Study On The Technology Of Stabilizing Wall And Preventing Deviation Drilling Fluid In The Weak Soil

With the application of Trenchless Technology in pipe laying engineering more and more widely,crossing engineering ushered in rapid development.However,nowadays,there are many complex problems in the crossing engineering,among which the most typical technical difficulty is the stability of hole wall in soft soil and the control of crossing trajectory.This difficulty will lead to a series of engineering problems:（1）in the construction of horizontal section and inclining section,it is difficult to guide,and the drill pipe has been withdrawn for many times to re guide;（2）the trajectory deviates from the design trajectory,and even breaks through other existing construction pipelines,and the farther away it is from the original design trajectory;（3）the mud ratio is unreasonable,and the buried drilling accident or hole collapse occurs when returning.Because the soft soil layer belongs to the type of heterogeneous and scattered occurrence with poor structure,it is characterized by poor structure,poor cementation,disintegration in case of cementation,low strength and poor self stability.In addition,due to the mutual influence of drilling tools,drilling fluid and soft soil deformation,if the rock and soil are under large stress,it will inevitably lead to excessive deformation and even damage of drilling tools,resulting in hole wall collapse,which will affect the accuracy of crossing trajectory.However,at present,the traditional technology of directional drilling crossing deviation prevention is mostly focused on the research of drilling rig and drilling tools,ignoring the important role of drilling fluid for trajectory deviation prevention while ensuring the stability of hole wall in soft soil crossing construction.In the process of drilling,the drilling fluid inevitably penetrates into the formation,which causes the change of physical and mechanical properties of soft soil,the change of drilling tool build-up strength,and the deviation of drilling track,or the instability and collapse of hole wall,resulting in the buried drilling accident,and the failure of drilling according to the established design track.Therefore,it is of great practical value to study the anti deviation and wall stabilization drilling fluid technology for soft soil crossing.Based on the analysis of the physical and mechanical characteristics of the soft soil in Chuansha area of Shanghai,this thesis studies the mechanism of borehole wall instability and borehole deflection in the soft soil,analyzes the instability and failure characteristics of drilling fluid invasion into the soft soil,and analyzes the action mechanism of plugging technology to curb the leakage of soil borehole wall,and analyzes the effect of granular,flaky,fibrous plugging materials and nano plugging materials Materials were optimized and evaluated.The mechanism of inhibiting soil water sensitive softening was studied,and the conventional inhibitors and surfactants were optimized and evaluated.The comprehensive performance indexes of the optimized water-based drilling fluid system for wall stabilization and deviation prevention are evaluated,and the field application of the optimized drilling fluid system is carried out through a crossing engineering example to verify its effect.The whole thesis is divided into six chapters,the specific structure is as follows.The first chapter introduces the problems encountered in soft soil crossing,leading to the purpose and significance of the study.This thesis summarizes the development status of crossing trajectory control technology and the research status of plugging and inhibition drilling fluid,so as to provide basis and reference for the later development of stable wall and deviation prevention drilling fluid formula.The second chapter:Based on the engineering characteristics of high porosity,strong compressibility,rich clay minerals,strong hydrophilicity,softening and swelling after soaking in water,reducing the strength and stability of pore wall.This thesis studies the material composition and mechanical properties of soft soil layer,analyzes the strength and deformation mechanism under the condition of one-dimensional consolidation and triaxial shear creep,and lays a foundation for the realization of anti deviation and wall stabilization drilling fluid technology to enhance the crossing of soft soil layer.Chapter 3:by analyzing the geological,technical,technological and drilling fluid factors of directional drilling through hole wall instability and borehole deviation in soft soil layer,the instability and failure characteristics of drilling fluid invading into soft creep closed formation,permeable formation and fractured leakage formation are analyzed;the borehole deflection strength model is established,and the model can guide the directional control in trenchless horizontal directional drilling construction,Verify the theory that drilling fluid can cause borehole trajectory deviation by affecting the build-up strength.Chapter 4:analyze the mechanism of plugging technology,summarize the evaluation methods of plugging materials,optimize and evaluate the granular,flaky,fibrous and nano plugging materials,and optimize the compound plugging agent formula.Chapter 5:the mechanism of hydration expansion of clay minerals is analyzed,the evaluation methods of inhibition materials are described,and the conventional inhibitors and surfactants are optimized and evaluated,and the compound inhibition and anti wetting formula are optimized.Chapter 6:optimizing the mud making clay and fluid loss control agent of water-based drilling fluid to establish a stable and anti deviation drilling fluid system for crossing weak strata.The basic performance,inhibition,anti pollution and temperature resistance of the drilling fluid system are tested.The field application of the drilling fluid system is evaluated to verify whether it can achieve the effect of wall stabilization and anti deviation.Through the above research work,the following conclusions and understandings are obtained:（1）The mineral composition of the soft clay is mainly quartz（51.1%）,feldspar（16.6%）,chlorite（12.7%）,with some montmorillonite（5.3%）,illite（2.4%）and kaolinite（2.6%）;the chemical composition of the soft clay is mainly Si O₂ and Al₂O₃,accounting for 74.45%,which is far higher than other chemical components such as Fe O,K₂O,Ca O,Mn O,Na₂O,etc.The water content of soft soil layer is in the range of 37-68%.With the increase of sampling depth,the water content of soft soil layer decreases continuously.The results show that the range of w _P is 22%-36%,the range of measured value of w _L is50%-62%,mainly about 57%,the range of I_P is 23-30,and the range of I_L is 0.25-1.11.（2）The maximum axial strain of undisturbed soft soil ranges from 11.5%to 14.5%,and that of remolded soft soil ranges from 13.5%to 15.0%,and the peak strain of remolded soft soil moves backward.The peak axial stress of undisturbed soft soil is21.6k Pa,while that of remolded soft soil is only 11.8k Pa,which decreases by 45.4%.Under the condition of one-dimensional consolidation,when the axial stress is low,the strain time curve changes rapidly from the vertical straight section to the curved section with small radian,and then gradually tends to the horizontal straight line.When the axial stress is high,the soft soil shows the characteristics of attenuation constant velocity creep with the increase of axial stress,and the constant velocity creep time increases with the increase of stress level.Under the condition of triaxial shear creep,under the same confining pressure,the larger the deviatoric stress is,the larger the strain is,that is,the relationship between the creep deformation and the applied deviatoric stress is positive.The stress-strain isochron curve of soft soil shows obvious nonlinear characteristics,and the yield stress is about 80 k Pa.The pore pressure increases with time,but the change rate of pore pressure decreases with time,the pore pressure tends to a stable value,and the deformation of the sample is gradually stable,and the decay creep occurs.（3）The plugging performance of granular plugging material:3%QS-2>2%QS-1>2%OCX-1,the reduction rate of mud cake permeability is 38.75%,36.31%and 31.99%respectively;the plugging performance of three kinds of flaky plugging material:2%NTS-TP>1.5%NTS-M>1.5%NTS-S,the reduction rate of mud cake permeability is23.58%,27.77%and 29.54%respectively;the plugging performance of fibrous plugging material:1.5%XFD-2>2.0%XFD-1>2.0%ASB-I,the reduction rate of mud cake permeability is 23.58%,27.77%and 29.54%respectively 52%,31.98%,17.34%respectively.Further,nano and nano materials were used to block the micro and nano holes in the soft ground,and the plugging formula for the leakage of the hole in the soil layer was optimized.The 3%QS-2+2%NTS-TP+1.5%XFD-2+1.0%nano emulsion+1.5%hydrophilic nano Si O₂+1.0%nano Ca CO₃ was used to evaluate the plugging effect.The leakage under normal pressure and 0.7MPa was 25ml and 38ml respectively,and the leakage rate was only 4.58%.（4）With the increase of inhibitor content,the inhibition effect was enhanced.The results show that the content recovery of polyamine is in the range of 23.67%-32.18%,the optimum dosage is 0.6%;the recovery of KHm is in the range of 23.52%-27.18%,the optimum dosage is 2%;the recovery of PLUS is in the range of 32.78%-52.28%,the optimum dosage is 0.6%;the recovery of KRAM is in the range of 32.32%-45.58%,the optimum dosage is 0.3%;the recovery of KCl is in the range of 25.32%-33.56%,the optimum dosage is 0.6%.The evaluation of the optimized compound drilling fluid shows that the rolling recovery under the condition of dual inhibitor compound is kept at 60.68%～68.95%,and the rolling recovery under the condition of triple inhibitor compound is kept at 75.25%～81.32%.The results show that the composite inhibitor:0.6%KCl+0.3%KPAM+0.6%PLUS has a good effect on inhibiting soil water sensitive swelling.（5）With the increase of surfactant concentration,the change of soil contact angle basically decreases first,then increases,and then decreases.The most obvious increase of contact angle is 0.01%SDBS and 0.08%CTAB,followed by 0.01%AS-1.The optimum composite surfactant is 0.01%fluorocarbon surfactant SDBS+0.08%CTAB+0.005%anionic surfactant AS-1.（6）The optimized wall stabilizing and anti deviation water-based drilling flu-id system:6%bentonite+0.2%Na₂CO₃+3%QS-2+2%NTS-TP+1.5%XFD-2+1.0%nano emulsion+1.5%hydrophilic nano Si O₂+1.0%nano Ca CO₃+0.6%KCl+0.3%KPAM+0.6%PLUS+0.01%SDBS+0.08%CTAB+0.005%AS-1+0.4%HV-CMC+2.5%S MP-1,and its comprehensive performance indexes were evaluated to test its bas-i c properties（density,viscosity,shear force and filtration loss）.The results show that the optimized drilling fluid system has good inhibition,salt and calcium res-istance,water activity,lubricity,anti pollution and temperature stability.The field application of the optimized drilling fluid system shows that the optimized drilli-ng fluid system can stabilize the wall and prevent deviation.The main innovation points of this thesis is as follows:（1）The strength and deformation characteristics of soft soil under one-dimensional consolidation and triaxial shear conditions are studied systematically.The change rules of stress-strain,strain time and pore pressure time are mastered under two conditions.（2）The traditional crossing trajectory only considers the control of the crossing trajectory by drilling or drilling tools.This thesis proposes a new method of crossing trajectory deviation prevention drilling fluid,and can also achieve the control effect of crossing trajectory.（3）Based on the research of the performance test and evaluation of various plugging and inhibition of drilling fluid,based on the optimization of slurry making clay,granular/flake/fiber plugging material,inhibitor,nano material,surfactant and filter loss reducing agent,a set of stable wall and anti deflection water-based drilling fluid system suitable for the crossing of soft soil layer is proposed,which can lay a technical foundation for horizontal directional drilling of weak stratum Foundation.