Accurately identifying the damage failure modes and causes of PDC cutters and PDC drill bits is a key step in the drilling tool selection and the drill bit iterative optimization. To improve the accuracy and objectivity of drill bit damage identification，failure analysis was conducted on hundreds of PDC bits tripped out of wells，and the main damage failure modes and causes of PDC cutters (including various shaped cutters) were summarized，leading to a dataset containing over ten thousand images of PDC cutter damage morphologies. Then，based on the convolutional neural network-based YOLOv7 image recognition algorithm，an intelligent recognition model for PDC cutter damage failure was established. This model can effectively infer damage types from PDC cutter images and automatically annotate the images with corresponding damage failure modes. The model was evaluated using multiple performance metrics，showing an identification accuracy of over 80%. Furthermore，this model was combined with the PDC drill bit design theory and damage failure mechanisms to develop a new intelligent recognition method for PDC drill bit damage failure，using statistical methods like causal inference. This method can automatically evaluate the damage failure modes of PDC cutters in different regions of the bit crown using only photos of bits tripped out of wells and determine the primary cause of PDC drill bit failure. The research findings provide references for intelligent drill bit damage identification and innovation in intelligent drilling technology.

Complex problems，such as HTHP，wellbore collapse，and lost circulation were encountered during drilling Hutubi Anticline. The fabric，mechanical properties，and in-situ stress state of the troublesome medium-deep shale formation were analyzed to determine the countermeasures necessary to stabilize the borehole and reduce risk. A multi-field calculation model for collapse pressure was established linking mechanical factors，drilling fluid chemistry，and fluid seepage. The mechanism of wellbore instability when using water-based drilling fluid in the middle-deep shale formation of Hutubi anticline was identified. The results indicate that the montmorillonite content of the illite-smectite mixed layers in the mudstone in Paleogene Anjihaihe-Ziniquanzi Formation （which collapses readily） exceeds 35%. The formation exhibits moderate expansion and high dispersion，with water expansion rate and recovery rate both being less than 10%. The formation strength also shows anisotropic properties. The mudstone in Cretaceous Hutubihe-Qingshuihe Formation shows reduced swelling and increased hardness and brittleness. Hutubi Anticline is subject to significant tectonic stress，with the maximum horizontal principal stress being equivalent to nearly 2.50 g/cm³，which is higher than the overburden pressure. Applying the multi-field coupling model indicates that the main causes of wellbore instability are seepage of drilling fluid along cracks，hydration of mudstone after contact with drilling fluid，and insufficient effective mechanical support of drilling fluid for the wellbore. The collapse pressure calculated using the multi-field coupling model is 0.05-0.25 g/cm³ higher than when only considering mechanical factors. It was established that the wellbore can be kept stable by maintaining the sealing ability of the drilling fluid to the fractured formation，preventing contact with easily hydrated mudstone during drilling，and increasing the density of the drilling fluid to slightly higher than the collapse pressure.

With oil and gas exploration and development approaching the deep-burial，deep-water and unconventional fields，the encountered formations become increasingly complex. Deep mudstone formations exhibit strong hard plastic characteristics during drilling，resulting in difficulties in penetrating of cutters into formations and low rates of penetration （ROP）. Given the challenge of improving ROP in hard plastic mudstone，rock-breaking simulation tests of PDC （Polycrystalline Diamond Compact） cutters were conducted for hard plastic formations，and the rock-breaking effects of various shaped cutters were analyzed. The results indicated that the 3D-shaped cutter exhibits the best rock-breaking efficiency and certain durability: it delivers a maximum ROP improvement of 116.4% in the hard plastic mudstone in Shengli Luojia Oilfield. Furthermore，a staggered cutter arrangement design，combining axe-shaped and 3D-shaped cutters，was proposed for drilling deep and complex formations，like sand-mudstone interbedding formations，which delivers the highest ROP increment of  215.7% in Yongjin Oilfield in Junggar Basin. Additionally，potential measures for enhancing ROP in hard plastic mudstone were discussed. The design principles of "sharp breakthrough，plane advancing and intensive scraping with small-diameter cutters" are recommended to improve the drilling efficiency. The research findings provide valuable insights for optimizing the design of PDC bits for hard plastic mudstone.

Based on actual engineering applications of conventional drilling and percussion drilling，and considering the material parameters and intrinsic model of rock dynamic mechanics，a numerical model of rock breaking of the cutters of Polycrystalline Diamond Composite（PDC） bit was established. The penetration depth，damage area，size of rock debris particles and rock breaking volume of PDC cutters under different percussive drilling models were compared and analyzed. The results show that the rock cutting pattern is very similar between the numerical simulation results and the laboratory physical experimental model of single-cutter. The penetration depth of single tooth of rotary，torsional，and combined percussive drilling increased by 19.8%，6.6% and 26.9% respectively compared with that of conventional drilling，and the combined percussive drilling saw the most significant increase in rate of penetration. When there is axial impact load during percussive drilling（such as combined percussive drilling or rotary percussive drilling），it will cause visible damage to the rocks below the cutting surface，which facilitates the “second cutting” after the drilling cutters turn 360 °，but large rock debris particles can be produced，so it is necessary to optimize the drilling fluid parameters to keep the wellbore clean. The fluctuation range of penetration depth of the cutter in torsional percussive drilling is small，which indicates that this method helps reduce the risk of bit stick-slip，and the rock debris particles produced are small which makes it easy to keep the wellbore clean. The research results are of great significance for the selection of different types of percussion drilling tools and tool parameters optimization.