Abstract:Deep reservoirs with abundant oil and gas resources are difficult to exploit safely and efficiently due to complex geological conditions and engineering factors. The problems of stuck drilling， well collapse， and well leakage caused by unstable wellbore walls have led to huge losses to drilling engineering. Therefore， this paper analyzes the mechanical mechanism of unstable wellbore walls and focuses on the influence mechanism of mechanics and multi-field coupling on unstable wellbore walls. Finally， it proposes suggestions for promoting the theoretical and technical development of drilling in weak side of deep stratified formations. The study found that the development of weak side， high temperature and high pressure environment， changes in rock layer inclination， and hydration of rocks are the main factors that weaken the mechanical strength of rocks and cause instability of the wellbore walls in deep reservoirs. The mechanical strength of rocks under different inclinations is significantly different， and the weak side of stratified rocks is more likely to swell due to hydration， which requires the rational optimization of drilling engineering parameters and drilling fluid density. This paper systematically summarizes the research on the rock mechanics and related aspects， deeply understands the mechanical influence mechanism of wellbore wall stability in deep reservoirs， and provides reference for actual production and engineering practice.

Abstract:HDCS-2 well is a coalbed methane parameter well and production test well deployed in the Nileke Depression of the Ili Basin. Through optimizing drilling fluid parameters， high viscosity drilling fluid flushing， explosive loosening and other technical measures， the drilling complexity problems are solved including block falling， drilling tool obstruction during the tripping， and buried drilling in long open hole of the coal bearing strata， ensuring the completion of the project and the achievement of the geological objectives. Rock mineral analysis testing and scanning electron microscopy observation were conducted using samples from Well HDCS-2， and a three pressure profile was constructed based on logging data to analyze the mechanism of wellbore instability. Improved measures for subsequent projects are suggested as follows： three-section well configuration and a high shear anti collapse drilling fluid system should be adopted， high viscosity drilling fluid （drip） can be configured for well flushing when encounteres falling blocks in the well， slow drilling and tripping， optimizing the drilling tool assembly as well as equip drilling vibration hammer during drilling in coal bearing strata. The study can provide valuable practical guidance for subsequent coalbed methane drilling in the region.

Abstract:During the drilling process in the covering layer of Zhumadian area in Henan Province， the Quaternary clay layer， sandy mudstone， loose sandstone unevenly interbedded with mudstone were encountered， resluting in difficult wall protection， prone to accidents such as block jamming， hole collapse and burial， and difficult in taking cores. Based on the geological conditions and the drilling construction data within the area， the dual-polymer anti-sloughing flushing fluid was used. In the on-site application， the stability of the hole wall was good during the drilling process of the long open hole well section， without any incidents of falling or collapes. The core recovery rate can meet the geological design requirements， moreover， the casing depth and construction cost were reduced.

Abstract:Well Xinsudi-2 is an oil and gas geological survey well deployed in the Xinjiang Tarim Basin. The well was drilled to 2468.50m with an open hole section of 2009.24m. After geological assessment， it was designed to be deepen drilling to 3168m. This article takes the 500~600m well section as an example to analyze the wellbore stability. The wellbore is soaked in drilling fluid for a long time， which causes the water content of the wellbore to increase. The cohesion and internal friction angle of the mudstone and other strength indicators decrease， resulting in the wellbore not having pressure-bearing capacity， slight disturbance will cause the well wall to become unstable. The project team adopted a new anti-pollution polymer anti-collapse drilling fluid system， a drilling tool assembly with a drill-while-drilling jar to relieve stuck conditions under complex well conditions， and the target layer was drilled using low drilling pressurelow rotational speedlow-displacement parameter combination drilling and other technical methods has solved a series of complex situations caused by long open-hole sections and long time soaked formations， ensured the smooth completion of the project and achieved the geological purpose， and accumulated the experience and technology of drilling long open hole and long-immersion formations.

Abstract:The stability of the slope of an open-pit mine is mainly affected by geological structures such as faults and joint of rock mass. In order to identify the distribution characteristics of the rock mass structural， the Reflex ACT Ⅲ tools were used to unify thecore orientation of 4 geotechnical survey holes. However， the proportion of highly reliable core orientation data for each borehole only 8.05%~34.29%， due to therock mass fragmentation and joint development near the contact zone between granite intrusions and sedimentary rocks， which affects the accuracy of core orientation. Therefore， this article took OTV/ATV survey to obtain lithology and structural characteristics， relationships and direction data effectively and improve the accuracy of geological structure information data of core orientation， through high-resolution， continuous and oriented 360° borehole wall images. Based on this， failure mode of the open pit mine was studied by equatorial polar projection theory and dynamic analysis. According to the result， the main failure mode is wedge sliding failure， with a probability of 12.66%~34.99%， followed by plane sliding， with a probability of 3.40%~20.36%， which provides the foundation for open-pit mining slope control.

Abstract:The complex drilling conditions of deep drilling put forward higher requirements for the performance of impregnated diamond bits. To improve the application range of electroplated diamond bits， the effects of MnCl2 and butynediol ethoxylate （BEO） on the surface morphology， microhardness， and thermal stability of the nickel base coating were studied. The drilling performance of pure Ni matrix diamond bit， Ni-Mn matrix diamond bit， and Ni-Mn matrix diamond bit with BEO as an additive after annealing at 300℃ for 1 hr was compared. The results show that the microhardness of pure Ni decreases significantly to 300HV after annealing at 300 ℃ for 1 hr， and the wear resistance of the annealed diamond bit with this matrix is too low， which leads to premature diamond shedding and a short service life to 2.94m. Both Ni-Mn coating and Ni-Mn coating with BEO added have good thermal stability， and the hardness increases to 640HV and 693HV respectively after annealing at 300℃ for 1hr. Ni-Mn matrix diamond bit has both suitable drilling life and drilling efficiency after annealing， and the bit life can reach 4.67m. However， the annealed Ni-Mn matrix diamond bit with BEO as an additive fails due to the matrix’s high microhardness.

Abstract:With the implementation of deep oil and gas exploration， high temperature hot dry rock exploration and deep earth exploration strategy， the drilling fluids have been in high temperature and high-pressure environment for a long time， and the stability of water-based drilling fluids under ultra-high temperature and high pressure is a key technology for ultra-high temperature well drilling. In this paper， the technical problems faced by drilling fluids in ultra-high temperature scientific drilling engineering are analyzed， and the design approach for high density water-based drilling fluids formula resistant to 240℃ ultra-high temperature are proposed. The key additives for 240℃ ultra-high temperature and high density water-based drilling fluids were selected by single factor method. Using the synergistic effect of different high temperature additives， a set of ultra-high temperature and high density water-based drilling fluid formula with temperature resistance of 240℃ and density of 2.0g/cm3 was preliminarily developed. The results show that after aging at 240℃ for 16h， the optimal formulation of drilling fluids have good rheology and filtration reduction performance. Its apparent viscosity change rate is less than 30%， and the filtration loss at 180℃ is less than 24mL.

Abstract:In this paper， taking the rock slope of an open-pit mine in Xizang as an example， based on the site investigation and engineering geological characteristics of mine slope， the engineering geological zoning of mine slope is studied， and the slope stability is qualitatively analyzed and quantitatively calculated by combining the stereographic projection method and Sarma method. The research results show that the slope stability evaluation results were consistent with the current slope status. The slope stability of mining area was not good in general， and the slope in local area has poor stability. Both qualitative and quantitative stability evaluation methods confirm each other， which provides an important basis for slope disaster control design and construction in the next stage， and this has a good reference for similar slope projects.

Abstract:Red beds are typically considered as “prone-to-slide strata”， and shallow soil landslides can easily occur under rainy conditions. Therefore， it is of great importance to study the stability of shallow soil slopes in red bed areas under rainfall conditions. In this research，the shallow soil slopes in the red bed areas of Hunan Province is taken as an example， the stability of shallow soil slopes in red bed areas under different slope gradients， rainfall intensities， saturated hydraulic conductivities， and initial water contents is investigated by employing the modified Green-Ampt infiltration model， the specific impact patterns of these factors on slope stability is also analyzed. When the slope gradient is less than 45°， the safety factor decreases as the slope increases； when the slope gradient is greater than 60°， the safety factor increases with the slope. The wetting front depth changes insignificantly with the rainfall intensity， and the safety factor changes insignificantly with the rainfall intensity； the depth of the wetting front increases and the safety factor of the slope decreases as the saturated hydraulic conductivity increases； the safety factor decreases as the initial water content increase. The results can provide a theoretical basis and practical guidance for slope protection engineering in red bed areas.

Abstract:In order to manage a landslide， a numerical analysis model of the slope was constructed based on the on-site investigation data， taking the inflection point of the displacement of the characteristic point of the slope as the criterion， and adopting the strength discount method to determine the stability coefficient of the natural working condition of the slope to be 1.05， it was determined that the stability level of the slope did not meet the requirements of the engineering specification， and it was in the state of understability. Combined with the numerical analysis results， experts’ on-site analysis opinions and the mechanism of slope reinforcement measures， three kinds of reinforcement and management programs are determined， Program 1 is “Circular anti-slip piles + anchors + intercepting and draining”， Program 2 is “Square anti-slip piles + Circular anti-slip piles + Anchors + intercepting and draining”， and Program 3 is “Square anti-slip piles + Circular anti-slip piles + Intercepting and draining”. Based on the finite element numerical model to analyze the stress field， displacement field and slope stability coefficient changes of the rock and soil body， anti-slip piles and anchors， the stability coefficients of natural working conditions of the slope corresponding to the three reinforcement schemes were calculated to be 1.39， 1.28， and 1.18， which were 32.4% higher than those before reinforcement， and the stability coefficients of the natural working conditions were calculated to be 1.39， 1.28， and 1.18， which were 32.4% higher than those before reinforcement. Before the reinforcement， the stability coefficients of the natural working condition of the slope were 1.39， 1.28 and 1.18， respectively， which were 32.4%， 21.9% and 12.4% higher than those before the reinforcement； after comprehensively comparing the reinforcement measures of the three kinds of reinforcement schemes and the changes in the stress and displacement of the slope， as well as their reinforcement effects and economic levels， Scheme 1 was comprehensively determined as the final reinforcement scheme.