Theoretical Modeling And Software Development Of Surge Pressure Calculation In Horizontal Wells

A precise computational model for surge pressure is the prerequisite to accurately predict the bottom-hole pressure in various drilling operations,including casing in narrow annular space,as well as drilling in slim holes,deep-water and extended-reach wells,which is also the prerequisite to avoid the occurrence of downhole complex situations,such as well kick,well loss,borehole instability and so on.The commonly used fluctuating pressure prediction models such as the Burkhardt model and the Schuh model are established for concentric annulus.However,the presence of gravity and cutting bed cause the drill-pipe to be eccentric in the annulus of the inclined section and horizontal section in horizontal wells.The calculation method of fluctuating pressure in eccentric annulus and concentric annulus is different.Ignoring the effect of eccentricity on fluctuating pressure can lead to an underestimation of penetration speed and an increase in non-production time and costs.The influence of the eccentricity of the horizontal section in the horizontal well on the fluctuating pressure is analyzed based on the factors that affect the calculation of the fluctuation pressure in this paper.An improved golden segmentation algorithm is proposed to optimize the rheological parameters of the drilling fluid and the rheological model.The speed distribution of the fluid in the annulus under different drill string working conditions is taken into account,and the effect of the drill pipe joint,the static force of the drilling fluid and the acceleration of the drill-pipe on the fluctuation pressure are taken into account as well.Secondly,the calculation model of the fluctuating pressure in the concentric annular section and the eccentric annular section is established for the steady and transient state of the fluid flow in the horizontal well.During the establishment process of the model,different drilling fluid rheological modes and different string working conditions are considered,and the rationality of the model is verified.The deviation between the calculated results of the steady-state fluctuation pressure calculation model of the four-parameter fluid in the concentric annulus and the eccentric annulus and the previous experimental data are basically less than 10%.The most seriousdeviations between the results of the transient fluctuation pressure model and field measurements of two wells recorded by Burkhardt and Clark are11.5% and 9.93% respectively.The fluctuation pressure calculation software is compiled by Matlab language according to the fluctuation pressure calculation model in the horizontal well.The parameter sensitivity of the fluctuation pressure transient model is analyzed based on the surge calculation results of one horizontal well.The results show that the fluctuation pressure of the bottom hole decreases with the increment of the eccentricity,and it is about 50% when the annular is fully eccentric.The fluctuation pressure increases with the depth of the kick off point,the running depth,the running speed and acceleration of the drill-string.Surge pressure increases with the increment of pump displacement when tripping in,and the bottom swab pressure decreases with the increment of pump displacement when tripping out.In the field of drilling operation,the influence of these factors on the fluctuation pressure should be fully considered,and ultimately the drilling speed should be limited to the maximum speed calculated by the software.