Material selection of (1) expansion casing
The basic requirements of expansion casing for pipeline are: high elongation of pipeline; Have certain plastic deformation ability; It has sufficient external compressive strength after expansion; Can meet the sealing requirements of the formation. At present, L-80, K55, N-80 and other casing materials are mainly used for oil and gas drilling expansion casing. The application and foreign tests show that the expansion casing can still meet the requirements of API standard. Its mechanical properties are shown in Table 3-8. Because of the small diameter and the depth of the hole, the strength requirement of the expansion casing is low in geological core drilling, so the low-carbon steel pipe with low strength, small wall thickness and good ductility can be selected.
Table 3-8 Mechanical properties of L 3-8 L-80 and K-55 materials before and after expansion
(2) Design of expansion mechanism
The expansion of casing is mainly driven by the expansion mechanism through hydraulic or mechanical means, so that the expansion tool moves in the pipeline along its axis direction, so that the pipeline is plastically deformed and expanded to a predetermined inner diameter and outer diameter. At present, most deployment mechanisms are mechanical deployment methods: solid reverse pulling method and rotary fitting method, as shown in Figure 3-22.
Figure 3-22 Mechanical expansion method
(1) Three-dimensional reverse painting method; (2) Rotating fitting method
Solid reverse pulling method is to make the solid expansion cone move along the axis under the action of external force, and increase its cross section when passing through the casing. It is characterized by simple expander, various structural changes, large friction resistance during expansion, and large expansion force and casing anchoring force provided by the required ground equipment, which is suitable for large-caliber and large-scale operation equipment.
The rotary fitting method adopts a dilator with a rotatable small cone wheel. When expanding, the tube expander moves both axially and rotationally, and the small cone wheel rotates along the center line of the tube expander under the action of frictional resistance caused by contact with the expansion casing, so the expansion force is small when expanding. This method is suitable for the construction of small equipment in small diameter drilling.
In the expansion operation of the expansion casing, the conical surface of the expansion cone mainly exerts pressure on the inner wall of the pipeline, causing plastic deformation. In the case of the same pipeline, the expansion force mainly depends on the cone angle. The main factors that should be considered in the design of cone angle of expanding cone are as follows: (1) the metal flow in deformation zone is as stable as possible; Conducive to the establishment of lubricant fluid lubrication conditions in the expansion deformation zone; Ensure that the axis of the expansion casing is consistent with the axis of the expansion tool; Make the expansion force as small as possible; Minimize the contact area between the expansion cone and the expansion tube to reduce the resistance. Typical expansion cone forms are shown in Figure 3-23.
Figure 3-23 Typical Expansion Cone Form
(3) Design of expansion casing connection
It is one of the key technologies in the process of pipe string expansion to effectively ensure the mechanical properties and sealing of expansion casing connection. The common threaded connection method can't meet the performance requirements of the expansion pipe. The special requirements for the connection of expansion pipes are as follows: after connection, the expansion pipes need to be flat inside and outside, that is, the inner diameter and outer diameter are the same as those of the expansion pipes; The internal pressure strength of the connecting part is consistent with the strength of the pipe body; The expanded casing can maintain high connection strength and good sealing performance.
According to relevant information at home and abroad, the connection modes of expansion pipes mainly include special threaded connection and rivet connection, as shown in Figure 3-24. For example, as shown in Figure 3-25, the threaded connection method of expansion casing designed and used in Changqing Oilfield adopts J55 pipe with the specification of Ф114.3 mm× 6.35 mm, and the external diameter after expansion reaches Ф139.7 mm. This joint is designed as a direct connection type without coupling. The connecting thread of expansion sleeve adopts trapezoidal thread (negative angle), and the angle of guide surface is 10, and the angle of bearing surface is -9. The thread is hook-shaped, and the outer shoulder is the main shoulder. Tighten it before contact. The inner shoulder is a conical and conical metal surface sealing structure, and is engraved with a sealing groove. When tightening, install elastic sealing ring to seal.
Figure 3-24 Schematic Diagram of Expansion Tube Connection Mode
(a) special threaded connection; (b) and (c) rivet connection
Figure 3-25 Basic Structure of Joint
The specific geometric dimensions of thread design are:
Tooth height: external thread 1.375mm, internal thread 1. 175 mm.
Pitch: 5 teeth per inch (25.4 mm)
Taper:1:32
Length of meshing thread: 80.2mm.
Thread pitch diameter interference: 0.088 0.03mm.
Interference of metal/metal seal: 0.025mm.