Deep and ultra-deep carbonate oil and gas reservoirs, with their vast reserves and immense potential, have emerged as critical strategic assets in global energy supply. However, the complex challenges posed by high-temperature, high-pressure environments, intricate pore-throat structures, and the coexistence of macro-pores, dissolution cavities, and fractures make traditional exploration and production technologies insufficient to manage such complexity. As exploration and development progress, precise reservoir characterization and seepage behavior research face significant hurdles, including advanced modeling, complex seepage experiments, and accurate description of reservoir properties. Therefore, this review offers an in-depth analysis of the latest developments and key challenges in the characterization and seepage behavior of deep and ultra-deep carbonate reservoirs. It provides a comprehensive summary of cutting?edge methods for detailed microstructural reservoir characterization and multi?attribute seismic interpretation techniques enhanced by artificial intelligence. The paper also explores the application and success of multi?scale characterization approaches in complex reservoirs,while outlining the primary technical strategies and emerging trends in reservoir identification and description. Additionally,the article emphasizes recent advancements in understanding seepage characteristics under high-temperature and high?pressure conditions in deep carbonate reservoirs, focusing on multi-scale seepage theory and gas-water two?phase flow mechanisms. By examining experimental data and theoretical models from both domestic and international research, the review highlights current challenges and future directions in seepage studies, providing valuable insights for the development and efficient exploitation of deep and ultra?deep oil and gas reservoirs.

In oil and gas extraction, coiled tubing technology has attracted much attention because of its advantages such as fast operation time, little damage to the formation low labor intensity, etc. The research of coiled tubing technology is a systematic project involving many aspects. This paper first starts the discussion from the domestic and international literature published and the main research scholars review the development process of coiled tubing technology, and summarise the relevant achievements existing in China. At present, the coiled tubing technology is in the stage of rapid development, but the research of coiled tubing in ultra-deep wells is minimal. The authors describe the relevant research carried out by the team on the downhole accessibility of coiled tubing in ultra-deep wells, the extension of the horizontal section of coiled tubing, the optimization of the construction parameters of coiled tubing operation, and the downhole safety assessment of coiled tubing operation. According to the current status of coiled tubing technology research in ultra-deep wells, it is suggested to carry out the research related to the real-time warning technology of coiled tubing fatigue life based on the digital intelligence technology, the ability of tractor?driven coiled tubing extension, and the research and development of high?temperature?resistant tools and fluids, to solve the technical difficulties of coiled tubing operation in ultra-deep wells.

There are several sets of formation pressure systems in Y structure of block X in Bohai Sea. Shahejie Formation and its upper strata are sedimentary undercompacted layers. dc index method is adopted to monitor formation pressure. The Mesozoic buried-hills are widely distributed in medium acid volcanic rocks, which are non-sedimentary underpressure layers. The formation pressure monitoring method of Sigma index is used to monitor the formation pressure. The real drilling shows that the formation pressure monitoring method of dc index has good applicability in the formation profile pressure monitoring dominated by sand and mudstone. The formation pressure monitoring method of Sigma index has a good application effect in the non-sand mudstone formation profile pressure monitoring, and the combined application of the two provides effective technical support for the smooth drilling. The application of Sigma index formation pressure monitoring method in deep and ultra?deep layers effectively improves the accuracy of the deep and ultra?deep layer pressure monitoring technology while drilling. The practical application shows that the results of formation pressure monitoring while drilling are in good conformity with the measured formation pressure results, and the formation pressure monitoring method of Sigma index has the value of popularization and application in deep and ultra-deep formation.

The terrestrial gas reservoirs in the northeastern Sichuan region have reserves of over 100 billion cubic meters in the Xujiahe River. In the early stages, small?scale sand fracturing or acid fracturing were mainly used for production, but no significant breakthrough in productivity was achieved. Due to the tight and high fracture pressure of the Xujiahe reservoir, the construction displacement is limited, making it difficult to add sand and resulting in poor transformation effects. By conducting research on the guarantee technology for the operation of potential tapping wells, the Xujiahe potential tapping well wellbore treatment and fine pressure control technology have been developed, which has solved the problems of wellbore control and pressure control during construction operations caused by the coexistence of original test layers and large differences in ground pressure coefficients. The idea of tapping the potential of multiple layers in a single pipeline column has been proposed, forming a combination of large?diameter oil pipes and segmented fracturing pipelines with packers. The interactive operation of 140.0 MPa and 105.0 MPa wellheads meets the requirements of ultra?high pressure large?scale sand addition operations and later production. The application has been carried out in YB6, YL15, and YL171 wells, successfully achieving potential tapping operations in three old wells. A layer by layer fracturing of the four reservoirs was completed in the YL171 well using a single string, resulting in a production of 32 5000 cubic meters per day at a hydraulic pressure of 71.0 MPa.