Greater Burial Depths Research Articles

Detecting subtle subterranean movement via laser speckle imaging.

A diversity of organisms live within underground environments. However, visualizing subterranean behavior is challenging because of the opacity of most substrates. We demonstrate that laser speckle imaging, a non-invasive technique resolving nanometer-scale movements, facilitates quantifying biological activity in a granular medium. We monitored fire ants (Solenopsis invicta) at different developmental stages, burial depths (1-5 cm) and moisture fractions (0 and 0.1 by volume) in a container of 0.7 mm glass particles. Although the speckle pattern from the backscattered light precludes direct imaging of animal kinematics, analysis of integrated image differences revealed that spiking during ant movement increased with the developmental phase. Greater burial depth and saturation resulted in fewer and lower magnitude spikes. We verified that spiking correlated with movement via quasi-2D experiments. This straightforward method, involving a laser and digital camera, can be applied to laboratory and potentially field situations to gain insight into subterranean organism activities.

EH6 enstatite chondrites Northwest Africa 7976 and Northwest Africa 12945: Implications for EH chondrite metamorphism

AbstractThe enstatite chondrite class is known to have complex thermal histories, often interpreted to include impact melting and shock metamorphism. Highly equilibrated (type 6) EH group enstatite chondrites are rare and thought to have formed through collisional heating. We studied two EH6 chondrites, NWA 7976 and NWA 12945, for their textural, chemical, and mineralogical characteristics. The samples we studied contain subhedral to anhedral grains of enstatite and plagioclase, suggesting solid‐state recrystallization. They show low degrees of shock and no evidence of shock melting. Additionally, the ubiquitous occurrence of daubréelite exsolution lamellae in troilite and the Ni content of schreibersite suggest slow cooling at greater burial depths in the parent body, rather than rapid cooling as a result of an impact event. Based on the characteristics and scarcity of type 6 EH chondrites, and the ubiquitous shock effects and melt rocks in the enstatite chondrite class, we conclude that the unshocked NWA 7976 and NWA 12945 were formed by heat derived from impact melt sheets, analogous to contact metamorphism.

Full-scale test on the mechanical behavior of longitudinal joints of NC-UHPC composite segments under compression-bending load

The performance of longitudinal joints in shield tunnel segments is crucial for ensuring structural stability and durability. This study presents an innovative segment structure combining normal concrete (NC) and ultra-high performance concrete (UHPC) (hereafter called NC-UHPC composite segment). Full-scale joint tests were conducted to analyze the mechanical response and failure characteristics of longitudinal joints in these segments. Compared to reinforced concrete (RC) segment joints, NC-UHPC composite segment joints exhibited a significant increase in initial cracking load by 197.93% under sagging moments and 435.3% under hogging moments. The ultimate load-bearing capacity increased by 55.71% and 67.10%, and the initial bending stiffness improved by 20.57% and 10.59% under sagging and hogging moments, respectively. Furthermore, NC-UHPC composite segment joints exhibited smaller crack distribution areas and fewer cracks, indicating superior crack resistance. No cracks or damage were observed at the NC-UHPC interface. Evaluation of joint toughness and ductility indices further highlighted the favorable performance of NC-UHPC composite segment joints. Finally, a refined numerical model was established to compare the deflection and bending stiffness of RC segment joints with NC-UHPC composite segment joints under varying axial forces. The findings suggest that NC-UHPC composite segments are more suitable for tunnel engineering with greater burial depth, higher water pressure, and larger axial forces.

Shale gas‐bearing capacity and its controlling factors of Wufeng–Longmaxi formations in northern Guizhou, China

Great progress has been made in marine shale gas of Wufeng–Longmaxi formations in the Sichuan Basin. However, shale gas exploration in the complex structural belt around the Sichuan Basin still faces great challenges. In this study, shales of Wufeng–Longmaxi formations collected from the northern Guizhou were taken as the studied target, organic matter (OM) characteristics, mineral composition, pore structure, methane adsorption capacity and in situ desorption gas content were measured, and the controlling factors of shale gas content were further discussed. The results indicated that the sedimentary facies of Wufeng–Longmaxi formations in north Guizhou varies from shallow‐water shelf facies to deep‐water shelf facies from south to north, and organic‐rich shales are primarily distributed in Daozhen‐Xishui areas, with a maximum thickness of about 80–100 m. Organic‐rich shales are characterized by high total organic carbon (TOC) content, high thermal maturation and type I–II1 kerogens, which can be comparable with those in commercially produced shale gas field in Sichuan Basin. High‐quality shale gas reservoirs generally have a high content of brittle minerals, making them easier to be fractured. OM pores are the dominanted pore type in the studied shales, followed by intergranular pores associated with brittle minerals, dissolution pores within carbonate grains and microcracks, while clay mineral‐related pores are poorly developed. The Wufeng–Longmaxi Formation shales generally have strong methane adsorption capacities, but these vary greatly across different areas. Shale gas adsorption capacity is primarily controlled by TOC content and thermal maturation level. Similarly, total gas content, including desorption gas and lost gas, varies greatly in different areas, and it is obviously lower than that in Fuling and Luzhou shale gas field, due to the loss of shale gas and low‐pressure coefficient in the complex structural zone. It is worth explaining that shale gas is not always low in northern Guizhou, which is determined by burial depth and the distance of great fractures. Shale gas content is relatively high in LY1 well and DY1 well in Xishui‐Daozhen area, and it is extremely low in TY1 well and AY1 well in Tongzi‐Zheng'an area. Shale gas content in the same structural unit is primarily influenced by TOC content, OM pore development degree and water saturation. However, different structural units have different shale gas contents, due to the differences in preservation conditions. Shale reservoirs with good preservation conditions, that is, wide and gentle structure, far from a large fault and great burial depth, generally have high shale gas contents.

Formation mechanism of carbonate cement in tight sandstone reservoirs in the depression zone of foreland basin and its impact on reservoir heterogeneity: The upper Triassic Xujiahe Formation in Western Sichuan foreland basin, China

The carbonate cements in tight sandstone reservoirs are diverse, complex, and important determinants of reservoir quality. This study provides a comprehensive analysis of the characteristics and formation mechanism of carbonate cement in the tight sandstone reservoirs of the Xu3 Member within the Xujiahe Formation in the depression zone of the Western Sichuan foreland basin. Core samples were examined on thin sections using cathodoluminescence and scanning electron microscopy, fluid inclusion analysis, in situ carbon and oxygen stable isotopes, and rare earth element analysis. The study reveals that the Xu3 Member primarily comprises sublitharenite and litharenite, which has three stages of carbonate cementation within the reservoirs. On average, the reservoirs exhibit a porosity of 3.82% and a permeability of 0.1mD. In the eodiagenetic stage, calcite and dolomite (δ13CPDB = 0‰ to −4.07‰; δ18OPDB = −5.64‰ to −12.69‰) formed, filling both intergranular pores and intragranular dissolution pores. This process is driven by the expulsion of organic acids through compaction from the clay and coal-bearing sections during shallow burial. The carbon sources originate from external organic acids and internal carbonate rock fragments, which combine with Ca2+ and Mg2+ ions released from the dissolution of carbonate rock fragments. During the mesodiagenetic stage A, the predominant formation of ferroan calcite and ankerite (δ13CPDB = −5.98‰ to −7.64‰; δ18OPDB = −14.47‰ to −19.87‰) occurred, filling intergranular residual pores and secondary intragranular dissolution pores. This phenomenon is caused by the expulsion of organic acids formed by the compaction of matured organic matter at greater burial depths. The carbon sources primarily originate from external organic acids and combine with Ca2+, Mg2+, and Fe2+ ions in the sandstone, alongside accompanying organic acids. During the mesodiagenetic stage B, coarse-macro crystalline calcites (δ13CPDB = −1.06‰ to −1.64‰; δ18OPDB = −17.95‰ to −20.36‰) with significant positive Eu anomaly-filled fractures were formed. These calcites are associated with hydrothermal fluids in the deep subsurface, precipitating directly in the fractures due to the presence of hot hydrothermal fluids rich in Ca2+ and CO32−. The Xu3 Member displays two sandstone superimposed types. In the mudstone overlain by sandstone type, carbonate cement is mainly present in the middle of the cycle, and reservoir quality is relatively high at both the bottom and top of the cycle. In the sandstone overlain by sandstone type, carbonate cement is predominantly found in the middle and top sections of the cycle, with higher-quality reservoirs primarily forming at the bottom of the cycle. It resulted in significant heterogeneity observed in the tight sandstone reservoirs of the depression zone in the Western Sichuan foreland basin.

Coal Structure Characteristics of the 2# Coal Seam in the Jiaozuo Mining Area and Its Geological Dependence.

To clarify the coal structure, spatial distribution, and controlling factors of the 2# coal seam in Jiaozuo mining, the drilling coal samples were collected to observe the coal type and coal structure. The coal macerals were identified by a MPVSP microscope photometer, and the spatial characteristics of the coal structure were obtained through interpreting deep lateral resistivity logging, natural gamma ray logging, density logging, and acoustic logging curves. The influence of coal properties, burial depth, geological stress, and faults on the coal structure were discussed correspondingly. The results exhibit that granulitic-mylonite coal was most developed in the 2# coal seam, followed by primary coal and cataclastic coal; the coal type was dominated by semibright coal, followed by clarain and semidull coal. Granulitic-mylonite, cataclastic, and primary coals were the main components of clarain, semibright coal, and semidull coal, respectively. Higher vitrinite and organic matter contents were conducive to the development of granulitic-mylonite. The coal structure combinations were spatially varied, and the granulitic-mylonite combinations were the most common. Granulitic-mylonite coal was developed in the east and south parts of the study area, and the coal structure was fragmented with a greater burial depth and larger thickness. The geological stress is the fundamental cause of coal structure damage as well as the cutting of faults.

Progress and prospects of EOR technology in deep, massive sandstone reservoirs with a strong bottom-water drive

The Triassic massive sandstone reservoir in the Tahe oilfield has a strong bottom-water drive and is characterized by great burial depth, high temperature and salinity, a thin pay zone, and strong heterogeneity. At present, the water-cut is high in each block within the reservoir; some wells are at an ultra-high water-cut stage. A lack of effective measures to control water-cut rise and stabilize oil production have necessitated the application of enhanced oil recovery (EOR) technology. This paper investigates the development and technological advances for oil reservoirs with strong edge/bottom-water drive globally, and compares their application to reservoirs with characteristics similar to the Tahe oilfield. Among the technological advances, gas injection from the top and along the direction of structural dip has been used to optimize the flow field in a typical bottom-water drive reservoir. Bottom-water coning is restrained by gas injection-assisted water control. In addition, increasing the lateral driving pressure differential improves the plane sweep efficiency which enhances oil recovery in turn. Gas injection technology in combination with technological measures like channeling prevention and blocking, and water plugging and profile control, can achieve better results in reservoir development. Gas flooding tests in the Tahe oilfield are of great significance to identifying which EOR technology is the most effective and has the potential of large-scale application for improving development of deep reservoirs with a strong bottom-water drive.

Deep shale gas exploration and development in the southern Sichuan Basin: New progress and challenges

There are abundant marine shale gas resources in the Sichuan Basin. After almost one decade of exploration and development, three national shale gas demonstration areas have been built in the Sichuan Basin and its periphery, and large-scale commercial development of middle and deep (above 3500 m in depth) shale gas has been successfully achieved. The volume of deep shale gas resources (3500–4500 m deep) of the upper Ordovician Wufeng Formation-lower Silurian Longmaxi Formation in the southern Sichuan Basin is 6.6 × 1012 m3, with huge exploration and exploitation potential, so it is an important area for large-scale shale gas production increase in China during the 14th Five-year Plan. Deep shale gas in the southern Sichuan Basin is influenced by complex geological engineering conditions, such as great burial depth, high temperature and pressure, and large stress and stress difference, and its high-quality development faces many challenges. After systematically summarizing the new progresses and achievements in deep shale gas exploration and development in the southern Sichuan Basin, this paper analyzes the difficulties and challenges in deep shale gas exploration and development and puts forward the next research directions. And the following research results are obtained. First, based on early practical exploration and independent innovation, key shale gas exploration and development technologies with good area selection, good well deployment, good well drilling, good well fracturing and good well management as the core are formed, and the cultivation mode of high production well is established, which supports the large-scale benefit development of deep shale gas in the southern Sichuan Basin. Second, systematical analysis indicates that the exploration and development of deep shale gas still faces a series of challenges in such three major fields as basic theory, key technology and management mode. Third, in the face of challenges, it is necessary to deepen basic theory research related to exploration and development, continuously improve key main technologies and constantly innovate mechanisms, systems and management modes. In conclusion, after years of continuous researches and pilot tests, a series of main exploration and development technologies suitable for the working conditions of deep shale gas in the southern Sichuan Basin have been basically formed, the first deep shale gas reserves of trillion cubic meters has been submitted, and the first deep shale gas production increase block of ten billion cubic meters has been selected. Thus, great progresses have been made in the exploration and development of deep shale gas, which confirms the confidence and determination in exploring and developing deep shale gas and is of great guiding significance to the rapid development of shale gas industry in China.

Deposition of cenomanian – Turonian organic-rich units on the mid-Norwegian margin: Controlling factors and regional implications

On the mid-Norwegian margin, extensive rifting and subsequent deposition of thick Cretaceous and Cenozoic sediments have buried the traditional Upper Jurassic organic-rich shales too deep. Consequently, these organic-rich shales are overmature and spent in the deep basins on the mid-Norwegian margin. The absence of well-control, variable seismic quality and in particularly, the great burial depth, makes it difficult to identify alternative Upper Jurassic and Lower Cretaceous organic-rich units. By combining high-resolution 2D seismic data, well logs, and Rock-Eval data, this study documents the presence of alternative organic-rich units in the Cretaceous succession on the Halten Terrace and the Vøring Basin. Multiple seismic horizons which correspond to regional flooding surfaces and define a series of seismic sequences have been mapped across the study area. The regionally extensive upper Cenomanian horizon is associated with wireline log signals and Rock-Eval parameters which imply the presence of a potential source rock unit. Source rock evaluation indicate that this unit contains mainly kerogen Type III on the Halten Terrace, suggesting an organofacies with significant contribution from terrestrial sources. In the Vøring Basin, the unit is sparsely drilled but appears to be mature, thus displaying a relatively limited potential. One well from the Vigrid Syncline demonstrate somewhat higher potential, with Rock-Eval data indicating a kerogen Type II composition. As such, more prolific units seems to exist in the Vøring Basin, albeit exhibiting a patchy distribution. We speculate that the deposition and preservation of this upper Cenomanian organic-rich unit record the development of an extended oxygen minimum zone attributable to increased primary production and sluggish water circulation, linked to the global Oceanic Anoxic Event 2 (OAE 2). However, local physiographic conditions, such as high sedimentation rates, erosion by gravity flows and periodically oxygenated conditions hindered preservation of a significant quantities of organic matter, thus limiting the thickness and quality of the upper Cenomanian organic-rich unit on the mid-Norwegian margin.

Hydrochemical characteristics and processes of groundwater in the Cenozoic pore aquifer under coal mining.

Mining activities considerably affect groundwater quality and resources. It is crucial to investigate water chemistry and hydrochemical processes under coal mining settings for water environment protection and sustainable utilization of groundwater resources. In this study, 36 groundwater samples from the Cenozoic pore aquifer in the Gubei coal mine in Huainan (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and inverse geochemical modeling. Results revealed a hydrochemical boundary around 100m below the ground surface, forming two flow zones participating in different hydrological cycles. In the shallow (circulation) zone above the boundary, the main hydrochemical processes are silicate dissolution and cation exchange, followed by evaporite dissolution. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are low and stable, forming low-salinity water (total dissolved solids [TDS] < 1g/L) dominated by Na*Ca*Mg-HCO3 and Na*Ca-HCO3 types. At greater burial depths, the pH, TDS, Na+ + K+, Cl-, and SO42- concentrations in the groundwater gradually increase, while the HCO3- concentration gradually decreases, which is mainly due to the enhanced evaporite dissolution and decarbonation in the deep (circulation) zone below the hydrochemical boundary. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are high and variable, forming high-salinity water (TDS > 1g/L) dominated by Na-Cl and Na-Cl*SO4 types. A hydrochemical evolution model of the Cenozoic aquifer was finally established, which advances our understanding of the evolutionary processes of groundwater chemistry under mining drainage.

Geochemistry and Mineralogy of Paleocene Coal from the Padhrar and Darra Adam Khel Coalfields of Pakistan

AbstractPakistan is rich in coal resources, which amount to around 186 billion tons. The Paleocene Padhrar and Darra Adam Khel coalfields are located in the Central Salt Range Punjab Province and the Khyber Pakhtunkhwa Province, Pakistan, respectively. Padhrar coal has not been studied in detail and the Darra Adam Khel coalfields are newly‐discovered, so no research has been done, due to security considerations. In this study, an attempt has been made to study the geochemical and mineralogical characteristics of the Padhrar and Darra Adam Khel coals, in order to learn about the coal quality, element enrichment mechanism, sedimentary medium conditions and potentially valuable elements for coal utilization. The Padhrar and Darra Adam Khel coals are low to medium ash, low moisture content, high in volatiles and high total sulfur coal. The vitrinite reflectance in Darra Adam Khel coal is higher than in Padhrar coal, indicating either a greater burial depth or the effects of Himalayan tectonism. The vitrinite content is dominant in the Padhrar and Darra Adam Khel coals, followed by inertinite and liptinite, the major minerals including quartz, clay minerals, calcite and pyrite. The trace elements Ni, As, Be Zn, Ge, Mo, Ta, W, Co and Nb, Sn, Hf, Ta, Pb, Th, Cd, In, Be, V, Cr, Zr, Ag, Li, W and Co are concentrated in some of the Padhrar and Darra Adam Khel coal samples, respectively. The Padhrar coal shows positive Ce, Eu and Gd anomalies, with most of the Darra Adam Khel coal showing negative Ce, Eu and positive Gd anomalies with high LREE. The Al2O3/TiO2 values indicate that the sediment source of the Padhrar and Darra Adam Khel coals is mostly related to intermediate igneous rocks. The Sr/Ba, SiO2 + Al2O3, Fe2O3 + CaO + MgO/SiO2 + Al2O3 and high sulfur content in the Padhrar and Darra Adam Khel coals indicate epithermal and marine water influence with a tidal flat, coal‐forming environment and a deltaic coal‐forming environment, respectively.

Comparative analysis of fetal pig decomposition processes in burials of variable depths and wrapping.

This research examined the effects that the variables of burial depth and presence of plastic wrapping had on the decomposition rate of fetal pig (Sus scrofa) remains in a New England environment. The decomposition of 56 fetal pigs was observed in four independent variable groups: 20 cm depth unwrapped, 20 cm wrapped, 60 cm unwrapped, and 60 cm wrapped, with exhumation at months 1, 2, 3, 6, 9, 12, and 18. The authors hypothesized that the rate of decay would be slower for wrapped remains and/or for remains at a greater burial depth. Analysis of these remains consisted of preburial and postburial mass, adipocere coverage, skeletal exposure, and decomposition quantified as Total Body Score (TBS). The difference between preburial and postburial mass was reported as a loss percentage to account for varying preburial masses. Wrapping was a significant influencer of mass loss percentage, with p=0.0298 but not for the TBS, with p=0.17565. Burial depth did not have a significant effect on either mass loss percentage or TBS, with p=0.1956 and 0.08969, respectively. This study suggests that wrapping has a greater influence on decomposition patterns than burial depth in this environment, particularly the mass loss percentage. It is suggested that there are limitations with the use of TBS in Postmortem Interval (PMI) estimation, such as variable burial conditions and body characteristics.

Deep and ultra-deep oil and gas well drilling technologies: Progress and prospect

In the period of “13th Five-Year Plan”, domestic deep and ultra-deep oil/gas well drilling technologies were developed quickly and a great number of technological achievements were obtained by means of continuous researches, including: (1) high-end devices, such as automatic drilling rig, managed pressure drilling, logging, cementing and completion technology, high-torque top drive system, and deep-well coiled tubing operation unit; (2) advanced tools, such as vertical drilling tool, non-planar tooth bit, high-strength expandable tubular, high-temperature, high-torque and long-life screw rod, torsion impact tool, synergistic damping based rock breaking tool, measurement while drilling tool, and safety monitoring tool; (3) core additives, such as temperature-resistance high-density oil based drilling fluid, high-performance water based drilling fluid, ductile cement slurry, and self-healing cement slurry; (4) life-cycle wellbore integrity technology system. Nevertheless, oil and gas well drilling and completion still faces severe challenges, including deep (great burial depth), steep (large formation dip), narrow (narrow pressure window), thick (thick gravel layer, salt bed and other complex intervals), difficult (complex multi-pressure system, abundant complex accidents and poor drillability) and high (high temperature, high pressure and high acid). Facing these challenges, the following suggestions are proposed. The key to the oil and gas reserve and production increase during the 14th Five-Year Plan and afterwards is till deep and ultra-deep layers. And it is necessary to focus on above mentioned geological difficulties to research key core technologies, such as automatic and intelligent drilling equipment, ultra-high temperature wellbore working fluid, pre-exploration while drilling and digital twin well construction, so as to realize the iterative upgrading of traditional superior technologies and improve the ability to drill deep and ultra-deep wells safely, quickly and optimally. In conclusion, during the 13th Five-Year Plan, China exceeded America in the number of ultra-deep wells for the first time and its well depth stepped up to a new stage of 8000 m, which plays an important role in supporting the development of deep oil and gas exploration and development and improving the market competitiveness of drilling and completion.

Fluid Properties and Genesis of Dolomites in the Devonian Guanwushan Formation of Upper Yangtze Platform, SW China

The Guanwushan Formation (GWSF) of Devonian dolomite are extensively developed in the northwest of Sichuan Basin in the Upper Yangtze region, but the properties of dolomitization fluid and the geneses are still unclear. Three types of dolomites can be divided by petrological characteristics: the fine-microcrystalline dolomites (FMD), the fine crystalline dolomites (FCD) and the medium crystalline dolomites (MCD). The order degree of these three types of dolomites increased in turn, and they all showed dark cathodoluminescence (CL) luminescence. The total amount of Rare Earth Elements (∑REE) of the dolomite was low, while the dolomite enriched with light REE and lacking heavy REE presented a distribution pattern consistent with that of limestone. The weak negative anomalies of the Ce and Eu indicated that the dolomites were formed in a weak redox environment with relatively low temperature. The dolomitization fluids were inherited from the original seawater. The respective δ13CPDB values of the three types of dolomites varied a little, indicating that they were not affected by the biological effects. Specifically, the δ18OPDB values of the FMD and FCD dolomites were higher than that of the limestone, indicating that the dolomitization fluid was influenced by evaporation at the penecontemporaneous stage. The interpretations were also supported by the 87Sr/86Sr ratios, as the 87Sr/86Sr ratios of FMD comparable to the Middle Devonian seawater. The δ18OPDB value of the MCD dolomite was lower than that of the limestone. It also showed poor automorphic extent, which clarified that the dolomite experienced more intense dolomitization in greater burial depth and at higher temperatures.

Structural characteristics, formation & evolution and genetic mechanisms of strizke–slip faults in the Tarim Basin

Exploration and development practices prove that intracratonic strike–slip faults control the development of carbonate reservoirs and the enrichment of oil and gas in the Tarim Basin. Intracratonic strike–slip faults are characterized by short displacement, small throw and great burial depth, so there are still many controversies on their structural evolution and formation mechanisms. In order to settle these controversies, this paper firstly analyzes the geometric and kinematic characteristics of the intracratonic strike–slip faults in the central Tarim Basin. Then, based on extensive high-accuracy 3D seismic data and 2D seismic data, the formation and evolution process of the intracratonic strike–slip faults in the Tarim Basin are discussed deeply, and their genetic mechanisms are explored. Moreover, the following research results are obtained. First, the strike–slip faults in the study area have the characteristics of vertical stratification, plane zonation and segmentation along the strike. Second, the movement directions of the deep transpressional strike–slip faults are simple. The NE and NNE strike–slip faults are sinistral, and the NNW strike–slip faults are dextral. However, the shallow transtensional faults are more different in the movement direction. The strike–slip faults have displacements of 400–1500 m, and they are classified as intracratonic strike–slip faults with small slip distance. Third, the strike–slip faults were formed in the middle Caledonian, and some faults were reactivated in the late Caledonian–early Hercynian, late Hercynian, and Yanshanian–early Himalayan. The distribution of faults is different in different periods. Fourth, the formation of the strike–slip faults in the middle Caledonian is controlled by the basement heterogeneity and the compression action from the closure and subduction of the Proto-Tethys Ocean. The transtensional faults are R-shear branch faults or tensile break faults generated by the later activation of middle Caledonian strike-slip faults, and their formation is controlled by the subduction and closure of oceanic basins around the basins in different periods. In conclusion, the structural characteristics, formation & evolution and genetic mechanisms of intracratonic strike–slip faults are in close relation to oil and gas, where great benefit of oil and gas exploration and development is achieved. Besides the Tarim Basin, the Sichuan Basin and the Ordos Basin have similar geological and structural settings, so the studies on typical basins will surely enrich and complete the theories on the intracratonic strike–slip faults in domestic micro land blocks and multi-cycle basins and point out the direction for the discovery of more oil and gas resource.

Experimental investigation on the effects of heating-cooling cycles on the physical and mechanical properties of shale

The deep shale gas reservoirs are characterized by great burial depth, high formation pressure, high temperature. During the hydraulic fracturing process, the fracturing fluids will inevitably exchange heat with the surrounding rock, causing the shale in the near-well zone to undergo temperature alternation, the physical and mechanical properties of shale reservoirs are significantly affected, which brings technical difficulties to fracturing optimization design. In this paper, the Longmaxi Formation shale is used to pay attention to the rock physical and mechanical characteristics of the shale undergo temperature alternation, the microstructure and damage and fracture characteristics of the shale undergo temperature alternation are analyzed. The results show that: (1)As the heat treatment temperature increases and the number of heating-cooling cycles increases, the permeability of the shale increases, the P-wave velocity decreases, the tensile strength (TS) decreases, and the brittleness index rises. (2) Heat treatment temperature and the number of heating-cooling cycles have little effect on the triaxial compressive strength (TCS) of shale. However, it has a significant effect on the failure mode of shale. The increase of temperature and the number of heating-cooling cycles will enhance the degree of fracture of the shale failure surface. (3) Based on industrial CT scanning and scanning electron microscopy (SEM) observations, the thermal cracks caused by heating-cooling cycles are mostly inter-granular cracks and inter-layer cracks, which unfold on the surface of the sample and extend to the interior. Heating-cooling cycles also lead to an increase in the diameter of organic pores. The study results can provide a certain theoretical basis for the optimization design of staged fracturing parameters for horizontal wells in the process of deep shale gas development.

A simulation experiment method for HTHP gas well productivity

In recent years, a series of major natural gas exploration discoveries and breakthroughs have been achieved in deep and ultra-deep carbonate gas reservoirs in the Sichuan Basin, and all discovered gas reservoirs are characterized by great burial depth, complex pore structures and high formation temperature and pore pressure. In order to accurately predict the gas flow rate of single well in high temperature and high pressure (HTHP) gas reservoirs and clarify the gas flow characteristics under formation conditions, this paper establishes a productivity simulation experimental device and method based on the formation temperature and pore pressure of carbonate gas reservoirs in the Middle Permian Qixia Formation of northwestern Sichuan Basin and the Upper Sinian Dengying Formation of central Sichuan Basin. Then, the cores of above mentioned gas reservoirs are selected to carry out the productivity simulation experiment under HTHP. Finally, the gas flow characteristics are studied. And the following research results are obtained. First, the newly established productivity simulation experimental device and method suitable for the conditions of 160 °C formation temperature and 100 MPa pore pressure is used to predict the natural gas AOF (absolute open flow) of Well S-1 in the Qixia Formation gas reservoir of northwestern Sichuan Basin. And the prediction result is better accordant with the calculation result of theoretical model, with a relative error of only 2.12%. Second, based on the Klinkenberg permeability under surface conditions, the single-well gas flow rate calculated from the productivity simulation experiment is better accordant with the gas flow rate from field completion testing; while based on the Klinkenberg permeability under formation conditions, the single-well gas flow rate calculated from the productivity simulation experiment is better accordant with the AOF. Third, the change of formation temperature and pore pressure has a significant influence on rock permeability, and the permeability is more sensitive to stress than to temperature. Fourth, to carry out the reservoir stress sensitivity experiment and the productivity simulation experiment, it is required that core samples be recovered to the formation conditions for aging, or the experimental results may have characteristics of strong stress sensitivity and cannot be used for reservoir engineering evaluation directly. In conclusion, the production rate and AOF of HTHP gas wells can be predicted accurately by means of productivity simulation experiment, based on drilling core samples. In addition, the Klinkenberg permeability under formation conditions can be evaluated by using the relational expression between surface or Klinkenberg permeability under formation conditions and single-well gas flow rate, combined with gas well testing data.

Seed traits correlate with herbicide resistance in Italian ryegrass (Lolium perenne ssp. multiflorum).

Italian ryegrass (Lolium perenne ssp. multiflorum) is one of the major winter annual weeds worldwide. In this research, diversity for seed morpho-physiological traits such as seed weight, seed size, awnedness, dormancy, speed of germination, and seed vigor among Italian ryegrass populations collected from the Texas Blacklands region were assessed, and potential association with herbicide resistance was investigated. A high degree of diversity was observed among the populations for 100-seed weight (125-256 mg), seed length (4.8-6.6 mm), awn length (0-6 mm), and total seedling length (9-14 cm at 21 days after seed germination). Inter-population range for seed dormancy was higher in the freshly harvested seed (31-85%), which reduced to 18 to 62% at 9months after harvest. Populations with high initial seed dormancy (> 70% dormancy) released dormancy at a faster rate than the low dormancy group (< 40%). Percent survival status to multiple postemergence herbicides was positively correlated with 100-seed weight and fresh or initial seed dormancy. Early emerging cohorts are easily controlled by pre-plant tillage and preemergence herbicides, whereas late emerging cohorts (facilitated by seed dormancy) are exposed to postemergence herbicides wherein greater opportunities exist for resistance evolution, likely explaining the occurrence of high seed dormancy in Italian ryegrass populations resistant to postemergence herbicides. High seed weights can further allow seedling emergence from greater burial depth, thereby exposing more seedlings to postemergence herbicides and increasing the likelihood of resistance evolution. Results provide unique insights into the association between seed traits and herbicide resistance in this species. © 2021 Society of Chemical Industry.

Key geological factors for shale gas accumulation in the Wufeng–Longmaxi Fms in the central Yangtze area

The Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in the central Yangtze area of southern China has a good prospect of shale gas exploration. So far, however, its complicated geological conditions and shale gas exploration and development potentials have not been understood completely, which affects its exploration achievements. In order to determine the main factors controlling shale gas enrichment in the Wufeng–Longmaxi Fms in this area, this paper studied the key shale gas enrichment conditions in the black shale there (e.g. sedimentary environments, reservoir development characteristics and preservation conditions) based on single-well comprehensive reservoir evaluation, combined with drilling, logging, core, outcrop and test data. In addition, it was compared with the main shale gas blocks in the Sichuan Basin, such as Jiaoshiba and Changning. And the following research results are obtained. First, the organic-rich shale section in this area was formed during the sedimentation from Wufeng Formation to the third submember of the first member of Longmaxi Formation. It is the deposit of deepwater continental facies, and its thickness is in a range of 15–39 m, presenting a trend of increasing from south to north. Second, the reservoir rocks in the high-quality shale sections are dominated by siliceous shale, and the reservoir porosity is in a range of 1.60–7.44%. The reservoir spaces are dominated by organic pores with good connectivity and high total organic carbon (TOC) content. The organic matter is of a sapropel–sapropel prone hybrid type, with a high thermal evolution degree, better gas bearing property and good fracturability. Third, the Dangyang synclinorium is characterized by better strata preservation, rock occurrence flat, less developed faults and thick and stable roofs and floors, so its shale gas preservation conditions are better. Fourth, different from the Changning and Jiaoshiba Blocks, the central Yangtze area is characterized by great burial depth, large bidirectional stress difference, and low formation pressure coefficient. In conclusion, the Wufeng–Longmaxi Fms is better in shale gas enrichment conditions and has a potential of further exploration. However, its commercial shale gas development and scale production increase in the future face challenges due to its large stress difference, great burial depth, and lower pressure coefficient.

Reservoir Characteristics and Its Comprehensive Evaluation of Gray Relational Analysis on the Western Sulige Gas Field, Ordos Basin, China

Although the Sulige gas field has been developed for several years, accurate reservoir classification, evaluation, and prediction is still a worth-exploring scientific issue as this is a necessary procedure which could give the guidance of well deployment during later gas field development. Here, based on the analysis of lithological features and diagenesis, we give an evaluation of gas reservoirs in the western Sulige gas field by using the improved method of gray relational analysis. Our results show that the study area Su-54 block is dominated by low permeability and low porosity litharenite and lithic silicarenite with clear evidence of strong diagenesis processes. Compaction is believed to be relatively strong due to the great burial depth and destroy most of the primary pores. Based on the premise of a lower limit of an effective reservoir, we select five parameters (permeability ( K ), porosity ( Φ ), effective sand thickness ( M ), effective sand/sand thickness ratio ( D ), and gas saturation ( S g )) to calculate the correlation coefficient, relational degree, and index weights for reservoir quality evaluation. By weighted gray correlation theory, the dynamic testing data—effective thickness of gas production data—is used as mother sequences. The results show that the predicted favorable areas for gas exploration and development coincide well with sedimentary and sand body distribution (e.g., point bars and central bars) in the study block; well blocks such as s372, s373, s374, and e24 could be future key development targets. This also indicates a broader application of the gray relational analysis to quality evaluation and distribution prediction of reservoirs. Therefore, our findings could give a new theoretical and practical guidance for the later gas exploration and development, for the search of hidden stratigraphic lithological traps, and for the improvement of the proven rate of oil and gas resources in this area.