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Key words: shale gas; fracturing; valve; sand control CLC number: TE934 Document code: A Article ID: 2095-2945(2018)29-0164-02
Abstract: This paper mainly compares the structure and performance of the valves with different structures used in fracturing operation in Chuanqing area at home and abroad, analyzes the advantages and disadvantages of each type of structure in sand control, and puts forward solutions to the difficult problem Of sand control in the design and application of valves.
Keywords: shale gas; fracturing; valve; sand control
The shale gas development in the Chuanqing area belongs to the national energy planning project. The main development technology is hydraulic fracturing, and the hydraulic fracturing fluid is a mixture of fracturing fluid and proppant. In some geological complex areas, the work construction pressure is even Up to 140MPa, under the harsh conditions of high pressure, high sand content and acid, the valve has different degrees of valve jam, switch not in place, seal leakage and other problems, which greatly plague the field operators and affect the fracturing construction progress. It may even lead to serious well control accidents.
1 Classification of valves for fracturing operations Valves in fracturing operations are mainly divided by caliber. Valves of 4-1/16′′, 5-1/8′′ and 7-1/16′′ are mainly installed in fracturing distribution manifolds. On the fracturing tree, the main channel of the fracturing fluid is formed by opening and closing the valve to realize the main casing fracturing; the valves of 2-1/16′′, 2-9/16′′ and 3-1/16′′ are mainly installed at the pressure. Splitting wellhead side outlets and side outlet manifolds, such as chip traps, desanders, throttling gas pipelines, etc., usually at pressures of 10,000 psi, 15,000 psi, and 20,000 psi. These valves have a commonality: medium is super High pressure, sand containing conditions.
2 Commonly used valve structure at the fracturing site From the overall structure, there are two common types of manual gate valves on the fracturing site. One is the open rod with the tail rod thread drive (as shown in Figure 1), which is suitable for small-diameter valves; The type is an open rod with a tail rod ball screw drive, suitable for large diameter valves (Figure 2); the overall characteristics of these two types of valves are three pieces of detachable, small operating torque, and obvious switch indication. Among the small-caliber series, foreign companies are mostly dark-rod type valves, which are compact (see Figure 3).
3 Common valve seat sealing structure characteristics comparison 3.1 Valve front sealing type wave spring structure (Figure 4), the wave spring deformation produces a large pre-tightening force, forming an initial low pressure seal, external O-ring seal. When sealing, the medium pressure and the spring preload force act simultaneously. Advantages: The valve is sealed before the valve is closed. When the valve is fully closed, the medium is not easy to enter the valve cavity. Disadvantages: difficult to install, special tools are needed, it is difficult to achieve online maintenance, the operating torque is large, the medium will gather in the front gap of the valve, and it is easy to jam.
Piston multi-valve structure (Figure 5), double seat piston design, O-ring seal, with sand retaining ring, initial seal by O-ring preload, pressure from two seats when medium pressure comes over Entering between them, and then acting on the valve seat respectively, pushing a valve seat to approach the shutter, and opening a close to the valve body to form a sealing effect after the sealing is pressed. Advantages of this type: When the valve is sealed, when the valve is fully closed, the medium is not easy to enter the valve cavity, and the installation is easier than the wave spring; Disadvantages: the operating torque is large, the medium will gather the gap, and there is a risk of jamming.
3.2 The FLS and FL structure is sealed behind the valve. The inner and outer rings of the FLS seat have sealing rings (Fig. 6), while the FL type seat has only one seal (Fig. 7). The structure of the seal is a spring V-shaped lip type (Fig. 8), the main seal material is PEEK, the protection ring is PTFE, the spring is stainless steel 316 or the corrosion resistant alloy EIGILOY or INCONEL material. The sealing principle is the same, the spring provides a pre-tightening force, so that the ram and the valve seat are fitted together to form an initial seal; at the same time, the spring opens the PEEK ring to form a seal and protect. The FLS double-ring design can effectively protect the sealing surface of the seat seat and prevent mutual protection while sanding, so as not to stab the sealing ring when the pressure is released. Advantages of this type: low pressure, high pressure seal, low torque, online repair; Disadvantages: the medium is easy to enter the valve cavity.
3.3 Double seat structure As shown in Figure 9, there is a rectangular PTFE seal between the small seat and the large seat and between the large seat and the valve body. The sealing principle is that the pressure acts on the gate and pushes the pressure of the gate. On the other side of the double seat, the rectangular ring provides an auxiliary seal and protects the downstream large seat and small seat, the sealing surface between the large seat and the valve body to prevent excessive contamination. The advantages of this type: reliable sealing after valve, online repair; Disadvantages: low pressure sealing effect is not ideal, the medium is easy to enter the valve cavity.
4 Valve sand control optimization Comprehensive comparison of the advantages and disadvantages of the front valve sealing and the rear valve sealing, the valve sealing is not easy to cause the jam due to the sealing area sand, the valve front sealing can delay the sand in the valve body, but the switch cannot be avoided. Sand problem in the process. The specific optimization measures are as follows:
(1) Design aspect: minimize the sealing gap between the gate and the valve seat and the valve body, and reduce the sealing surface; the sealing ring adopts a sand retaining structure with a lip with a spring; the valve stem seal adopts a combined spring energy storage ring type seal Increase the sealing contact area to prevent the sand from wearing the valve stem; the inside of the valve is provided with a support plate to reduce grease loss; the gate adopts a guiding design, and the side opens the sand groove to facilitate the extrusion of the bottom grit during the movement of the gate; The bottom and the upper part are provided with a flushing sanding port, which is convenient for external water source sanding when sanding; the whole structure of the valve adopts a three-piece structure as much as possible, which is convenient for disassembly and maintenance; the position of the inverted sealing should not be too deep to prevent sand deposition; The valve is installed in a horizontal position as much as possible.
(2) Use: When using online, it needs to be greased and maintained in time. There is grease in the inner cavity to avoid sand sinking. At the same time, shorten the grease injection cycle, observe in time, and immediately add grease when the torque is increased.
5 Conclusion According to the author's experience, the valve behind the valve seal structure is conducive to the smooth entry of sand into the valve cavity. The valve installation position is suitable, for example, the valve is laid flat as much as possible. The valve is sealed and repaired online. It has a flushing port to ensure the valve is effective. Switching stroke, the valve will perform well in actual use. Regular maintenance can greatly extend the online service life of the product. It is not realistic to achieve permanent sand control by the structure itself. Before the valve is used, the operator should get the training of the system to understand the product structure and the working conditions of the site. In actual operation, it is necessary to carry out the corresponding standard operating procedures, and the maintenance specifications and timeliness.
references:
[1] Wu Hanchuan, Liu Boxiu. Development of fracturing equipment in unconventional natural gas exploration and development[J]. Journal of Oil and Gas Technology, 2011, 06(33).
[2] Sun Xiaoying, Yi Xianzhong, Deng Jinxian. Development of HH-PSL3G-PR2 gas seal gate valve resistant to H2S corrosion[J].Petroleum Mine Machinery,2013,06.
[3] Zhu Youguang, Dai Jinxing. Research and Exploration Prospects of Natural Gas Containing Hydrogen Sulfide in China[J]. Natural Gas Industry, 2004, 24(9): 1-4.
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9. Heel grips: These can prevent your feet from slipping out of your shoes and also help reduce friction and blisters.
10. Shoe clips: These can be used to add a decorative touch to your shoes and can be easily removed or swapped out for a different look.
Abstract: This paper mainly compares the structure and performance of valves with different structures used in the fracturing operation in Chuanqing area at home and abroad, and analyzes the advantages and disadvantages of sand control of various structures, so as to solve the problem of sand control in valve design and application. Method.