Improving a Rugged Oil and Gas Well Logging Data Acquisition System with Virtual Instrumentation

Author(s):
Corin Chepko - Rocky Mountain Wireline Service Inc.

Industry:
Oil and Gas/ Refining/ Chemicals

Products:
PXI/CompactPCI, LabWindows/CVI

The Challenge:
Developing a rugged data acquisition system capable of withstanding the demanding environmental conditions for oil and gas well operation.

The Solution:
Using National Instruments LabWindows™/CVI software and PXI hardware to develop a highly reliable and flexible system resulting in reduced downtime and increased accuracy.

Rocky Mountain Wireline Service Inc. is an oil and gas perforating and logging company. After an oil or gas well is drilled, steel casing is lowered and cement is pumped in to create a seal between the casing and the surrounding rock formation. We then conduct a number of electronic surveys to log cement quality, gamma radiation, temperature, and depth.

The data acquisition system we traditionally use is rack-mounted in a wireline truck and must withstand the vibration and dust generated as the truck moves to different locations over rough roads. These demanding conditions cause problems with industrial PCs. For example, the RAM chips and A/D cards often vibrate out of position, even with retainer bars and clips holding them in place. Computer maintenance requirements and resulting truck downtimes presented a problem; we needed a new system that was reliable and easy to repair or replace in the case of failure.

The primary purpose of our data acquisition system is to record acoustic cement bond logs, which are used to determine the quality of the cement between the well casing and the surrounding rock formations. An acoustic bond tool emits a 22 kHz “tick” 20 times per second and measures the reflected arrivals of sound for 1,000 microseconds. The acoustic tool is stacked with a gamma ray tool, which emits a pulse when it detects a gamma ray, and a casing collar locater tool that adds a low-frequency component. The signal that comes up from the single conductor wireline is separated into two signals before it enters the A/D boards – one with the low-frequency component of about 10 Hz removed so that the analog trigger pulse remains on a flat baseline, and the other with the low frequency intact. A digital input from an optical encoder calculates the tool depth. When the acoustic tool ticks, a -5 V trigger pulse is sent up the line to indicate the arrival of the sonic signal. Upon detecting the acoustic trigger, the system scans the analog channels at 256 kHz each for just under 1/20^th of a second (11,800 samples), then transfers the data for processing and rearms the trigger to be ready for the next acoustic trigger.

We have used NI LabWindows/CVI software as our development platform since 1998, when we upgraded from an MS-DOS system to a Windows-based system. We decided to use National Instruments PXI hardware for our latest system upgrade because of its ruggedness and modularity. We plan on expanding the system’s capabilities in the future, so we chose the NI PXI-1050 chassis because it has eight PXI slots to accommodate our application as well as four SCXI slots for signal conditioning if we add more inputs, such as line tension. We wanted to improve our signal resolution over our current 12-bit card, so we chose a high-accuracy NI PXI-6281 A/D module with 18 bits of vertical resolution. The previous system used the 12-bit card to scan two channels simultaneously at 256 kHz per channel, resulting in a total scan rate of 512 kHz. This rate is just beyond the PXI-6281 multichannel scan rate of 500 kHz, so we use an NI PXI-6251 module for scanning the second channel and inputting the digital signal from an optical encoder. The new system uses an analog start trigger in the PXI-6281 and shares that trigger with the PXI-6251. This PXI combination offers significant improvement in durability and capability over our previous system, with plenty of room to expand for future upgrades.

LabWindows/CVI has made it much easier to create Windows applications since our 1998 development platform upgrade. It also facilitated the recent software upgrades to the PXI system, which took less than two weeks to finish. We encountered only one unexpected challenge for our acoustic bond logging program – the time it takes for the PXI-6281 to rearm the analog trigger. Initially, the system could only scan and rearm five times per second, well below the required rate of 20 times per second. Using a similar example from National Instruments LabVIEW software, we overcame this limitation by committing the task to the A/D module memory using the “DAQmxTaskControl” function – an easier and less time-consuming solution than converting the program to support continuous scanning. For less demanding applications, such as our casing collar logging program in which a single voltage needs to be measured versus depth, we can dramatically improve quality and speed due to the increased vertical resolution of the PXI-6281.

In the end, upgrading our software for the PXI system was quick and easy, and we can achieve significantly better logging performance with the superior NI PXI hardware. The upgrade to a PXI data acquisition system resulted in valuable time savings as well as plenty of room to upgrade our system’s functionality in the future. Using LabWindows/CVI made the software transition fast and easy. The new system reduces truck downtimes and computer maintenance, and technicians do not need to solve problems immediately in the oil field because modules can simply be replaced and fixed at a later time. With the increased accuracy of our hardware, we can deliver a higher-quality cement bond log to our customers and a quicker depth determination with our casing collar logging program. National Instruments software and hardware has resulted in faster application development and superior performance over other solutions.

For more information, contact:

Corin Chepko

Rocky Mountain Wireline Service Inc.

cchepko@gmail.com

(970) 985-9685

 

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