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Completion packer slips have the effect of supporting the packer by anchoring and locking packer rubber in high temperature and high pressure (HPHT) wells, which are an important component for ensuring the reliability of the packer. There are interactions when slips and casing contact with each other, which would generate interactive forces, and the supporting forces of slips mainly relay on the interactions between slips and casing. In this paper, the interactions between slips and casing have been studied by theory and finite element method based on ANSYS. The depth of slip bit into casing and the rules of interaction between slips and casing were found from above research. It was found that the bite depth of HPHT completion packers was generally about 0.7 mm. And, the load acted on the slip elements tip will increase with the increase of the axial load acted on the cone, while decrease with the slip elements number. Introduction The slips of the packer are important components ensuring the reliability of the packers . After the packer down to the desired depth, the setting force is transferred to the slip cone through the packer cone under the action of axial loads. Due to the cone angle is generally small, it will produce a large radial load, under which slips bit into the casing wall for a certain depth, so the clips card on the casing wall, which have the effect of supporting packer. The formula of contact force between slips and casing would be obtained according to the mechanical analysis of the slips, and the finite element model of the slip system composed of cone, slips and casing was established in this paper. The depth of the slip bit into the casing and the law of interaction between slips and casing would be obtained through the analysis. Analysis of contact force between slips and casing in HPHT wells The completion packer in HPHT wells is slip-type packer. When the axial force acting on the completion is too large, or the parameters of the slips are unreasonable, the slips or casing may be damaged. Therefore, it is quite necessary to analysis the contact force between completion packer slips and casing in HPHT wells. As shown in Fig. 1, when the packer was set and the slip was anchored, the slip had been fractured. With the assumption of integrated slip being divided into the same pieces of the symmetry, force equilibrium equations of each slip can be established :    + = − = ) cos (sin ) sin (cos α φ α α φ α tg Q Q tg Q Q R z R r . (1) 2nd International Conference on Machinery, Materials Engineering, Chemical Engineering and Biotechnology (MMECEB 2015) © 2016. The authors Published by Atlantis Press 338 From the Eq. 1 above, we can get: ) ( ) ( 1 φ α φ α + = + = ntg W tg Q Q Z r . (2) Where, Qz is the axial load acting on each slip, Qr is the radial load at the contact point in each piece of slips and casing wall, QR is the load acting on each slip, W1 is the total axial load acting on the slips of the packer, φ is the friction angle, α is the inclined angle at the top of slip, and n is the number of the slips. Fig. 1 Schematic diagram of slip Fig. 2 Radial distribution force of the slip exerted by the axial force As shown in Fig. 2, with the assumption of Qr being uniformly distributed along the radial direction on the inner wall of the casing, the relationship of uniformly distributed loads q, Qr and W1 on the contact region between slip and casing can be obtained. β α θ θ α β β sin 2 cos ql d ql Qr = = ∫− . (3) β φ α α β α sin ) ( 2 sin 2 1 + = = tg nl W l Q q r . (4) Where, rCi is the inner radius of casing, β is the half-angle of slips at the outer surface, l is the axial length of slips at the outer surface, q is the uniformly distributed load along the radial direction on the contact region between slips and casing. Analysis of the depth slips biting into casing in HPHT wells Because the casing is thin-wall tube, bite mark will form on the interface of casing when the slip bites into casing, and the casing may be damaged if the biting depth is too large. The shear force of the slip is related to the biting depth. The stress concentration appears because of the contact of slip element and casing, so it is necessary to analysis the depth of slip biting into casing with finite element method based on ANSYS. (1) Elements in finite element model Solid182 20 node element was chosen when analysis the contact process of slip and casing, and the surface to surface contact element of Targe169 and Con-ta174 on contact couple was chosen in ANSYS. (2) Materials of casing, slip and cone THT permanent packer has an integral slip for each side. This slip reliability of fit mode has been confirmed by the over cable setting permanent packer. Generally, this slip made by 125MY materials , which are low carbon steels, and easy to grind and milling, and the elements which treatment by carburizing can ensure bite high strength casing. Material of casing is P110, and the material data of slip, cone and casing are shown in Table 1.

Analysis of the Interaction between Casing and Completion Packer Slip in HPHT Wells