Advanced Casing Design With Finite-Element Model of Effective Dogleg Severity, Radial Displacements, and Bending Loads

Abstract

A purpose-built finite-element model (FEM) is applied to simulate radial displacement of a casing string constrained within an outer wellbore. The FEM represents a fully stiff-string model wherein the casing is approximated by general-beam elements with six degrees of freedom at each node to account for all possible physical displacements and rotations. Results predicted include deflection of the casing centerline from the wellbore centerline, effective dogleg curvature, bending deformation, wall-contact forces, and bendingstress magnification. These results will provide for a more-accurate assessment of well integrity in terms of casing-stress safety factors and centralization before cementing, as well as more accurate prediction of running loads during the drilling phase.In critical-well-casing design, accurate assumptions regarding bending stiffness may be necessary to avoid overly conservative as well as nonconservative analysis. Challenging finite high-pressure/ high-temperature (HP/HT) and extreme-temperature wells are opportunities for increased design efficiency by avoiding overly conservative and costly designs, which can be crucial. Alternatively, design for extreme loads such as overpull loads in long deviated wells may be nonconservative if severe bending stresses are not considered.A realistic case study is presented that demonstrates the possibility to achieve cost efficiency by means of optimized casing design. A case study also is presented in which a nonconservative design may result if severe bending loads are not modeled. The purpose-built FEM code is in many ways preferable to the use of commercial finite-element-analysis (FEA) packages because of the time-consuming effort required to build up the detailed model.In typical casing and tubular-stress design, a soft-string model assumes casing strings are coincident with the wellbore centerline. The known or assumed wellbore curvature is applied directly to the casing string. Any effect of casing-string stiffness and allowable radial displacement within the outer wellbore is ignored. In many cases, this results in an overly conservative analysis. Likewise, the impact of bending-stress magnification is typically ignored, along with the effects of centralizer placement. This may also be nonconservative for critical overpull situations, such as in extended-reach-drilling (ERD) and horizontal wells.

Modeling contact of pipes within elliptic and spiralled wellbores using finite element analysis

“…Various models are used in oil industry to estimate the forces on drillpipes [1][2][3][4][5][6]. These tools provide various benefits, such as estimating torsional and axial drag, bending moments, load distribution along the drillpipe and critical buckling loads for a given hole-pipe-wellbore combination.…”

Modeling the Energy-Saving Regimes of Curvilinear Bore-Hole Drivage

“…3(b)) f = fsr + fc+ffr + fin, m = mfr = mf / t (12) Here, fgr is gravity, f° is the force of contact interaction between the surfaces of the DS and bore-hole, ffr is the force of friction interaction between these surfaces, f"1 is the inertia force, and mfr is the distributed moment of friction forces. 3(b)) f = fsr + fc+ffr + fin, m = mfr = mf / t (12) Here, fgr is gravity, f° is the force of contact interaction between the surfaces of the DS and bore-hole, ffr is the force of friction interaction between these surfaces, f"1 is the inertia force, and mfr is the distributed moment of friction forces.…”

“…2(a)) [10], plane harmonic wavelets or ripplings ( Fig. 2(c)) [9][10][11][12], and others. 2(c)) [9][10][11][12], and others.…”

“…In publications [10][11][12], special attention is paid to influence of the bore-hole tortuosities on the resulting friction forces. It is accentuated that typically, the irregularities of bore-hole can have the shapes of 3D spiral wavelets ( Fig.…”

New Analytical Method to Evaluate Casing Integrity during Hydraulic Fracturing of Shale Gas Wells

“…e results of a series of finite element studies of the cemented casing under a variety of stress conditions for both burst and collapse were presented, demonstrating the inadequacy of accepted design equations under many cemented conditions [11]. A purpose-built finite element model was applied to simulate the radial displacement of a casing string constrained within an outer wellbore [12]. Casing stress on the inner wall under the condition of elliptic casing was calculated and analyzed to improve the designing and correction of casing strength [13].…”