Demand Activated Technology.

Sending a command signal to a tool in a flowing well using existing well equipment:

In recent years there has been an increasing requirement to communicate with downhole tools for commanding them into operation for a great variety of tasks and functions. Historically, physically moving the pipe, dropping balls (and similar) inside the pipe or using pressure to shear a rupture disc were crude but reliable means of achieving this.

More recently, devices conveyed on cables and ratcheting tools which respond to pressure cycles have provided more sophisticated options. With the emergence of the micro processor, electronic tools which can communicate both upwards and downwards through a fluid column have become possible with great application in the drilling phase where the drilling mud is used as a transfer medium.

When a production well is completed and the drilling mud (or other fluid) is replaced by oil and gas, it has no longer been possible to use this approach with other choices such as use of hydraulic control lines, electric cables and fibre optic systems being the only option. These systems all have various limitations, not least their expense and reliability. Additionally, well construction has advanced in the last ten years such that these technologies are often not suitable due to a variety of physical limitations.

Many tools exist featuring a delay time set on a clock mechanism. Following expiry of the delay, the tool will function. This may open a previously closed valve, detonate an explosive charge to perforate casing or set a packer. More sophisticated versions contain a pressure transducer and micro processor. These tools may be programmed at surface to recognise a specific pressure pulse of a known height and duration or a series of pulses. By doing this, the possibility of early operation of the tool due to unforeseen delays is mitigated. This technology is well proven and has multiple applications with recent examples made by ourselves in areas such as our Command Activated Sandface Valves (SFV).

The SFV is installed in the closed position at the bottom of the completion – pre programmed with a set delay – to isolate a section of the well. When the well is ready to flow, a signal is sent to all the valves (as many as 8 or more) and the valves will all start to count down their individual programmed delay time. They will all open sequentially allowing the poorest performing parts of the well (or the furthest away parts) to flow first and the best last. This technique increases the overall productivity of the well and the amount of reserves available to recover. The downside of this method is that once programmed and activated, the sequence is executed with no flexibility to accommodate a change in events or circumstances. Obviously, individual control and signalling to each valve would be a significant advantage with the opening of each valve being determined by well conditions rather than an arbitrarily chosen delay time. Whilst engaging with this problem, the Demand Activation technology was produced by ourselves.

“Demand Activation” in our context, refers to sending a signal in real time to a downhole tool to command it to operate. As previously described, in a fluid filled well, this is easily achieved by connecting a pump to the well and increasing / decreasing pressure to produce a signature which the downhole tool will recognise. Only this particular signature will be recognised by the programmed tool.

In a production well, the contents of the well will be a combination of oil and gas with the compressibility of the gas making it impossible to meaningfully signal using the above method. Additionally, where previously there was a closed chamber which could be pressured, a flowing well is open at one end and pumped pressure would merely inject the oil and gas back into the formation. Using the existing Sandface Valve Pressure Monitoring Unit (PMU) but with an alternative operating programme, we can signal to the valve by altering the flowing well characteristics twice within a specific time span. For example, if the SFV is programmed to sample pressures once every six hours for one hour only, the DA (Demand Activation) programme will compare readings (within a pressure tolerance) for similarity. If the well receives a choke change (e.g. from 1.0” to ½”) at 12:30 and back to normal 15 minutes later in the first period and senses and records the same pressure profile at the same time (within a time tolerance) in the second period, then this equates to the “activate” signal and the valve will be opened. It is completely unlikely that this unusual pressure profile would be repeated twice in succession let alone twice within the time tolerance required between the two readings.

As the downhole tool contains no pre programmed pressure profile, the tool is effectively programming itself on the first cycle and executing on the second – provided that the time criteria is met. This means that any pressure event is acceptable provided that it is exactly matched the second time. The well may therefore be signalled by a choke change, shutting the well in, pumping or injecting into the well, switching on or off an E.S.P. switching on or off a gas lift system and many others. The well may be a producer, an injector, a gas well or an oil well. Static wells are also considered appropriate for this technique.

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