Research On Risk Assessment And Control Technology Of Drilling Engineering

The drilling engineering is the basic work of oil and natural gas exploration and development.It is a systematic project involving many departments,many connections,complex technology,more investment and greater risk.Because of the particularity of drilling operation,the uncertainty of geological conditions,the complexity of operation environment factors,the variability of construction methods and design parameters,many uncertain factors are hidden in the process of oil and gas drilling construction.The drilling engineering risks such as kick,lost,collapse and sticking may occur when some decisions are made based on these incomplete,inaccurate or incomplete information.This will seriously restrict the safety and efficiency of drilling.It is of great significance to prevent and control the development of drilling engineering risk and reduce the loss to the maximum extent if the early warning information and risk control measures are given in the early stages.This paper proposes to establish a set of drilling risk assessment and control system,which integrates "pre drilling risk prediction,drilling risk monitoring and post drilling risk summary analysis" : drilling risk prediction and optimization of engineering design before drilling;drilling risk monitoring in the course of drilling based on the comprehensive use of logging,LWD or other data;drilling risk summary analysis after the completion of the drilling operation.The research of this paper provides technical guidance and scientific basis for optimizing drilling engineering design and avoiding drilling engineering risk.It is necessary to evaluate the safety of drilling engineering design before drilling.Once the drilling risk may be found,the design scheme can be rationally optimized to reduce the risk probability and even avoid risk.The drilling geomechanics parameters provide basic pressure information for drilling risk assessment.Considering the influence of the complexity of oil and gas geological environment,the fuzziness of interpretation data,precision of mathematical model on the drilling geomechanics parameters,through the collection of regional seismic data and logging data,based on the theory of uncertainty,Monte Carlo simulation,probability and statistics,the quantitative uncertainty characterization method for drilling geomechanics parameters is established.On this basis,the construction of 3D model of drilling geomechanics parameters with uncertainty is constructed using the Geostatistics.And the visualization algorithm is used to realize the 3D visualization of the model.Combining the 3D drilling geomechanics parameters model with the well trajectory,we can get the prediction results of geomechanical parameters along the well trajectory,that is,formation pore,collapse and fracture pressure with uncertainty.Then based on the principle of pressure balance of open hole section,the quantitative assessment model for the probability of drilling risk which is coursed due to insufficient casing design is established.According to the risk probability model of the pre drilling engineering design established in this paper,the risk assessment of the pre drilling well can be treated.If there is no risk,the drilling can be carried out according to the original design.If the risk is high,we must adjust the casing program,and re-evaluate the new design until it meets the requirement of safety drilling.How to make full use of real-time and dynamic data such as mud logging,LWD is the key to ensure safety and effective drilling in the course of drilling operation.In order to solve the problem of large risk prediction error and lack of effective control method during drilling operation in complex geological environment,it is necessary to carry out the analysis of multisource information data in drilling process.If LWD data are available,then,based on the predrilling model and combining with LWD data,the pre-drilling model can be modified based on Bayes theory to achieve real-time and more accurate description of drilling geomechanical parameters at position of the drilling bit.Or based on the grey prediction theory,the geomechanics parameters of the drilling formation in front of the bit are predicted,which can provide more accurate pressure information for dynamic risk assessment.At the same time,through theoretical modeling and mathematical derivation,the quantitative description method of the equivalent circulating density of drilling fluids with uncertainty is established.And the equivalent circulating density of drilling fluids at position of the drilling bit with uncertainty is obtained.On the basis of the above research results,the drilling risk probability at position of the drilling bit is obtained by using the established drilling risk probability model.If there is no risk,continue drilling.If there is a risk,we can avoid and control the risk by adjusting the equivalent circulating density of drilling fluids.If the LWD is lacking,the dynamic risk assessment can be carried out according to the comprehensive logging data.In this paper,a dynamic risk assessment model based on PSO optimization BP neural network is constructed.By collecting regional drilling logging data and risk statistics analysis report,the change law of comprehensive logging characteristic parameters under different working conditions and abnormal conditions can be obtained.Then,the training samples were constructed by the normalization method,and the dynamic risk assessment model was trained by the training samples.Finally,the real-time judgment of the risk types and prediction of risk probability can be realized based on the analysis of the comprehensive monitoring of logging data.In this way,early warning information can be given at the early stage of risk.After completion of the well construction,all data and information obtained in the whole drilling cycle are collected and sorted out.And the database of risk drilling engineering is established,which can provide technical support for the formulation of subsequent drilling programs.There are two main work on the risk summary and analysis: The first is to compare the risk assessment results with the actual engineering risk,to analyze the adaptability of the risk assessment model and to improve the risk assessment model.The second thing is to make use of the measured values of drilling geomechanical parameters or log interpretation results after drilling to correct the model coefficients in the calculation formula of geomechanical parameters.By continuously improving the regional geomechanical parameter model and reducing its uncertainty,it provides more accurate basic pressure information for subsequent well drilling risk assessment and reasonable casing program design.According to the risk assessment method constructed in this paper,combined with the characteristics of drilling design and construction,a set of drilling engineering risk assessment and control software is compiled by using the programming language of VB,MATLAB and SQL Server 2008,which has been successfully applied to more than 30 wells and achieved good results by the field application test.