The main function of a High-Pressure Drilling Fluid Manifold is to connect the mud pump discharge outlet to the swivel inlet. It supports single-pump and dual-pump operation and meets drilling-site requirements such as pressure relief and mud filling. A complete manifold is composed of high-pressure hoses, valve groups, Hammer Union, standpipes, swivel joints, rotary hoses, pressure gauges and related pipework. Its flow capacity and pressure rating shall match the mud pump.
A typical complete set includes seven 4 in mud gate valves, three vibration-resistant pressure gauges, two or three high-pressure hoses including the rotary hose, 4 in steel pipe, and high-pressure Hammer Union or flanges. The main components are described below.
Schematic diagram of a High-Pressure Drilling Fluid Manifold
1. Gate-Valve Assembly
Two types of slab-gate-valve assemblies are commonly produced domestically: 4" GX-Z43X-200 and 4" GX-Z43X-350. Their basic construction is similar. The main difference is pressure rating: one is rated for 200 kg/cm2 and the other for 350 kg/cm2. These ratings can generally meet the requirements of various drilling rigs.
Gate-valve assembly
The Y-body and T-body of the gate-valve assembly are cast from cast steel and then connected by Hammer Union. The valve used here is different from an ordinary wedge gate valve. It is an assembled rising-stem slab gate valve with a rubber sealing seat.
Slab Gate Valve
Sealing is achieved when the slab gate moves downward and deforms the rubber valve seat, creating a self-sealing effect. This rubber seat is relatively durable, especially when the conveyed medium contains sand particles. It has a long service life, requires relatively low closing torque, and is simple to replace. The valve end connections may be high-pressure union type, threaded type or flanged type.
For convenient connection, high-pressure union connections, namely Hammer Union, are widely used for field pipelines. Their advantage is that the two connected ends do not have to be on the same centerline. Because the connection uses a spherical fit, the two ends may be positioned in space at a certain angle. The angle should not be too large and is generally within 8 degrees.
Hammer Union
2. High-Pressure Hose
High-pressure drilling fluid must be delivered downhole. On the surface, it enters the drill pipe through the swivel. During drilling, the swivel moves up and down, so a flexible hose is required to connect the standpipe to the swivel. This hose is commonly called a rotary hose. In addition, to speed up installation between the mud pump and the surface pipeline, hoses are also used at the high-pressure outlet of the mud pump and at the drilling-fluid-manifold connection.
High-pressure hoses used in oilfields are generally divided into two types. One type is made by winding coarse steel wire around a fabric-reinforced rubber hose and then vulcanizing another layer of fabric-reinforced rubber on the outside. The other type uses fine steel wire that is braided or wound into multiple layers and then vulcanized together with rubber. Because the first type has relatively poor flexibility and cannot withstand very high pressure, it is gradually being phased out.
The connection between hose and steel pipe is made through hose fittings. There are two types of hose fittings. One is the vulcanized fitting, which is directly vulcanized together with the hose and supplied by the manufacturer at a fixed length. The other is a mechanical fitting, including ferrule type, slip type, swaged type and other structures. Rotary hoses in oilfields often use the slip type. Its structure includes a core tube inserted into the hose, slips fitted around the hose, and an outer fitting shell outside the slips. The shell and core tube are tightened by bolts through a flange so that the hose is firmly pressed onto the core tube. This type of fitting can easily damage the hose at the connection, but it can be repeatedly installed in the field.
Rotary hoses and high-pressure hoses are identified by inside diameter, working pressure and length. Common sizes include 2 in (51 mm), 2-1/2 in (64 mm), 3 in (76 mm) and 4 in (102 mm). Working pressures include 100 kg/cm2, 160 kg/cm2, 210 kg/cm2, 300 kg/cm2 and 350 kg/cm2. The length can be manufactured according to user requirements. In general, the rotary hose on a drilling rig is about 18 m long, while the mud-pump connection hose is about 3 m long.
