Study On Borehole Stability And Engineering Countermeasures Of Horizontal Wells In Shale Oil Reservoirs In Huabei Oilfield

The shale oil reservoir has obvious weak bedding characteristics,and serious well collapse and lost circulation.Based on the geological and engineering data of the exploration well in the target block,this paper analyzes the wellbore of the shale oil layer in the lower Shahe oil layer of the Lixian slope in Raoyang sag.Stabilize analytical work for use in field drilling engineering practice.Firstly,the elastic modulus,Poisson’s ratio,cohesion and other rock mechanical parameters of the target block are calculated based on the logging data;the shale oil reservoir temperature and pressure system in the exploratory well area is considered to be normal through the regression analysis of the offset well data,and established based on the Eaton method The regional formation pressure profile shows that the pore pressure gradient of the shale oil reservoir is between 1.01 and 1.05g/cm3.The regional in-situ stress gradient is established by using the six-five model.The isotropic wellbore stress model and the transversely isotropic wellbore stress model are established respectively,and the shale oil reservoir collapse pressure considering Mohr-Coulomb,Drucker-Prager and Mogi-Coulomb criteria is calculated based on the isotropic wellbore stress model.Cloud map,the results show that the collapse pressure calculated by the Mohr-Coulomb criterion is the highest,followed by the Mogi-Coulomb criterion,and finally the DruckerPrager criterion.According to the wellbore stability analysis process,the safe mud density window for exploratory wells was calculated,and the isotropic wellbore model,the wellbore model with bedding weak plane and the transverse isotropic wellbore model were analyzed by ABAQUS finite element software.The stress around the wellbore will decrease at the position where the bedding plane intersects the wellbore in the formation of the weak plane.There are differences in the influence of rock elastic modulus and Poisson’s ratio transverse isotropy on the stress distribution of the borehole.The in-situ stress difference σV/σH(overlying in-situ stress ratio to the horizontal maximum in-situ stress)has a significant influence on the stress distribution around the wellbore,and the larger the difference is,the easier the wellbore is to be unstable.Finally,adjusting the drilling fluid density parameters,it is found that high mud density will increase the radial stress of the transversely isotropic formation and reduce the circumferential stress.