Research On Safe Drilling Technology Of Narrow Pressure Window Formation In Yingqiong Basin

The natural gas resources with high-temperature high-pressure(HTHP)in the Ying-Qiong(YQ)basin is expected to exceed 4 trillion cubic meters,which is two-thirds of the total resources and has huge resource potential.The abnormal high pressure of the target layer in YQ basin makes the safe drilling operation window very narrow and drilling accidents occur frequently.In this paper,the accurate prediction model,precise control technology of equivalent circulating density(ECD)and Managed Pressure Drilling(MPD)schemes.for offshore HPHT wells are established based on the study of the geological and the pressure characteristics of the HPHT formation with narrow pressure window in YQ basin.This paper focuses on the study of ECD in YQ basin.Based on the dynamic temperature field theory,a set of calculation model of wellbore temperature field is established using microelement method and energy conservation law;The prediction model of drilling fluid rheology is established,and the influence of temperature and pressure on drilling fluid rheology is analyzed;based on the calculation model of wellbore temperature field and the prediction model of drilling fluid rheology,equivalent static density(ESD)and ECD temperature pressure coupling prediction model,within the drilling process in the HPHT formation with narrow pressure window,is established,and ECD parameters sensitivity analysis is conducted;through the building of cyclic pressure loss model of different locations in the process of drilling and the analysis of the impact of different drilling parameters on the cyclic pressure loss,MPD principles are established,MPD design requirements are proposed and key parameters of MPD are optimized,and thus the ECD fine control technology schemes is established.A set of ECD precise calculation model and ECD refinement control technology schemes established in this paper have been successfully applied to HPHT drilling operation in YQ basin.The prediction accuracy of the established ECD prediction model can reach more than 90%.The ECD fine control technology scheme achieves the safe drilling of the narrow pressure window formation and reduces the operating time of the target layer by 2.37 days,which has certain guiding significance for the field operation.