Subsea production system configuration
Subsea production equipment can be configured in multiple ways based on the field specifications and operator’s approach to operation. Field development planners need to work closely with the reservoir and drilling engineers early in the planning stages to establish a good well location plan. Once the reservoir is mapped and reservoir models created, the number of wells, types of wells, and their locations can be optimized. Well layout is usually an exercise of balancing the need to space the wells out for good recovery of the reservoir fluids against the cost savings of grouping the wells in clusters. Add to this the consideration of using extended reach wells, and the number of possible variables to consider becomes great. A further consideration, reservoir conditions permitting, is the use of fewer, high production rate wells through horizontal well completions or other well technology. Here again, there are cost trade-off considerations.
Contents
Satellite Well System
A satellite well is an individual subsea well. Satellite wells are typically used for small developments requiring few wells. Often the wells are widely separated and the production is delivered by a single flowline from each well to a centrally located subsea manifold or production platform. Various field layouts must be examined. This evaluation must involve hydraulic calculations and cost sensitivity analyses taking into consideration flowline cost, umbilical cost, and installation cost and flow assurance issues.
Template and Clustered Well System
If subsea wells can be grouped closely together, the development cost will usually be less than that for an equivalent number of widely dispersed wells. Well groupings may consist of satellite wells grouped in a cluster, or a well template, in which the well spacing is closely controlled by the template structure.
Clustered Satellite Wells
Clustered satellite subsea well developments are less expensive than widely spaced satellite wells mainly because of flowline and control umbilical savings. If several satellite wells are in proximity to one another, a separate production manifold may be placed near the wells to collect the production from all of the wells and deliver it in a single production flowline that is connected to the production facility. In addition, a single umbilical and umbilical terminal assembly (UTA) can be used between the well cluster and the production platform. A field with eight clustered dictated by a desire to be able to position the drilling rig over one well without imposing dropped object risk on adjacent wells. It is hard to precisely control the spacing of individual satellite wells, so crossover piping and control umbilicals must be able to accommodate the variations in spacing.
Production Well Templates
A template is a seabed structure that provides guidance for drilling and/or other equipment. It also works as the structural framework supporting other equipment, such as manifolds, risers, wellheads, drilling and completion equipment, and pipeline pull-in and connection equipment. The structure should be designed to withstand any load from thermal expansion of the wellheads and snag loads on the pipelines. Production from the templates may flow to floating production systems, platforms, shore or other remote facilities.
The production well template is used to support a manifold for produced fluids. Wells would not be drilled through such a template, but may be located near it or in the vicinity of the template. The clustering wells can also be arranged by means of a well template. Well templates are structural weldments that are designed to closely position group of well conductors. The well template is typically used to group several subsea wells at a single seabed location. Apart from reservoir considerations, the number of wells in a well template is limited by the size of the well template that can be handled by the installation vessel.
Small templates are usually deployed from the drilling rig. Larger ones may require a special installation vessel with heavier lift capacity or better handling characteristics. The advantages of the production well template compared to the Clustered satellite Wells are summarized as,
- Well are precisely located and manifold piping and valves are incorporated in the templates.
- Piping and Jumpers may be prefabricated and tested before deployment offshore, therefore, installation time is reduced and less expensive.
Daisy Chain
A daisy chain configuration connects wells in serious, one after the other by flowlines. The flowline can be either connected to the wells by subsea jumpers, or directly connected to the flowbase of the wells if applicable. A flowline loop connected to the individual subsea wells along its route, which forms the daisy chain layout. The daisy chain field layout is considered as an economic solution comparing to the cluster manifold layout in case there are several satellite wells e.g. from different marginal fields.
Typical example of daisy chain field architecture is Canyon Express field which is located in GoM. This project involvs 10 subsea wells in three different deepwater fields. Staring from the Canyon Station platform, one flowline connects 2 wells in the first field, 2 in the second, and is ended by a sled, which is then connected to the third field by a subsea jumper. Another flowline connects 2 wells in the third field, 2 in the second and the remained 2 wells in the first and finally tied back to the platform. These dual flowlines formed a daisy chain piggy loop. The daisy chain approach of Canyon Express not only makes use of flowline and equipment already used and paid for, but also saves on the capital expenses comparing to a cluster manifold solution according to a conceptual study made in the early phase of the project. Typical features of daisy chain field architecture include:
- Inline sleds may be installed at each well location thus Xmas trees can be connected to the flowline by means of jumpers;
- Subsea multiphase flow meters may be required to ensure accurate flow allocation among different wells;
- Flow assurance analysis is key in formulating the production envelop for the daisy chain flowlines;
- Subsea chokes may be necessary on each well/Xmas Tree;
- Round-trip pigging is possible to ensure timely removal of wax build-up in the flowline.
References
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