Abstract:Medium and deep geothermal energy is a kind of renewable energy which is abundant， widespread， stabable and reliable. It is characterized of green and low-carbon， clean and environmental protection， safe and high quality， sustainable and stable energy supply， which plays an important role in the implementation path of carbon peak and carbon neutrality. Combined with an engineering case in Changsha Basin， this paper tests the hardness， uniaxial compressive strength and lithology of rock samples using the rock pression sclerometer， electric-stress direct shear instrument and polarizing microscope.The influence of rock cementing material， mineral particles and bedding development degree on the drillability of the strata is analyzed and studied. The drillability grade of the strata is established， and some suggestions on the drill bit optimization are put forward， which has certain reference significance for drilling engineering in this area and such similar areas.

Abstract:The near-bit measurement while drilling （MWD） system effectively avoids the data latency issues faced by traditional MWD systems， and antenna parameter design and optimization are crucial for improving signal transmission distance and stability. This paper presents an optimization study on the antenna parameters of a near-bit MWD system， exploring the relationships between antenna coil diameter， number of turns， load， and magnetic core with signal transmission distance through experiments. The results show that with an emitting coil of 100 turns and a diameter of 0.8mm， and a receiving coil of 180 turns and a diameter of 1.0mm， combined with a secondary power amplifier circuit and the use of ferrite cores or ferrite sheets， the signal transmission distance and stability are optimal. The research findings provide theoretical basis and practical guidance for optimizing the antenna design of near-bit MWD systems.

Abstract:In order to solve the problem of low efficiency of core drilling in ultra-long horizontal holes， a cordless core drilling process is proposed to complete the delivery and recovery of the inner tube assembly by mud hydraulic drive. To this end， this paper designs a positive/reverse circulation switching mechanism for the borehole mud that assists the delivery and recovery of the inner tube. This mechanism can realize the positive/reverse circulation switching by changing the mud flow direction through the mutual cooperation of two dual-channel ball valves. Through the ANSYS software， the L type double channel of the positive/reverse circulation switching mechanism is simulated， and the results show that after the fluid passes through the L type channel， the high-velocity fluid only accounts for 50% of the total amount of fluid， and the pressure drop of the fluid through the ball valve channel is 1008.1Pa， and the fluid near the inside of the channel will produce a lot of turbulence， resulting in different degrees of backflow. For this reason， the shape of the channel was optimized， the original L channel was changed to a circular channel， simulation results show that the fluid through the circular channel， high-speed fluid accounted for 90% of the total amount of fluid through the ball valve channel pressure drop is only 105.3Pa， and the fluid trace overall smooth， only a small amount of fluid reflux occurred. The optimized fluid channel is effective in reducing the pressure drop through the ball valve. The optimized fluid channel effectively reduces the head pressure loss and ensures the stable transportation of the fluid.

Abstract:In response to the technical difficulties in ultra-deep shale gas horizontal well drilling in the Da’an block， such as low mechanical drilling speed in difficult drilling formations， high failure rate of rotary steering instruments at high temperatures， and long drilling cycles. In aim of efficient and rapid development of Da’an shale gas， the characteristics of encountered formations and technical difficulties in drilling were analyzed. Through the technical research and application such as optimization of wellbore configuration， selection of efficient drill bits， rapid identification of “Platinum targets”， density reduction and speed increase in the horizontal section， surface cooling of oil-based drilling fluid， high-temperature resistant white oil-based drilling fluid system， and equal wall thickness screw technology， the optimal and fast drilling technology for ultra-deep shale gas horizontal wells in the Da’an block was formed. This technology was tested on-site in the Da’an 104H ultra deep shale gas horizontal well， where the actual drilling depth was 6789m， with a horizontal section length of 2406.13m and an average mechanical drilling speed of 10.60m/h， which is 30.54% higher than the average value of 8.12m/h in the block. It can provide technical support for the efficient development of shale gas in Da’an.

Abstract:Reservoir damage mechanism has been widely studied， but the research of reservoir protection technology needs to be further in-depth. In view of the importance of reservoir protection， an acid soluble fiber is prepared by alkali oxidation method. By optimizing its particle size distribution and evaluating its acid solubility， it is confirmed that the combination of the fiber and rigid particles can achieve the purpose of reservoir protection. Drilling fluid additives （lubricants， fluid loss reducing agents and coating agents） for reservoir protection were optimized. The evaluation of lubricity， fluid loss reduction and rheology showed that the additives had good lubricity， fluid loss reduction and rheological properties. A drilling fluid system that can be used in reservoir was prepared. When acid soluble fiber and drilling fluid for reservoir are used at the same time， its rheological property can meet the construction requirements， with excellent salt resistance， good sedimentation stability and excellent reservoir protection performance. The field application in A coalbed methane well in Qinshui Block shows the excellent performance of acid soluble fiber and drilling fluid for reservoir， which is expected to be further applied.

Abstract:Geothermal resource is a kind of clean energy. It plays an important role in promoting energy structure transformation and achieving carbon peak and carbon neutrality. With accelerating development of geothermal resources， geothermal directional wells have been increasing year by year. Directional drilling technology has become more and more important in developing and utilizing geothermal resources. In order to improve geothermal directional drilling speed and efficiency， paper analyzed the technical issues of geothermal directional drilling technology and the wellbore structures of geothermal directional wells in Tianjin. Geothermal directional drilling technology optimization includes anti-deflection technology optimization of vertical well section， choice of KOP， optimization of BHA and parameters， improved drilling fluid system. Application of geothermal directional drilling technology optimization can ensure better well trajectory and improve directional efficiency in 6 wells in Tianjin.

Abstract:Drilling engineering is a heavy physical work. At present majority does it basically by experience. That situation should be changed， the drilling by experience should be changed up to the science. Russian drilling specialists have proposed comprehensive research on the three indexes， i.e. rate of penetration， bit penetration rpm and energy consumption per meter in diamond drilling and developed a software controlling optimization of drilling process. Good results have been obtained by using the software and it is worth for us to learn from.

Abstract:Accurate prediction of rate of penetration （ROP） in deep geological drilling process can help to improve drilling efficiency and reduce drilling costs， which can provide key technical support for safety and efficient deep geological drilling construction. In this paper， a dynamic prediction method of ROP in deep geological drilling process based on regional multi-well data optimization and model pre-training is proposed. First， the deep geological drilling data warehouse is designed by selecting lithology identification software， drilling process intelligent monitoring cloud platform， and geological cloud system as data sources. Secondly， the regional multi-well data optimization technique is used to select the matching data with the target well in the data warehouse， and the ROP model is pre-trained on this basis. Finally， the ROP prediction model is dynamically updated through combining the actual drilling data of deep geological drilling process， and introducing techniques such as the wavelet filtering， extreme learning machine， and incremental learning strategy. The experimental comparison results verify that the proposed method has strong ROP prediction performance and generalization capability.

Abstract:Scientific drilling is an important technical means for obtaining underground physical data， anaylzing underground structures， and verifying important geological theories. The key underground instrument is an important basic guarantee for ensuring the smooth implementation of drilling projects. However， during the myriametric scientific drilling process， the requirements of underground working conditions and craftwork such as high temperature， high pressure， long drilling period， and large specification parameters seriously challenge the working performance of underground instrument. To the end， this paper analyses the structural characteristics and failure reasons of key underground instrument such as drill string， downhole mud motor， and auxiliary synergistic tools under the myriametric drilling working condition， and proposes corresponding measures on optimizing the structure of drill pipe joint， designing metal gear drill， improving the structure of hydraulic oscillator and injection-type torque thruster， and materials selection and setting up surface strengthening techniques， which can provide technical reserves for earth interior detection.

Abstract:A cap-plate logging while drilling tool experienced internal leakage in downhole operation due to the penetration crack between the inner channel and the T-groove bottom. The original location of the crack was determined through analysing the morphology of the penetrating crack， and then the cause for the penetrating crack was determined through the macro- and micro-analysis of the fracture. Finally， the structure of the tool was optimized with the finite element analysis to improve the service life. The analysis results show that the presence of large stress concentration and the cutting marks at the bottom edge of the T-shaped groove led to the fatigue penetration crack， which causes the intrusion of drilling mud， and the crack originated from both sides of the through bore at the bottom of the groove. The stress distribution can be improved by optimizing the groove bottom fillet and other measures.