Rock Drillability Analysis And Logging Research On Bit Selection In Northeastern Sichuan

The northeastern Sichuan region belongs to the southern marine stratigraphie oil and gas exploration area,which is mainly faced with the problems of complex well body structure,deep large-size borehole depth,complicated lithology,hard rock,large dip-angle of strata,difficult fracture,poor formation drillability and high abrasiveness.These are also the main reasons for the difficulty in selecting and designing the drill bit,difficult drilling speed,long drilling cycle and high exploration cost in exploration area.Therefore,it is necessary to study the drillability analysis and bit selection of formation rocks in northeast Sichuan.In this paper,the Marine carbonate strata in northeastern Sichuan are taken as the research object,and the rock mechanics is taken as the theoretical basis.The research work in five aspects is mainly carried out:① complex formation lithology and well logging calculation of rock mechanics parameters;② formation drillability abrasiveness experiment and well logging calculation and profile establishment;③drill bit selection of anti-drilling sensitive parameters extraction and selection model establishment;④well area stratified section of the bit selection recommendation and personalized bit design;⑤software development and multi-well logging data processing.Through the above work,the following understandings have been obtained:(1)Based on the NCRA method,the formation lithology and physical property parameters are calculated.The core density-acoustic time difference measurement experiment and the construction of the shear wave time difference curve are used to accurately calculate the rock mechanics parameters such as Poisson’s ratio,three-intensity and three-modulus,and lithology volume analysis profile and rock mechanics parameter profile are established.(2)Based on the core density-acoustic time difference,rock uniaxial and triaxial drillability,and abrasiveness determination experiments,the experimental values of rock drillability and abrasive property and the calculated values of well logging were compared and calibrated.It is found that the drillability level and abrasiveness increase with the decrease of acoustic time difference.Consequently,the drillability level,abrasiveness and hardness of rock are calculated continuously by logging curve.Based on the model and method of surface,it is found that the hardness of carbonate formation is high,the drillability of rock is poor and the abrasiveness is strong;by evaluating the anisotropy of rock drillability,a mathematical model of calculating anisotropy index of rock drillability by using the value of vertical drillability grade is established.(3)Based on the commonly used anti-drilling parameters(rock mechanics parameters,hydraulic parameters and mechanical parameters,and experience parameters),the effective stress and drillability anisotropy coefficient,based on well logging parameters of the grey correlation analysis of drill bit type selection model,layered segment selected match wellblock formation of bit type.(4)Aiming at the existing problems in the process of using the bit,according to the evaluation of the anti-drilling characteristics and combined with the field experience,the optimization was carried out from the aspects of bit profile shape,blade structure,cutting tooth size,cutting tooth working angle and tooth density,as well as hydraulic structure.The PDC bit suitable for efficient drilling of carbonate formations provides a basis for the selection of PDC bit in the work area.(5)Using FORTRAN and VB programming language,a set of drilling bit optimization software for the complex lithologic strata of Northeast Sichuan is built on the Forward platform.The software runs stably,and the selected bit type is consistent with the sections with high actual drilling speed and aging,which provides an important decision for increasing drilling speed.The results of this paper provide a theoretical basis for the analysis of the drillability of strata in the working area and a certain guidance for the selection of drill bits in the field.