Study On Cuttings Settlement And Migration Law Of Gulong Shale Oil Horizontal Well

The potential of continental shale oil resources is huge,and the physical properties of shale determine that long horizontal wells must be used for development.When the drilling fluid circulation is stopped by replacing the drill bit and connecting a single piece,the cuttings will settle in the drilling fluid,and the cuttings bed will be formed in the high-angle well section and the horizontal well section.The key parameters such as the final velocity of cuttings settlement,the thickness of the bed,and the re-starting speed of the particles on the surface of the cuttings bed are related to the sedimentation resistance coefficient of the cuttings.Therefore,it is necessary to establish a prediction model of the settlement resistance coefficient of debris particles in non-Newtonian fluid,and further study and improve the migration mechanism of debris particles.Firstly,in view of the problems existing in the current prediction model of particle sedimentation resistance coefficient,that is,the rheological parameters of non-Newtonian fluids are mostly measured by six-speed viscometers,and the mainstream shape description parameters are difficult to accurately measure the cuttings particles with irregular shape and height.In this study,the full-speed rheometer was used to accurately measure the rheological parameters of different fluids,and the particle roundness,a feasible and easy-to-measure particle shape description parameter,was used to describe the shape of the particles.Based on the experimental results of the sedimentation velocity of spherical particles and cuttings,a model capable of predicting the sedimentation resistance coefficient of irregular cuttings under Newtonian and non-Newtonian fluids was established.It lays a foundation for the subsequent establishment of cuttings migration model.Furthermore,in view of the shortcomings of the existing critical velocity model,the assumption that there is no debris deposition in the annulus cannot predict the height of the debris bed.Based on the three debris bed particle starting modes of particle sliding migration,rolling migration and lifting migration,the mechanical equilibrium relationship under the critical starting state of the particles is analyzed,and the dynamic model of the particles is established and improved.The effects of different factors(drilling fluid rheology,drilling fluid density,annulus flow pattern,deviation angle,particle size,particle density,eccentricity and borehole size,etc.)on the particle start-up speed and the height of the cuttings bed were analyzed theoretically.The data of cuttings deposition and particle migration above the cuttings bed were recorded by laboratory experiments to verify the proposed prediction model.The average relative error of the cuttings resistance coefficient is 4.99 %,which verifies that the model prediction results are in good agreement with the experimental results.Through the established dynamic model of cuttings,the height of cuttings bed can be predicted under the condition that the drill pipe does not rotate,so as to predict the law of cuttings migration and evaluate the effect of hole cleaning..