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Understanding the principles of fluid flow through the production system is important in estimating the performance of individual wells and optimizing well and reservoir productivity. In the most general sense, the production system is the system that transports reservoir fluids from the subsurface reservoir to the surface, processes and treats the fluids, and prepares the fluids for storage and transfer to a purchaser.
Elements of production system
Fig. 1 depicts the production system for a single well system. The basic elements of the production system include the:
- Tubular goods and associated equipment
- Surface wellhead, flowlines, and processing equipment
- Artificial lift equipment
Fig. 1—Production System and associated pressure losses.
The reservoir is the source of fluids for the production system. It is the porous, permeable media in which the reservoir fluids are stored and through which the fluids will flow to the wellbore. It also furnishes the primary energy for the production system. The wellbore serves as the conduit for access to the reservoir from the surface. It is composed of the drilled wellbore, which normally has been cemented and cased. The cased wellbore houses the tubing and associated subsurface production equipment, such as packers. The tubing serves as the primary conduit for fluid flow from the reservoir to the surface, although fluids also may be transported through the tubing-casing annulus.
The wellhead, flowlines, and processing equipment represent the surface mechanical equipment required to control and process reservoir fluids at the surface and prepare them for transfer to a purchaser. Surface mechanical equipment includes the wellhead equipment and associated:
- Treatment equipment
- Metering devices
- Storage vessels
In many cases, the reservoir is unable to furnish sufficient energy to produce fluids to the surface at economic rates throughout the life of the reservoir. When this occurs, artificial lift equipment is used to enhance production rates by adding energy to the production system. This component of the system is composed of both surface and subsurface elements. This additional energy can be furnished directly to the fluid through subsurface pumps, by reducing the backpressure at the reservoir with surface compression equipment to lower wellhead pressure, or by injecting gas into the production string to reduce the flowing gradient of the fluid.
Flow through production system
Recognizing the various components of the production system and understanding their interaction generally leads to improved well productivity through analysis of the entire system. As the fluid flows from the reservoir into and through the production system, it experiences a continuous pressure drop (as Fig. 1 shows). The pressure begins at the average reservoir pressure and ends either at the pressure of the transfer line or near atmospheric pressure in the stock tank. In either case, a large pressure drop is experienced as the reservoir fluids are produced to the surface. It is the petroleum engineer’s responsibility to use this pressure reduction in an optimal manner. The pressure reduction depends on the production rate and, at the same time, the production rate depends on the pressure change. Understanding the relationship between pressure and production rate is important to predicting the performance of individual oil and gas wells.
To design a well completion or predict the production rate properly, a systematic approach is required to integrate the production system components. Systems analysis (more commonly called nodal analysis), which allows the petroleum engineer to both analyze production systems and design well completions, accomplishes this. For proper management of the well and reservoir it is critical to understand the flow of reservoir fluids through the production system, particularly inflow performance, which is the reservoir pressure-rate behavior of the individual well, and outflow performance, which is the flow of reservoir fluids through the piping system.
Systems analysis is an excellent engineering tool for optimizing the design of a new well completion or analyzing the behavior of a current production system. The application of systems analysis requires a thorough understanding of the relationship between flow of reservoir fluids in the subsurface reservoir and fluid flow through the well completion and tubulars to the surface stock tank. Unfortunately, this understanding is often lacking in practice. Inefficient operations may occur, because the petroleum engineer does not have a complete understanding of the fluid-flow process or fails to take a comprehensive look at the production system. The proper application of systems analysis provides a basis for determining the interaction of the various components in the production system to optimize the desired production rates for both oil and gas wells.
- Mach, J., Proano, E., and Brown, K.E. 1979. A Nodal Approach for Applying Systems Analysis to the Flowing and Artificial Lift Oil or Gas Well. Paper SPE 8025 available from SPE, Richardson, Texas.
Noteworthy papers in OnePetro
Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read
Xiong, Hongjie. "Optimizing Cluster or Fracture Spacing: An Overview." The Way Ahead. Society of Petroleum Engineers. 25 May 2017. https://www.spe.org/en/twa/twa-article-detail/?art=3007