Reservoir Accumulation Research Articles

Simulasi Pemodelan Numerik Hidrodinamika dan Aliran Sedimen pada Bendung PLTA Musi – Bengkulu

This research aims to identify Hydro-Power Plant (PLTA) sedimentation in Musi-River, Bengkulu, Indonesia. Based on field
 observation and simulation modeling Surface Modeling System 8.01.
 High sediment levels cause accumulation of reservoirs and loss of
 direct storage, which in turn causes loss of production potential for the Musi Hydro-Power Plant, Bengkulu. The data used in this modeling are bathymetry, current velocity of measurement results, water level, and grain size of sediment. Based on field observations, it was found that basic sediment types were dominated by silt and sand. The highest elevated sediment content values of 0.166 gr/l, current velocity in the upstream was 0.54 - 0.61 m/s while the middle section was 0.43 m/s. After the hydrodynamic model is carried out, then the sedimentation model has values that vary throughout the area model, this is influenced by several factors, one of which is the current movement that can affect the amount of water bottom friction. Volume of sediments obtained in the weirs at the PLTA Musi is 211,588 m3 during the simulation of 1 month if multiplied in 1 year, then it obtained 2539,056 m3. From the results of this research, PLTA Musi must prevent this sedimentation bymaking sediment traps in the upstream.

The Anyue Giant Gas Field in the Sichuan Basin as the Largest Gas Field in Marine Carbonate Deposits from Domestic China

Abstract —The Anyue gas field is located in the middle part of the Sichuan Basin, SW China. It occurs in the oldest marine carbonate strata and is characterized by the highest degree of thermal evolution and the largest gas reserves in China. A significant breakthrough was made with the Gaoshi-1 risk-taking exploration well deployed in 2011. As of 2015, the proven geologic reserves of natural gas were 657.4 billion m3, and the total gas reserves including proven reserves, controlled reserves, and predicted reserves exceeded 1.5 trillion m3. A total of three sets of gas-bearing strata are developed in the Anyue gas field in a descending sequence: The gas reservoir in the Cambrian Longwangmiao Formation (Є1l) is treated as a structure-lithologic gas reservoir; the gas reservoir in Section No. 4 of the Dengying Formation (Z2dn4) is a structure-stratigraphic gas reservoir; and the gas reservoir in Section No. 2 of the Dengying Formation (Z2dn2) is a structural gas reservoir. A comparative analysis of the gas sources has shown that the gas Cambrian of reservoirs was mainly from mudshale of the lower Cambrian Maidiping and Qiongzhusi formations and the gas of the Dengying Formation reservoirs was from mudshale of the Qiongzhusi Formation and mudstone of Section No. 3 of the Dengying Formation. All gas reservoirs are referred to as reservoirs of dry gas with medium or low contents of sulfur and medium contents of CO2. Gas reservoirs in Є1l are characterized by a large burial depth, a high temperature, and a high pressure, while the gas reservoirs in Z2dn2 and Z2dn4 are characterized by an ultralarge depth, a high temperature, and a normal pressure. The accumulation of gas reservoirs is controlled mainly by two factors. The distribution of hydrocarbon generation centers is controlled by the late Sinian–early Cambrian intracratonic rift, which acts as effective updip sealing conditions for gas reservoirs in the Dengying Formation. The late Sinian–early Cambrian Gaoshiti–Moxi paleouplift experienced a long-term inherited development, which controlled the generation and distribution of three sets of large-scale high-quality reservoirs in Z2dn4, Z2dn2, and the Longwangmiao Formation and the generation of three sets of high-quality reservoir–caprock assemblages. An inherited giant structural trap with a longterm stable development is always a favorable zone for petroleum accumulation.

Controls on hydrocarbon accumulation by facies and fluid potential in large-scale lacustrine petroliferous basins in compressional settings: A case study of the Mesozoic Ordos Basin, China

Large-scale lacustrine basins in compressional settings are an important type of petroliferous basin, and the study of the characteristics of hydrocarbon accumulation in such basins is of great significance. This synthesis paper takes the Mesozoic Ordos Basin (central China) as a case study to establish lateral and vertical hydrocarbon accumulation patterns in this basin type, and highlights how facies and fluid potential control hydrocarbon accumulation in such basins. Based on systematic analyses of the Mesozoic source rocks, sedimentary facies, migration and accumulation patterns, and characteristics of the oil reservoirs, the hydrocarbon accumulation characteristics in the Mesozoic Ordos Basin are discussed. The analysis indicates that sedimentary facies controlled the characteristics and distribution of hydrocarbon source rocks and reservoirs, while diagenetic facies controlled the quality and distribution of the reservoirs. Excess pressure and fluid potential controlled hydrocarbon migration directions and paths, whereas facies and potential controlled the locations of oil accumulations and traps. It is concluded that source rocks controlled oil-bearing regions, sedimentary facies controlled oil-bearing plays, and fluid potential controlled the locations of accumulations. For shallow intervals, because fluid migration is mainly controlled by buoyancy, paleotopographic highs played an important role in controlling hydrocarbon accumulations. For deep layers (Chang 7 to Chang 10 members), since buoyancy is less than the capillary pressure, excess pressure caused by the undercompaction of mudstone and hydrocarbon generation at depth provides the driving force for lateral and vertical migration of oil, and becomes the main migration force. The reservoir accumulation characteristics differ laterally between regions of the basin; at the periphery of the basin, reservoir units are stacked in a step-wise manner, whereas at the center of the basin, multiple reservoir intervals are vertically stacked in the form of multistorey accumulations. Vertically, layers with different burial depths have different accumulation characteristics; the paleotopography controlled hydrocarbon accumulation in shallow intervals; instead excess pressure, fluid potential, and paleotopography controlled accumulation in deep intervals. This understanding could be used to inform prospecting in other large-scale lacustrine petroliferous basins in compressional settings such as the Eocene Green River Basin in the U.S.A. and the Middle Triassic Gunnedah Basin in Australia.

Dating and characterizing primary gas accumulation in Precambrian dolomite reservoirs, Central Sichuan Basin, China: Insights from pyrobitumen Re-Os and dolomite U-Pb geochronology

Primary gas accumulation with trillions of cubic meters of gas volumes was discovered recently in the Precambrian Dengying Formation of the Gaoshiti-Moxi block, Central Sichuan Basin, China. In this study we investigated the pervasive saddle dolomite cements and solid bitumens within karst vugs in the Dengying dolomite reservoirs. Using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in situ U-Pb dating, we obtained a high-precision absolute age of 259.4 ± 3.0 Ma for the saddle dolomite cementation, consistent in timing with the eruption of Emeishan flood basalts (262–251 Ma). Combined with high homogenization temperatures (Th) and salinities of primary fluid inclusion, as well as rare earth element (REE) compositions, we consider that the saddle dolomite precipitation was likely related to hydrothermal activity driven by the Emeishan mantle plume.The identification of rare surviving oil inclusions and extensive solid bitumens within the dolomite vugs is indicative of the presence of paleo-oil reservoirs. These bitumens are characterized by high equivalent vitrinite reflectance (Requ), no fluorescence, and deformed fibrous textures, typical of highly mature pyrobitumens. Gas geochemistry data indicates that only minor thermochemical sulfate reduction (TSR) has occurred. Thus the pyrobitumen was interpreted to result mainly from the thermal cracking of paleo-oils, and its associated Re-Os isochron age of 154 ± 21 Ma, representing the timing of dry gas formation. Petrographical evidence suggests that the paleo-oil charge must have taken place after sparry dolomite cementation but prior to pyrobitumen generation. This, combined with coeval aqueous inclusion Th data and published thermal-burial models, constrains the time of paleo-oil emplacement to ca. 222–205 Ma, suggesting an oil-filling event related to the Indosinian Orogeny. This study documented the first chronological data constraining the complex evolution history of a petroleum system in one of the oldest primary gas reservoirs in the world.

Assessment of Chimkurgan water reservoir sedimentation processes

Uzbekistan is an inland country with very dry summers and cold winters. The main course of the economy is agriculture. There are two basic kinds of agriculture in terms of irrigation: rainfed and artificial irrigation systems. Therefore, in long dry summers it is reasonable to build water reservoirs to keep enough water resources for vegetation period. Because of sedimentation transport water reservoirs sometimes quickly filled with sediment. Estimating the effects of potential sediment accumulation in reservoirs is an important element in the planning of the dam project. Sediment accumulation in a reservoir may reduce the useful storage of water in this reservoir, change the water quality near the dam, increase flooding level upstream of the dam due to sediment aggradation, influence the stability of the stream downstream of the dam, affect stream ecology in the dam region, etc. This article provides a correlation between the reservoir volume reduction from the bottom to a given level, based on the amount of water flowing into the Chimkurgan reservoir and the river basin monitoring data. Based on the results of observations and calculations, the current state of the reservoir was formed on the basis of GIS tools. In the first step we constructed a flow duration curve, which is the cumulative distribution curve of the stream runoff passing the dam.

Logging response characteristics and formation process of flushed zone in the Orinoco heavy oil belt, Venezuela

Abstract The origins and logging responses of flushed zones in some blocks of Orinoco heavy oil belt, Venezuela are still unclear. To solve this issue, we examined the conventional logging, nuclear magnetic resonance logging, fluid viscosity, core analysis and oil field production data comprehensively to find out the logging responses and origins of the flushed zones. The results show that the main reason for the formation of flushed zone is surface water invasion, which leads to crude oil densification. The crude oil densification produces asphalt membrane (asphalt crust) which wraps up free water, causing special logging responses of the flushed zones. According to the different logging responses, we classified the flushed zones into two types and analyzed the formation processes of the two types of flushed zones. According to the characteristics of logging curves after water flush, we confirmed that the water flush began earlier than the reservoir accumulation.

Fracture development and hydrocarbon accumulation in tight sandstone reservoirs of the Paleogene Huagang Formation in the central reversal tectonic belt of the Xihu Sag, East China Sea

Abstract By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement (12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement (9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging (9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day (0–3 Ma ago), the fractures are tectonic ones developing successively; matching with the second stage (0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.

Miocene Biogas Generation System in the Carpathian Foredeep (SE Poland): A Basin Modeling Study to Assess the Potential of Unconventional Mudstone Reservoirs

This paper presents the results of a research project aimed at evaluating the unconventional natural gas potential of the autochthonous Miocene sediments in the Polish part of the Carpathian Foredeep. The primary objective of the study was to re-evaluate the biogenic gas generation system within Miocene sediments, paying special attention to unconventional gas resources accumulated in tight mudstone formations. The four-dimensional (4D) petroleum system modeling method (PetroMod software) was used to reconstruct the basin geometry and three-dimensional (3D) evolution through a geological timescale, in particular the progress of gas generation, migration, and accumulation processes, as well as their consequences for gas exploration and development. Special attention was paid to the dynamics of gas generation processes and the advancement of sediment compaction and their time dependence, as well as to the progress and outcomes of gas migration and accumulation processes. The results indicate significant potential for unconventional gas accumulations in mudstone reservoirs. However, part of the biogenic gas resources occurs in a dispersed form. Analysis of the dynamics of biogenic gas generation and accumulation conducted on a basin scale and within particular sedimentary complexes and depth intervals allowed an indication of the premises regarding the most favorable zones for mudstone–claystone reservoir exploration.

Origin, hydrocarbon accumulation and oil-gas enrichment of fault-karst carbonate reservoirs: A case study of Ordovician carbonate reservoirs in South Tahe area of Halahatang oilfield, Tarim Basin

Abstract Based on comprehensive analysis of tectonic and fault evolution, core, well logging, seismic, drilling, and production data, the reservoir space characteristic, distribution, origin of fault-karst carbonate reservoir in Yueman block of South Tahe area, Halahatang oilfield, Tarim Basin, were studied systematically. And the regular pattern of hydrocarbon accumulation and enrichment was analyzed systematically based on development practice of the reservoirs. The results show that fault-karst carbonate reservoirs are distributed in the form of “body by body” discontinuously, heterogeneously and irregularly, which are controlled by the development of faults. Three formation models of fault-karst carbonate reservoirs, namely, the models controlled by the main deep-large fault, the secondary fault and the secondary internal fault, are built. The hydrocarbon accumulation and enrichment of fault-karst carbonate reservoirs is controlled by the spatiotemporal matching relation between hydrocarbon generation period and fault activity, and the size and segmentation of fault. The study results can effectively guide the well deployment and help the efficient development of fault-karst carbonate reservoirs of South Tahe area, Halahatang oilfield.

Accumulation and exploration of petroleum reservoirs in west slope of northern Songliao Basin, China

Abstract On the basis of the present situation of oil and gas exploration and geological research of the west slope in the northern Songliao Basin, the factors controlling reservoir formation, oil and gas migration and accumulation, have been re-examined from the aspects of structure, deposition and reservoir formation. The results show that: (1) The west slope is a gentle slope which overlaps to the west, and nose structure is developed near the hydrocarbon generation depression, which is in the dominant direction area of hydrocarbon migration. A series of NE structural belts are developed on the slope and are favorable places for oil and gas accumulation. (2) The west slope can be further divided into the upper slope and the lower slope, and there are many kinds of oil and gas reservoirs, including structural, structural-lithologic and lithologic ones. In the upper slope, the major oil layer is Sartu controlled by structure; in the lower slope, multi-layers are oil-bearing, and the oil reservoirs are mostly composite ones. (3) Faults, unconformity surfaces and continuous sand bodies are the main channels of oil and gas migration; structure, sand body and fault jointly control the oil and gas enrichment in the slope; and the matching relationship between micro-amplitude and sand body, small fault and sand body control the oil and gas accumulation. On the basis of the above research, fine identification and effectiveness evaluation technology of composite trap has been developed through extensive study. Combination traps were identified by multiple technologies, including fault classification, micro-amplitude structure identification, fine sedimentation research, and lithologic trap identification by waveform indication inversion; and then the configuration relationship between fault and sand body, structural amplitude and sand body were analyzed to set up the evaluation criteria of effective traps. According to the criteria, the traps were selected to enhance the exploration success rate.

An improved method to characterize the full-scale pore system and dual pore model of tight sands

Tight sands have pore systems with complex structures and widely distributed pore sizes. We have studied the characteristics of these pore systems to better understand their important role in the accumulation and migration mechanisms of oil and gas reservoirs, which may enhance our ability to evaluate reservoir quality and predict reservoir production. To this end, we carried out thin-section analysis, scanning electron microscopy, pressure-controlled porosimetry (PCP), and rate-controlled porosimetry (RCP) to describe the pore systems of a typical tight-sand reservoir in East Asia. We improved a differential-distribution-based splicing method to reveal the full-scale pore systems using PCP and RCP. We found that the typical pore radius distribution in our target reservoir exhibits two peaks: at radius [Formula: see text] and at radius [Formula: see text]. Based on pore shapes and connections, intergranular pores are network structures and clay-host pores are tree-like structures. Intragranular pores, in contrast, can be different structures under different conditions. If wide throats are present, intragranular pores function as typical tree-like pores; if throats are narrow, they serve as the pore parts of a network-pore system. Network pores are the primary contributors to porosity and permeability, whereas tree-like pores mainly contribute to porosity. In some high-clay sands, however, the tree-like pores may also contribute to permeability. Based on their fractal characteristics, we divided the pore systems of tight sands into three types: (1) a network-structure-controlled intergranular pore system, (2) a tree-like-structure-controlled clay-host pore system, and (3) a network-structure-controlled intergranular-intragranular pore system.

Discovery of the high-yield well GT1 in the deep strata of the southern margin of the Junggar Basin, China: Implications for liquid petroleum potential in deep assemblage

The accumulation assemblages in the deep Jurassic and Cretaceous strata of the southern margin of the Junggar Basin (SMJB) have favorable petroleum accumulation conditions. Due to the huge burial depth, gas/condensate gas reservoirs are expected as the main targets, however, barely any exploration breakthrough has been achieved. The recently drilled well GT1 has obtained a high oil production of >1200 tons/day in the deep Cretaceous strata, which was classified as low gas-to-oil ratio (GOR) light oil. This is the first significant breakthrough in the deep assemblages in the SMJB which brings to the question of its genesis and preservation and the true petroleum potential in the area. In this study, we have presented integrated geochemical analyses including GC × GC-TOFMS, GC-MS and stable carbon isotopes and thus to conclude that the GT1 oil was sourced from Jurassic coal-measure source rocks with maturity of 0.7–0.9%Ro. As only a small amount of diamondoids and ethanodiamondoids were detected, the GT1 oil was classified as normal mature oil well preserved from thermal cracking despite its huge burial depth. The associated gas is coal-type gas with relatively high wetness and the similar maturity to that of the oil. According to the hydrocarbon accumulation analyses, the main source rocks were developed in the Lower-Middle Jurassic with present-day maturity of 1.0%–2.0%Ro. The sandstones developed in the transitional facies in the overlying Lower Cretaceous Qingshuihe Formation were impacted by the tectonic compression and preserved as belt-like distribution in anticline traps. Regional Cretaceous Tugulu Group also overlie these sandstone facies. This forms a favorable source-reservoir-seal assemblage for oil and gas accumulations in the area. Therefore, the deep assemblage in the SMJB is favorable for the accumulation and preservation of large-scale oil reservoirs and shows great potential for liquid petroleum exploration.

Seismic stratigraphic patterns and characterization of deepwater reservoirs of the Mundaú sub-basin, Brazilian Equatorial Margin

Abstract In recent years, the Brazilian Equatorial Margin has drawn attention due to its similarity to areas with new hydrocarbon discoveries in the African conjugated margin, and in French Guiana. However, studies on the tectonic regimes associated with transform margins and their evolution, structures, and petroleum potential are still lacking due to the geological complexity of this region. To address this knowledge gap, research has been done to better understand the geological structures, as well as to identify potential hydrocarbon accumulations in the deepwater Ceara Basin. To achieve this, we performed an integrated interpretation of a large 2D seismic data, new exploratory borehole data, as well as older well data with revised biostratigraphy. This data analysis refines the basin architecture and the Cretaceous-Paleocene tectonic evolution, including implications for hydrocarbon prospectivity in the Ceara Basin deepwater. 2D seismic interpretation was performed using modern concepts of continental break-up. To accomplish this, the transition of continental-oceanic crust was taken into account for restoration of the sediments of the rift stage in the basin. The analysis also identifies potential hydrocarbon accumulations in turbiditic reservoirs and presents new insights about the dimensions of the underlying rift features situated in the continental slope. The results reveal a high potential for drift sequences in deepwater where the Late Albian-Early Cenomanian-Turonian sediments reach thicknesses of approximately 3048–4894 m. Moreover, this research shows evidence of Cretaceous to Paleocene magmatism, indicated by the well-imaged volcanoes and associated sills in the seismic data. This analysis indicates that the Mundau sub-basin can be classified as a volcanic passive margin that was developed during the oblique dextral separation between South America and Africa. The variety of stratigraphic and structural features developed through the Cretaceous history of the Mundau sub-basin offers a variety of potential hydrocarbon traps and plays in a number of rift and post-rift sequences.

Distributions of gas hydrate and free gas accumulations associated with upward fluid flow in the Sanriku-Oki forearc basin, northeast Japan

Abstract We applied automated velocity analysis to a 3D seismic data volume to obtain a high-resolution seismic velocity model that we used to investigate the influence of fluid behavior on the subsurface distribution of gas in the Sanriku-Oki forearc basin, northeast Japan. We identified free gas accumulations as zones of low P-wave velocity separated from overlying high-velocity gas hydrates by the clear seismic boundary of the bottom-simulating reflection (BSR) between them. We then used conductive modeling to map upward heat flow in our study area from the depth of the BSR derived from the velocity model. The estimated heat flow demonstrates that upward fluid flux has considerable influences on the distributions of both gas hydrate and free gas. The areas of high heat flow (representing high fluid flux) correspond to underlying permeable geological features such as gas chimneys, faults, and the edges of porous slumps, suggesting that these features provide fluid migration pathways from Eocene to Oligocene source rocks to free gas and hydrate accumulations in overlying sedimentary rocks. The techniques we have employed can contribute to the high-resolution mapping of gas hydrate and free gas accumulations in similar deep-water reservoirs off the eastern continental margin of Japan and at tectonically similar plate subduction margins in other regions.

Stochastic and analytical approaches for sediment accumulation in river reservoirs

ABSTRACTSediment accumulation in a river reservoir is studied by stochastic time series models and analytical approach. The first-order moving average process is found the best for the suspended sediment discharge time series of the Juniata River at Newport, Pennsylvania, USA. Synthetic suspended sediment discharges are first generated with the chosen model after which analytical expressions are derived for the expected value and variance of sediment accumulation in the reservoir. The expected value and variance of the volume of sediment accumulation in the reservoir are calculated from a thousand synthetic time series each 38 years long and compared to the analytical approach. Stochastic and analytical approaches perfectly trace the observation in terms of the expected value and variability. Therefore, it is concluded that the expected value and variance of sediment accumulation in a reservoir could be estimated by analytical expressions without the cost of synthetic data generation mechanisms.

FACTORS AFFECTING FLOOD MANAGEMENT IN BIHAR, INDIA

Bihar is facing a flood problem every year. This paper includes all the major factors which increase flood level in Bihar such as heavy rainfall, a large number of rivers, topography of the area, sand mining, and silt accumulation. There are some factors which are directly responsible and others are indirectly responsible for flood hazard. Heavy rainfall and a large number of rivers are directly responsible factors. The capacity of rivers and reservoirs is reduced due to silt accumulation and deforestation upstream in Nepal is the reason behind silt accumulation in rivers and reservoirs through heavy rainfall. Watershed management is not very successful because most of the plain area. The hydrology of Bihar is also disturbed due to excess sand mining. The built-up area of the state is increasing and this is resulting in heavy surface runoff, because there is no open area to hold the water. The increased flow also washes the fertile soil of the agricultural area of Bihar

Methodological advances to biomonitor water quality with transplanted aquatic mosses

The active biomonitoring technique has been demonstrated to be an excellent tool for monitoring water quality; however, further improvement of the protocol is urgently needed. The present study was carried out to determine the best options for various methodological aspects of monitoring some metals and metalloids (i.e. Al, As, Cd, Co, Cu, Fe, Hg, Ni, Zn and Pb): i) the type of transplant, ii) pre-exposure washing (with or without cellular extractants), iii) the ratio between moss weight and bag surface area, and iv) the depth at which the bags are exposed. The importance of the different methodological aspects in the outcome of biomonitoring studies was also assessed by considering the results of the present and other previously published studies. Regarding the type of transplant, the traditionally used net bags were the best option for enclosing the moss; in addition, washing the moss with extracellular extractants (i.e. EDTA) prior to exposure increased the sensitivity of the technique and reduced the required exposure time (i.e. one week). For the amount of moss packed in each bag, a ratio of 12.5 mg cm−2 was the best choice. Finally, the depth at which the transplants were exposed did not affect pollutant accumulation (in shallow rivers, reservoirs or dams). Pollutant concentrations were also not affected by the existence of thermocline in deep waters during warmer months. Different methodological aspects involved in applying this technique determine the final concentrations of metals in moss. Although the influence of those was variable, for most elements (i.e. As, Cd, Co, Cu, Hg, Pb, Zn) 80% of the total variance was explained by 3–4 aspects, being species selection, devitalization treatment, duration of exposure, and number of transplants exposed the most important.

Oaks: an evolutionary success story.

The genus Quercus is among the most widespread and species-rich tree genera in the northern hemisphere. The extraordinary species diversity in America and Asia together with the continuous continental distribution of a limited number of European species raise questions about how macro- and microevolutionary processes made the genus Quercus an evolutionary success. Synthesizing conclusions reached during the past three decades by complementary approaches in phylogenetics, phylogeography, genomics, ecology, paleobotany, population biology and quantitative genetics, this review aims to illuminate evolutionary processes leading to the radiation and expansion of oaks. From opposing scales of time and geography, we converge on four overarching explanations of evolutionary success in oaks: accumulation of large reservoirs of diversity within populations and species; ability for rapid migration contributing to ecological priority effects on lineage diversification; high rates of evolutionary divergence within clades combined with convergent solutions to ecological problems across clades; and propensity for hybridization, contributing to adaptive introgression and facilitating migration. Finally, we explore potential future research avenues, emphasizing the integration of microevolutionary and macroevolutionary perspectives.

Hydrocarbon accumulation of composite-buried hill reservoirs in the western subsag of Bozhong sag, Bohai Bay Basin

There are abundant hydrocarbon resources in the western subsag of Bozhong sag in the Bohai Bay Basin, where oil–gas discoveries have been made in those shallow Neogene and Paleogene reservoirs and deep Mesozoic buried hill reservoirs, but no better understandings have yet been achieved in terms of the process of hydrocarbon accumulation and the relationship between deep buried hill reservoirs and the allocation of shallow reservoirs. Based on the organic geochemical analysis of source rocks and basin modeling of hydrocarbon generation evolution, distribution characteristics of fluid inclusion and homogeneous temperature measurement, combined with the characteristics of oil-source biomarkers, the process of hydrocarbon accumulation in this study area was resumed based upon the regional tectonic background. The following findings were obtained. (1) There are 3 sets of source rocks in the third and first members of Paleogene Shahejie Fm, and the second lower member of Paleogene Dongying Fm; the reservoirs in the peripheral uplift zones include Mesozoic volcanic rocks, Archean metamorphic rocks, and Paleogene–Neogene delta–fluvial porous sandstones. Hydrocarbon generated in this sag migrated along the fault and the unconformity surface to the slope before accumulated in the peripheral tectonic zones, resulting in 3 sets of source–reservoir–caprock assemblages formed with the characteristics of reservoir formation in compound oil and gas accumulation zones. (2) The stratum in the third member of Shahejie Fm is the main source rock. (3) The above three assemblages went through four periods of generating process during the geological time of 11–1 Ma. Vertically hydrocarbon sources first filled in the deep Mesozoic and Archean reservoirs, then migrated and accumulated in the shallow Neogene and Paleogene reservoirs, where multiple shore-term rapid filling of high-temperature fluids led to this typical oil and gas pooling mode.

Organic matter enrichment and hydrocarbon accumulation models of the marlstone in the Shulu Sag, Bohai Bay Basin, Northern China

Hybrid unconventional systems are composed of juxtaposed organic-rich and organic-lean intervals. Organic matter enrichment, hydrocarbon migration, and the spatial relationship of source rocks and reservoirs have important influences on differential hydrocarbon accumulation within the system. Most studies have ignored the complexity of hydrocarbon accumulation in unconventional oil reservoirs. A typical hybrid lithology system with a combination of marlstone and rudstone has been discovered in the lower part of the third member of the Shahejie Formation of the Shulu Sag, Bohai Bay Basin, Northern China. The basin showcases a strong heterogeneity in unconventional hydrocarbon production and is an appropriate case to study hydrocarbon accumulation within hybrid unconventional systems. However, relevant work in the study area was scarce. A study of the mechanisms of organic matter enrichment and hydrocarbon accumulation was required to understand the heterogeneity of the oil reservoirs. Nine units in ascending order, namely IL, IU, IIL, IIU, IIIL, IIIU, IV, VL, and VU, were proposed in this study. A detailed geochemical analysis was carried out to distinguish the organic matter sources and preservation conditions among the different units, and assess the migration patterns of the hydrocarbons. The results show that Unit IIL has the highest total organic carbon (TOC) content. Unit IIL has a higher quantity of aquatic sourced organic matter, with relatively high abundance of short chain n-alkanes, C27/C29 sterane, and 4-methyl steranes. Based on the low ratios of pristane to phytane, the varve-like lamination structure of the lithology and suitable salinity, we can speculate that good organic matter preservation conditions existed in Unit IIL. Maturity of the source rocks increases with depth. Biomarkers indicate that hydrocarbons within the marlstones were retained in situ, whereas hydrocarbons within the rudstones were derived from source rocks via short- or long-distance migrations. Fractures can act as effective pathways for hydrocarbon migration. Organic matter sources, preservation conditions, maturity, and hydrocarbon migration ways jointly controlled the formation of oil reservoirs in the Shulu Sag. The results of this study provide a better understanding of organic matter enrichment and hydrocarbon accumulation and guide further exploration in the basin.