Oil and gas wells are the necessary information and material channels for human exploration and development of underground oil and gas resources. Oil and gas drilling is a technology and capital-intensive project around the construction and measurement of oil and gas wells. The development of petroleum industry from vertical wells to directional wells and cluster wells is a historic leap. This leap has brought about the saving of land resources and the reduction of drilling cost, and solved complex engineering problems such as rescue, obstacle avoidance and offshore drilling, which is especially beneficial to the exploration and development of special oil and gas reservoirs. In particular, the development of oil drilling from directional wells to horizontal wells is considered to be a revolutionary technological progress in today's oil industry and has been highly valued by all countries in the world. However, in the drilling engineering of directional wells, cluster wells and horizontal wells, how to control the well trajectory to reach the underground target along the design trajectory is a complex scientific and technical problem. Gao Deli has been studying this problem for ten years in close connection with two national key scientific and technological projects, namely, "Research on drilling technology of directional wells and cluster wells" and "Research on drilling technology of petroleum horizontal wells". Starting with studying the anisotropy of formation and the whiplash characteristics of downhole drilling system, he established the interaction model between drill bit and orthotropic formation for the first time at home and abroad, put forward the new concepts of effective drilling force and orthotropic drilling theory, and divided the formation into 12 categories according to anisotropy (only two of them were put forward by predecessors), and discussed their influence laws on borehole trajectory drift respectively. The research results reasonably solve the problems of objective understanding and directional control criteria of borehole trajectory drift, and take a big step forward on the basis of previous research, which has attracted the attention of peers at home and abroad. In order to put forward the technical countermeasures of directional control, he conducted in-depth research on downhole drilling system (or "bottom hole assembly"), established the corresponding three-dimensional nonlinear dynamic control equation, successfully solved the three-dimensional nonlinear mechanical problems of vertical bending and horizontal bending large deflection bottom hole assembly by using the weighted residual method, and developed a numerical simulation calculation system (software), which is unique at home and abroad. At the same time, he also broke through the limitations of the traditional statics anti-deviation theory (based on the rotation of drill string) and put forward the "dynamic anti-deviation theory" based on the whirling of drill string, which provided a scientific basis for overcoming the technical problems of anti-deviation and fast drilling in complex formations. On this basis, he developed the software technology of borehole trajectory prediction and control, which was widely used in Dagang, Jianghan, Sichuan, Xinjiang, Haiyang and other oilfields. The research results have published more than 40 academic papers and published a monograph on wellbore trajectory control 1 Department, and won the special prize of scientific and technological progress of China Oil and Gas Corporation (ministerial level) and the first prize of national scientific and technological progress successively.
Study on evaluation method and application of actual drilling formation characteristics
With the support of "Innovative Fund for Young People in Petroleum Science and Technology" and key scientific and technological projects of China Petroleum and Natural Gas Group Company, Gao Deli led his research team to conduct in-depth and systematic theoretical and methodological research on drillability and orthogonality of drilled strata, established optimized inversion model and calculation method of formation characteristic parameters based on drilled information, and developed corresponding calculation software system. The main innovations are as follows:
1) Based on the interaction model between drill bit and orthotropic formation, the evaluation method of actual drilling formation characteristic parameters is put forward, and the optimized inversion model of formation orthotropic index is established. At the same time, a prediction model (time series analysis) describing the dynamic characteristics of downhole process is established. Based on the nonlinear characteristics of neural network and the principle of inverse system identification, a neural network model for inverting the characteristic parameters of actually drilled strata is established.
2) Formation drillability refers to the degree of difficulty of formation rock breaking under certain drilling conditions. In the actual drilling process, drilling time logging carries a lot of formation information, among which the change of drilling time can best reflect the influence of formation drillability. Aiming at the problem of deep well drilling, a new idea of using microscopic drillability coefficient to represent the drillability of actually drilled formation is put forward, and an inversion model of microscopic drillability coefficient is established, so that the microscopic drillability coefficient of formation can be extracted by logging while drilling data.
3) The relationship between the drillability of actually drilled formation and acoustic wave velocity and spectrum eigenvalue is systematically analyzed, and the formula for calculating the drillability and anisotropy of formation according to P-wave velocity is established; The correlation dimension index and Hurst index are put forward to describe the morphological characteristics of formation drillability sequence, which can quantitatively describe the characteristics of formation drillability sequence and is of great significance to the prediction of regional formation drillability law.
4) Considering the influence of bit structure, formation characteristics, hydraulic parameters and drilling parameters, the evaluation model of formation anti-drilling strength and bit wear degree is established, and the coupling effect of tooth wear and formation anti-drilling strength change during drilling is described by user-defined parameters, and the basic characteristic parameters of bit rock breaking are determined by using the actual drilling data of new bit, which provides a basis for distinguishing the influence of formation change and bit wear. This method can not only monitor formation changes and bit conditions while drilling, but also provide quantitative basis for post-drilling analysis and bit optimization.
5) Aiming at the evaluation of deep formation pressure, on the basis of analyzing the evolution characteristics of formation pressure time series, the method of establishing intelligent identification model of formation pressure neural network is discussed, and the intelligent identification software system of formation pressure based on MATLAB neural network toolbox is compiled. At the same time, the "rock strength method" is studied and applied to monitor formation pore pressure while drilling.
Based on the above research results, not only nearly 30 academic papers have been published, but also they have been successfully applied in the field. The two projects won the first prize of 1998 Beijing Science and Technology Progress Award and the second prize of China University Science and Technology Progress Award in 2000 respectively.
3 Oil and gas well string mechanics and engineering research
Dr. Gao Deli was supported by the National Science Fund for Distinguished Young Scholars 1998 (approval number: 598251KLOC-0/5) for his outstanding scientific research achievements, and led his research team to focus on the research on the mechanical behavior and optimal control of oil and gas well strings in combination with the applied basic research project of the Key Laboratory of Petroleum Pipeline Mechanics and Environmental Behavior of China Petroleum and Natural Gas Group Corporation. After more than four years of unremitting efforts,
1) Considering the influence of structural and material properties, load characteristics, borehole constraints and other factors, the sinusoidal and spiral buckling configurations of tubing string under different borehole constraints are obtained by establishing and solving the differential governing equations, and the critical load of tubing string buckling behavior under compression and torsion and the relationship between axial deformation of tubing string and load are given (verified by experiments, which is different from previous assumptions), thus determining the post-buckling path of tubing string in oil and gas wells.
2) consider high temperature (>180 c) and high pressure (>; 100MPa), an effective calculation model of axial force and deformation of test string is established by applying the incremental theory of plastic mechanics and through experimental verification. A comprehensive calculation model of casing additional load caused by wellbore temperature change in high temperature and high pressure oil and gas well testing is established. The model considers casing temperature effect, expansion effect, buckling effect, fluid thermal expansion effect and volume compression effect, and is suitable for calculating casing confining pressure and axial force changes caused by temperature change.
3) The optimal design theory of compound pipe string in oil and gas wells under complex geological conditions is put forward, which provides engineering scientific basis for the development and application of new high anti-collapse casing products. At the same time, the optimal design model of composite casing string with load and casing strength as space-time functions, as well as a more accurate calculation model of casing internal pressure, a general calculation model of axial force and a combined external pressure model describing discontinuous external pressure distribution are established, forming an advanced theory and calculation method of composite casing string (sorting and screening method) and developing a fully functional optimal design system (software).
4) The general calculation model and algorithm of downhole friction and torque are established, especially considering the buckling effect of downhole string, so that the friction and torque distribution of tubing string in three-dimensional borehole can be calculated more accurately. On this basis, a fully functional downhole friction torque calculation system (software) is developed.
Based on the above research results, more than 40 academic papers have been published, which have been successfully applied in oil field casing damage drilling prevention, extended reach well engineering and high temperature and high pressure deep well engineering, and two of them have won the first prize of provincial and ministerial scientific and technological progress respectively.