## 2.5.4 Horizontal and inclined flow

### 2.5.4.1 Introduction.

In production operations, horizontal and inclined two-phase flow usually occurs in surface flowlines connecting the wellhead to a field separator. The pressure drop in the flowline, if compared to that arising in the well tubing, is of a lesser magnitude. This situation is because flowlines are usually horizontal or near horizontal, therefore no hydrostatic losses are present in the pipe. In summary, horizontal two-phase pressure drop in flowlines is generally of minor importance in the total production system consisting of the formation, the well, and the surface equipment. Exceptions to this rule are offshore wells where the length and especially the profile of the flowline do not meet the previous criteria and considerable pressure drops can be experienced because of inclined two-phase flow. The same way, substantial pressure losses can arise in long-distance pipelines transporting a two-phase mixture over a hilly terrain.

For the purposes of this chapter, i.e. the discussion of production engineering basics, only conventional wells situated on land locations are considered. In such cases, the importance of two-phase pressure drops in surface lines is much less pronounced than those occurring in wells. Accordingly, much less space is devoted to the presentation of pressure drop calculation models.

In order to develop the basic formula for calculating two-phase pressure drops in horizontal or inclined pipes, one solves the General Energy (Bernoulli) Equation for the pressure gradient (see also Section 2.4.2). The resulting formula is, according to Equation 2.90:

where: ?

##### Products & Services
Wellhead equipment is used to connect the tubing and casing to an oil or gas pipeline.
Gate Valves
Gate valves and knife valves are linear motion valves in which a flat closure element slides into the media stream to shut off flow.
Cyclone Separators
Cyclone separators and centrifugal separators utilize centrifugal, gravitational, and inertial forces to remove fine particles suspended in air or gas.
Globe Valves
Globe valves are linear motion valves with rounded bodies, from which their name is derived.  They are widely used in industry to regulate fluid flow in both on/off and throttling service.
Artificial Lift Equipment
Artificial lifting equipment refers to the systems which increase the flow rate of a production well. This is beneficial when reservoir pressure are low or nonexistant to increase the flow rate of water or crude oil.

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