Sand Bodies Research Articles

Efficient development technology of Upper Paleozoic Lower Shihezi tight sandstone gas reservoir in northeastern Ordos Basin

Abstract The Lower Shihezi Formation of the Upper Paleozoic at the northeastern margin of the Ordos Basin develops widely distributed thick massive and multilayer gas reservoirs. How to formulate an effective development policy is a difficult and hot spot. In this article, reservoir characteristics and production capacity influencing factors of the tight gas sandstone in Lower Shihezi Formation in this area are systematically studied, and optimization schemes of development measures for massive and multilayer gas reservoirs are proposed. The results show that the petrophysical characteristics of the small pore–mesopore type gas reservoir in the target layer are the best, with the average porosity, permeability, and coordination number of 7.6%, 0.74 mD, and 3.3, respectively. Thick sand body, high structural position, good petrophysical properties, and high drilling rate of sandstone are all conducive to drilling high production gas wells. Development policies for massive and multilayer gas reservoirs have been formulated: (1) the preferred well type for massive gas reservoir is vertical well + horizontal well, while the preferred well type for multilayer gas reservoir is horizontal well + stepped horizontal well; (2) the reasonable horizontal segment length of massive gas reservoir is 1,000 m, and the reasonable horizontal segment length of multilayer gas reservoir is 1,250 m; (3) similar to massive and multilayer gas reservoirs, the more the fracture stages, the higher the cumulative gas production, and the optimal fracture stage number of both gas reservoirs is 8; (4) the optimal fracture half-length and the angle between the fracture and the horizontal section are 140 m and 90°, respectively; and (5) the reasonable well spacing of vertical wells is 600 m and that of horizontal wells is 750 m. The development policy proposed in this study is suitable for the efficient development of complex tight sandstone gas reservoirs in similar areas.

Prediction of Oil Source Fault-Associated Traps Favorable for Hydrocarbon Migration and Accumulation: A Case Study of the Dazhangtuo Fault in the Northern Qikou Sag of the Bohai Bay Basin

In order to study the distribution pattern of oil and gas near the lower-source, upper-storage type of oil source faults in the hydrocarbon-bearing basins, a set of prediction methods favourable to oil and gas migration and accumulation were established by superimposing the parts of the oil source fault-associated traps, the contiguously distributed sand bodies and the lateral sealing position of faults. The trap associated with a fault can be determined by the fault’s convex part on the fault plane’s morphology map, the fault throw displacement curve and the intersection of faults on the structure map. The set of sand bodies can be determined by the sand-to-shale ration of the formation. The lateral sealing position of faults can be investigated by the shale content of the fault. This study is based on our case study of the Dazhangtuo Fault in the lower sub-member of the 1st member (Es1L) of the Shahejie formation in the northern Qikou Sag of Bohai Bay Basin. The results illustrate 4 fault nose traps formed by fault line deflection in the Es1L formation of the Dazhangtuo Fault, 2 each in the middle and eastern end. The Dazhangtuo Fault is favorable for oil and gas migration except at the eastern and western ends and the middle part of the fault. The fault-associated traps in the Es1L formation that are highly favorable for hydrocarbon migration and accumulation (overlapping site of associated traps and favorable location for oil and gas migration) are distributed in the eastern and central parts of the Dazhangtuo Fault. In contrast, those moderately favorable for hydrocarbon migration and accumulation (associated trap at a certain distance from the favorable location for oil and gas migration in the Dazhangtuo Fracture) are locally distributed in the east. Both traps are conducive to accumulating hydrocarbons from the underlying source rock in the Es3 formation. Such observations are consistent with the current confirmed hydrocarbon distribution, thus validating the feasibility and accuracy of predicting the distribution of traps related to oil source faults favorable for hydrocarbon migration and accumulation, it can be used to guide the exploration of the lower-source, upper-storage type of hydrocarbon accumulations in the hydrocarbon-bearing basins.

Prediction of tight sandstone reservoirs by multiwave joint prestack inversion technology: A case study of the Qiulin area in the Sichuan Basin

The Shaximiao (SXM) Formation of the Middle Triassic in the central Sichuan Basin is a river-lake sedimentary system with an average burial depth of 2800 m. The channel sand bodies of the SXM Formation in the Qiulin area are developed with large lateral variation and high- and medium-porosity sand. This leads to great differences in the seismic response and difficulty in predicting the sand bodies and reservoirs using P-wave data. We carry out well-log analysis for different types of sand bodies. The no. 8 sand body of high porosity can be effectively identified using P-wave impedance (PI). Whereas for the no. 7 sand body of relatively lower porosity (mainly due to the higher shale content in the no. 7 sand compared with the no. 8 sand), sandstone and mudstone can be distinguished using S-wave impedance (SI), and reservoirs can be recognized by the P- to S-wave velocity ratio ([Formula: see text]/[Formula: see text]). Based on the PP wave and the P-to-S converted wave (PS wave) (after matching) angle-stacked data, a prestack inversion of multicomponent data is performed. Multiwave joint inversion results (SI and [Formula: see text]/[Formula: see text]) have better accuracy and stronger stability than the PP-wave inversion in practical application. In addition, the PI of the joint inversion more clearly describes the distribution and boundaries of the channel sand and better matches the prediction and drilling data in sand 8. The SI of the joint inversion can identify subtle sand bodies (weak PI contrast) that are difficult to be detected by PP-wave inversion. The distribution of the reservoir predicted by the [Formula: see text]/[Formula: see text] of the joint inversion is clearer (the no. 7 sand body) and better than that by the PP-wave inversion. This study demonstrates the advantage of the multiwave joint inversion technology in tight sand identification.

Application of the high-resolution layer-stripping constrained seismic inversion method in thin reservoirs: a case study of Triassic reservoir prediction in Lunnan, Tarim Basin, NW China

The Lunnan Oilfield’s Triassic reservoir is a braided river delta deposition, exhibiting notable characteristics such as rapid lateral sand body changes, thin reservoir thickness, and deep reservoir burial. However, the conventional seismic inversion technique used in this geological context is hindered by the low accuracy of the low-frequency model, resulting in inversion outcomes with limited vertical resolution. Consequently, accurately characterizing the reservoir distribution becomes challenging, posing a significant obstacle for the subsequent exploration and development. In this study, we introduce an enhanced seismic inversion approach using high-resolution layer-stripping constraints. The process begins with the creation of a fine-grained layer sequence grid on wells through Integrated Prediction Error Filter Analysis (INPEFA) technology. Subsequently, this grid aids in interpreting high-resolution sequence layers on the seismic volume, obtained through a frequency division RGB (Red, Green, and Blue) fusion technique. Finally, a novel nonlinear stochastic inversion method is formulated, utilizing the high-resolution sequence to refine both the initial model and inverted results. This innovative seismic inversion technique significantly enhances accuracy, particularly in predicting thin reservoirs, approximately 3 meters thick. The application of this method in a case study on Triassic reservoir prediction in Lunnan, Tarim Basin, NW China, demonstrates its promising future applications.

Petrophysical Evaluation of Arkoses Reservoirs Based on Well Logs and Plug Samples: A Case Study From Alagamar Formation, Southeastern Portion of Onshore Potiguar Basin, Brazil

The Potiguar Basin is a sedimentary basin located in northeastern Brazil. It covers about 48,000 km² and extends from onshore to offshore. The onshore basin is thought to have formed during the Late Cretaceous, as a result of the opening of the Equatorial South Atlantic Ocean, filled with a thick sequence of sedimentary rocks, including sandstones, shales, and limestones, which were deposited in a variety of processes, including marine, deltaic, and fluvial. The study area is in the southern portion of the basin and the reservoir is composed of arkose sandstones deposited by alluvial fan and fluvial systems of the Upanema Member of the Alagamar Formation, which belongs to the post-rift phase of the Potiguar Basin. Recently, new drilling campaigns revealed a reservoir heterogeneity in these deposits, which requested a new petrophysical approach. Using conventional well logs and petrophysical laboratory analysis of plug samples, this study evaluated the best way to calculate the effective porosity, and shale volume and to understand the stratigraphic controls in the distribution of these properties. Three reservoir zones were mapped: the basal one, Zone 3, has disconnected sand bodies, low porosity, and high shale content; Zone 2 has better petrophysical properties, lateral distribution, and connectivity between the fans and Zone 1 is the better reservoir zone with larger sand bodies, higher porosity values, and well-connected fans.

A novel approach to understanding the genesis and distribution of widespread reservoirs at the basin edge: A case study of gas-bearing sandstone in the Sangonghe Formation, Junggar Basin, Western China

A 20 m thick sandstone drilled in the second member of the Sangonghe Formation in the Qianshao area of the Junggar Basin has been identified to be a high-quality gas-bearing reservoir. However, recent missions reveal an uncertainty in reservoir distribution and bring high risk to the subsequent gas development, although the gas-bearing reservoir has been encountered by several drillings and proved to be widespread. To investigate the accurate distribution and reveal the evolution of the reservoir, we reconstruct the stratigraphic framework and depositional stages by a high-revolution sequence stratigraphic method, effectively identify the gas-bearing reservoir by seismic attributes refusion and seismic stratigraphic slices, and finally map the distribution strata distribution at different stages. The results indicate that the landward onlap phenomenon in the seismic data indicates a retrogradational stratigraphic structure during the water level rise rather than the equal-thickness stratigraphic pattern under stable water conditions. According to the retrogradational stratigraphic structure, the real driver for the widespread characteristic of a gas-bearing reservoir is the backward staggered movement of multistage sand bodies during the transgressive process rather than single-stage deposition. The fusion of seismic acoustic impedance and main frequency attributes provides an effective survey to identify the accurate distribution of the reservoir, by which interpretation of a stratigraphic slice along the vertical centerline of the reservoir extracted from the multiattribute fusion survey can present the distribution and evolution of the three stages on only one map. Achieved by an appropriate interpretation on the map, two sandy debris flow bodies are identified as being deposited at the bottom successively during the first two transgressive stages. They are completely staggered in the source direction with a clear boundary between well Qs9 and Qs7. Subsequently, the subsequent rise of the water level led to the deposition of a large-scale multibranch shallow-water delta, which exhibits the characteristics of multistage, multisource, and multibranch. The results not only advance our comprehension of widespread sand bodies but also furnish fundamental insights for the development of lithologic condensate gas reservoirs in the Qianshao area.

Infill Well Location Optimization Method Based on Recoverable Potential Evaluation of Remaining Oil

Infill well location optimization poses significant challenges due to its complexity and time-consuming nature. Currently, determining the scope of infill wells relies heavily on field engineers’ experience, often using single indices such as the remaining oil saturation or abundance of remaining oil reserves to evaluate the potential of remaining oil. However, this approach lacks effectiveness in guiding the precise tapping of remaining oil in ultra-high water cut reservoirs. To address this, our study comprehensively considers the factors influencing the recoverable potential of remaining oil in such reservoirs. We characterize the differences in reservoir heterogeneity, scale of recoverable remaining oil reserves, water flooding conditions, and oil–water flow capacity to construct a quantitative evaluation index system for the recoverable potential of remaining oil. Recognizing the varying degrees of influence of different indices on the recoverable potential of remaining oil, we determine the objective weight of each evaluation index by combining an accelerated genetic algorithm with the projection pursuit model. This approach enables the construction of a recoverable potential index for remaining oil and forms a quantitative evaluation method for the recoverable potential of remaining oil in ultra-high water cut reservoirs. Subsequently, we establish a mathematical model for infill well location optimization, integrating and optimizing the infill well location coordinates, well length, well inclination angle, and azimuth angle. Using the main layer sand body of an oilfield in Bohai as a case study, we conducted evaluations of the remaining oil potential and infill well location optimization. Our results demonstrate that the assessment of the remaining oil potential comprehensively characterizes the influence of the reservoir’s physical properties and oil–water diversion capacity on the remaining oil potential across different regional positions. This evaluation can effectively guide the determination of infill well location ranges based on the evaluation results. Furthermore, infill well location optimization can effectively enhance reservoir development outcomes.

The Environmental History of the Navazo Agroecosystem in Late Holocene Sand Bodies Along the Atlantic Coast of Andalusia, Spain

ABSTRACT Since the late Spanish Enlightenment, the agroecosystem of the Atlantic coast of Andalusia, through which coastal dune systems are cultivated via sunken gardens between sand berms, have attracted scholarly attention. The environmental history of these systems, known as Navazo, is the focus of this article. Through analysis of historical aerial photographs, we identify eight areas in which traditional Navazo land use was practiced. By studying landscape diversity and historical documentation we identify key aspects of the emergence and evolution of this agroecosystem. The results of this study indicate that Navazos originated through a combination of the natural properties offered by the region's coastal dune geomorphology, which was cultivated as vineyards since ancient times, as well as external cultural influences. Coinciding with the popularisation of potato consumption in the eighteenth century, earlier vineyards were, in some cases, completely replaced by Navazos. Due to transformations in traditional land use practices, created a contemporary version of the Navazo. The location and physical configuration of the Navazos, meanwhile, display strong similarities with archaeological remains of Plot-and-Berm agroecosystems from the southeastern Mediterranean dating from the Early Islamic period. This study presents evidence to better understand the function, cropping practices and irrigation of these systems. .

Seismic Prediction Technology for Channel Sand Body of Fuyu Oil Layer in Xinmin Area, Southern Songliao Basin

The Fuyu reservoir in Xinmin area is a delta plane-front facies deposit, and the channel sand body in this area is the main reservoir of oil and gas. Due to the complex sedimentary environment, the sand body shows great variation in thickness and distribution. In this study, the method of combining well vibration, model forward modeling and stratum slicing are used to predict the sandstone bodies of different thickness successfully. Especially for the thin sand body with a thickness of less than 5 meters, this study found that the GR curve can effectively distinguish sandstone and mudstone through the intersection analysis of logging curves, and applied the GR curve co-simulation inversion technology to perform fine characterization. In addition, the study also reveals that the northeastward twisting fault zone in Xinmin area is a favorable accumulation area of the reservoir, which provides a new direction for oil and gas exploration. This study not only improves the accuracy of sandstone prediction, but also provides a valuable reference for oil and gas exploration under similar complex geological conditions.

Impacts of sedimentary characteristics and diagenesis on reservoir quality of the 4th member of the Upper Triassic Xujiahe formation in the western Sichuan basin, southwest China

The 4th member of Xujiahe Formation (Xu4) in the western Sichuan Depression is a typical porous tight sandstone reservoir. Finding reservoirs with relatively high porosity controlled by sedimentation and diagenesis is crucial for successful tight gas exploration. In this study, the Xu4 sandstone was studied by diverse methods, including outcrop and core observation, logging data interpretation, thin section and cathodoluminescence examination, scanning electron microscopy analysis, and X-ray diffraction, to determine sedimentary and diagenetic characteristics and to discuss their impact on the sandstone reservoir quality. During the depositional period of Xu4, subaqueous distributary channel sandstone of braided river delta front developed extensively under controls of bidirectional provenance (LASP and SASP), mainly consisting of litharenite and sublitharenite, with low feldspar and high rock fragments volume, respectively. Strong compaction and carbonate cementation have largely destroyed primary porosity, while secondary pores constitute the main pore space in the Xu4 sandstone. The sediment provenance, sedimentary microfacies and A/S determine the clastic composition of sandstone, genetic type and thickness of sand bodies, furthermore affect the subsequent diagenetic variations. The larger the thickness of the sand body indicates a higher-energy depositional environment, coarser grain size, better sorting, and lower shaliness content of the sandstone during deposition period. This results in stronger resistance to compaction of the sandstone, which is conducive to the preservation of primary pores and dissolution of organic acids, resulting in better physical properties of sandstone. Among them, the physical properties of the sandstones of the Xu4s and Xu4x are better than those of the Xu4z; moreover, LASP's sandstone is superior to SASP. It is worth noting that subaqueous distributary channel sandstones with thickness exceeding 13 m in Xu4s and Xu4x from LASP represent favorable areas for high-quality reservoirs. The work can be used as a reference for the exploration and evaluation of similar tight sandstone gas in the world.

A Novel Method for Analyzing Sandbar Distribution in Shelf-Type Tidal Deltas Using Sediment Dynamic Simulation

Shallow marine shelf sedimentation is a hot and difficult topic in today’s reservoir sedimentology research, and it is widely present in the world. The shallow marine shelf sedimentation is not only affected by complex hydrodynamic effects such as tides and waves, but also controlled by bottom tectonic features, forming a complex and varied sedimentation pattern. During the Middle Jurassic period, the northern part of West Siberian Basin was characterized by a shallow marine shelf sedimentary environment. In the central reion of this basin, a typical tectonic uplift zone developed, forming a tectonic background of “one uplift zone between two depressions”. Simultaneously, the dominant influence of tides in the shallow marine shelf environment facilitated the formation of a typical shelf-type tidal delta sedimentation system in the Jurassic strata of the northern part of West Siberian Basin. This sedimentation constitutes a significant natural gas reservoir, and it is important to investigate the sedimentary evolution of shelf-type tidal deltas and to clarify the internal structure and distribution of sedimentary sand bodies and interlayers in shelf-type tidal deltas, which is the basis for the fine development of this type of reservoir. This paper takes the Jurassic strata in the Y region of northern part of West Siberian Basin as the research object, and conducts numerical simulation based on sedimentary dynamics for the shelf-type tidal delta sedimentation formed under the tectonic background of “one uplift zone between two depressions”. In addition, tidal amplitude and initial water level were selected for different hydrodynamic factors to study the main controlling factors of shelf-type tidal delta sedimentation. The simulation results show that tidal amplitude is positively correlated with three-dimensional configuration characteristic parameters of the sedimentary sand bodies, and the development of tidal bars becomes more and more limited as the initial water level increases. This paper systematically investigates the sedimentary evolution of shelf-type tidal delta under the tectonic background of “one uplift zone between two depressions” by the sedimentary dynamics method, which deepens the understanding of the shelf-type tidal delta sedimentation process and provides a new thinking for the development of this sedimentary reservoir type (School of Geosciences China University of Petroleum (East China)).

Właściwości złoża jurajskiej formacji Khatatba: Pole naftowe Tut, Pustynia Północno-Zachodnia, Egipt

The Tut oil field is in the North-western part of the Western Desert. This work aims to study the reservoir characteristics, to evaluate the hydrocarbon potentiality of the Upper and Lower Safa Members based on the available subsurface data obtained from open-hole well log records of four wells distributed in the study area. Numerous isopach and lithofacies maps have been constructed. The petrophysical evaluation, in terms of determining reservoir net-pay thickness, shale content (Vsh), effective porosity (∅eff), water saturation (Sw) and hydrocarbon saturation (Sh), were estimated. The vertical and the lateral distribution of the reservoir characteristics, in the form of litho-saturation cross-plots, iso-parametric maps and lithologic-matrix cross-plots were constructed. Three hydrocarbon charged zones in the Khatatba Formation were defined and represented by the Upper Safa-Top, Upper Safa-Bottom and Lower Safa-Top. The upper most part of Upper Safa Member (Upper Safa-Top) reservoir represents an oil producing zone where it consists of shallow marine to alluvial sediments. The Lower most part of Upper Safa Member (Upper Safa-Bottom) reservoir represents gas producing zone where it consists of a thick alluvial sand body. Finally, the upper most part of Lower Safa Member (Lower Safa-Top) reservoir represents an oil-gas producing zone consisting of shallow marine sediments with high terrestrial input. The iso-parametric maps show that Northern and central parts of the study area are the most favorable parts for hydrocarbon accumulation due to the increase in net-pay thickness and average effective porosity and decrease in water saturation toward these parts.

Evaluation of the Pilot Test Effect of Steam Stimulation in Horizontal Wells of Sand Bodies 1-1308 in Bohai L Oilfield

In order to reduce the risk of large-scale thermal recovery of heavy oil in Bohai Oilfield, L Oilfield is selected to carry out horizontal well steam stimulation pilot tests. Previous studies have summarized the rationality of the injection parameters and initial production characteristics of this experiment, but the evaluation of its development effectiveness is still blank. Based on the study of the decline law of A23H well cold recovery using reservoir engineering methods, this article evaluates the initial production capacity, production increase effect, technical recoverable reserves, and throughput cycles of steam stimulation. The results show that the thermal recovery production of steam stimulation is three times that of cold recovery, which can significantly improve the production capacity of a single well. The initial daily oil production of two wells is 74m<sup>3</sup>/d and 90m<sup>3</sup>/d, respectively, which is 3.0 times and 3.6 times that of the initial production of cold recovery, exceeding the design level of the reservoir; The first round has the best yield increase effect, with an average daily oil increase of 31m<sup>3</sup>/d, and gradually decreasing thereafter. By the fifth round, it was only 13m<sup>3</sup>/d. In terms of yield increase multiples, each round can reach about 2 times; The technically recoverable reserves are 19.03 × 10<sup>4</sup>m<sup>3</sup>, requiring 8-9 rounds. Through this performance evaluation, we have strengthened our confidence in promoting the application of steam injection technology in Bohai Oilfield to achieve large-scale thermal recovery.

Intelligent geological interpretation of AMT data based on machine learning

AMT (Audio Magnetotelluric) is widely used for obtaining geological settings related to sandstone-type Uranium deposits, such as the range of buried sand body and the top boundary of baserock. However, these geological settings are hard to interpret via survey sections without conducting geological interpretation, which highly relies on experience and cognition. On the other hand, with the development of 3D technology, artificial geological interpretation shows low efficiency and reliability. In this paper, a machine learning model constructed using U-net was used for the geological interpretation of AMT data in the Naren-Yihegaole area. To train the model, a training dataset was built based on simulated data from random models. The issue of insufficient data samples has been addressed. In the prediction stage, sand bodies and baserock were delineated from the inversion resistivity images. The comparison between two interpretations, one by machine learning method, showed high consistency with the artificial one, but with better time-saving. It indicates that this technology is more individualized and effective than the traditional way.

Geochemical and detrital zircon U[sbnd]Pb geochronology of the qigequan formation in the yuejin 2 area: Implications for tectonics and uranium sources

The Yuejin 2 mining area lies within the Mangya region, situated on the northwestern periphery of the Qaidam Basin. Recently discovered, it harbors a medium-sized uranium deposit within the basin. Nonetheless, investigations into the sedimentary provenance and paleoclimate of the Neogene Qigequan Formation in this locale have been sparse. This study delves into a meticulous examination of petrogeochemical attributes and the detrital zircon UPb geochronology of sandstones from the Qigequan Formation within the mining area, aiming to discern their origins and tectonic context. By scrutinizing the trace and rare earth element signatures of the rocks, we discern that the lower strata of the Qigequan Formation primarily originate from felsic sedimentary sources, indicative of a continental island arc tectonic. Detrital zircon ages from the Qigequan Formation manifest primarily in three distinct periods: 169–292 Ma, 327–505 Ma, and > 670 Ma, corresponding with geological ages documented in the Altyn Tagh and East Kunlun Mountains orogenic belts. Predominantly, the Altyn Tagh orogenic belt and the Qimantag Mountains in the eastern Kunlun Mountains serve as the principal source of the Qigequan Formation. The chemical weathering index (CIA*) is 70.54, suggesting a moderate level of chemical weathering within the source region. Additionally, the angular morphology of the detrital zircon implies proximity between the source area and the basin. During the late sedimentary epoch of the Qigequan Formation, rapid uplift of the Altyn Tagh led to a notable rise in temperature within the Yuejin 2 area, transitioning from a reducing to an oxidizing environment. Surface water enriched with uranium and eroded source rocks gradually infiltrated the sand bodies of the lower Qigequan Formation. Interaction with reducing agents facilitated the enrichment and formation of ore. Paleoclimatic shifts instigated the oxidation–reduction sequence necessary for uranium mineralization. Favorable conditions, characterized by oxygen-rich paleo-water, facilitated the activation, migration, and re-enrichment of uranium. Moreover, the Himalayan movement acted as a driving force and a pivotal factor in creating the conducive conditions imperative for large-scale uranium mineralization in the area.

Disturbance characteristics test about double-line shield tunnel excavation in grouting-reinforced water-rich sand stratum

To study the disturbance characteristics of double-line shield tunnel excavation on sand bodies in grouting-reinforced water-rich sand stratum, a similar model test was carried out. Firstly, the physical parameters and strength indexes of the overlying soil strata of the tunnel in the water-rich sand stratum were determined by laboratory tests. The similar soil and tunnel support structures of each stratum were prepared. Then, considering the different seepage modes of upper and lower soil strata under the influence range of tunnel excavation, the model test of double-line shield tunnel excavation in a grouting-reinforced water-rich sand stratum is conducted. The variation rules of sand deformation, surface settlement, and sand body stress during the excavation of a double-line shield tunnel are analyzed utilizing monitoring and analyzing systems such as a flowmeter, micro earth pressure sensors, and dial indicators. It is found that during the excavation of the double-line tunnel, the self-stabilization ability of the grouting reinforced sand bodies is strong under the action of stable seepage. Under the influence of grouting reinforcement, the seepage path around the tunnel structure will change, the fluid-solid coupling effect will decrease, and the sand stratum will be uplifted to varying degrees. The sand body will change its mechanical properties due to the influence of seepage. The fluid-solid interaction effect will be enhanced. The fluid-solid coupling effect of soil particles and water will be further enhanced when the excavation of the subsequent tunnel is carried out. The effect of unsaturated seepage in the overlying soil stratum leads to greater stress at the arch waist of the arch tunnel. In the actual construction process, the grouting amount and grouting time should be strictly controlled. The tunnel basement is supported by anchor spray support to prevent the tunnel structure and surface uplift.

Differences in hydrocarbon accumulation and controlling factors of slope belt in graben basin: A case study of Pinghu Slope Belt in the Xihu sag of the east China Sea Shelf basin (ECSSB)

The Pinghu slope belt in the Xihu sag of the East China Sea Shelf Basin (ECSSB) is a crucial hydrocarbon production area in eastern China. However, due to the complex geological conditions, publications have lacked comprehensive research on the spatial-temporal coupling relationships of primary factors that impact hydrocarbon accumulation in the Pinghu slope belt. Furthermore, the hydrocarbon distribution patterns and the controlling factors across different study areas within the same slope belt are not yet fully understood. This study extensively utilized three-dimensional seismic data, well logging data, geochemical analysis, fluorescence analysis, and oil testing and production data to address these issues. Following a “stratification and differentiation” approach, the study identified seven distinct hydrocarbon migration and accumulation units (HMAU) in the Pinghu slope area based on the structural morphology characteristics, hydrocarbon source-reservoir-cap rock patterns, hydrocarbon migration pathways, and hydrocarbon supply range. Detailed analysis was conducted to examine the hydrocarbon distribution patterns and controlling factors within each migration and accumulation unit across different structural units, including high, medium, and low structural components. All data sources support a “southern‒northern sub-area division, eastern‒western sub-belt division, and variations in hydrocarbon accumulation” pattern in the Pinghu slope belt. The degree of hydrocarbon accumulation is controlled by the factors of structural morphology, hydrocarbon generation potential of source rocks, the spatial position of source slopes, fault sealing capacity, and sand body distribution. Furthermore, different coupling patterns of faults and sand bodies play a pivotal role in governing hydrocarbon enrichment systems across various migration and accumulation units. These observations indicate that three hydrocarbon accumulation patterns have been established within the slope belt, including near-source to far-source gentle slope with multiple hydrocarbon kitchens in the XP1−XP4 zones, near-source to middle-source gentle slope with dual-hydrocarbon kitchens in the XP5 zone, and near-source steep slope with a single hydrocarbon kitchen in the XP6−XP7 zones. These findings contribute to enhancing the theoretical system of hydrocarbon accumulation in the slope belt.

Experimental Study on Surface Segregation Law of Three-Dimensional Accumulation Body of Sand and Stone Particles by Binary Mechanism

Sand and stone materials are one of the important raw materials for infrastructure construction. In recent years, natural sand resources have decreased rapidly. In order to protect rivers and DAMS and ecological balance, local governments have increased the control power of natural sand mining, and replacing natural sand with mechanically broken parent rock formation mechanism sand has become an inevitable trend of the industry development. During the crushing process of parent rock, sand particles of different particle size range are produced, and particle segregation occurs in the process of stacking in the yard, which brings great trouble to the calculation of particle grading and material sample detection, and hinders the large-scale application of machine-made sand. In this paper, three-dimensional stacking tests of irregular particles were carried out to identify the particle distribution on the surface of the stack by digital image technology, analyze the relationship between particle size composition of particle mixture and the particle distribution of the accumulation body, and study the distribution law and segregation characteristics of the accumulation body. The experimental results show that the mixture with different coarse particle content will produce the corresponding distribution on the surface of the accumulation body after the accumulation. On the surface of the accretion body, the content of coarse particles is vertically distributed along the height of the accretion body. The content of coarse particles in the lower part of the accretion body is greater than that in the upper part of the accretion body. The overall segregation coefficient on the surface of the pile decreases with the increase of coarse particle content, and the variation is the largest in the lower part of the pile surface with the initial coarse particle content. Based on the test results in this paper, it provides a basis for formulating the sampling and inspection method of machine-made sand, ensuring the quality of machine-made sand and improving the utilization rate of machine-made sand.

Genetic mechanism and main controlling factors of high-quality clastic rock reservoirs in deep and ultradeep layers: A case study of Oligocene Linhe Formation in Linhe Depression, Hetao Basin, NW China

Based on new data from cores, drilling and logging, combined with extensive rock and mineral testing analysis, a systematic analysis is conducted on the characteristics, diagenesis types, genesis and controlling factors of deep to ultra-deep abnormally high porosity clastic rock reservoirs in the Oligocene Linhe Formation in the Hetao Basin. The reservoir space of the deep to ultra-deep clastic rock reservoirs in the Linhe Formation is mainly primary pores, and the coupling of three favorable diagenetic elements, namely the rock fabric with strong compaction resistance, weak thermal compaction diagenetic dynamic field, and diagenetic environment with weak fluid compaction-weak cementation, is conducive to the preservation of primary pores. The Linhe Formation clastic rocks have a superior preexisting material composition, with an average total content of 90% for quartz, feldspar, and rigid rock fragments, and strong resistance to compaction. The geothermal gradient in Linhe Depression in the range of (2.0–2.6) °C/100 m is low, and together with the burial history of long-term shallow burial and late rapid deep burial, it forms a weak thermal compaction diagenetic dynamic field environment. The diagenetic environment of the saline lake basin is characterized by weak fluid compaction. At the same time, the paleosalinity has zoning characteristics, and weak cementation in low salinity areas is conducive to the preservation of primary pores. The hydrodynamic conditions of sedimentation, salinity differentiation of ancient water in saline lake basins, and sand body thickness jointly control the distribution of high-quality reservoirs in the Linhe Formation.

Sedimentary characteristics and geological significance of a mixed-process delta for petroleum exploration in the Zhuhai formation of the Baiyun Depression, Pearl River Mouth Basin, China

The Zhuhai Formation in the Baiyun Depression of the Pearl River Mouth Basin in the northern South China Sea is a marine delta influenced by multiple hydrodynamic forces, including rivers, waves, and tides, resulting in a mixed-process delta. As a result of the combined effects of these forces, the distribution patterns and reservoir structures in the sandstone formations of the Zhuhai Formation are extremely complex. This paper provides a detailed description of the coring section of the Zhuhai Formation drilled in the Baiyun Depression, focusing on the lithology, sedimentary structure, special containers, and depositional dynamics of the coring section. It also summarizes the characteristics of a hybrid power delta controlled by rivers, waves, and tides, and explores the geological significance of this mixed-process delta for oil and gas exploration. The study reveals that sedimentation controlled by rivers primarily consists of medium-to-fine sandstones with interbedded cross-bedding and parallel bedding. Scour-fill structures and a bell or box-shaped natural gamma ray logging curve (GR) are also observed. Seismic reflection exhibits strong amplitude and high continuity. Wave-controlled sedimentation, on the other hand, predominantly consists of silt and fine sandstones with scouring, wave-formed cross-bedding, abundant bioturbation, and a serrated and funnel-shaped GR curve. Seismic reflection shows medium amplitude and high continuity. Tidally-controlled deposits are characterized by thin interbeds of mudstone, siltstone, and fine sandstone, as well as vein laminations, undulating composite laminations, lenticular laminations, and biclastic layers. The GR curves for tidally-controlled deposits are sharp or jagged with funnel shapes, and seismic reflections exhibit medium amplitude and continuity. The hydrodynamic features controlling sedimentation during the depositional period of the Zhuhai Formation in the Baiyun Depression exhibit evident zonation on a planar scale, influenced by sedimentary paleogeography and sea-level changes. River control is predominant in the northern Zhuhai Formation, with local wave influence and minimal tidal influence. In the southern part, tidal action becomes increasingly important. In terms of reservoir properties, wave-controlled reservoirs display significantly better porosity and permeability compared to tidally-controlled and river-controlled reservoirs. Tidally-controlled reservoirs exhibit high heterogeneity with a wide range of porosity and permeability values. The varying influences of different hydrodynamic drivers in different locations have led to significant variations in the size, morphology, and physical properties of sand bodies within the marine delta sediments of the Zhuhai Formation in the Baiyun Depression. Thus, the type and intensity of sedimentary hydrodynamics become the primary controlling factors for the development of high-quality reservoirs.