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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.

Conventional Measurement-While-Drilling (MWD) technology is unable to function statically at the predicted temperatures of deep formations exceeding 200 °C in wells reaching depths of 10,000 m. It is limited to measuring downhole engineering parameters through purely mechanical means, such as inclination. However, the accurate long-distance transmission of drilling fluid pulse signals poses a significant bottleneck, restricting the application of these mechanical measurement methods. To address these issues, this paper develops and designs an algorithm to identify and analyze the amplitude characteristics of deep well mud signals. By employing a signal coding algorithm, a signal processing analysis method, and a signal feature recognition algorithm based on grey correlation degree, we construct a signal recognition method capable of decoding mud amplitude encoded signals. Key techniques such as filtering, smoothing, and feature extraction are utilized in the signal processing, and the proposed method's effectiveness is verified through the analysis of collected signals. Furthermore, long-distance simulation analysis software is developed to evaluate waveform distortion during extended transmission, confirming the feasibility of the recognition algorithm. Laboratory experiments demonstrate that this algorithm can accurately recognize and demodulate signals generated by mechanical inclinometer structures, providing a novel decoding method for signal transmission in deep and ultra-deep wells. [ABSTRACT FROM AUTHOR]

The stable isotope technique has been used in tracking nitrogen cycling processes, but the isotopic characteristics are influenced by environmental conditions. To better understand the variability of nitrate isotopes in nature, we investigated the influence of organic carbon sources on isotope fractionation characteristics during microbial denitrification. Denitrifying cultures were inoculated with freshwater samples and enriched with five forms of organic compounds, that is, acetate, citrate, glucose, cellobiose, and leucine. Though the isotope enrichment factors of nitrogen and oxygen (15ε and 18ε) changed with carbon sources, 18ε/15ε always followed a proportionality near 1. Genome‐centred metagenomics revealed the enrichment of a few populations, such as Pseudomonas, Enterobacter, and Atlantibacter, most of which contained both NapA‐ and NarG‐type nitrate reductases. Metatranscriptome showed that both NapA and NarG were expressed but to different extents in the enrichments. Furthermore, isotopic data collected from a deep reservoir was analysed. The results showed δ18O‐ and δ15N‐nitrate did not correlate in the surface water where nitrification was active, but 18ε/15ε followed a proportionality of 1.05 ± 011 in deeper waters (≥ 12 m) where denitrification controlled the nitrate isotope. The independence of 18ε/15ε from carbon sources provides an opportunity to determine heterotrophic denitrification and helps the interpretation of nitrate isotopes in freshwaters. [ABSTRACT FROM AUTHOR]