Rasto Formation (Middle/Upper Permian), Paraná Basin, Brazil: faciological and taphonomic context

ABSTRACT: In this contribution, we present an analysis of the main faciological features of the Sao Jeronimo da Serra Site, related to the Morro Pelado Member of Rio do Rasto Formation (Middle/Upper Permian), from Parana State, Brazil, integrated to its taphonomic context. The outcrop, rich in vertebrates and bivalves remains, presents a succession of red siltstones bedded with fine to medium sandstones in which three architectural elements were observed: SF (sheetflood deposits), FF (fine of flood plain) and CS (crevasse). These data, allied to the taphonomic signatures of fossils assigned to eight levels, allowed the identification of three taphofacies. The taphofacies I is characterized by preserved bones in floodplain facies, with different articulation grades and absence of any sign of transport. The taphofacies II is composed by small isolated or fragmented bones and fish scales deposited in terminal splay facies. The taphofacies III is characterized by sandy layers with bivalve shells and fish scales, preserved in crevasse-splay deposits. The obtained data shows that the studied sedimentary succession was generated on a dry trend environment, with sporadic water supply, which conditioned the fossil preservation.

Turbidite Fasies of Lower Penosogan Formation in Karanggayam Area, Kebumen, Indonesia

A continuous clastic sedimentary rock outcrop in the Karanggayam Area, Kebumen represents the complete deep marine fan facies of the Middle Miocene Lower Penosogan Formation. Lithology association and vertical succession were observed from a 63 meters detailed measured section along the Karanggayam River. This study aims to identify and classify the turbidite succession as well as the depositional environment of the formation within the North Serayu Basin, Central Java. From the bottom to top the Lower Penosogan Formation is divided into: A2, B2, C2, D2 and F2 facies which represents basin plain, overbank (levee and distal levee), crevasse splay, channel-fill and frontal splay facies respectively. Changes in the depositional environment are interpreted to be influenced by the dynamic changes in morphology and global climate change caused by underwater volcanic activity as a result of Middle Miocene tectonic activity.

Regional study of controls on reservoir quality in the Triassic Skagerrak Formation of the Central North Sea

Abstract An improved understanding of the controls on reservoir quality is key to ongoing and future exploration of the Central North Sea Triassic play. This paper presents a regional integrated study of 50 000 ft of wireline log data, 10 000 ft of core, 4431 routine core analyses measurements and 377 thin sections from 86 cored wells. Triassic Skagerrak Formation sandstones represent thin-bedded heterogeneous reservoirs deposited in a dryland fluvial–lacustrine setting. Fluvial-channel facies are typically fine–medium grained and characterized by a low clay content, whilst lake-margin terminal splay facies are finer grained, more argillaceous and micaceous. Lacustrine intervals are mud-dominated. Primary depositional textures retain a primary control on porosity evolution through burial. Optimal reservoir quality occurs in aerially and stratigraphically restricted fluvial-channel tracts on the Drake, Greater Marnock, Puffin and Gannet terraces, and the J-Ridge area. These primary textural and compositional controls are overprinted by mechanical compaction, the development of early overpressure and diagenesis. Anomalously high porosities are retained at depth in fluvial sandstones that have a low degree of compaction and cementation, including chlorite. Forward modelling of reservoir quality using Touchstone™ software has been validated using well UK 30/8-3 where reservoir depths are >16 000 ft TVDSS (true vertical depth subsea).

Storm-reworked shallow-marine fans in the Middle Triassic Baise area, South China

Shallow-marine fans have been analyzed for sedimentary characteristics and genetic mechanisms far less commonly than deep-marine fans. Based on outcrop observations, this study reveals that large-scale submarine fans in the Middle Triassic Baise area, south China, consisted of a braided channel-levee facies complex in the inner fans; sinuous channel-levee facies complex, overbank facies and crevasse splay facies in the medial fans; and sand sheet facies in the outer fans, which present different lithology assemblages and depositional successions. The lithofacies of dominant massive sandstone, secondary graded sandstone and laminated sandstone from bottom to top is similar to the Bouma sequence, indicative of gravity flow processes. However, the laminated sandstones mostly bear sedimentary structures of gutter casts, wave-generated ripple marks, hummocky cross-bedding, wave-generated cross-bedding and ripple bedding, and were thus attributed to frequent storm reworking processes. Moreover, discontinuous deposition recorded by abrupt sediment grain-size changes, distinct interfaces and divergent paleocurrent orientations occurred between the laminated sandstones and the underlying massive (or graded) sandstones. Accordingly, storm reworking processes together with abundant fossils of Daonella, Ammonite and Crinoidea indicate a shallow-marine paleo-environment. As a whole, this study provides a good example of large-scale shallow-marine fans and laminated sandstones resulted from storm reworking.

New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin areaNew sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

The scarcity of stratigraphic data has hindered the demarcationof the outcropping area of Miocene deposits of the AmazonBasin, represented informally by the Novo Remanso Formation.Moreover, this unit is characterized by a sparse and irregular geographicdistribution due to its sedimentological features and rare fossilcontent. Miocene deposits cropping out in central Amazonas Basinarea were described in sedimentological terms and analyzed palynologically.All analyses were undertaken in samples collected at theUatumaRiver banks (Itapiranga and Sao Sebastiao do Uatuma cities).Lithostratigraphic data shows that Novo Remanso Formation consistsof sandstones, with subordinate conglomerates and pelites, characteristicof a meandering fluvial paleosystem, with fluvial channel, pointbar, floodplain and crevasse splay facies. The palynoflora retrieved fromfive samples consists exclusively of continental-origin palynomorphsdominated by angiosperms species. Trilete spores are well represented,while gymnosperms pollen grains are minor components. The presenceof Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouriaseamrogiformis and Polypodiaceoisporites potoniei ensure these depositsfits into the Grimsdalea magnaclavata palynozone (Regali et al.1974a, b), and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshoovenipalynozones of Jaramillo et al. (2011) considered MiddleMiocene age. This age is confirmed by the zonation of Jaramillo et al.(2011), based on the LADs of Bombacacidites baumfalki (11.57Ma)and Crototricolpites annemariae (12.91Ma); and the FAD of Psilastephanoporitestesseroporus (14.00Ma). With these new data presentedherein, it is possible to assume that the Miocene strata represented bythe Novo Remanso Formation covers a larger area in the basin thanpreviously considered, and that it may be extended for about 300 kmuntil the Manacapuru village, indicating a Miocene subsidence phase.

New sedimentological and palynological data from surface Miocene strata in the central Amazonas Basin area

ABSTRACT The scarcity of stratigraphic data has hindered the demarcation of the outcropping area of Miocene deposits of the Amazon Basin, represented informally by the Novo Remanso Formation. Moreover, this unit is characterized by a sparse and irregular geographic distribution due to its sedimentological features and rare fossil content. Miocene deposits cropping out in central Amazonas Basin area were described in sedimentological terms and analyzed palynologically. All analyses were undertaken in samples collected at the Uatumã River banks (Itapiranga and São Sebastião do Uatumã cities). Lithostratigraphic data shows that Novo Remanso Formation consists of sandstones, with subordinate conglomerates and pelites, characteristic of a meandering fluvial paleosystem, with fluvial channel, point bar, floodplain and crevasse splay facies. The palynoflora retrieved from five samples consists exclusively of continental-origin palynomorphs dominated by angiosperms species. Trilete spores are well represented, while gymnosperms pollen grains are minor components. The presence of Psilastephanoporites tesseroporus, Syncolporites poricostatus, Jandufouria seamrogiformis and Polypodiaceoisporites potoniei ensure these deposits fits into the Grimsdalea magnaclavata palynozone (Regali et al. 1974a, b), and the Grimsdalea magnaclavata/Crassoretitriletes vanraadshooveni palynozones of Jaramillo et al. (2011) considered Middle Miocene age. This age is confirmed by the zonation of Jaramillo et al. (2011), based on the LADs of Bombacacidites baumfalki (11.57Ma) and Crototricolpites annemariae (12.91Ma); and the FAD of Psilastephanoporites tesseroporus (14.00Ma). With these new data presented herein, it is possible to assume that the Miocene strata represented by the Novo Remanso Formation covers a larger area in the basin than previously considered, and that it may be extended for about 300 km until the Manacapuru village, indicating a Miocene subsidence phase.

Large striated burrows from fluvial deposits of the Neogene Vinchina Formation, La Rioja, Argentina: A crab origin suggested by neoichnology and sedimentology

This study includes three aspects: 1) the ichnotaxonomic treatment of large and dominantly vertical burrows ornamented with sharp bioglyphs from the fluvial Neogene Vinchina and Toro Negro formations (northwest Argentina); 2) the description and interpretation of the sedimentary facies where these burrows occur; and 3) neoichnologic observations on large ornamented burrows from seasonal wetlands of the Río Pilcomayo National Park (Argentina) as possible modern analogues of the trace fossils and the sedimentary environment. A new ichnogenus and ichnospecies, Capayanichnus vinchinensis, is proposed to include the large striated burrows. The new ichnotaxon is distinguished by a combination of a predominantly vertical orientation, overall “L” shape (when fully developed), absence of lining and burrow bifurcation, a distinct surface texture, and lack of burrow enlargements. The hosting sedimentary facies of the Vinchina Formation can be grouped into fluvial channel and splay (floodplain) facies associations. The rivers of that unit were of two main types: single channel rivers with frequent channel avulsion and overbank flow and multichannelised rivers with poorly defined margins. At least some of these rivers were ephemeral or with intermittent discharge. The climate was probably seasonal and semiarid, as suggested by sedimentologic evidence. C. vinchinensis was dominantly recorded from the top of fluvial channels (interpreted as abandoned channels) and proximal, intermediate and distal splay facies. The large ornamented burrows found in an extant comparable example were constructed by freshwater crabs. These burrows can be distinguished by the overall architecture, the taxonomy and sex of its occupants, and the environmental setting where they were found. The neoichnologic signatures used in the interpretation of the fossil example include the common oval burrow cross-section and the surface texture. In particular, the surface texture in the modern crab burrows includes abundant comma-shaped marks, sets of grooves oblique to burrow axis, and long segmented grooves. The predominantly oval cross-section, absence of lining, and the strongly ornamented burrow surface suggest that C. vinchinensis was produced by freshwater crabs. The key features of the surface ornament are long sets of three–four ridges whose width is in average one third of the burrow major axis. Other features that also point to a crab origin are a massive filling, common burrow ends in a casing mudstone, chevron pattern in sets of surface ridges, and possible cheliped marks. The new ichnotaxon is restricted, in the Vinchina and Toro Negro formations, to fluvial facies and is absent in shallow lacustrine facies.

Sedimentology of the fluvial and fluvio-marine facies of the Bahariya Formation (Early Cenomanian), Bahariya Oasis, Western Desert, Egypt

The Lower Cenomanian Bahariya Formation in the Bahariya Oasis, Western Desert, Egypt, was deposited under two coeval environmental conditions. A fully fluvial system occurs in the southern portion of the Bahariya Oasis, including depositional products of meandering and braided streams, and a coeval fluvio-marine setting is dominant to the north. These deposits are organized into four unconformity-bounded depositional sequences, whose architecture is shaped by a complex system of incised valleys. The fluvial portion of the lower two depositional sequences is dominated by low-energy, meandering systems with a tabular geometry, dominated by overbank facies. The fluvial deposits of the upper two sequences represent the product of sedimentation within braided streams, and consist mainly of amalgamated channel-fills. The braided fluvial systems form the fill of incised valleys whose orientation follows a southeast–northwest trending direction, and which truncate the underlying sequences. Four sedimentary facies have been identified within the braided-channel systems, namely thin-laminated sandstones (Sh), cross-bedded sandstones (Sp, St), massive ferruginous sandstones (Sm) and variegated mudstones (Fm). The exposed off-channel overbank facies of the meandering systems include floodplain (Fm) and crevasse splay (Sl) facies. The fluvio-marine depositional systems consist of interbedded floodplain, coastal and shallow-marine deposits. The floodplain facies include fine-grained sandstones (Sf), laminated siltstones (Stf) and mudstones (Mf) that show fining-upward cycles. The coastal to shallow-marine facies consist primarily of mudstones (Mc) and glauconitic sandstones (Gc) organized vertically in coarsening-upward prograding cyclothems topped by thin crusts of ferricrete (Fc). The four depositional sequences are present across the Bahariya Oasis, albeit with varying degrees of preservation related to post-depositional erosion associated with the formation of sequence boundaries. These unconformities may be overlain by braided-stream channel sandstones at the base of incised valleys, or marked by ferricrete paleosols (lithofacies Fc) in the interfluve areas.

Sedimentology of the coal-bearing Mist Mountain Formation, Line Creek, Southern Canadian Cordillera: relationships to coal quality

A detailed sedimentological investigation of the Jurassic–Cretaceous Mist Mountain Formation in the southern Canadian Cordillera was undertaken to determine what, if any, sedimentological factors control coal quality and seam geometry. In the Line Creek area, the Mist Mountain Formation is divisible into two units based on abundance and lateral continuity of facies. The lower unit consists of alternating laterally extensive coal seams and thick, widespread channel sandstones interspersed with crevasse splay and flood plain facies sediments. The lower unit was deposited in an interdeltaic coastal plain environment protected from marine incursion by the beach ridge–dune sandstones of the underlying Morrissey Formation. The upper unit of the Mist Mountain Formation was deposited in a distal alluvial–fluvial flood plain environment and has similar facies to the lower unit but coal seams and channel sandstones are less laterally continuous and thinner than in the lower unit. Channel sandstones decrease in number and thickness up-section, and are replaced by an increasing abundance of coal seams, flood plain and crevasse splay facies sediments. Seam geometry and ash data indicate that clastic sedimentation had only limited influence on peat (coal) accumulation in the Mist Mountain Formation. While the geometry of the seams reflects the proximity of under- and overlying channel sandstones, neither abundance nor mineralogy of the coal ash reflects changes in surrounding clastic sediments. The Mist Mountain Formation peat mires were thus not obviously influenced by coeval fluvial activity. Characteristics of the lower unit suggest peat mires developed only during hiatus in clastic deposition, whereas upper unit coals appear to have formed in at least partially domed mires contemporaneous with clastic sedimentation. The vitrinite content of the coal increases up-section at the expense of semifusinite, possibly reflecting an increase in the proportion of arborescent vegetation in the mire with time and a lower susceptibility to fires.

Abstract: Fluvial Deposits and Leaky Aquitards of the Late Pleistocene Shallow Subsurface in Southwest Louisiana 

ABSTRACT Shallow subsurface Pleistocene deposits underlying southwest Louisiana exhibit multiple cycles of fluvial deposition, each herein referred to as a fluvial system. The fluvial systems are discernible in a geologic model that reflects correlations and facies analysis on a scale of approximately 200 to 300 feet. The fluvial systems consist of point bar, channel-fill, levee, crevasse splay and flood plain facies. Channel sequences up to 60 feet thick are composed of several fining-up sandy sequences each on the scale of 10 feet thick. Lateral to the upper portions of the channel sequence are sediments interpreted as crevasse splay deposits. Marsh and estuarine deposits representing flooding surfaces cap these fluvial cycles. Relatively thin, clays deposited on aggraded floodplains overlie some fluvial cycles. Laterally persistent flooding surfaces are locally eroded by successive channels. Fluvial systems exhibit distinctive hydrologic characteristics with similar water levels in each system. These systems form a leaky aquitard overlying the Chicot Aquifer. Factors responsible for the leaky nature of the clay-rich section are: 1) fractures in the clay-rich flood plain deposits that increase the vertical permeability, 2) scour of fluvial systems that erodes thin, relatively impermeable, fine-grained organic-rich sections capping the sequences causing vertical connections between different systems and 3) stress caused by water withdrawal from the underlying aquifer. Well-developed, highly permeable point bar sequences act as reservoirs and connect thin permeable, silty layers ubiquitous in these fluvial and interfluvial deposits. This discussion will illustrate the model with data acquired from a roughly one square mile study area. End_of_Record - Last_Page 1-------

Fluvial Architecture of Selected Middle Pennsylvanian Sandstones, Port of Catoosa, Rogers County, Oklahoma: ABSTRACT

Abstract The facies architecture of fluvial-dominated delta plain systems were reconstructed for several Middle Pennsylvanian sandstones. The study area incorporates approximate 640 acres centered on the Amoco experimental drilling site near Port of Catoosa. Data included conventional logs from 11 wells, and core plus microresistivity images from a single well. Architecture elements recognized are divided in four hierarchical levels, in order of decreasing rock volume: multistacked discrete genetic interval; individual discrete genetic interval (DGI); facies; and stratification pattern of a single facies. Conventional logs are used to correlate and map multistacked DGI, individual DGI, and facies. Core and microresistivity images are used to resolve facies and stratification patterns in the vicinity of the experimental well. Using azimuthal relationships among architecture elements, the location of the experimental well within the depositional systems are determined. Examples of architectural reconstruction include the following. The Bartlesville sandstone consists of splay facies in the upper part and channel-fill facies on the lower part as two individual discrete genetic intervals. The channel-fill facies shows a fining-upward profile with cross strata at the bottom to parallel strata and ripple laminae at the top. The splay facies is made up of small-scale cross strata, climbing ripple laminae, and parallel strata. Lower Skinner sandstone is 50 feet thick and in conventional well logs forms a single bell-shaped log profile. However, the microresistivity log clearly shows that it is composed of two DGI's, each represented by channel-fill facies.

Application of Facies Analysis to Improve Gas Reserve Growth in Fluvial Frio Reservoirs, La Gloria Field, South Texas: ABSTRACT

Geologically based infill-drilling strategies hold great potential for extension of domestic gas resources. Traditional gas-well drilling and development have often assumed homogeneous and continuous reservoirs; uniform gas-well spacing has resulted in numerous untapped reservoirs isolated from other productive sand bodies. Strategically located infill wells drilled into these undrained reservoirs may ultimately contact an additional 20% of original gas in place in Texas gas fields. Tertiary formations in the Texas Gulf Coast commonly exhibit multiple fluvial and fluvial-deltaic reservoirs that contain vertical and horizontal permeability barriers. For example, the Frio La Gloria field (Jim Wells and Brooks Counties, Texas) contains isolated and compartmentalized reservoirs that can be related to the irregular distribution of heterogeneous facies. Net-sand and log-facies maps in areas of dense well spacing delineate relatively continuous pay defined by lenticular point-bar and channel-fill deposits 1,500-2,500 ft wide. These point-bar deposits are flanked laterally by sand-poor levee and splay facies that isolate the reservoirs into narrow, dip-elongate bands.

Facies and Depositional Environments of the Energy Shale Member (Pennsylvanian) and their Relationship to Low-sulfur Coal Deposits in Southern Illinois

ABSTRACT Thick deposits of Energy Shale (Carbondale Formation, Desmoinesian) are associated with low-sulfur coal deposits in the underlying Herrin (No. 6) Coal Member in southern Illinois. The Energy Shale consists of wedges up to at least 26 m thick, which thin away from the Walshville channel (interpreted as a major channel deposit), and local pods or lenses which occur farther from the channel. Facies recognition and interpretation of depositional environments are based on paleoecology, lithology, sedimentary structures, vertical and lateral relationships, and geometry. Supplementary evidence was obtained from total sulfur content and boron content. Six facies are recognized in the areas studied. The thickest and coarsest facies is adjacent to the Walshville channel and is characterized by numerous fining-upward channel-fill sandstones, siltstones, and silty shales. This facies is interpreted as a series of crevasse-distributary channel-fill, levee, and interchannel deposits formed in the proximal portions of the splays. The proximal splay facies grades laterally into a distal splay facies, which consists of shale with abundant plant remains, thin coal beds (splits from the Herrin Coal), rare siderite concretions, and siltstone lenses. The distal splay facies grades laterally into or overlies shale with laterally persistent siderite layers, interpreted as a nonmarine bay facies. The nonmarine bay facies grades vertically and late ally into shale, which is bioturbated and contains euryhaline bivalves and is interpreted as a brackish to marine bay facies. The brackish to marine bay facies grades vertically into shale, containing a moderately diverse marine fauna with some small, possibly stunted, individuals. This facies is interpreted as a marginal marine deposit. Local lenses of organic-rich, dark gray to black shale underlie isolated pods of the marginal marine facies and probably were deposited in freshwater ponds developed on the Herrin peat swamp. The Walshville channel, the proximal and distal crevasse-splay facies of the Energy Shale, and possibly the black shale pond facies of the Energy Shale were partly contemporaneous with Herrin peat deposition. The sulfur content of the Herrin Coal is highest beneath the proximal splay and marginal marine facies of the Energy Shale and is lowest (less than 1.5%) beneath the distal splay facies and the nonmarine bay facies. The sulfur content of the Herrin Coal is related to the thickness, permeability, and environment of deposition of the facies of the overlying Energy Shale.

Adverse Effects of Crevasse-Splay Deposits in an Appalachian Coal Mine, Eastern Kentucky: ABSTRACT

Facies analysis of highwall exposures, roof and pillar information, and 56 core descriptions indicate that a series of narrow, bifurcating paleochannels and associated sheet sandstones in an eastern Kentucky coal mine were deposited by at least three crevasse-splay and overbank flooding events that occurred during and immediately following peat accumulation in a fluviolacustrine flood-basin environment. The proximal crevasse facies is channel-form, dominantly gray, very fine to fine-grained sandstone exhibiting ripple-drift, current-ripple, and small-scale trough cross-bedding, abundant micaceous laminae, and common disseminated plant and stem debris. The proximal crevasse channels grade laterally, and are incised into distal splay sandstones, shales, claystones, and coal riders. Sandstones of the distal splay facies are gray, sheet form to wedge shaped, shaly to very fine grained, and exhibiting ripple-drift, irregular, and massive bedding, disseminated and well-preserved plant and stem fossils, micaceous concentrations, coal spar, and rooting structures. Shales of the distal splay facies are gray and laminated, with abundant, well-preserved plant and stem fossils, sideritic nodules, claystone, and coal laminae. Economic problems resulting from the crevasse-splay facies include 1) multiple washouts of the coal seam, 2) increased parting thickness and frequency, 3) split wedges in the coal seam, and 4) significant roof stability problems. Largemore » roof falls in the crevasse-splay (stackrock) roofs result from 1) thin bedding of facies, 2) rapid lateral and vertical changes of facies, 3) internal bedding weaknesses, such as fossil plant and micaceous concentrations, sideritic nodules, and coal spar, 4) thin coal riders and streaks in the roof, and 5) slickensided shale beneath sandstone channels. Mapping of the crevasse-splay facies may help to predict coal quality and roof stability problems in unmined areas.« less

Fluvial plain/lacustrine facies transition in the Cretaceous Sindong Group, south coast of Korea

Along the south coast of Korea, a 250 m stratigraphic interval corresponding to the uppermost Hasandong and lowermost Jinju Formations of the Cretaceous Sindong Group has been studied in terms of facies transition. The interval displays a passage from a fluvial plain facies association consisting of floodplain, levee, crevasse splay and channel facies to a lacustrine facies association composed of crevasse splay, channel, overbank sheet splay, marginal lake, open lake and stream mouth bar facies. Between these two associations a transitional facies association occurs in which some facies of both associations alternate. In the lacustrine association, shallow marginal lake deposits including channel facies are gradually replaced upwards by deeper open lake deposits made up of open lake and stream mouth bar facies. During the Hasandong/Jinju period, small channels, which originated in the uplifted areas beyond the fault(s)-bounded western margin of the Gyeongsang Basin, flowed through alluvial fans developed along the fault(s) and a fluvial plain to a lake which occupied the central part of the basin. As a result, the lake shoreline was non-coincident with the basin margin. Sinuosity of the streams increased downstream, reaching a maximum near the shoreline, but decreased in the marginal lake areas. The fluvial plain was progressively submerged by the transgression of a non-deltaic shoreline, resulting in a deepening of the depositional sites from a fluvial plain through a marginal lake to an open lake setting. Intermittent channel overflows deposited levee and crevasse splay facies in the fluvial plain, and crevasse splay and overbank sheet splay facies in the marginal lake. Stream mouth bars were developed at the ends of the sublacustrine channels by hyperpycnal density flows operated mainly during floods. The non-deltaic shoreline was formed due to: (1) maintenance of shallow and wide marginal lake areas; (2) dispersal of sediments by small channels; (3) continuous shifting of the channels and their mouths; and (4) direct transport of coarser sediments to the open lake and their subsequent wide dispersions.