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:The M6 coal seam in Jintai Coal Mine has complex occurrence characteristics such as roof and floor breakage， apparent dip angle controlled by double dip angle （XZ view inclination 17°， YZ view inclination 3°）， thin seam thickness （1.08~1.68m） and large variation in thickness. In the construction of directional drilling along strata， there are some problems such as difficulty of actual control， easy deviation from coal seam into unstable roof and floor， lower construction efficiency and ineffective penetration in multi-branch hole construction. Based on the calculation formula of apparent dip angle， this paper introduces the dip angle parameter of borehole along the working face to optimize the trajectory design method for the plane turning section of borehole， and carries out the verification test in Jintai Coal mine. The results show that： Compared with the original trajectory design method， the optimized trajectory design method can keep the borehole drilling along the middle of the coal seam， overcome the interference of the thickness change of the coal seam， and realize the accurate drilling along the coal seam of the plane turning section of the borehole， and the effective footage rates are 48.82%， 76.72% and 100%， respectively. The gas monitoring data of test borehole No. 8~10 show good gas extraction effect.

Abstract:Hydraulic fracturing is an effective technical method to exploit subsurface shale gas resources. To investigate the law of fracture propagation in shale hydraulic fracturing can provide proper guidance for high-efficient exploitation of shale gas. By using the extended finite element module of ABAQUS which is a large finite element software to investigate the influence of the position， azimuth and number of the initial fractures in homogeneous shale， and the structural direction， internal dip angle and lithology of the bedding shale on hydraulic fracture propagation at different ground stress deviations. The results show that for vertical hydraulic fractures， with the increase of the horizontal principal stress， the fracture is more difficult to propagate， the fracture propagation length decreases， and the initiation pressure increases. At the same injection volume， the length of hydraulic fractures formed by simultaneous initiation at both ends of the initial fracture is larger than that formed only on one side. When the initial fracture is located in the middle of shale with a direction of 45°， the fracture will deflect to the direction of the maximum horizontal principal stress， and the degree of deflection increases with the maximum horizontal principal stress. In the process of time-sharing multi-cluster fracturing， the propagation of fractures will interfere with each other， and it will greatly affect the attitude of fracture propagation and initiation pressure， but it has little influence on the fracture width at the injection point. For shale with horizontal and vertical bedding structures， hydraulic fracture deflection will be deflected to different degrees when the internal dip angle of bedding is changed， and the deflection degree of hydraulic fractures decreases with the increase of the internal dip angle of bedding. For shale with structural bedding in the direction of 45°， the deflection degree of hydraulic fractures increases successively in sandstone， coal rock and mudstone， and the fracture migration ratio increases with the maximum horizontal principal stress.

Abstract:In view of the complex geological structure of Dawan coal mining area, advancing open branch hole distribution was adopted to detect the location of coal seam roof and floor for accurate determination of the coal seam and provide the basis for gas drainage, tunneling and mining and preparation for the follow-up work. Dawan coal mine is been defined as gas mine in the past years’ gas identification, while by ordinary drilling process in gas hole construction, large drilling workload with unqualified hole depth, difficult drilling trajectory accurate control and low gas concentration extraction rate will often be encountered. Long distance drilling in the proven coal seam can be constructed with bedding directional hole construction method to realize long-distance gas extraction in the complicated coal seam. The field test shows that by the advancing open branch hole technology, the accurate probe of complex coal seam top in the geological structure can be completed, it is found that the coal section is 75% of drilling length in a borehole. By optimizing drilling design and high precision control of borehole trajectory, the bedding directional hole coverage is greatly increased in the complex coal seam, coal section is up to 63.7% in another borehole, the gas extraction efficiency is also improved, which provides a basis for gas extracting, tunneling and mining.

Abstract:Bedding formations are often encountered in drilling operations. On the basis of the stress tensor coordinate transforming relation and the borehole stress concentration equation, both the weak-plane shear slip criterion and rock mass Mogi-Coulomb criterions are introduced to build an analysis model for borehole stability. Researches on the reasonable drilling fluid density and safe drilling direction in typical reservoirs show that the existence of bedding plane significantly aggravates the rock damage and changes the damage position on the borehole wall; the collapse pressure of horizontal well continually varies along with the changes of drilling direction, thus the minimum collapse pressure is obtained in a particular drilling direction; in the inclined borehole, the minimum collapse pressure direction acquired is not vertical to the bedding plane experimentally, while the symmetrical inclined boreholes about principal planes have the same fracture pressure in space; the optimum drilling direction is the one with both larger safe density window of drilling fluid and smaller collapse pressure, and the drilling trajectory curve should be controlled strictly in the azimuth where the density window of drilling fluid changes greatly.

Abstract:According to the complicated long-section well kick & circulation loss, loose and broken formations, the drilling method with foam mud or aerated mud is put forward to balance the formation pressure, which has dual role on wall protection and flushing fluid leakage prevention to realize continuous plugging and wall protection, and is helpful to improve drilling efficiency and reduce cost. This is a new technical means developed for drilling construction in water deficient area and full loss stratum.

Abstract:In the Mid-eastetn part of Zhejiang, sedimentary rocks are widely distributed, because of the bedding development and the weak interlayer, the bedding landslide is often occurring. Based on the engineering example, the design process and the construction method of the pre-stressed anchor cable to control the landslide are analyzed. The monitoring results show that the control measures are safe and effective.

Abstract:Rock-embedding is more and more required in diaphragm wall engineering. According to the low rock embedding efficiency of the grab widely used at this stage, take the characteristics of grabbed formation as the starting point, the analysis was made on the reasons of low rock embedding efficiency; with rock fragmentation theory as theoretical basis, some improvement suggestions were put forward in the grab weight, cylinder closing force, bucket teeth arrangement and grabbing mode.

Abstract:Based on the analysis and comparison of advantages and disadvantages of traditional deep foundation pit enclosure systems, a new enclosure system was created by combining high-pressure jet grouting curtain with pre-stressed reinforced concrete square pile, which was applied in the projects, and the construction cost was greatly reduced with huge economic benefits.

Abstract:In the construction of highway and railway in mountainous areas in China, the slopes with poor stability are often produced, which causes the deformation and failure cases frequently. Take the subject of a large-scale landslide in bedding rock in Guiyang to Xinzhai highway construction, by the field exploration and the investigation on the external factors of unfavorable geological environment and human being activities, the simulation is made on the characteristics of tractive landslide activity and the analysis is made on the causes of the landslide. According to the characteristics of tractive landslide, the corresponding control measures are put forward.