Abstract:In geothermal well construction， cementing is indispensable to ensure the outlet water temperature and enhance wellbore durability. Currently， class G cement remains the primary choice for geothermal well cementing. However， complex environments such as large geothermal gradients， fractured formations and the presence of corrosive media require more strict performance requirements for traditional portland cement systems. This paper analyzes existing technical strategies and future development trends of portland cement systems from three aspects： high-temperature resistance， corrosion inhibition， and low-density performance. The results indicate that the most commonly used method to overcome the deterioration of high-temperature performance of cement is adding silica powder or silica sand and reducing the calcium silicon ratio of the system to adjust the hydration product type. Corrosion inhibitors have evolved from single organic/inorganic inert materials to water-based latex， acid responsive latex， and organic/inorganic composite multi-component anti-corrosion systems. The lightweight cement system formed by absorbing water and tackifier， low density reducing agent or foam still has some shortcomings， such as difficult density maintenance， slow strength development， poor stability， etc. In the future， emphasis should be placed on analyzing the main controlling factors of the strength degradation mechanism of cement and developing new strength degradation inhibitors. Establish multiphase dynamic corrosion conditions and conduct research on the corrosion mechanism of cement stone body and bonding interface. Forming a high-temperature resistant， corrosion-resistant， lightweight leak proof cement system by taking into account the complex environment of geothermal cementing and supplementing with fiber or other sealing materials. Facing the geothermal cementing environment， a comprehensive understanding of the current technical status and development trends of the existing portland cement system can provide reference for the research and development direction of geothermal cement.

Abstract:Oil shale reservoirs are a kind of sedimentary rocks rich in organic matter. The proven reserves of oil shale resources in China rank third in the world. Realizing the commercial development of oil shale resources is one of the important measures to ensure the energy security of our country. Oil shale underground in-situ conversion process has the advantages of green environmental protection， small footprint and can develop deep oil shale resources. It is an important technical means to realize the efficient development of middle and deep oil shale resources. This paper introduces the application and research results of hydraulic fracturing technology， supercritical CO₂ fracturing technology， acidizing fracturing technology and clear water fracturing technology in the process of in-situ exploitation of oil shale， and compares the advantages and disadvantages of four kinds of reservoir reconstruction technology. Meanwhile， the current applications and progress of hydraulic fracturing technology in experimental research， numerical simulation and pilot test project are highlighted. Finally， the deficiency and future development direction of oil shale reservoir reconstruction technology are discussed.

Abstract:Drilling is the most direct and effective investigation method for tunnel engineering， however， for deep-buried long tunnels， traditional vertical boreholes have limitations such as less effective footage， significant challenges in equipment relocation， etc. Directional drilling technology offers a solution by allowing off-site borehole placement （e.g.， along mountainsides or valleys） and controlled drilling trajectories to investigate the geological conditions of the tunnel structure， demonstrating high economic efficiency. A branch-type directional exploration hole was successfully implemented in the water diversion project from Yangtze River to Hanjiang River. The main hole reached a depth of 630.8m， with a branch hole extending 81m， a total of 158 coring runs were conducted， recovering 166.3m of rock core， achieving a 95% core recovery rate in the target zones. Additionally， acoustic wave logging， borehole imaging， and hydrogeological tests were performed. This project established a comprehensive investigation method integrating directional drilling and in-hole testing for hydropower and water conservancy engineering. It provides a new approach for deep-buried tunnel exploration and serves as a valuable reference for applying directional drilling technology in similar projects.

Abstract:It is difficult to achieve a clear understanding during the survey period before deep buried long tunnels construction， which may affect the construction of the project to some extent. The application of directional drilling technology for the geological forecasts before the construction of deep buried long tunnels is propsed， in which the good guiding function and rapid long distance drilling characteristics are utilized to achieve advanced detection of major risks ahead of tunnel excavation， and it can compensate for the shortcomings of conventional long-distance advanced detections. In this paper， different types of drills are used for geological forecast of 7# tunnel in the water diversion project from Yangtze River to Hanjiang River based on different geological conditions and prediction priorities， moreover， the advanced forecast results and the geological conditions revealed by excavation are compared and analyzed. It is thought that the directional drilling application is aiming to detect major disaster bodies in front of the tunnel excavation face in advance， and the goals can be generally achieved combining the drilling characteristics and physical measures. Furthermore， the timeliness of forecast can be improved while drilling without coring. Based on the current technological level， the efficiency of directional drilling is higher than tunnel excavation of blasting and TBM method， which is feasible in the advanced detection of tunnels constructed by blasting or TBM method.

Abstract:Horizontal directional drilling technology has broad application prospects in urban underground space development， resource exploration， and other fields. However， it has complex rock breaking process， making the study of the dynamic characteristics and parameter response patterns of horizontal directional drilling processes crucial. This paper takes the PDC bit and roller bit as research objects， a three-dimensional finite element simulation model of horizontal directional drilling formations based on ABAQUS is established， in which the deformation， failure of rock mass and the forces acting on the bit during drilling are simulated， the response curves of bit reaction forces and torques are obtained， and the dynamic differences in rock breaking characteristics between the two types of bits are analysed. Through parametric simulation， the influence of different drilling parameters and rock mechanics parameters on the dynamics properties of bit’s rock breaking is investigated. A multivariate parameter regression prediction model for bit reaction forces and torques is developed based on response surface analysis， and the drilling speed prediction equations for both types of bit are derived， and the accuracy of these equations is verified. These researches provide a theoretical basis for optimizing drilling parameters and improving drilling efficiency.

Abstract:The Paleogene strata is widely distributed in the tunnel of the Yellow River to Xining water diversion project in Qinghai Province， and the tunnel burial depth is deep. It is of great significance for tunnel design and construction to evaluate the deformation and stability of tunnel surrounding rock based on the study the physical mechanical characteristics of the Paleogene strata. In view of the stability of the surrounding rocks in Paleogene strata， A preliminary study on the physical mechanics of soft rock was conducted using experimental and empirical analysis methods. The results showed that the Paleogene strata has low density and high water absorption rate. Under saturated conditions， the uniaxial compressive strength of rocks decreases sharply， and the softening coefficient is extremely low； Some types of rock have expansibility and a small amount of rock has poor resistance to disintegration； The mechanical properties of the rock are poor under water-rich conditions， which is detrimental to the stability of the surrounding rocks. When the burial depth is over 127m， the surrounding rocks may undergo severe to extremely severe compression deformation. During the construction， targeted engineering measures should be taken based on the deformation characteristics of the surrounding rocks to reduce the hazard of surrounding rock deformation.

Abstract:Rockburst is one of the major engineering geological problems faced by the construction process of deep-buried tunnels. Accurately determining the possibility of rockburst occurrence and the rockburst level is of vital significance for engineering construction， and it also poses a great challenge to the geological investigation. At present， during the geological investigation of water conservancy projects， only the strength-stress ratio is taken into consideration when determine the rockburst in tunnels using the industry standards. To thoroughly assess the rockburst potential in a deep-buried diversion tunnel， this study first applied the linear elastic energy criterion （W_e=40~100 kJ/m3） based on survey data and measured in-situ stress results to preliminarily predict the rockburst level. The results indicated an elastic energy density of 45 kJ/m3 in the surrounding rock， corresponding to a moderate rockburst risk. Subsequently， a three-dimensional geomechanical model was established using the finite difference method to invert the in-situ stress field and simulate the excavation-induced unloading process. It is revealed that elastic energy concentration zones were primarily distributed along the tunnel sidewalls. The numerical results mutually validated the energy criterion predictions， both confirm the spatial characteristics of moderate rockburst risk， and moreover the velocity and distance of the rock mass ejection during rockburst in the surrounding rocks are quantitatively predicted， which provide a basis for dynamic support design， and proposed reference value to the rockburst prediction of the deep-buried long tunnels investigation in the other water conservancy projects.

Abstract:This paper relies on the horizontal directional drilling project in the preliminary investigation stage of the expansion and reconstruction project of the Lion Rock Tunnel in Hong Kong. Based on the engineering geological data， borehole television images， acoustic wave data， and water pressure test data， a method combining qualitative and quantitative analysis is adopted to explore its application in the zoning of homogeneous areas. The optical imaging of borehole television makes up for the deficiency in obtaining the dip angles of the fracture orientations when the rock is fragmented. Acoustic logging and water pressure tests provide data on the integrity and permeability of the rock mass. The joint zoning of homogeneous areas using multiple methods helps to improve the accuracy and reliability of the classification of tunnel surrounding rock. The experimental results are highly consistent with the actual situation， demonstrating that the comprehensive geophysical exploration method can efficiently detect the development of stratum fractures， and the method for zoning homogeneous areas of the surrounding rock is accurate， providing technical support for engineering investigation.

Abstract:With the advancement of national large-scale engineering projects， the construction of deep-buried tunnels has increased significantly， posing challenges to lining structure design under high external water pressure. Existing hydrogeological test devices and methods for deep-buried tunnels exhibit multiple limitations. This paper introduces a stratified hydrogeological test device and methodology for deep-buried tunnels based on controllable pressure relief equipment. The device isolates the test section from hydraulic connections with upper and lower rock strata using packer plug， employs a controllable pressure relief device to reduce high groundwater pressure within the test section， and measures groundwater pressure recovery time and final stratified groundwater pressure through piezometers. By establishing a dynamic equilibrium relationship between the built-in air vessel gas， groundwater pressure， and total infiltrated water volume， the permeability coefficient of rock strata can be calculated， enabling hydrogeological testing under groundwater inflow conditions. This device and method feature operational simplicity， strong applicability， and low cost， and have been successfully applied in a large-scale water resources allocation project， providing reliable references for structural design and safe operation of deep-buried tunnels.

Abstract:Traditional water pressure test equipment has many limitations in data collection and test operation， and it is difficult to meet the needs of high-precision projects. This paper introduces a set of water pressure test methods and equipment suitable for kilometer-level horizontal directional holes， which incorporates an advanced automatic collection system， integrates high-precision sensors and intelligent control modules， innovatively designs the water-stop plug structure. This set of equipment can directly measure the actual pressure of the test section excluding pipeline losses. It can also judge the sealing performance of the test section and improve the test reliability. The key parameters in the test process can be recorded in real-time， continuously and accurately， avoiding problems such as manual operation errors and untimely data collection. The design of the new water-stop plug reduces the accident rate. The supporting test method is optimized according to the characteristics of the intelligent complete set of equipment， realizing the automatic operation and efficient management of the test. According to the test data， the water level elevation of the test section in the horizontal hole of the water pressure test can be accurately calculated. Verified by practical engineering applications， this new type of water pressure test equipment and test method significantly improve the reliability and accuracy of test data， enhance the work efficiency， provide more scientific and accurate basic data for geological surveys and engineering designs in fields such as geotechnical engineering， water conservancy and hydropower engineering， which have important engineering application value and popularization significance.

Abstract:The hot-water drill is considered to be the most efficient， safest and cleanest drilling equipment for exploring subglacial lakes in polar regions. A return-water cavity must be built when using hot-water drill to explore subglacial lakes. However， at present， the structure and thermal characteristics of the return-water cavity are still not clear. This paper first sorts out the main structure of return-water cavities of deep hot-water drill. Subsequently， a method for calculating the construction depth of the return-water cavity is established based on the pressure of the overlying ice on the subglacial lakes， and the initial shape of the return-water cavity is determined and the calculation methods for its dimensions is proposed. Then， the methods for calculating the critical temperature of return-water and the critical flow rate of injected hot water are proposed by establishing the physical and mathematical model of the ice temperature field surrounding the return-water cavity. Later， the influence of various factors on the two parameters are systematically analyzed. The research shows that the double-layer main/secondary hole structure is preferred for the return-water cavity when it is used for drilling subglacial lakes. The distance between the main hole and the secondary hole should be less than 1m， the diameter of the main or the secondary hole should be between 0.3m and 0.6m， and the length of the return-water cavity should be 2~3m longer than that of the submersible pump. The construction depth of the return-water cavity mainly depends on the thickness of the overlying ice sheet. In practical engineering， the construction depth of the return-water cavity should be 15~30m greater than the theoretical value. The critical temperature of return-water and the critical flow rate of injected hot water decrease with time. In normal conditions， the critical temperature of return-water does not exceed 2~3℃ and the critical flow rate of injected hot water does not exceed 12L/min.

Abstract:The research on the formation damage mechanism of conventional and unconventional oil and gas reservoirs is relatively well-established， but there has been a lack of attention towards the type classification and formation damage mechanism of geothermal reservoirs. Currently， only two types of geothermal reservoirs are recognized in the exploration and development of geothermal resources， namely， sandstone and karst. Because of the unclear concept and type of reservoir， the incorrect drilling method， drilling fluid selection and wrong resource assessment are caused. Furthermore， there is no formation damage mechanism and damage assessment criteria， so that the geothermal well completion process is missing， and leads to small water volume， low temperature， and even abandonment. On the basis of a large number of geothermal engineering， this paper focuses on the research of geothermal reservoir types and formation damage mechanism， aiming at the outstanding problems and referring to the conventional petroleum reservoirs research results. Researches show that geothermal reservoirs can be categorized into four types， which are porous， fissure， karst， and compound type. This categorization allows for more accurate drilling methods， selection of drilling fluids， and resource assessment. The main modes of thermal reservoir damage are porosity blockage or failure in the structure； The damage caused by intrusion from drilling fluid as well as static and dynamic pressure from liquid column within wells are the primary factors and inevitable common problems. The formation damage types of geothermal reservoirs can be divided into five categories： stress damage， flow rate damage， water sensitivity damage， alkali sensitivity damage and acid sensitivity damage.

Abstract:With the increasing demand for deep-sea and deep-earth drilling， the downhole drilling tools using traditional PDC bits are severely worn out and cannot fully meet the drilling requirements of deep wells in hard formations. Therefore， special-shaped cutter PDC bit， especially V-shaped cutter PDC bit， has become the focus of research. There are fewer studies on the effect of wear on the contact area of V-shaped cutter PDC bit. The contact area affects contact pressure of cutter， which in turn affects the depth of penetration into the rock and drilling efficiency， so it is of great significance to study the change rule of contact area of V-shaped cutter. In order to calculate the contact area of V-shaped cutter with the rock during wear， the expressions for contact area as a function of the wear height and the geometric parameters of V-shaped cutter， such as chord length and tangent angle， were derived using the method of planar oblique intersection of the cylindrical surface on which the cutter is located， and the effects of the geometric parameters of V-shaped cutter and wear height on contact area and contact pressure were analyzed. The results show that the cylindrical cutter and V-shaped cutter have the same contact area in the early stage of wear， when the cutter is worn to a certain stage， the contact area of the V-shaped cutters is smaller than that of the cylindrical cutter. The smaller the chord length and tangent angle are， the smaller the contact area is. Under the same load and the wear height of the cutters， the contact pressure between the V-shaped cutter and rock is larger than that of the cylindrical cutter， so the V-shaped cutter has the ability to penetrate deeper into the rock. For wellsite applications， the driller can measure and record the wear height and the corresponding ROP of a batch of bits of the same type after lifting. The statistical relationship between the wear height and ROP can be obtained for this type of bit， and then the contact area can be estimated from the wear height. This method makes it easy to adjust the weight on bit in time to maintain a high ROP， or to optimize the V-shaped cutter geometry parameters during design， which also helps to improve drilling efficiency.

Abstract:In drilling engineering， borehole inclination is often encountered. The borehole inclination depends on many factors， such as formation conditions， bit design， drilling parameters， operation level， management ability and so on. Among them， the formation conditions objectively exist and can not be changed by human will. In the formation conditions anisotropic rocks are encountered often. An important problem in drilling of the anisotropic rocks is production of overturning moment（produced from rock reaction force）， leading to deviation of bit matrix top and as a result to serious inclination of the borehole. To resolve the problem， Russian specialists have proposed designing the drill bit to resist （balance） of the overturning moment by using the bending moment produced by the eccentric matrix top while drilling and got patents and good results obtained. That deserves our attention.

Abstract:As one of the key technologies in the exploration and development of geothermal resources， the efficiency and effect of DTH hammer drilling largely depend on the performance of the drill bit， especially the quality and life of PDC spherical cutters. In response to the current issues such as low drilling efficiency and short service life due to the breakage， detachment， and severe wear of cutters in air-assisted percussive drill bits. This paper conducts a macroscopic and microscopic analysis of the PDC spherical cutter， investigates the causes of failure and the failure mechanisms， and proposes targeted measures for improvement. The results show that the main failure modes of PDC spherical cutters are tooth fracture， wear and fall off. The main reason for the failure of the cutter is that the cutter is damaged by tangential impact compression and normal tensile stress at the same time， and the poor performance of the cutter materials themselves， and the combination strength of the diamond layer and the cemented carbide matrix are also important reasons for the failure. In order to improve the performance and service life of PDC spherical cutters， the stress burden of the cutters can be reduced by optimizing drilling parameters and adjusting external operating conditions. In addition， innovation and improvement of the material formulation， structural design and manufacturing process of PDC spherical cutters is also an effective way to improve its impact resistance and wear resistance. Through these comprehensive performance improvement methods， the reliability of PDC spherical cutters can be effectively improved， thus improving the operational efficiency of downhole drilling and the service life of the bit.

Abstract:This paper studies the impact dynamics process of the CDH-125 pneumatic down-the-hole （DTH） hammer， accurately analyzing the force state during the motion of the valueless distribution piston. Subsequently， based on the finite difference method， the thermodynamic and dynamic differential equations of the DTH hammer during its working process are iteratively solved to obtain the dynamic working characteristics of the DTH hammer piston and air chambers. These characteristics include the relative relationship between piston displacement and velocity， and the pressure and temperature exchange relationships in the front and rear air chambers. The results obtained from the finite difference method were compared and validated using the multiphysics simulation software SimulationX， showing a maximum speed discrepancy of 3% for the piston stroke， 19% for the return stroke， and 5% for the working frequency. Based on these results， further calculations and analyses of the air viscous friction force between the piston and the inner cylinder were conducted. The results indicate that， compared to the ideal situation with non-viscous fluid， the viscous friction force reduces the working frequency of the DTH hammer by 0.15% per working cycle and increases the maximum energy consumption of the piston stroke by 0.05~1.34J per cycle. The impact of viscous friction on the dynamic performance of the DTH hammer cannot be ignored.

Abstract:The crusher is one of the key components of the slurry balance shield machine， which generally uses hydraulic motors to drive the roller mechanism to crush rocks. Its hydraulic system is a closed system. The impact load on the crusher can sometimes cause it to momentarily stop， and the pressure on the low-pressure side of the hydraulic motor drops sharply to negative pressure for a short period of time， causing the hydraulic motor to become empty and resulting in motor damage. This article focuses on the problems existing in the hydraulic system of crushers， analyzes the reasons for the pressure suction on the low-pressure side of the hydraulic motor when the crusher suddenly stops under impact load conditions， and proposes an optimization scheme to increase the oil replenishment accumulator. Through simulation analysis and experimental verification of the scheme， it is proposed to adopt an optimized solution of adding a 4L accumulator at each outlet of the left and right drive motors of the crusher， in order to solve the problem of damage caused by pressure suction of the hydraulic motor of the crusher.

Abstract:During the drilling process of shallow strata in karst landform areas， a large number of complex situations such as leakage and water inflow occur. The widely developed fracture and cave network in the strata forms fluid migration channels， and the pressure difference between drilling fluid and formation water is also an important influencing factor. Conventional pore pressure prediction methods cannot effectively characterize shallow pore pressure. To explore the actual distribution of shallow pore pressure in karst landform areas， a shallow pore pressure profile based on the actual distribution of groundwater was constructed based on hydrogeological and fluid mechanics principles. The effectiveness of the profile was verified by an exploration well drilling in west Guizhou Province. The results showed that there were multiple pressure zones in the shallow layer of karst landform areas， which were closely related to the distribution of groundwater. No pore pressure exists above the groundwater level. The calculation of pore pressure in the groundwater layer should be based on the groundwater surface， which is a typical low-pressure zone. The pore pressure of a confined aquifer depends on the difference in location between the recharge and discharge zones， and may manifest as high pressure， low pressure， or normal pressure. The adaptability of plugging materials， clean water drilling， and air down the hole hammer drilling in karst landform areas are analyzed. It is recommended to fully utilize hydrogeological data in drilling design to construct shallow pressure profiles， based on which， selecting drilling processes or drilling process combinations， and determining the depth of drilling for each drilling section to avoid complex drilling situations and improve drilling efficiency. This study can provide reference for the design and implementation of drilling projects in karst landform areas.

Abstract:Complex geological factors such as fractures， faults， weak surface structures in unconformity contact， and multiple pressure systems in Sichuan-Chongqing region result in multi-layers and multi-mechanisms leakage in the same open hole. The traditional plugging technology has problems such as slow establishment of pumping channels for large particle plugging materials， long plugging time， and poor stability of existing plugging tools， resulting in slow effectiveness and low efficiency， which poses challenges to the normal development of drilling work. In view of this， this article adopted the working principle of quickly establishing a plugging channel by switching flow channels through ground injection of work balls，carried out optimization design of repeatable on-off fast circulating valve， formulated leak sealing operation processes， and completed the research on multiple leakage layers plugging without tripping out based on fast circulating valve. Through on-site drilling applications， it is possible to achieve plugging up to 5 leakage layers without tripping out and on-site test improved the efficiency of plugging operations by 74% and reduced the cost of plugging. This provides a new technological means for quickly plugging complex leakage layers while drilling.

Abstract:The development of geothermal resources in Xiong’an New Area faces multiple drilling technology challenges， mainly reflected in the dual pressure of complex geological conditions and environmental protection. Deep geothermal reservoirs generally have high-temperature. The high downhole temperature makes it difficult to regulate the performance of the drilling fluid. In the fractured carbonate reservoirs， downhole complex situations such as lost circulation and wellbore collapse are likely to occur. Even irreversible lost circulation and pipe sticking accidents may occur， which seriously affect the drilling coring and mud logging operations. The rocks in the target reservoir are characterized by high hardness and strong abrasiveness， which seriously affect the rate of penetration. In response to the complex geological conditions of the karst geothermal reservoirs in the Xiong’an New Area， detailed geological research has been carried out， and the wellbore structure design has been optimized， mainly focusing on the three-section wellbore structure. In the face of the high-temperature environment， high-temperature-resistant positive displacement motors are used in combination with a high-temperature-resistant drilling fluid system. For the fractured non-target reservoirs， the lost circulation control technology while drilling is adopted， and nano-blocking materials and fiber-reinforced lost circulation materials are used in supporting. When drilling in the target layer of the karst geothermal reservoir， technologies such as clear water drilling， clear water with air injection drilling， and double-wall drill pipe drilling are adopted to solve the problem of formation lost circulation. In terms of environmental protection， the key work is to carry out harmless treatment of the waste drilling fluid， and a closed-circuit circulation system is applied to reduce the discharge of waste.