Basic Research On In-Situ Stress Measurement Based On The Integration Of Borehole Deformation And Drilling Vibration Response

In-situ stress,also known as in-situ stress of formation,generates great impact on regional rock deformation during the exploitation of shale oil gas,coalbed methane,metal deposits and other mineral resources.Accurate in-situ stress data is conductive to understand the mechanical properties of rock,in addition formulate reasonable resource exploitation,geological disaster prediction and early warning programs.It is of great significance to ensure safe,efficient,and green production.However,obtaining in-situ stress data is still a scientific and engineering problem in the field of geology.The existed methods are constrained by the small amount of data,discontinuity,and small measurement depth.The deformation of borehole is closely related to the horizontal principal stress.It contains rich information of in-situ stress,moreover the drilling vibration response contains rich information of rock mechanics.Thus,the whole thesis was conducted from two aspects of borehole deformation and drilling vibration response.Firstly,the prediction model of horizontal principal stress is established by conducting quantitative study on the relationship between the structure parameters of borehole deformation and horizontal principal stress.Subsequently,the quantitative relationship between drilling vibration response and rock mechanics parameters was conducted,obtaining the continuous profile of rock mechanics parameters needed for horizontal principal stress prediction,so as to comprehensively realize the continuous prediction of horizontal principal stress.Therefore,it is of great scientific,exploratory,and practical significance to establish a continuous prediction method of in-situ stress based on the combination of hole structure characteristics,drilling,and vibration response,which can break through the existing bottleneck of in-situ stress measurement and enrich the methods of in-situ stress acquisition.In this paper,by means of theoretical research,numerical simulation,laboratory test and field interactive verification,the quantitative relationship between borehole deformation and horizontal principal stress,as well as the relationship between drilling vibration response and rock mechanical parameters were studied systematically and comprehensively.The following work was conducted and corresponding results were obtained:(1)Based on the basic theory of elasticity,the stress state of the borehole was theoretically analyzed,and the deformation characteristics of the borehole structure under the action of the bidirectional non-equilibrium horizontal principal stress component were obtained,that is,the trajectory of the borehole deformation presented the quasi-elliptic mode.On this basis,the quantitative relationship model between elliptic structure parameters and horizontal principal stress was obtained by calculation,and an algorithm system of in-situ stress calculation based on borehole variation structure characteristics was constructed.(2)The numerical simulation of borehole deformation is conducted and the geological factors impacting borehole deformation were obtained.The results showed that lithology,the non-equilibrium of horizontal principal stress,Young’s modulus and Poisson’s ratio were closely related to the deformation of borehole structure.For the same lithology,the greater non-equilibrium horizontal principal stress was,the more elliptic the standard circular pore structure tended to be.For different lithology,the larger the compressive strength and Young’s modulus of the rock,the smaller the Poisson’s ratio,the less ellipsoid the borehole structure was.(3)Physical simulation experiments were conducted to study the rock mechanical properties of the cubic rock sample with pre-drilled borehole and standard cylinder rock sample,then the deformation characteristics of the borehole structure under different loading conditions were obtained.From the experimental aspect,it was confirmed that the deformation characteristics of the borehole structure under in-situ stress were ellipsoidal,moreover,the accuracy of the calculation method of horizontal principal stress based on the deformation parameters of the perforated structure was verified.(4)Numerical simulation and experiments of drilling vibration were conducted.From the aspect of numerical simulation,the vibration response characteristics of different rock strengths(vibration displacement,vibration velocity,vibration acceleration,vibration frequency)were obtained,and the impact factors of drilling vibration response of rocks were obtained,indicating that it had obvious differences in the vibration response of rocks with different strength.From the aspect of experiment,this difference was confirmed.The results showed that it had an intrinsic correlation between rock mechanics parameters and drilling-vibration response,which proved the feasibility of applying drilling vibration response to calculate rock mechanics parameters needed for in-situ stress prediction.(5)By introducing multivariate statistics,BP neural network and grey correlation theory,the regression training of drilling parameters and vibration response parameters was conducted,and the originally fuzzy qualitative relationship was characterized quantitatively,thus the quantitative correlation degree between drilling parameters,vibration parameters and rock mechanics parameters was obtained,moreover,the grey weighted regression prediction model and BP neural network prediction model were established.Particle swarm optimization algorithm(PSO)was introduced to optimize the BP neural network prediction model,and PSO-BP neural network prediction model was established.The idea of applying drilling response and vibration response parameters to predict rock mechanics parameters was realized,and a set of rock mechanics parameter prediction method based on drilling response and drilling vibration response was formed.(6)The accuracy of the in-situ stress prediction method based on multiinformation of borehole deformation,drilling parameters and drilling vibration parameters was verified by selecting the verification borehole of coal-bed methane in the region of Xinjiang.The error was about 3%-18%.The predicted in-situ stress was in line with the actual geomechanical characteristics,which proved that the in-situ stress prediction method based on borehole information was feasible.By applying the predicted horizontal principal stress data of a single well,the characteristics of stress distribution in the plane region of the study area were obtained,and the influence of horizontal principal stress distribution on the permeability of coal reservoir was verified.The results showed that the horizontal principal stress was inversely proportional to the permeability of coal reservoir,and the higher the maximum horizontal principal stress was,the lower the permeability was.It is an important trend to realize continuous prediction of in-situ stress in engineering in the future.This paper makes comprehensive use of drilling,drilling response information and logging information during the drilling to provide new idea and method dimension for the method of obtaining in-situ stress,and conducts exploratory research on continuous in-situ stress prediction methods,making the evaluation of in-situ stress and rock mechanics parameters towards the goal of systematic and multi-method interactive verification.It enriches the theoretical basis of obtaining in-situ stress data based on drilling method,and provides sufficient and continuous basic data support for the actual hydraulic fracturing of tight oil gas and coalbed methane reservoirs.It can be widely popularized and applied in actual oil gas fields,coal mines and tunnel projects.The research results of this paper can provide theoretical reference and design ideas for the subsequent research and development of joint in-situ stress monitoring equipment that integrates drilling and drilling-vibration information.