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The main source rocks, hydrocarbon generative subbasins, hydrocarbon generation periods, resource potential, and the relationship between the trap evolution history and hydrocarbon generation history are important problems associated with oil and gas exploration. In this study, we develop a three-dimensional geological model with respect to the Mesozoic and Cenozoic strata of the northern margin of the Qaidam Basin based on the most recent geological data. Using this model, the burial depth, temperature, maturity, and gas generation history of the source rock, the plane diagram of the source-rock current maturity, the gas generation intensity map, and the amount of gas generation during each geological period and within different subbasins can be obtained. Based on the obtained maps, we can state that the maturity of the source rock controls the distribution of natural gas (i.e., natural gas is located within and in the vicinity of mature and highly mature source rocks). We also observed the following: (1) the Lower Jurassic section is the main gas source rock; (2) the Yibei subbasin is the main hydrocarbon generative subbasin, followed by the Kunteyi, Pingdong, and Lenghu subbasins; (3) the main gas generation period is after the upper member of the lower Ganchaigou Formation deposition, with maximum gas generation occurring during the upper Ganchaigou Formation deposition and gradually decreasing thereafter—the majority of the structures in the inner basin are formed after lower Youshashan Formation deposition, demonstrating the tectonic activity coincided with periods of natural gas formation; and (4) the amount of natural gas resource becomes 1.23 trillion cubic meters. From these analyses, we can demonstrate that the late tectonic belts formed in the four gas-generating subbasins exhibit considerable promise for exploration.

Breakthroughs have been made for the natural gas exploration of the Middle Devonian and the Middle Permian formations in the Sichuan Basin in recent years. Nevertheless, its natural gas source is still not clear, which then affects the next exploration deployment decision. A comprehensive study is conducted on the geochemical characteristics of the Middle Devonian and the Middle Permian natural gas, the biomarkers of reservoir bitumen, and the source rocks. The results show that these natural gases are secondary cracking dry gas that includes more than 86% of methane content, a small amount of ethane, propane, and a non-hydrocarbon gas (e.g., nitrogen, carbon dioxide, and hydrogen sulfide). The natural gas maturity varies slightly in different regions. The carbon and hydrogen isotope values of natural gas are as follows: δ13C1 ranges from −35.7‰ to −27.3‰, δ13C2 ranges from −38.7‰ to −26.6‰, δ13C3 ranges from −37‰ to −26.5‰, δ2HCH4 ranges from −141‰ to −138‰, and δ2HC2H6 ranges from −164‰ to −112‰. The isotope values indicate that the genetic type of natural gas is the sapropelic type and the mixture type is dominated by sapropelic type. The difference between natural gas values of δ13C1, δ13C2, and δ2HCH4 in different regions is related to the contribution ratio of source rocks from different ages. The gases of the Middle Devonian and the Middle Permian of the Shuangyushi structure in Northwestern Sichuan, the Middle Permian of Southwestern Sichuan, and the Middle Permian of Paleo-uplift in Central Sichuan are mainly derived from the Cambrian Qiongzhusi Formation and the Middle-Lower Permian source rocks. The Middle-Upper Permian natural gases of the volcanic reservoir in Southwestern Sichuan is mainly from the Qiongzhusi source rock. The Middle Permian natural gases of the Hewanchang structure in Northwestern Sichuan, Eastern Sichuan, and Southern Sichuan are mainly derived from the Silurian Longmaxi source rock. The research results have important guiding significance for developing exploration and deployment solutions for natural gas of the Middle Devonian and the Middle Permian formation in the Sichuan Basin.

Natural gas resources in the Qaidam Basin are abundant and of various types. On the basis of the natural gas carbon isotope distribution characteristics, the western Qaidam Basin mainly comprises o...

The northern margin of the Qaidam Basin is an important area for natural gas exploration that includes the recently discovered Dongping and Niudong gas fields. However, the origins of the natural gas and the primary factors controlling gas accumulation in the region are unclear, particularly in the piedmont zone. Planning and exploration strategies are limited by a lack of knowledge about natural gas accumulation mechanisms. In this study, various comprehensive geochemical, geophysical and geological techniques were applied to investigate the origin and distribution of natural gas in this area, as well as the main factors controlling gas accumulation. The results demonstrate that the gas deposits are dominated by gaseous hydrocarbons with C1/C1–5 ratios in the range 0.76–0.99. The natural gases are characterized by wide variations in δ13C1 values (−19.1‰ to −36.1‰) and relatively heavy δ13C2 values (−19.82% to −25.42%). The oil and gas in the investigated area exhibit a zonal spatial distribution and have features typical of coal-generated gases. The locations of major hydrocarbon-generating depressions and source rock maturity exert primary control on the distribution of oil and gas reservoirs. Paleo-uplifts and paleo-slopes controlled the direction of hydrocarbon migration and accumulation, while faults and conducting systems connected to the hydrocarbon source rocks constituted channel systems that controlled the transport of oil and gas. Suggestions for future exploration have been put forward, which will provide significant guidance for gas exploration in the area. Future promising areas for exploration include the paleo-uplifts in the east of the Altun Mountains and the west of the Qilian Mountains front and the Eboliang-Lenghu structural belt in the northern margin of the Qaidam Basin. These results will also provide guidance to natural gas exploration and research efforts in other basins with similar geological settings.

In case of a four-screw ship, the propellers show different hydrodynamics performance due to the asymmetric distribution of the wake. And the particularity of the scale effect on wake field for this type of ship would make a more complicated characteristics on propeller bearing force. In this paper, a numerical simulation study of scale effect on propeller unsteady bearing force of a four-screw ship was performed by employing RANS method. The load variation of the single-blade is analyzed to understand the fluid mechanism of the interaction between the propeller blade and wake flow. The larger wake field difference between inside and outside propeller disk aggravates the unbalanced load distribution for the full-scale ship. The results of propeller bearing force highlight that the fluctuation values of full-scale ship are smaller than those of model one. Moreover, the scale effect of outside propeller is strong with respect to the inside one. The above findings can provide theoretical guidance for load balancing and vibration reduction of the four-screw ships.

The Songliao Basin is a large-scale petroliferous basin in China. With a gradual decline in conventional oil production, the exploration and development of replacement resources in the basin is becoming increasingly important. Previous studies have shown that the Cretaceous Qingshankou Formation (K2qn) has favorable geological conditions for the formation of shale oil. Thus, shale oil in the Qingshankou Formation represents a promising and practical replacement resource for conventional oil. In this study, geological field surveys, core observation, sample tests, and the analysis of well logs were applied to study the geochemical and reservoir characteristics of shales, identify shale oil beds, build shale oil enrichment models, and classify favorable exploration areas of shale oil from the Cretaceous Qingshankou Formation. The organic matter content is high in shales from the first member of the Cretaceous Qingshankou Formation (K2qn1), with average total organic carbon (TOC) content exceeding 2%. The organic matter is mainly derived from lower aquatic organisms in a reducing brackish to fresh water environment, resulting in mostly type I kerogen. The vitrinite reflectance (Ro) and the temperature at which the maximum is release of hydrocarbons from cracking of kerogen occurred during pyrolysis (Tmax) respectively range from 0.5% to 1.1% and from 430 °C to 450 °C, indicating that the K2qn1 shales are in the low-mature to mature stage (Ro ranges from 0.5% to 1.2%) and currently generating a large amount of oil. The favorable depth for oil generation and expulsion is 1800–2200 m and 1900–2500 m, respectively as determined by basin modeling. The reserving space of the K2qn1 shale oil includes micropores and mircofractures. The micropore reservoirs are developed in shales interbedded with siltstones exhibiting high gamma ray (GR), high resistivity (Rt), low density (DEN), and slightly abnormal spontaneous potential (SP) in the well-logging curves. The microfracture reservoirs are mainly thick shales with high Rt, high AC (acoustic transit time), high GR, low DEN, and abnormal SP. Based on the shale distribution, geochemical characteristics, reservoir types, fracture development, and the process of shale oil generation and enrichment, the southern Taikang and northern Da'an are classified as two favorable shale oil exploration areas in the Songliao Basin.

With the rapid development of mobile applications and online social networks, users often encounter a frustrating challenge to set privacy and security policies (i.e., permission requests) of various applications correctly. For instance, in an Android system, it is hard for users, even programmers, to identify malicious permission requests (policies) when they install a third-party application. To simplify the task of policy management, in this paper, we propose a novel policy administration method where the policy settings from users' friends will be used as a key recommendation to guide policy administration, and the security of friends' privacy will be protected. We propose to let a user invite his or her friends to help with policy setting in applications, and we call such a method socialized policy administration (SPA for short). We designed two types of SPA: basic SPA and composite SPA. Both types of SPA are equipped with a privacy preserving mechanism that enables users' friends to help users without leaking the friends' preferences. In our prototype based on Telegram, i.e., one of the most popular instant messaging applications, we utilize partially homomorphic encryption cryptosystems to implement our framework. Based on the performance evaluation, SPA is able to configure almost all types of policies of current popular Android applications with a modest performance overhead.

Deep natural gas in the northern margin of the Qaidam Basin is characterized by low exploration degree and large resource potential, but the genesis of deep gas reservoirs is complex. In particular, Jurassic source rocks do not develop in west of Altun foreland. The mechanism of deep accumulation is unknown, which restricts the exploration of deep gas reservoirs. Using gas components, isotopes and other data, combined with the geological characteristics of the Altun foreland, this study analyzes the genesis and source of deep gas in this area, and establishes the accumulation procesess of the deep gas reservoirs. Analysis shows that the gas in the Altun foreland is dominated by coal-type gas with the characteristics of oil cracking gas in deep reservoirs. The Jurassic source rocks in the Qaidam Basin are mainly lacustrine mudstones, with black mudstones and oil shale developed, which have the material basis for forming large oil reservoirs. The deep reservoir has experienced the process of long-term deep burial and high-temperature cracking, and has the conditions to form oil cracked gas. Accumulation in deep bedrock gas reservoirs is characterized by early oil filling, later high-temperature cracking into gas, and late adjustment. Reservoirs formed in early stage can be deeply cracked into gas reservoir under high temperature in the process of deep burial. The ancient uplifts along the basin margin and large anticline traps in the late tectonic zone are favorable exploration areas for deep gas. The exploration area for natural gas in the Qaidam Basin has been expanded by the discovery of deep oil cracking gas in the Altun foreland, which has crucial significance for guiding and intensifying deep gas exploration in the Qaidam Basin.

The vertical water-entry processes of a hollow cylinder with three different velocities are investigated both numerically and experimentally. Three different closure patterns and flow characteristics of the air-entraining cavities induced by water-entry processes are discovered and discussed. Our results show that three different closure patterns appear with the increase of entry velocity, the deep-closure, the surface closure on the through-hole jet and on the geometry wall. Three high-speed regions also appear during the water entry process and their characteristics are different with various closure patterns. Besides, with the increase of water entry velocity, the velocity variation will vary from increase to decrease, but their water depths all increase linearly due to the short time and small variations of velocities.

On the basis of salinity and organic geochemical analyses of mudstones, this paper analyzed the relationship between salinity and sedimentary facies of different strata; studied influences of salinity on organic matter richness, types, and thermal maturities of source rocks; and built the organic enrichment accumulation model for the Paleogene and Neogene saline lakes of the western Qaidam Basin. In the western Qaidam Basin, saline lake depocenters and high salinity areas migrated eastward, and chloride ion (Cl–) concentration of source rocks showed an increasing trend from the Paleocene to Pliocene. The relationship between organic matter content and salinity of the Paleocene and Pliocene source rocks shows a three-interval model: both TOC (total organic carbon) content and chloroform bitumen content have low values at the low salinity stage, first increase to the peak and then decrease to the lowest values at the medium salinity stage, and sustain the lowest values at the super saline stage because of t...

The vertical water-entry of a low-speed hollow cylinder is studied numerically and experimentally in this work. The special flow characteristics of the hollow cylinder during the water entry have been revealed and discussed. Different from water entry of typical solid bodies, a through-hole jet with a bubble attached at the top forms at the impact stage, and the deep closure occurs around the circumference of the through-hole jet, and the secondary jet generated during the pinch-off has the shape of a hollow thin cylinder. Moreover, its head cavity includes both external and internal parts, and the internal cavity is more complicated and instable. The reasons for above differences have also been explained and discussed. Furthermore, the numerical results agree well with corresponding experimental data.

Dynamic revocation of permissions of installed Android applications has been gaining popularity, because of the increasing concern of security and privacy in the Android platform. However, applications often crash or misbehave when their permissions are revoked, rendering applications completely unusable. Even though Google has officially introduced the new permission mechanism in Android 6.0 to explicitly support dynamic permission revocation, the issue still exists. In this paper, we conduct an empirical study to understand the latest application practice post Android 6.0. Specifically, we design a practical tool, referred to as revDroid, to help us to empirically analyze how often the undesirable side effects, especially application crash, can occur in off-the-shelf Android applications. From the analysis of 248 popular applications from Google Play Store, revDroid finds out that 70% applications and 46% permission-relevant calls do not appropriately catch exceptions caused by permission revocation, while third-party libraries pay much more attention to permission revocation. We also use revDroid to analyze 132 recent malware samples. The result shows that only 27% malwares and 36% permission-relevant API calls of malwares fail to consider the permission revocation. In fact, many of them perform specialized handling of permission revocation to keep the core malicious logic running. Finally, revDroid can be used to help developers uncover the unhandled permission revocations during development time and greatly improve the application quality.