Multi-Objective Optimization For Geological Drilling Trajectory Considering Nonlinear Constraints And Parameter Uncertainty

Promoting the technological innovation of geological drilling is the key to ensuring the supply of resources and energy and expanding the field of geological prospecting.Facing the complex geological environment,drilling trajectory optimization is significant to achieving efficient and safe drilling.Aiming at the complex geological drilling process,researches in this thesis consider the formation characteristics and the geometric characteristics of drilling trajectories.Faced with the nonlinear constraints and parameter uncertainties in the multi-objective optimization of geological drilling trajectories,the trajectory optimization problems and multi-objective evolution algorithms are studied from three aspects: borehole stability,real drilling trajectory uncertainty,and multiobjective multi-constraint.The main research content and innovative work of this thesis are as follows:(1)Scheme of trajectory optimization for efficient and safe geological drilling processThe trajectory optimization considering the formation characteristics is studied to ensure the drilling direction conforms to the wellbore stability conditions.A trajectory optimization problem considering formation constraints is to be established.The multiobjective optimization algorithm for the optimization problems with small feasible region is to be studied.The deviation between actual drilling trajectory and the designed trajectory will affect the prediction of trajectory optimization index,especially for extended-reach directional wells.Trajectory optimization considering the deviation of actual drilling trajectory is to be proposed.A trajectory optimization problem considering parameter uncertainty and the multi-objective optimization algorithms for the optimization problems with parameter uncertainties are to be studied.Aiming at the trajectory optimization problems with high target requirements,the multi-objective optimization algorithm for the three-objective multi-constraint trajectory optimization problem are to be studied,as well as the decision-making method based on fuzzy comprehensive evaluation.(2)A multi-objective optimization algorithm for a drilling trajectory constrained to wellbore stability is proposedThe drilling process will destroy the in-situ stress balance of the formation.Controlling the mud weight can maintain the wellbore stability.Using the relation model of the safe mud density and drilling directions and aiming to minimize the trajectory length and drill-string torque,a trajectory optimization problem constrained by wellbore stability is established.To handle the strict constraints,the knee point and the inverted generational distance are introduced to ensure the convergence and diversity of the optimization results.Finally,using stress logging data and a drilling trajectory instance,simulation experiments are done.Compared with other methods,the result proves that the proposed method can obtain solutions with better convergence and diversity.Among solutions with minimum safe mud weight change rate,the one obtained by the proposed method has a smaller trajectory length and drill-string torque.(3)A multi-objective drilling trajectory optimization considering parameter uncertainties is proposedIn complex formations,there is a deviation between the actual drilling trajectory and the designed trajectory,which makes the prediction of the trajectory optimization index inaccurate.The underestimation of the trajectory complexity index may cause problems such as blockage during tripping.Using actual logging data,the deviation of the inclination angle and azimuth angle of the drilling trajectory is analyzed,and the probability density function of uncertain parameters is established.Then,the drill-string torque is estimated by random sampling method.The multi-objective trajectory optimization problem is established by taking trajectory length and drill-string torque as objective functions.Using outlier removal,a nondominated sorting genetic algorithm is proposed to reduce the influence of uncertain parameters on the optimization results.The drilling trajectory optimization problem with parameter uncertainties is researched by the proposed algorithm.The result of an instance proves that the proposed algorithm can obtain solutions with the best diversity and the most stable trajectory design plan compared with other methods.(4)Trajectory optimization and decision-making methods based on fuzzy comprehensive evaluation is researchedIn drilling projects such as sidetracking and trajectory correction,not only the coordinates of the endpoint but also the target-entering direction is restricted.Aiming to minimize trajectory length,wellbore profile energy,and target error,this research establishes a trajectory optimization problem according to its geometric characteristics.The mathematical model of the optimization problem is analyzed to reduce decision variables and simplify constraint conditions based on the correlation of trajectory parameters.To solve the drilling trajectory optimization problem with nonlinear functions,multi-constraint,and multi-objective,the adaptive penalty function method and the decomposition-based multi-objective optimization algorithm are used.The solutions obtained by the proposed algorithm have better convergence and distribution than other methods.Membership functions are established based on the minimum fuzzy entropy.Solutions obtained by multi-objective optimization are classified,and the final trajectory design plan is decided by the fuzzy comprehensive evaluation method.The proposed decision method is more in accord with the preference of the decision-maker than other decision-making methods.Finally,the proposed trajectory optimization method and decision-making method are applied to the trajectory optimization system of the laboratory.Studying the multi-objective optimization problem of drilling trajectory with nonlinear constraints and parameter uncertainties provides new solutions for drilling trajectory optimization in complex formations,which is significant for reducing the cost and improving the efficiency and safety of the drilling process.With the development of technologies such as measurement while drilling,the calculation efficiency of the algorithm can be further improved in future research,and online trajectory prediction and optimization can be realized.