Overpressure generation and evolution in Lower Paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation

Overpressure generation by disequilibrium compaction or hydrocarbon generation in the Paleocene Shahejie Formation in the Chezhen Depression: Insights from logging responses and basin modeling

Natural fractures, as the main flow channels and important storage spaces, have significant effects on the migration, distribution, and accumulation of tight oil. According to outcrop, core, formation micro image (FMI), cast-thin-section, and scanning electron microscopy data from the tight reservoir within the Permian Lucaogou Formation of the Junggar Basin, tectonic fractures are prevalent in this formation mainly on micro to large scale. There are two types of fractures worth noticing: diagenetic fractures and overpressure-related fractures, primarily at micro to medium scale. The diagenetic fractures consist of bedding fractures, stylolites, intragranular fractures, grain-boundary fractures, and diagenetic shrinkage fractures. Through FMI interpretation and Monte Carlo method evaluation, the macro-fractures could be considered as migration channels, and the micro-fractures as larger pore throats that function as storage spaces. The bedding fractures formed earlier than all tectonic fractures, while the overpressure-related fractures formed in the Middle and Late Jurassic. The bedding fractures and stylolites function as the primary channels for horizontal migration of tight oil. The tectonic fractures can provide vertical migration channels and reservoir spaces for tight oil, and readjust the tight oil distribution. The overpressure-related fractures are fully filled with calcite, and hence, have little effect on hydrocarbon migration and storage capacity. The data on tight oil production shows that the density and aperture of fractures jointly determine the productivity of a tight reservoir.

Influence of Natural Fractures on Tight Oil Migration and Production: A Case Study of Permian Lucaogou Formation in Jimsar Sag, Junggar Basin, NW China

The Huanghua depression located in the hinterland of the Bohai Bay Basin in eastern China is a typical area for the research of multistage magmatic activities with hydrocarbon enrichment, many high-yield wells related to igneous rocks were discovered within the Cretaceous strata in recent years. However, the spatial and temporal distribution of Cretaceous igneous rocks remains unclear, and the relationships among magmatic sequence, lithology, and hydrocarbon enrichment have been poorly studied. In order to solve these problems, core observation, logging analysis, major element analysis, zircon U-Pb chronology, oil-bearing grade statistics and reservoir spaces analysis were used to subdivide the magmatism cycles and to investigate the characteristics of igneous reservoirs. Our results show that the Mesozoic magmatism in Huanghua depression started in 140.1±1.4 Ma and could be divided into two stages including the Early Cretaceous stage and Late Cretaceous stage. The Early Cretaceous magmatism principally developed basic-intermediate rocks in the north zone, and could be subdivided into 3 cycles with their forming ages of 140, 125–119, and 118–111 Ma, respectively. By contrast, the late stage mainly developed intermediate-acid rocks centralized in the south zone and formed at 75–70 Ma. The GR and SP curves are good indicators for the contrast of different lithologies, lithofacies and for magmatic sequences division. Intensive magmatism may have an advantage to form reservoirs, since basalt in cycle III in the Early Cretaceous and dacite porphyrite in the Late Cretaceous have great exploration potential. Lithology and tectonic fractures have an important influence on the formation of reservoir spaces and hydrocarbon enrichment. The characteristics of Cretaceous magmatism and igneous reservoirs in Huanghua depression and adjacent areas are summarized, providing important information for igneous reservoirs research and oil-gas exploration in the Cretaceous in related areas.

Characteristics of the Cretaceous Magmatism in Huanghua Depression and Their Relationships with Hydrocarbon Enrichment

The pore pressure gradient and fracture gradient (PPFG) are critical parameters for drilling mud weight design in the energy industry. Successful drilling operations can be achieved successfully through the understanding of the pore pressure and fracture pressure in the subsurface succession. The scope of this research is to use an integrated approach that encompasses well-logging, basin modeling, drilling-based interpretations, and reservoir measurement methods to gain a reasonable PPFG model and decrease the drilling uncertainties in the El Morgan oil field in the Gulf of Suez. Moreover, it investigates the overpressure generation mechanisms in the basin, which have not been studied before in this area. In this work, PPFGs of more than 16 km of cumulative thick sedimentary succession were modeled and evaluated using an integrated approach. This study utilizes Eaton’s sonic and resistivity-based methods for pore pressure evaluation, while vertical stress was calculated based on the composite density profile. The study revealed that the top geo-pressure was detected at a depth of 1,030 m of Tortonian sediments. Late Miocene sediments reveal hard over-pressure with a maximum gradient of 0.55 PSI/feet, while Middle Miocene sediments exhibit mildly over-pressured, normal, and sub-normal pore pressure zones. The lowest pore pressure values were measured in the Langhian-Serravalian Kareem reservoir with a gradient of 0.29 PSI/feet. With the exception of a slight difference in the reservoir section, the pore pressure profiles in the northern and southern parts of the El Morgan oil field are relatively similar. Reservoir connectivity is believed to be the main reason behind pore pressure magnitude differentiation in the Middle Miocene reservoirs. The key mechanism for generating overpressure has been identified as disequilibrium compaction, and reservoir overcharging may contribute as an excess-pressure generation mechanism at the reservoir level. The presented approach can be applied in PPFG studies for both development and exploratory geomechanical studies in other areas of the Gulf of Suez basin or elsewhere in the world. Graphical Abstract

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A multi-proxy approach to detect the pore pressure and the origin of overpressure in sedimentary basins: An example from the Gulf of Suez rift basin

The Chezhen depression, located in the south of Bohai Bay Basin, is an oil-producing basin in China. The third and fourth members of the Shahejie Formation (Es3 and Es4) are the main source rock series in the Chezhen depression. Widespread overpressures occurred in the Es3 and Es4 from the depths of approximately 2 000 to 4 600 m, with the maximum pressure coefficient of 1.98 from drillstem tests (DST). Among the sonic, resistivity and density logs, sonic-log is the only reliable pressure indicator and can be used to predict the pore pressure with Eaton’s method. All the overpressured mudstones in the source rock series have higher acoustic traveltimes compared with normally pressured mudstones at a given depth. The overpressured mudstones in the Es3 and Es4 units are characterized by a normal geothermal gradient, high average density values up to 2.5 g/cm3, strong present-day hydrocarbon generation capability, abundant mature organic matter and high contents of residual hydrocarbons estimated by the Rock-Eval S1 values and chloroform-soluble bitumen “A” values. All suggest that the dominant mechanism for overpressure in the mudstones of source rock series in the Chezhen depression is hydrocarbon generation. A comparison between the matrix porosity of the normally pressured sandstones and overpressured sandstones, the quantitative evaluation of porosity loss caused by compaction and the conventional thin section inspection demonstrate that the sandstones in the Chezhen depression were normally compacted. The high contents of hydrocarbons in the overpressured reservoirs prove that the overpressure in the sandstones of the source rock series was caused by pressure transmission from the source rocks.

Main Mechanism for Generating Overpressure in the Paleogene Source Rock Series of the Chezhen Depression, Bohai Bay Basin, China

Surface functionalization of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, also known as MXenes, is a powerful approach for modification of their physical and chemical properties for new applications. In this study, we demonstrate the synthesis of a bifunctional Ti3C2Tx MXene modified with amine and thiol groups through a facile condensation reaction. We successfully employed the resulting NH2/SH-Ti3C2Tx MXene as a solid phase in the ultrasonic-assisted dispersive micro solid-phase extraction (d-μ-SPE) method for the analytical determination of heavy metals at trace levels in food and soil samples. The prepared NH2/SH-Ti3C2Tx MXene showed remarkable performance in the ultrasonic-assisted d-μ-SPE method with limits of detection of 0.12 and 2.30 ng mL-1, with linear dynamic ranges of 0.50-90 μg L-1 and 10-120 μg L-1 for cadmium (Cd2+) and lead (Pb2+) ions, respectively. Furthermore, the extraction efficiencies were greater than 97%, with a relative standard deviation of less than 3% for five separate batch experiments in the determination of 5.0 μg L-1 of Cd2+ and Pb2+. This study shows that NH2/SH-Ti3C2Tx can be used as a simple, rapid, reliable, selective, and sensitive material in the d-μ-SPE method for the trace determination of Cd2+ and Pb2+ in soil and agricultural products. This study demonstrates the utility of MXenes for analytical chemistry and suggests that further advances in methods for the functionalization of MXenes can open new applications for these already exciting materials.

Bifunctional Amine- and Thiol-Modified Ti3C2Tx MXene for Trace Detection of Heavy Metals.

MXenes, two-dimensional transition metal carbides, nitrides, and carbonitrides, are known for their exceptional electronic and mechanical properties. Yet, the experimental efforts toward the realization of MXene-based nanoelectromechanical systems (NEMS) combining electrical and mechanical functionalities of MXenes at the nanoscale remain very limited. Here, we demonstrate a high-yield fabrication of the electromechanical devices based on individual suspended monolayer MXene flakes. We employed Ti3C2Tx, the most popular MXene material to date, that can be produced as high-quality micrometer-scale monolayer flakes with a high electrical conductivity of over 10 000 S cm-1 and a high effective Young's modulus of about 330 GPa. These Ti3C2Tx flakes can be transferred over prefabricated trenches in a Si/Si3N4 substrate at a high yield, potentially enabling fabrication of hundreds of electromechanical devices based on suspended MXene monolayers. We demonstrate very clean, uniform, and well-stretched membranes with different dimensions, with Ti3C2Tx flakes suspended over trenches with gaps ranging from 200 nm to 2 μm. The resulting Ti3C2Tx monolayer membranes were electrostatically actuated, while their vertical displacement was monitored using a tip of an atomic force microscope (AFM). The devices reliably responded to the electrostatic actuation in ambient conditions over multiple cycles and with different measurement parameters, such as AC frequency, AC voltage amplitude, and AFM tip loading force. The demonstration of the high-yield fabrication of working electromechanical devices based on suspended Ti3C2Tx MXene membranes at the ultimate monolayer limit paves the way for the future exploration of the potential of MXenes for NEMS applications.

Shengyuan Luo

Papers

Main Mechanism for Generating Overpressure in the Paleogene Source Rock Series of the Chezhen Depression, Bohai Bay Basin, China

Bifunctional Amine- and Thiol-Modified Ti3C2Tx MXene for Trace Detection of Heavy Metals.

High-yield fabrication of electromechanical devices based on suspended Ti3C2Tx MXene monolayers.