By Toni Miszewski, AnTech Ltd.
SOLVING THE BLIND SPOT PROBLEM WITH RE-ENTRY COILED TUBING DRILLING
1st March 2017
While the main drilling attention over recent years has been about new unconventional and deep water wells, nearly 70% of the worlds hydrocarbon production comes from declining fields. There is a compelling economic case that extracting more from known reservoirs is a better idea than the cost and risks of a new project. In practice, working over mature fields involves various enhanced oil recovery (EOR) techniques and re-entering wells to drill horizontal laterals from a window cut in the existing wellbore. An established, if not yet widely adopted technique to do this is to use Coiled Tubing Drilling (CTD) to drill in underbalanced conditions.
The Declining Well Challenge
An efficient operation is an essential requirement for working over wells that may have a limited production capacity but at the same time still have significant unrecovered reserves. It is not realistic to expect a multi-year payback time especially with a low and uncertain oil price. Drilling in the right direction is a fundamental requirement of directional drilling and drilling in the wrong direction, even if the error is only small, is one of the easiest ways to reduce efficiency. This is surprisingly easy to do because of the distorting effect of steel casing on the magnetic sensors of a CTD BHA which creates a blind spot when first exiting the window. This effect may extend as far as 20ft from the vertical casing. Whilst this is a problem for all casing exits, the problem is worse for CTD operations. There is often limited vertical depth between the window and the target formation so high build rates are required and this leaves little room for error.
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