Continuous composite coiled tubing with embedded electric conductors can provide uninterrupted flow of data from downhole tools. This capability makes monitoring borehole stability throughout the entire drilling process possible, even when conventional mudpulse telemetry tools are not operating and cannot provide information in real-time.
An operator faces many borehole stability problems: stuck pipe, pack-off events, lost circulation, kicks, leakoff tests, and formation integrity tests, all of which can result in periods of non-circulation. However, an operator no longer has to rely solely on surface gauges to provide downhole information to deal with these problems because downhole readings are now available. The benefits of downhole pressure and tension data throughout these problematic and routine activities provide valuable information on events during these most critical operating procedures. Consequently, corrective actions can be taken to prevent and cure borehole stability problems almost as soon as they develop.
In addition, the downhole data can help reduce drilling time. The borehole is under constant scrutiny. Drilling, tripping, non-circulating, and circulating operations can be optimized while avoiding other potential problems. For example:
Swab and surge pressures can be monitored constantly while tripping without circulating.
Ledges and tight spots can be identified before they cause severe damage.
Time for leak-off test (LOT) and formationintegrity tests (FIT) can be minimized.
The early indications of borehole ballooning can be identified before ballooning becomes a major borehole stability issue.
Hole Cleaning intervals can be optimized reducing drilling time.
This paper covers a series of examples where continuous, uninterrupted data transmission can be used to anticipate and prevent borehole stability problems and optimize the drilling procedure.
The embedding of copper electrical conductors in Advanced Composite Coil Tubing (ACCT) allows a stream of high speed, high density of data to be transmitted in real-time between the downhole components and the surface system. This uninterrupted communication enables the operator to receive all of the data, all of the time, regardless of the operating activities underway.
In pipe-conveyed drilling, the real-time application of the pressure while drilling (PWD) data has been well documented. It is a very useful tool when used in conjunction with all the other drilling parameters to measure and anticipate drilling problems.123 However, the extent to which mud-pulse telemetry data can be used during all operating activities is limited. The realtime application of PWD data has been hindered because of the constraints placed on the amount of data that can be pulsed to surface. Ironically, one of the times when PWD data is most useful occurs when it can not be pulsed up. This could be due to low flow rates or the pumps having to be switched off to avoid damaging the borehole or getting stuck. Surface gauges then have to be relied upon for downhole measurements.
With the ability to have "real-time data all the time," pump-off data that could not be seen until the end of the run can be seen immediately. Formation integrity tests (FIT) and leak-off tests (LOT) can be monitored through the PWD tool, rather than the standpipe or choke pressure gauge.