ability to achieve all (or most) of the objectives of the well
Well objectives determine how a specific well should be designed. Several more common well objectives include:
sand control for reservoirs made up of unconsolidated reservoir rock or rock susceptible to Fines Movement (movement of fine-grained materials within the rock)
zonal isolation for reservoirs with multiple zones (to allow each individual zone to be shut in, if required)
well stimulation for reservoirs with low permeability or susceptible to well damage
artificial lift for low rate wells
Five common well design considerations are:
well orientation
completion design
tubing size
artificial lift
well stimulation
Three common well orientations for crude oil and natural gas production are:
vertical wells
deviated (or slanted) wells
horizontal wells
These well orientations have different applications in field development including costs and the avoidance of surface locations that are costly, environmentally sensitive, unsafe, or lack appropriate infrastructure (road access, water sources, etc.).
The well completion is defined as the portion of the well that connects the reservoir to the tubing. Three common forms of a well completion are:
an open-hole or bare foot completion
a screen or liner completion
a cased and perforated (a cased and perf’ed) completion
Sand control is required in wells producing from unconsolidated or weakly cemented reservoir formations. It is required because fines movement caused by the pressure drop (drawdown) in the reservoir and fluid production dragging loose rock material and debris to the well. Production of this loose material may accumulate in the well as sand fill which may cause production, logging, and workover problems for the well.
Sand is controlled in the well design through the well completion. The most common form of sand control is some form of gravel pack:
gravel pack (with slotted liner or screen)
pre-packed liner
pre-packed screen
frac-pack
Unwanted fluid production is defined as the production of fluids other than the fluid(s) for which the well is designed. This may include gas and water from oil wells or water from gas wells. The well is typically designed for the fluid(s) that achieve the highest revenues from the well. Unwanted fluid production may come from:
lateral fluid migration through the reservoir
downward coning of gas from a primary or secondary gas cap or upward coning of water from a bottom-water reservoir
injection from offset injection wells
Unwanted fluid production is controlled in the well design by a well completion with zonal isolation. By far, the most versatile well completion for zonal isolation is a cased and perforated well completion. Zonal isolation in a cased and perforated well may be controlled with (amongst others):
packers
bridge plugs
sliding sleeves
Multiple well completions may achieve the desired zonal isolation (i.e., there is no unique well completion for a well). The overriding well design considerations (first bullet point above) are used to select the final well completion.
Tubing is the conduit for fluids from the completion to the surface. The flow of fluids up the tubing is governed by well hydraulics in the form of a Tubing Performance Curve.
Plotting the Inflow Performance Relationship (IPR) on the same graph and the Tubing Performance Curve (TPC) is the foundation of nodal analysis. The IPR defines the rate of fluid production from the reservoir at a given flowing pressure, while the TPC defines the that the rate that fluids can be “pushed up” the tubing at the same flowing pressure. The intersection of these two relationships defines the operating point of the well at the current reservoir and tubing conditions. The Inflow Performance Relationship – Tubing Performance Curve analysis (nodal analysis) provides a powerful tool for defining the appropriate:
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