Multilateral Wellbore Parameter Optimization In Hydrothermal Systems

Hydrothermal geothermal energy is a kind of clean renewable energy with abundant reserves.It has the advantages of optimizing energy supply,improving environment and realizing green and low-carbon development.It is of great significance to explore new economical and efficient development methods for its large-scale utilization.Multilateral well can exploit different intervals by using multiple lateral wells in the same wellbore,which has the advantages of large sweep area and high production of single well.It is expected to become an effective way for economical and efficient development of hydrothermal geothermal energy.Borehole parameters such as number of laterals,lateral spacing,lateral length and well trajectory are the key factors affecting the development.Based on the ensemble theory,perturbation algorithm and fast marching method,the optimization of wellbore parameters for the hydrothermal geothermal multilateral well is studied in this dissertation.The hydrothermal geothermal reservoir is mainly composed of sandstone and carbonate.Based on the distribution of geological parameters and sensitivity analysis by coupling ensemble theory and perturbation algorithm,a potential map,which reflects the distribution of geothermal productivity potential in different regions,is established with hydrothermal geothermal heat extraction as objective function.Using Kriging method and discrete fracture model,the permeability and fracture distribution characteristics of sandstone and carbonate geothermal reservoirs are obtained,and the productivity potential map of hydrothermal geothermal reservoir is established.Based on the productivity potential map and aiming at maximizing productivity,a semi-analytical model is established for optimizing multilateral well configuration in hydrothermal geothermal reservoirs.For the sandstone geothermal reservoir,the dynamic changes of swept area of different laterals are studied by fast marching method.Taking into account the interference between laterals,the wellbore parameters,such as number of laterals,lateral spacing and lateral length,in the sandstone geothermal reservoir are optimized.According to the characteristics of multi-fracture development in the carbonate geothermal reservoir,the reservoir is divided into different target blocks for different laterals.Considering the connectivity between wellbore and fracture,the multilateral well configuration that penetrates high productivity fracture area are optimized,and the wellbore parameters,such as number of laterals,lateral spacing and lateral length,in the carbonate geothermal reservoir are obtained.By using the fast marching method and aiming at the maximum cost-benefit rate,an optimal design model of multilateral well trajectory for hydrothermal geothermal reservoirs is established,which takes into account the curvature limitation of wellbore.The target location and well trajectory of both the main wellbore and the lateral can be obtained.The effects of different curvature limitations of wellbore and reservoir heterogeneity on the optimization results of well trajectory are analyzed.Applicability of the well trajectory optimization model is verified in different hydrothermal geothermal reservoirs.For the uncertainty of fracture distribution in carbonate reservoir,a probability model of multilateral well trajectory optimization is established by using discrete fracture model and well trajectory optimization model.The reliability of well trajectory design results is obtained under different threshold probability conditions.This paper presents the productivity potential map of hydrothermal geothermal reservoir,based on the sensitivity analysis of ensemble and perturbation theory.By using the fast marching method,the optimization models of multilateral well configuration and well trajectory are established.A set of optimum design methods for wellbore parameters of multilateral well is established for different hydrothermal geothermal reservoirs,which is expected to provide theoretical guidance for field application.