Sometimes oil and natural gas reserves are located in separate layers underground and multilateral drilling allows producers to branch out from the main well to tap reserves at different depths.
This increases production from a single well and reduces the number of wells drilled on the surface.
A multilateral well is a single well with one or more wellbore branches radiating from the main borehole.
It may be an exploration well, an infill development well or a reentry into an existing well.
It may be as simple as a vertical wellbore with one sidetrack or as complex as a horizontal, extended-reach well with multiple lateral and sublateral branches.
General multi- lateral configurations include:
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multibranched wells, forked wells, wells with several laterals branching from one horizontal main wellbore, wells with several laterals branching from one vertical main wellbore, wells with stacked laterals, and wells with dual-opposing laterals.
These wells generally represent two basic types:
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vertically staggered laterals and horizontally spread laterals in fan, spine-and-rib or dual-opposing T shapes.
A successful multilateral well that replaces several vertical wellbores can reduce overall drilling and completion costs, increase production and provide more efficient drainage of a reservoir. Furthermore, multilaterals can make reservoir management more efficient and help increase recoverable reserves.
Regardless of the level of complexity, multi- lateral wells today are drilled with state-of-the art directional drilling technology, but there is always a certain risks ranging from borehole instability, stuck pipe and problems with overpressured zones to casing, cementing and branching problems.
Advantages of multilateral systems increasingly outweigh the disadvantages.
Multilateral wells configuration enhance productivity.
In shallow or depleted reservoirs, branched horizontal wellbores are often most efficient, whereas in layered reservoirs, vertically stacked drainholes are usually best.
In fractured reservoirs, dual-opposing laterals may provide maximum reservoir exposure, particularly when fracture orientation is known (From Schlumberger Oilfield review)
From Oil & Gas Portal
