Drilling Multilateral Wells Using Coiled Tubing
By Adam Miszewski, AnTech Ltd.
The oil and gas industry is constantly driving to reduce capital expenditure and increase economic recoverability while minimising environmental impact and surface footprint. By combining the three advanced drilling techniques of multi-lateral drilling, underbalanced drilling (UBD), and directional coiled tubing drilling (CTD), an operator can capture significant value out of known reserves. To be classified as a multi-lateral well, the well must have one or more additional wellbores branching off from the main wellbore.
The fundamental principles behind maximising return on investment from a well are: reducing capital expenditure and maximising well productivity. The highest well productivity is achieved through maximising reservoir contact per well/surface slot and minimising reservoir damage. Multi-lateral drilling reduces capital expenditure through drilling multiple reservoir sections per surface slot, and also, increases reservoir contact per surface slot. UBD minimises reservoir damage which maximises the productivity of each lateral. CTD is inherently set up for underbalanced operations (UBCTD) and CTD bottom hole assemblies (BHAs) can achieve high build rates, of up to 50 deg/100ft, to allow for multiple targets to be accessed from the motherbore. Viewed separately, it is easy to see how the three drilling technologies combine to make a compelling value proposition for an operator.
BHA Selection consideration when drilling multilaterals
A directional CTD BHA consists of a coil connector, a cablehead, an electric or mechanical disconnect, a downhole orienter, a sensor package, a motor or turbine with a bent housing, and, of course, a drill bit. Drilling directionally on coiled tubing is very similar to conventional slide and rotate drilling on a rotary. As coiled tubing cannot be rotated from surface, all the rotation needs to be carried out downhole through the orienter. The rotating orienter allows the toolface to be set from surface or for the motor to be rotated to drill a straight hole. High quality service companies can also provide additional BHA modules such as a gyro module for orienting a whipstock and for drilling in the presence of magnetic interference, immediately after exiting the casing.
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