Content summary: This article introduces the technical parameters, structural performance and main components of the GH-700 manifold.
A fracturing manifold is important equipment in fracturing operations. In the past, China had no fixed manufacturer producing this type of product in batches. When oilfields adopted fracturing operation processes, they each made some equipment by themselves, and the structures were different.
To meet the needs of the rapid development of the petroleum industry, to speed up the pace of socialist construction, to realize the grand goal of achieving the Four Modernizations by the year 2000 proposed by our beloved Premier Zhou Enlai in the government work report of the Fourth National People's Congress, and to support world revolution, our plant undertook the trial-production task for the Model 70 fracturing manifold in 1974. The manifold was designed by the Drilling and Production Equipment Research Institute of Jianghan Petroleum Administration. In December 1975, two sets were trial-manufactured and were sent successively to Shengli Oilfield and Dagang Oilfield for industrial tests. In the tests, fracturing and sand-control operations were carried out respectively. The main fracturing fluids included water, crude oil and sesbania gum. Four wells and five well operations were completed. The maximum pressure was 320 kg/cm2. Two ground dynamic-pressure tests were also carried out, with a maximum pressure of 640 kg/cm2, a duration of 24 minutes and 20 m3 of water pumped. After joint appraisal by the design, manufacturing and user organizations, it was reported to the Manufacturing Group of the Ministry of Petrochemical Industry for approval and is currently in small-batch production.
1. Technical Parameters of the GH-700 Manifold
The manifold structure is shown in Figure 1.
Figure 1. GH-700 manifold structure
1- 2 in high-pressure union; 2- one-way valve; 3- phi 45 x 700-atm union; 4- plug valve; 5- bleed-off valve.
1. Suitable for fracturing operations up to 700 kg/cm2.
2. Maximum working pressure: 700 kg/cm2.
3. Seal test pressure: 800 kg/cm2.
4. Strength test pressure: 1000 kg/cm2.
5. Main line bore: phi 54.
6. Branch line bore: phi 64.
2. GH-700 Manifold Structure and Operating Notes
The manifold is mainly composed of one-way valves, plug valves, bleed-off valves, unions, tees, crosses and pup joints. It has 14 connections in total. The 10 connections equipped with one-way valves can connect respectively to 10 fracturing trucks. The connection equipped with the bleed-off valve connects to the bleed-off line. One connection on the branch line behind the plug valve is equipped with a one-way valve and can connect to a balancing truck. The two main-line connections connect to the fracturing wellhead.
The middle of the manifold consists of two main lines with a center distance of 779.5 mm. The assembly can be fixed on the frame of a CA-10 or CA-30 Jiefang truck to form a manifold truck. The branch-line ends are equipped with 2 in unions and can connect directly to SYC-700 and YLC-500 fracturing trucks.
3. Main Components of the Manifold
1. One-way valve. The structure is shown in Figure 2.
Figure 2. One-way valve
1- gland; 2- spring; 3- valve assembly; 4- valve seat; 5- valve body.
The one-way valve is relatively simple to manufacture and convenient to repair. Its valve assembly is similar to that of the AC-700 fracturing truck, so it works safely and reliably and is not prone to sand sticking. During fracturing, if a fracturing truck fails and must be stopped for repair, the one-way valve can automatically cut off the high-pressure fluid in the line under differential pressure, allowing repair while the fracturing operation continues as usual.
2. Plug valve. The structure is shown in Figure 3.
Figure 3. Plug valve
1- handwheel; 2- plug; 3- valve body; 4- valve plate; 5- gland.
A pair of valve plates is arranged between the plug and the valve body. The clearance among the valve plates, valve body and plug can be adjusted through the gland, so the valve can seal while still opening and closing with relatively low effort. The valve cavity is filled with high-pressure sealing grease to improve sealing and lubrication. The valve is easy to disassemble and assemble, opens and closes quickly, and is used to change the flow direction. Its limitation is that it is not easy to turn under pressure. The main plug-valve components are the valve body, plug and valve plates.
Valve body: the material is 35CrMo steel, quenched and tempered to HB 204-280. At first the 1:7 tapered bore was ground. Because alignment errors occurred, the tapered bore and the straight bores at the upper and lower ends were not concentric, and the pressure test only reached 50 kg/cm2. Later, precision turning was adopted for each bore. During rough turning of the side bores, the opposite side was not drilled through, which helped ensure tapered-bore quality. Trial manufacture showed that precision turning was a better process.
Valve plates: two problems were encountered during trial manufacture.
A. Material. The design required ductile iron. At first, casting quality was poor, so ordinary cast iron was used instead. When the pressure test reached 50 kg/cm2, the valve plate fractured. Three consecutive parts failed in the same way. After ductile iron was used, the part succeeded, showing that ordinary cast iron was unsuitable for the valve plate.
B. Machining the sealing groove of the valve plate. Because it is difficult to machine an equal-depth circular groove on a conical surface, a special fixture was made. The circular groove is formed through combined translation and rotation. The fixture is used on a vertical milling machine. The fixture is fixed on the table, then the milling head is rotated to an angle parallel to the workpiece. A cutter disk is mounted on the spindle, and the cutter position on the disk must ensure that its rotation diameter matches the required groove diameter of the workpiece.
Figure 4. Circular-groove milling fixture
1- workpiece; 2- cutter disk; 3- bearing; 4- bearing bracket; 5- fixture shaft; 6- bearing; 7- rack; 8- gear; 9- rack support; 10- small slide; 11- nut; 12- lead screw; 13- handle.
The fixture works as follows: turning handle 13 drives lead screw 12, and nut 11 moves small slide 10. The slide carries bearing seat 4 with bearings 3 and 6. Fixture shaft 5 is installed in the bearings. The right end of the shaft holds workpiece 1, and the left end carries gear 8. The gear meshes with fixed rack 7. As the workpiece moves forward, it rotates backward around the fixture shaft, allowing the sealing groove to be milled.
The design principle is that milling the sealing groove requires two motions: translation and rotation in the opposite direction to the translation. Analysis shows that the gear travel distance should equal the cutter-disk diameter. Because the fixture gear and the workpiece are mounted on the same shaft, their rotation angles are equal. Therefore, the pitch-circle arc length through which the gear rotates equals the cutter-disk diameter, as shown in Figure 5.
Figure 5. Forming an O-ring sealing groove
3. Bleed-off valve. The bleed-off valve works reliably, is relatively easy to machine, opens and closes with low effort under high pressure, and is suitable for use as a pressure-relief valve. During fracturing or when reverse circulation is needed after fracturing, the wellhead gate valve can be closed and the bleed-off valve opened to release pressure from the surface line. After the plug valve is switched to the required position, the master gate valve can be opened for reverse circulation. The structure is shown in Figure 6.
Figure 6. Bleed-off valve
1- gland; 2- valve body; 3- valve element; 4- valve seat; 5- pressure cap; 6- valve stem.
At present, understanding of the Model 700 manifold is still insufficient. It needs to be further tested in use, improved continuously and perfected step by step.
