Lacustrine Delta Systems Research Articles

Coevolutionary Diagenesis in Tight Sandstone and Shale Reservoirs within Lacustrine-Delta Systems: A Case Study from the Lianggaoshan Formation in the Eastern Sichuan Basin, Southwest China

Tight sandstone and shale oil and gas are the key targets of unconventional oil and gas exploration in the lake-delta sedimentary systems of China. Understanding the coevolutionary diagenesis of sandstone and shale reservoirs is crucial for the prediction of reservoir quality, ahead of drilling, in such systems. Thin-section description, scanning electron microscopy (SEM), X-ray diffraction (XRD), fluid inclusion analysis, porosity and permeability tests, high-pressure mercury intrusion (HPMI) measurements and nuclear magnetic resonance tests (NMR) were used to reveal the coevolutionary diagenetic mechanisms of a sandstone and shale reservoir in the Lianggaoshan Formation of the Eastern Sichuan Basin, China. The thermally mature, organic-matter-rich, dark shale of layer3 is the most important source rock within the Lianggaoshan Formation. It started to generate abundant organic acids at the early stage of mesodiagenesis and produced abundant hydrocarbons in the early Cretaceous. Porewater with high concentrations of Ca2+ and CO32− entered the sandstone reservoir from dark shale as the shale was compacted during burial. Potassium feldspar dissolution at the boundary of the sandstone was more pervasive than at the center of the sandstone. The K+ released by potassium feldspar dissolution migrated from the sandstone into mudstone. Grain-rimming chlorite coats occurred mainly in the center of the sandstone. Some silica exported from the shale was imported by the sandstone boundary and precipitated close to the shale/sandstone boundary. Some intergranular dissolution pores and intercrystal pores were formed in the shale due to dissolution during the early stages of mesodiagenesis. Chlorite coats, which precipitated during eodiagenesis, were beneficial to the protection of primary pore space in the sandstone. Calcite cement, which preferentially precipitated at the boundary of sandstone, was not conducive to reservoir development. Dissolution mainly occurred at the early stage of mesodiagenesis due to organic acids derived from the dark shale. Calcite cement could also protect some primary pores from compaction and release pore space following dissolution. The porosity of sandstone and shale was mainly controlled by the thickness of sandstone and dark shale.

Sequence stratigraphy in post‐rift river‐dominated lacustrine delta deposits: A case study from the Upper Cretaceous Qingshankou Formation, northern Songliao Basin, northeastern China

The Upper Cretaceous Qingshankou Formation in the northern Songliao Basin was deposited in river‐dominated lacustrine delta systems. Three third‐order sequences and two types of sequence architecture were recognized using core observations, logging curve interpretations, and three‐dimensional (3‐D) seismic profiles in Qingshankou Formation. One type of sequence architecture was developed in a syndepositional flexural slope break, and the other was deposited on a gentle slope. The studied sequences were deposited in a high accommodation setting, which was due to the large rate of subsidence of the basin basement, and a tropical to semi‐tropical and a humid to semi‐humid climate. The episodic tectonic/thermal subsidence of the basin controlled the development of the sequence architecture. Turbidite bodies within transgressive systems tracts and early highstand systems tracts were deposited predominantly in the basinward part of the syndepositional flexural slope breaks, and they were favourable exploration targets, particularly for stratigraphic traps.

Seismic geomorphology of shallow-water lacustrine deltas in the Paleocene Huanghua Depression, Bohai Bay Basin, eastern China

The most important sedimentary facies comprising shallow-water lacustrine deltas are distributary channels, and these form abundant ribbon-shaped sand bodies that are excellent petroleum reservoirs. However, distributary channel sandstones are notoriously difficult to correlate and characterize in the subsurface based on well data alone. Here, we show how seismic geomorphology can be used to map lacustrine deltaic sedimentary successions in the First Member of the Kongdian Formation within the Zilaitun Oilfield, Huanghua Depression (China). Using core and wireline logs, this study identified distributary channels as the dominant sedimentary facies. Together with mottled gray-green or maroon mudstones and locally shingled progradational seismic reflection architecture, this indicates that deltas were built in a weakly-oxidized shallow-water lacustrine environment. Next, core observations were linked to seismic data to produce a successive series of stratal slices and root mean square amplitude attribute (RMSAA) maps. The RMSAA maps allowed distributary channel, mouth bar, and beach bar facies to be identified and mapped across the study area. Two patterns of distributary channels emerged from the data: (1) a distributive pattern with a lower concentration of distributary channels; and, (2) an anastomosing deltaic pattern with a high concentration of bifurcated distributary channels. Based on the seismic geomorphological analysis we show that the succession records three phases of delta evolution - retrogradation, aggradation, and progradation - which combine to form 3rd-order sequences. From a petroleum reservoir point of view, the distributive pattern yields narrower, thicker, and less connected sand bodies than the anastomosing pattern. This is consistent with observations from modern shallow-water lacustrine delta systems, providing independent support for the interpretation and highlighting the effectiveness of using seismic geomorphology.

Earthquake imprints on a lacustrine deltaic system: The Kürk Delta along the East Anatolian Fault (Turkey)

AbstractDeltas contain sedimentary records that are not only indicative of water‐level changes, but also particularly sensitive to earthquake shaking typically resulting in soft‐sediment‐deformation structures. The Kürk lacustrine delta lies at the south‐western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re‐evaluates water‐level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic‐reflection profiles and side‐scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water‐level changes provides a temporal framework for the depositional record. In addition to the common soft‐sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake‐induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (137Cs and 210Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X‐ray imagery, X‐ray diffraction, loss‐on‐ignition, grain‐size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post‐seismic sediment reworking of earthquake‐triggered landslides.

The Middle Pleistocene tunnel valley at Schöningen as a Paleolithic archive

Schöningen represents one of the key sites for Lower Paleolithic archaeology in central Europe, where a Middle to Late Pleistocene sedimentary succession, locally up to 45 m thick, has been preserved in an Elsterian tunnel valley. After deglaciation, the tunnel valley remained underfilled and provided the accommodation space for Holsteinian interglacial deposition and also kept the artifact-bearing strata below base level for subsequent erosion. The Holsteinian (MIS 9) succession consists of laterally and vertically stacked lacustrine delta systems, which were controlled by repeated lake-level changes. In the face of changing climatic and environmental conditions the long-lived interglacial lake provided an attractive site for animals and early humans. Artifacts were deposited on the subaerial delta plain and became embedded during lake-level rise. Although the area was considerably affected by erosion and glacitectonic deformation during the subsequent Saalian glaciation, the artifact-bearing Holsteinian strata were preserved in the deeper part of the tunnel valley.Tunnel valleys should be regarded as potential archives for interglacial deposits, which may contain important Paleolithic sites. Tunnel valleys may provide accommodation space and also have a high preservation potential. Interglacial lakes situated within underfilled tunnel valleys represented attractive sites for animals and early human hunter-gatherers.

Caracterização palinoflorística e paleoambiental da Formação Santana (Cretáceo Inferior), Poço 4-BO-1-PE, bacia do Araripe, Nordeste do Brasil

A paleoenvironmental characterization of the Santana Formation sedimentary rocks (4-BO-1-PE well), Araripe Basin, Late Aptian-Early Albian, was accomplished through qualitative and quantitative analyses of the palynofl ora. Palynological and lithological evidence indicate a predominantly continental depositional environment for this section, composed by a fl uvial, lacustrine deltaic system in a semi-arid climate. The detection of a single dinofl agellate cyst suggests that small sea ingressions took place during Aptian-Albian times in the region, as also verifi ed in other coeval strata of marginal Brazilian Cretaceous basins. Comparisons with palynofl oras from other continents support the hypothesis that this assemblage belongs to the North-Gondwana microfl oristic province.

Taphonomic patterns of a dinosaur accumulation in a lacustrine delta system in the Jurassic Morrison Formation, San Rafael Swell, Utah, USA

Taphonomic patterns of a dinosaur accumulation in a lacustrine delta system in the Jurassic Morrison Formation, San Rafael Swell, Utah, USA

Interplay between tectonics and compaction in a rift‐margin, lacustrine delta system: Miocene of the Eger Graben, Czech Republic

AbstractThe Early Miocene Bílina Palaeodelta consists of fluvio‐deltaic and lacustrine clastics deposited along the south‐eastern margin of the extensional Most Basin, part of the Eger Graben in north Bohemia (Czech Republic). The Bílina succession shows evidence of repeated advances of an axial deltaic system across a thick accumulation of organic material and clay in the hangingwall of an active fault. Exposures up to ca 4·5 km long in the Bílina open‐cast mine help bridge the gap between seismic scale and typical outcrop scale of observation and thus allow the relationships between small‐scale and basin‐scale stratal geometries to be evaluated. The Bílina Palaeodelta deposits include sand‐dominated, fluvial channel fills and heterolithic sheets interpreted as delta plain strata, sand‐dominated mouth‐bar wedges and heterolithic sheets of prodeltaic deposits, passing distally into lacustrine clays. The depositional environment is interpreted as a fluvial‐dominated, mixed‐load, lacustrine delta with a high degree of grain‐size segregation at the feeder‐channel mouths. On the largest temporal and spatial scales, variable tectonic subsidence controlled the overall advance and retreat of the delta system. The medium‐term transgressive‐regressive history was probably driven by episodes of increased subsidence rate. However, at this temporal scale, the architecture of the deltaic sequences (deltaic lobes and correlative lacustrine deposits) was strongly affected by: (i) compaction of underlying peat and clay which drove lateral offset stacking of medium‐term sequences; and (ii) growth of a fault‐propagation fold close to the active Bílina Fault. At the smallest scale, the geometries of individual mouth bars and groups of mouth bars (short‐term sequences) reflect the interaction among sediment loading, compaction and growth faulting that produced high‐frequency relative lake‐level fluctuations and created local accommodation at the delta front.

Architectural units and heterogeneity of channel reservoirs in the Karamay Formation, outcrop area of Karamay oil field, Junggar basin, northwest China

Reservoirs of the Karamay Formation occur as oil sandstones in outcrop in the Karamay oil field. Two types of high-quality reservoirs are present in this field: low-sinuosity channel sandstones and distributary-channel sandstones, each having different sediments, bounding surfaces, and architectural units. The low-sinuosity channel has coarse-grained sediments, a smaller scale, and relatively simple architectural units composed of intrachannel units and lithofacies that occur in a vertically stacked pattern. The distributary channel has fine-grained sediments, a larger scale, and relatively complex architectural units, which are reflected in the following three ways. (1) The distributary channels have three multiorder architectural units: an intrachannel unit, a macroform accretion unit, and a lithofacies unit. (2) Isolated barrier beds, whose permeability is lower, occur near third-order and fifth-order surfaces. (3) The evolution of the distributary channels has two stages. In the flooding stage, the sediments were coarse grained, and the intrachannel units were in a vertically stacked pattern. In the waning stage, the sediments were fine grained, and the intrachannel units were in a laterally stacked pattern. Reservoir heterogeneity of distributary-channel sandstones is revealed in the following three scales. (1) In a microscale range, the growth of pores is associated directly with lithofacies. The pore diameter and the throat width both increase with the coarsening of the grain size in the sediments. The anisotropic pore structure is reflected in the variation of permeability. The horizontal permeability parallel to the paleocurrent is the largest; the horizontal permeability perpendicular to the paleocurrent is intermediate; and the vertical permeability is the smallest. (2) At a channel scale, the fluid-flow units are demarcated according to the isolated barrier bed and porosity and permeability inside the distributary channel. The fluid-flow unit, distributed mainly in the middle–lower interval of the distributary channel or the intrachannel unit, is associated closely with third-order or fifth-order surfaces. The porosity and permeability inside the fluid-flow unit decrease gradually from its center to the margin and upper interval, depending on the spatial distribution of lithofacies. In this kind of lithofacies, which is characterized by a low matrix content and by coarse-grained sediments with large trough cross-beds, high porosity and permeability are commonly found. (3) In a lacustrine delta system, the distributary-channel sandstone has the best porosity and permeability and is the best reservoir.

Seismic Expression and Geological Significance of a Lacustrine Delta in Neogene Deposits of the Western Snake River Plain, Idaho

High-resolution seismic reflection profiles and well data from the western Snake River plain basin are used to identify a buried lacustrine delta system within Neogene Idaho Group sediments near Caldwell, The delta system is detected, 305 m (1000 ft) deep, near the center of the basin by progradational clinoform reflections having dips of 2-5°, a slope typical of prodelta surfaces of modern lacustrine delta systems. The prodelta slope relief, corrected for compaction, indicates the delta system prograded northwestward into a lake basin 255 m (837 ft) deep. Resistivity logs in the prodelta mud and clay facies are characterized by gradual upward increase in resistivity and grain size over a thickness of about 100 m (300 ft). Lithology of the prodelta is mostly c lcareous claystone, with several layers of fine sand, some of which fine upward, indicating a density-flow mechanism of transport and deposition. Delta-plain and front sediments are mostly very fine-grained, well-sorted sand separated by thin mud layers. These sediments produce several to five cycles of horizontal, high-amplitude reflections with a toplap relationship to prodelta clinoforms. The sands have an abrupt lower contact with prodelta muds and have high resistivity on logs. In this study, permeable lacustrine sands within a predominantly mud and clay section are located by using high-resolution seismic reflection data. Identification of a delta system in the Idaho Group provides insight into the history of Pliocene Lake Idaho. The present depth of the delta/prodelta facies contact of 305 m (1000 ft) is 445 to 575 m (1460-1900 ft) below the lake deposits on the margins. Estimated subsidence from compaction is 220 m (656 ft), and the remaining 225 to 325 m (740-1066 ft) is attributed to tectonic downwarping and faulting. The original lake area had been reduced to one third of the original 13,000 km2 (5000 mi2) by the time the delta front prograded to the Caldwell area. The original lake area may have been sufficient to evaporate most of the inflow, and the lake may have only occasionally spilled into other basins. Diminished area for evaporation later in the history of the lake, combined with reduced evaporation accompanying onset of the ice ages, may have caused the lake to rise and overtop a basin sill about 2 Ma, and subsequently deepen Hells Canyon.

A Predictive Model of Reservoir Continuity in Fluvial Sand Bodies of a Lacustrine Deltaic System, Colton Formation, Utah

Abstract The Paleocene/Eocene Colton Formation of east-central Utah is interpreted to be a fluvial-dominated lacustrine deltaic sequence that prograded from the southeast into ancient Lake Uinta. Predictability of reservoir continuity is based largely on understanding the nature of impermeable mudstone drapes within multilateral and multistory sandstone bodies. Fluvial sandstones are categorized into three systems according to associated facies, channel morphologies, and percent sandstone found within the section. Suspended-load systems dominate the western distal end of Colton exposures and are characterized as follows: meandering to sinusoidal fluvial systems, abundant multilateral accretion sets, and low sandstone percent (< 30%). Reservoir characteristics include poor porosity (< 9%) and permeability (< 0.6 md), poor reservoir continuity, small reservoir size, and good potential for development of numerous hydrocarbon traps. Mixed-load systems are typified by sinusoidal fluvial channels, large multilateral accretion sets, and intermediate sandstone percent (25-45%). Reservoirs display good porosity (approx. 18.5%) and permeability (< 50 md), intermediate reservoir continuity, intermediate to large reservoir size, and good potential to develop numerous hydrocarbon traps. Bed-load systems are characterized by relatively straight channels, very few point bar sequences, and high sandstone percent (< 45%). Reservoir characteristics display very good porosity (19.6-22.6%) and permeability (0.133-2.657 darcies), good reservoir continuity, large reservoir size, and less potential for hydrocarbon trap development. Distributary mouth bar sandstones display excellent reservoir characteristics including good porosity (20%) and the most homogeneous permeability (< 200 md) of the four volumetrically important sandstone facies. Recognition criteria of the four reservoir sandstone facies include sandstone percent in the section, grain size, thickness of the sandstone body, thickness of the sandstone interval, porosity and permeability of sandstones, and the nature of mudstone drapes between multilateral and multistory sandstone bodies. Improved technology in horizontal drilling may be used to link large noncommunicating multilateral accretion sets.

Haybarn Field, Fremont County, Wyoming, an Upper Fort Union (Paleocene) Stratigraphic Trap: ABSTRACT

End_Page 1352------------------------------In the fall of 1981, Northwest Exploration Co. drilled the discovery well for Haybarn field. The field is located in the Wind River basin of Wyoming and produces stratigraphically trapped 43° API gravity, 80°F pour point oil and associated gas from the Paleocene upper Fort Union Formation; these rocks are thought of generally as poor exploration targets and gas-prone at best. The reservoir is an arkosic sandstone deposited along the front of a lacustrine delta system. Clays in the reservoir are almost entirely secondary. Despite the precipitation of diagenetic kaolinite and chlorite, the reservoir capacity has remained high with porosities ranging from 18 to 26% and averaging about 20%. Reservoir permeabilities average about 7 md. Transmissibility has been enhanced in some z nes by natural vertical fractures. The fractures also provide an avenue for water from lower water sands. The resistivities of the formation waters are variable, making electric log calculations difficult. The Rw of the productive sand tongue in the discovery well ranges from 0.35 ohm-meters at the top to 1.40 at the base, over a vertical distance of 75 ft (23 m). Oil production is limited to the upper, more saline portion. Both the petroleum source and the trapping mechanism for the field appear to be the lacustrine Waltman Shale. The depositional system responsible for Haybarn field is not unique. Similar oil fields remain to be found in other parts of the Wind River basin. End_of_Article - Last_Page 1353------------