PETROLEUM ENGINEERING 405 1 Well Drilling Engineering Drilling Hydraulics (cont’d) Dr DO QUANG KHANH 2 10 Drilling Hydraulics (cont’d) Effect of Buoyancy on Buckling The Concept of Stability Force [.]
Well Drilling Engineering Drilling Hydraulics (cont’d) Dr DO QUANG KHANH 10 Drilling Hydraulics (cont’d) Effect of Buoyancy on Buckling The Concept of Stability Force Stability Analysis Mass Balance Energy Balance Flow Through Nozzles Hydraulic Horsepower Hydraulic Impact Force READ: ADE, Ch HW #: ADE # 4.14, 4.15, 4.16, 4.21 Fh Buckling of Tubulars Fh - Fb l Neutral Point l Slender pipe suspended in wellbore Partially buckled slender pipe Neutral Point Fb Buckling of Tubulars • Long slender columns, like DP, l Neutral Point have low resistance to bending and tend to fail by buckling if • Force at bottom (Fb) causes neutral point to move up • What is the effect of buoyancy on buckling? • What is NEUTRAL POINT? Neutral Point Fb What is NEUTRAL POINT? • One definition of NEUTRAL POINT is the point above which there is no tendency towards buckling l • Resistance to buckling is indicated, in part, by: Neutral Point The Moment of Inertia Neutral Point I= π ( d 64 n −d ) { in } Consider the following: 19.5 #/ft drillpipe Depth = 10,000 ft Mud wt = 15 #/gal ∆PHYD = 0.052 (MW) (Depth) = 0.052 * 15 * 10,000 ∆PHYD = 7,800 psi Axial tensile stress in pipe at bottom = - 7,800 psi What is the axial force at bottom? What is the axial force at bottom? Cross-sectional area of pipe = (19.5 / 490) * (144/1) = 5.73 in2 Axial compressive force = pA lbf = 7,800 ∗ 5.73 in in = 44,700 lbf Can this cause the pipe to buckle? Axial Tension: FT = W1 - F2 FT FT = w x - P2 (AO - Ai ) At surface, FT = 19.5 * 10,000 - 7,800 (5.73) = 195,000 - 44,700 = 150,300 lbf At bottom, FT = 19.5 * - 7,800 (5.73) = - 44,700 lbf Same as before! F2 Stability Force: Ai FS = Aipi - AO pO FS = (Ai - AO) p (if pi = pO) At surface, FS = - 5.73 * = At bottom, FS = ( - 5.73) (7,800) = - 44,700 lbs THE NEUTRAL POINT is where FS = FT Therefore, Neutral point is at bottom! PIPE WILL NOT BUCKLE!! 10