Study On The Prediction Model Of Radial Horizontal Well Extension Capacity And The Optimization Of Hydraulic Parameters

With the development of China’s oil industry and the limitation on crude oil and gas reserves,production efficiency in many oil fields have reduced and the difficulty in developing has increased as the result of increase in the number of old wells and depleted wells in recent years.The developing cost in these wells also increases,consequently.Therefore,Enhancing oil recovery has become a top priority for the stable development of oil fields.The self-propelled radial horizontal well drilling technology,making use of high-pressured water jets to break rock and drill multiple branch boreholes in the horizontal section,is one of the most important ways to exploit low-permeability oil and gas reservoirs and increase the production of depleted wells.Its extension ability is an important factor influencing the design of drilling and the increase of oil and gas production.Domestic and foreign scholars have studied the two key issues of the self-propelled mechanism and the extension capability of the radial horizontal well drilling technology.However,there is neither relevant theoretical research nor predictive model for the extension capability or the drill bit structural parameter optimization.This paper takes jet head and high pressure hoses of radial horizontal wells as the main research object and conducts the compare from three aspects-theoretical research,numerical simulation,and experimental evaluation.Based on the research,the calculation model of drill self-advancing force is improved and the prediction model of radial horizontal well extension ability is established.A comparative study has been conducted to analyze the influence of its extension ability and optimize the bit structure parameters,which verifies the accuracy of the extended capability prediction model and the feasibility of field applications.The main research content are as follows:(1)A prediction model of the radial horizontal well extension capability is established and the influencing principle of the displacement,wall friction coefficient,high pressure hose diameter as well as the flow ratio on the extension capacity are analyzed based on investigating previous literature.The results show that the displacement is positively correlated with the ultimate extension length.The friction coefficient and the diameter of the high pressure hose are negatively related to the ultimate extension length.By analyzing the numerical example,the optimal value of the front and back nozzle flow ratio is obtained and ranges from 0.2 to 0.3.(2)The influence of the drill bit parameters on the self-advancing force is analyzed through establishing the physical model drill bit in radial horizontal wells by numerical simulation.The results show that the magnitude of the self-advancing force in radial horizontal well is negatively related to the number of front nozzles and the back tilt angle,and the magnitude of the self-advancing force of the radial horizontal well is positively correlated to the number of back nozzles and the front tilt angle.In order to ensure the rock breaking ability and the rock clearing ability of the radial horizontal well drill bit,the structural parameters of the drill bit are optimized and the front and back nozzle flow ratio formula is used for calculation.The calculation result is in line with the optimum range of flow ratio and the accuracy of the drill bit optimization parameters is verified.The front nozzle diameter optimization test is used to verify the feasibility of the optimal value of the front nozzle diameter.(3)The high-pressure water jet test is used to measure the self-propelled force of a radial horizontal well and the value obtained from jet test with four drilling media is used to compare self-propelled force calculation model in radial horizontal well,which helps to verify the accuracy of the prediction model of the radial horizontal well’s extension ability and the possibility of field application.The research results can provide theoretical and experimental support for the horizontal extension capability of radial horizontal wells.Based on research,the theoretical support is provided for the analysis of the influencing factors of the radial horizontal well’s extension ability.It also provides a basis for the prediction of the radial horizontal well’s extension ability and the optimization of the structural parameters of the jet bit,which have great guiding significance for reducing the risk of drilling on-site radial horizontal wells,lowering production cost as well as enhancing oil recovery of oil field.