- Permanent & Temporary SRO Downhole Gauges
Surface readout or SRO is a generic term for sending downhole data to the surface via electric line. There are three important aspects to a SRO setup: Your surface connection, the type of SRO cable and the downhole tool. The same thing applies for a permanent installation or a temporary setup.
Using the Hawk with the Gopher SRO option an operator can communicate downhole with our regular downhole tools equipped with a SRO transmitter or optionally our permanent downhole tools can be used.
Intrinsically Safe Connection
In a short term testing situation it usually necessary for the cable to go through a lubricator. This area is a Div1 Class 1 Hazardous location so CalScan has made the Gopher SRO output on the Hawk CSA/UL certified intrinsic safe. If the cable parts, there is not enough energy to cause a spark and therefore a explosion. This is ideal for testing, as the operator does not have to change is procedures at all to ensure safety and an explosion proof solution would be very difficult to install or even manufacture.
The Hawk supplies power as well as the logging functions for the downhole tool. Unfortunately the internal battery on the Hawk is not enough energy to supply all the power. If you have a local source of power, standard 24 volt instrument power supplied through a IS safety barrier can be used for permanent installations. For installations without a power source CalScan has developed the Corvus Solar Battery.
The Corvus is a Class1 Div1 Solar Battery has at least a 10 day reserve with our Wolverine quartz tool at a 10 second sample rate and with the Badger/Mole at 1 second sample rate. With these rates it can keep the battery fully charged at -40°C with only one hour of sunlight a day. The Corvus is so compact it can be mounted directly on the wellhead, perfect for temporary well tests. On a permanent install since its all in one all the operator has to do is plug it in. There is very little install expense. If a short range wireless link is needed, the 10 km line of sight radio is a cost effective option too.
There are basically two types of cables, braided electric line or E-Line and encapsulated tubing or Slick E-line. Slick E-Line is more often used for permanent applications as braided line has a higher tendency to leak as it is difficult to seal braided line for long term.
Surface Feed Through
On the surface for a short term job an operator will typically use a standard lubricator to allow the SRO cable to be feed into the well.
Maximum Cable Length
Calscan SRO solution can work with over 275 ohms of total line resistance, so even the difficult to use, high impedance electric lines will work. By total line resistance the center conductor resistance as well as the outside armor/wire ground return. The total capacitance and inductance of the wire is a small factor mainly for intrinsically reasons. Total capacitance must not be over 2uF and 1mH well above any reasonable cable value.
The Hawks Gopher cards onboard 60Hz AC rejection allows the gauge to run near electric power lines down the well. This is handy when downhole electric pumps or other submersible equipment is running downhole.
Downhole Tool Selection
Our permanent downhole gauge uses slick e-line for a more durable long term seal
All our standard downhole tools are capable of SRO readout. A SRO transmitter and typically a GO cable head adapter is all that is needed for the tool to have SRO output. This is very convient when a short test is being done using braided cable such as a drop spool application or on an E-Line truck.
When a permanent gauge is needed CalScan manufactures a 3/4" and 1.25"version designed for sealing with slick e-line. Slick E-Line is a 1/8" or 1/4" tubing with a single encapsulated conductor running down the middle of it. The big advantage is there are three seals in this version, greatly reducing the change of a catastrophic leak.