Mechanical Model Of Cuttings Transport And Evaluation Of Hole Cleaning Effect In Horizontal Wells

As the domestic reserves of high-quality conventional oil and gas resources continue to decrease,China's oil and gas exploration and development is gradually developing into the fields of ultra-deep,deep water,and unconventional oil and gas resources such as shale oil,shale gas,coalbed methane,and natural gas hydrates.Using horizontal wells with long horizontal sections to exploit oil and gas resources can improve the development effect of oil and gas reservoirs,and is more and more widely used in the exploration and development of oil and gas resources such as shale oil and shale gas.However,during the drilling of extendedreach wells and horizontal wells,cuttings are easily deposited on the lower side of the annulus under the action of gravity,forming a cuttings bed,causing the hole cleaning problem.Therefore,theoretical research on cuttings transport can provide a theoretical basis and engineering application guidance for the safe and high-efficiency drilling of horizontal wells.In recent years,under the guidance of the law of cuttings transport,based on adjusting drilling parameters or hydraulic parameters to improve the hole cleaning effect,in engineering practice,people have innovatively proposed the use of hole cleaning devices to improve the hole cleaning effect.Researching the transport law of cuttings under the action of the hole cleaning device has a profound impact on guiding the effective application of the hole cleaning device in engineering and evaluating the hole cleaning effect of the technology.This paper surrounds the core theoretical problem of cuttings transport in the process of horizontal well drilling,based on the cuttings transport mechanical model,using the research methods of theoretical analysis,experimental research,and numerical simulation,constructs "settling drag coefficient model ? theoretical framework of the axial incipient model of particle? circumferential incipient model of particle constructs ? particle critical starting swirl intensity concept ? hole cleaning effect evaluation of hole cleaning device" as the primary research line,the mechanical model of cuttings transport in horizontal wells and the evaluation of hole cleaning effect is carried out,and a set of feasible mechanical analysis model of cuttings transport is proposed.The main research contents of this paper are as follows:(1)The prediction model of particle settling drag coefficient was established.The settling velocities of 172 groups of spherical particles and 522 groups of irregular sand particles in Newtonian / non-Newtonian fluid were obtained by experimental means.The drag coefficient prediction model based on Haider & Levenspiel's five-parameter equation was established for fluid(Newtonian fluid,power-law fluid,and Herschel-Bulkley fluid)having different rheological models,respectively,and compared with the existing spherical particle settling drag coefficient model.Verify the effectiveness of the proposed model.By introducing a shape description parameter(circularity),the drag coefficient prediction model of irregular shape sand particles was established,laying a theoretical foundation for the subsequent construction of the cuttings transport mechanics model and evaluating the effective action distance of the hole cleaning device.(2)The equilibrium relationship of particle axial incipient is improved,and the mechanical equilibrium model is established.Aiming at the incipient modes of cuttings bed particles such as sliding transport,rolling transport,and lifting transport,the mechanical equilibrium relationship of particles in the axial incipient state is analyzed,and the Manning formula is introduced to calculate the height of cuttings bed according to the parameters such as borehole geometric information and eccentricity.Through parameter analysis,for drilling fluids with different rheological models(Newtonian fluid,power-law fluid,and Herschel-Bulkley fluid),the effects of annulus flow pattern(laminar and turbulence),well inclination angle,particle size,particle density,drilling fluid density,annulus circulation velocity,rheological parameters,eccentricity,and borehole size on particle incipient velocity and the height of cuttings bed surface are analyzed.The cuttings transport experiment is carried out through the indoor flow loop to observe the cuttings deposition and the transport behavior of particles above the cuttings bed.The prediction results of the proposed model were verified.(3)Exploring the mechanical equilibrium relationship of particle circumferential incipient and established a mechanical equilibrium model.The mechanical balance relationship between the particles in the circumferential incipient state was analyzed,and the particle circumferential incipient model and the determination of the particle circumference starting speed were realized.The circumferential shear force exerted by drill pipe rotation on drilling fluid is simplified into ideal Taylor-Couette flow to obtain the radial circumferential velocity distribution law of drilling fluid.Then,a quantitative evaluation model of the hole cleaning effect is proposed for drill pipe rotation under laminar flow.The model is used to predict the hole cleaning effect of different hole inclination angles,particle size,rheological parameters,eccentricity,and initial cuttings bed height,and the prediction results of the model are verified by indoor experiments.The CFD-DEM coupling method was used to simulate the cuttings transport numerically,and some flow details during the drill pipe rotation were obtained.(4)The characterization parameter of particle incipient swirl intensity is proposed,and a new method for evaluating the cleaning effect of hole cleaning devices was established.The types and characteristics of existing hole cleaning devices are summarized,and their characteristics are divided into the straight-shaped blade and V-shaped blade of hole cleaning devices.The decay behavior of blade-induced swirl flow was numerically simulated by the CFD method.The decay behavior of swirl intensity along the flow direction was obtained under different rotating speeds,helical angle,and rheological parameters.The calculation model of particle incipient swirl intensity was established to calculate the swirl duration of tool-induced decaying swirl flow,and combined with particle redeposition time to evaluate the effective action distance of the hole cleaning device.The blade entity is printed by 3D printing technology,and indoor experimental are carried out to observe the transport law of cuttings after the action of hole cleaning device,and evaluate the effective action distance.