The COMBO tool is used to make high-resolution pressure and temperature measurements in producing wells, and also provides digital wireline telemetry/power supply functions. Power is transmitted from the surface panel at a high voltage and low current to minimize line losses, and the voltage is stepped down in the Combo tool by a factor of at least four times to supply the downhole sensors. Both the power-supply and the digital telemetry have been designed to operate on up to 35,000 feet of 7/32″ monocable and have seen success in ultra-deep offshore wells. The tool can also operate with conductor-slickline in situations of very high pressure producing wells.
It includes a Platinum-Resistance sensor probe that samples the temperature of fluids flowing past the tool and a unique Silicon-on-Sapphire strain-gauge pressure sensor, together with an electronics section that digitizes the sensor outputs with 22-bit digital accuracy. The super-high resolution of 0.001 degrees F. and 0.01 psi with a time response of only 0.1 seconds allows sensitive analysis of flow regimes in turbulent and cross-flow situations.
The tool also interrogates up to 11 other compatible tools stacked below the Combo at a rate of 16 times per second. Each tool is programmed internally with a unique digital address, which can be changed easily if necessary. This allows multiple sensors of the same type to be combined for special applications.
The graph below shows typical pressure measurement accuracy of the Combo Tool. The accuracy specification of our Dead-Weight tester is +/- 5 PSI. The accuracy is similar to the performance of Quartz gauges, but with greater ruggedness, lower cost, and no thermal lag effects. The tool has been successfully used in pressure-drawdown testing with results equal to or better than quartz gauges.