Research On Simulation Law And Improvement Measures Of Cuttings Migration In Shale Gas Horizontal Well

In the process of onshore and offshore oil exploitation,the application of extended reach and horizontal Wells is more and more widely,which can significantly improve the efficiency and economic benefits of oilfield exploitation.However,in the complex drilling process,due to the action of gravity,the cuttings produced in the extended displacement and horizontal well section will be deposited in the low speed zone at the lower part of the annular wellbore,which will cause the cuttings difficult to transport,stuck pipe,increased friction,drill string fracture and other downhole accidents,seriously affecting the efficiency and economic benefits of drilling.Therefore,according to the characteristics of high density drilling fluid used in shale gas drilling in Sichuan-Chongqing area,this paper proposes a scheme to improve the efficiency of cuttings migration in extended reach and horizontal well sections.In this paper,the two-phase flow of annular cuttings migration was investigated,and the interaction between drilling fluid,particles and particles,particles and drill pipe and borehole wall was fully considered.CFD-DEM(Discrete Element Method)was used to numerically simulate the process of cuttings migration in wellbore,and a three-dimensional borehole cuttings migration model of horizontal well was established.In order to make the model calculation more accurate,the grid independence is verified,which fully verifies the accuracy of CFD-DEM method.Secondly,the position of high speed zone and low speed zone of fluid in the eccentric annulus of traditional rigid drill pipe borehole is analyzed.Combined with the position of high speed zone and cuttings bed of annulus fluid,and the characteristics of high density drilling fluid used in shale gas drilling,and according to the standard aluminum alloy drill pipe structure,a new suspension aluminum alloy drill pipe structure is designed.The internal flow field analysis and finite element simulation analysis of the improved drill pipe strength analysis respectively provide a reference for the design of the new aluminum alloy drill pipe structure.Finally,in view of the level and high Angle hole drilling and reverse circulation cuttings discharge operation,two kinds of conditions to establish traditional just drill pipe and the new model of the aluminium alloy pipe hole cleaning,is obtained by numerical simulation analysis of the two types of drill pipe clean cutting mechanism,the traditional way of steel pipe cuttings migration in the direction of the well's mouth in three layers of way,The new aluminum alloy drill pipe moves towards the wellhead in the form of suspension layer.The following conclusions can be drawn by comparing the cuttings migration efficiency of the two types of drill pipe:(1)suspension of new aluminium alloy pipe to the upper annulus or concentric,through theoretical analysis,deposited at the bottom of the annular cuttings in the fluid always high-speed area or close to the area position,compared with the traditional steel pipe in wellbore annular cuttings settlement decreased obviously,hole cleaning time is greatly shortened,the decrease of the quality of the cuttings unit time.(2)Compared with the traditional steel drill pipe,the new aluminum alloy drill pipe mode still has higher cuttings migration efficiency for the rotating speed of drill pipe and the large cuttings particle size,and the drill pipe eccentricity has little effect on the cuttings migration efficiency.(3)Compared with the traditional steel drill pipe,the drilling fluid in the wellbore annulus has better fluidity,the cuttings flow in the suspended mass,and the cuttings retention is less,so as to avoid the cuttings buried in the drill pipe,reduce the friction and torque of the drill pipe,and inhibit the formation of the cuttings bed.