To address the common challenges of rheological deterioration，excessive fluid loss，and wellbore instability for drilling fluids under high temperature，high salinity，and high stress conditions in ultra-deep wells，a cationic nanogel viscosifier and plugging agent，P（AM-DMC），was designed and synthesized from acrylamide （AM） and methacryloxyethyltrimethylammonium chloride （DMC） via inverse suspension polymerization. This material combines the viscosity-enhancing property of flexible polymer chains with the high interfacial activity and size effects of nano-particles. Scanning electron microscopy （SEM） showed the material has an irregular polyhedral morphology and a particle size distribution of 200-500 nm. The performance of the developed material was systematically evaluated in a low solid water based drilling fluid，including rheology，filtration control，and salinity tolerance，while the contact angle and Zeta potential measurements were used to reveal the micro-interfacial properties. The material exhibited high hydrophilicity （a contact angle of 13°） and excellent dispersion stability，facilitated by its strong positive surface charge （Zeta potential of +59.1 mV），which forms the basis of the synergistic viscosity-enhancing and plugging mechanism. Results demonstrated that P（AM-DMC） significantly improves the structural viscosity and shear resistance capacity of the drilling fluid through strong electrostatic adsorption between its cationic chains and clay particles，along with the formation of a three-dimensional network of the materials. Increasing the dosage of P（AM-DMC） markedly enhanced the apparent viscosity and yield point while significantly reducing both API and HTHP fluid loss. The system maintained excellent rheological stability and low fluid loss after aging at 170°C，confirming its outstanding thermal stability. It is indicated that P（AM-DMC） nanogel is a novel additive for high-performance drilling fluids in deep complex formations，offering efficient viscosity enhancement，fine plugging，and superior temperature resistance and thus holding significant engineering value for the safe and efficient drilling of ultra-deep wells.

Given the current situation that some operating parameters of the gas extraction system in Hutubi gas storage deviate from the optimal value to cause low energy-saving efficiency，the energy efficiency of the gas extraction system is analyzed through pinch analysis and exergy analysis methods. A simulation study is performed based on HYSYS software，giving rise to the scheme of energy conservation and consumption reduction. The scheme mainly includes the selection of the gas-gas heat exchanger，the optimization of the glycol-rich liquid inlet temperature，the optimization of the reflux ratio of the regenerator，and the optimization of the phase-change furnace. The calculation model between the inlet pressure and J-T valve back pressure and the theoretical KA value of the gas-gas heat exchanger is established to optimize the selection of the heat exchanger. The optimum inlet temperature of the glycol-rich liquid is determined to be 67 ℃，and the reflux ratio of the regenerator is 0.06. During the operation of the top condenser of the regenerator，the consumption of glycol can be reduced by 84.6%. The energy consumption of the system can be reduced by 9.0% by using the waste heat of the exhaust gas from the regenerator to preheat the external transmission gas. This optimization scheme effectively reduces the total energy consumption of the gas extraction system with minimum alteration.

Due to the extremely rich oil and gas resources in deep-sea area, the deep-sea oil and gas exploration at home and abroad has been heated up in recent years. The actual drilling in northern basins of South China Sea proves that the oil and gas resources are abundant and the exploration prospect is bright. As an operator, CNOOC has completed a total number of 8 deepwater wells with the depth of 1500 m in northern basins of South China Sea, forming a complete set of key drilling and completion technologies, such as shallow disaster prevention and control, well structure design and optimization, surface conduit injection and running, formation pressure monitoring while drilling, narrow window safe operation, hydrate prevention and control, drilling and completion fluid and cementing. Mastering this set of technologies is important to promote the sustainable development of China's offshore oil industry. It is of great significance to increase oil and gas production and ensure energy security. Taking the first deepwater well completed by CNOOC as an operator in Lingshui Block as an example, this paper introduces the key technologies and application results of deepwater drilling and completion in this area. 

Bohai Oilfield is an important support for increasing offshore oil and gas reserves and production in China. In view of the complex geological conditions， the coexistence of multiple pressure systems， poor wellbore stability， highly risky drilling operation， and the great difficulty in comprehensively improving inefficient wells in Bohai Oilfield， an analysis and study of the system of innovative technologies to improve drilling speed and efficiency are conducted with safe drilling operation as the criterion. These technologies have been applied successfully in field， which include the wellbore stability study-based extreme extending techology for ERW， the technology of twin holes in monobore to use the slot more efficiently， the well structure optimization technology to minimize casing stages and sizes， the dynamic comprehensive analysis and optimization technology for coated tubulars， and the decision-tree model-based refined sidetracking technology. The future development trend of reducing cost and increasing efficiency for drilling in Bohai Oilfield is also looked into in order to provide technical reference for the efficient development of Bohai Oilfield. 

At present，extended-reach well（ERW）drilling has become an important means for oil and gas exploration and development，and trajectory design optimization is the key to the successful drilling of ERW and the improvement of operating efficiency. With the continuous increase in horizontal displacement and horizontal length to vertical depth ratio，ERW drilling is facing many serious challenges. Therefore，it is necessary to comprehensively analyze and evaluate the factors affecting trajectory design，such as trajectory control ability and wellbore stability，so as to form an integrated technical thinking. In this study，a matrix of trajectory evaluation indicators was first established by analyzing the characteristics of ERW drilling technique，and then scores and weights of all indicators were determined based on expert experience. Consequently，quantitative evaluation was used to judge the selection of ERW trajectory，and applied to the ERW design in an oilfield. Drilling operations were carried out in the field strictly following the selected trajectory plan，and finally a high-quality trajectory was achieved for the whole well. The results show that the evaluation method is practicable and feasible，and provides a technical basis and guiding method for selecting the design plan of ERW trajectory.

The casing deformation problem in the process of multistage fracturing in Jimsar shale oil is prominent. Based on an analysis of its development status,casing deformation in shale oil wells in the demonstration area was counted to give a clear picture on the forms of casing deformation,as well as the characteristics of its temporal and spatial distribution. The influencing factors of casing deformation were analyzed from the perspective of engineering and geology. The analysis results show that the casing deformation in shale oil wells is characterized by shear deformation. Casing deformation points are located near target A,middle section and target B accounts for 50.0%,32.2% and 17.8%. Casing deformation mostly occurs in the process of fracturing. Formation lithologic interfaces,natural fractures and fault development degree are the main influencing factors,while cementing quality,casing wall thickness and rigidity have little influence. Reducing pump rate and pump pressure is conducive to mitigating casing deformation. Finally,the control methods of wellbore integrity are put forward which can provide reference in controlling the wellbore integrity failure for shale oil.