Enhancing the efficiency of downhole operations with DAS. By Stuart Large

After 18 months of extreme volatility, which has seen operators make cutbacks and halt capital investments, the oil and gas market has begun to show real signs of recovery. At the heart of this improvement was the commitment made by Opec members at the end of 2016 to cut production by 1.2 million barrels per day, while nonmember nations pledged to reduce their output by 558,000 barrels per day for the first six months of 2017.

This commitment has restored some confidence in the industry. Not only will the decisions, assuming they are strictly adhered to, decrease the market’s surplus inventory by 46 per cent, but more immediately prices also saw a welcome rise with Brent Crude experiencing its highest increase since July 2015.

Such measures and market predictions are clearly a positive sign for the industry. The recent rebound in oil prices should bring a welcome bout of stability to the market in 2017, giving operators a chance to review their processes and re-evaluate their production decisions.

That said, it is important to remain realistic. Prices are still nowhere near the $100+ mark that they reached during their peak. This continues to put pressure on operators. As such a major focus will be on optimising production performance, operational efficiency and completing downhole operations as efficiently and cost-effectively as possible. Therefore, investment into the latest technologies is going to be crucial for operators to remain profitable amid production cuts.

A key area for investment should be the adoption and deployment of the latest sensing technologies to monitor production activities, as well as inform and accelerate decision-making. One of major technologies that can offer this detailed, sophisticated insight is Distributed Acoustic Sensing (DAS).

DAS works by converting a single fibre optic cable, which runs either just outside the casing or inside the production tubing of the well, into the equivalent of thousands of highly sensitive individual vibrational sensors. The DAS interrogator unit uses a laser to send thousands of pulses of light every second into the optical fibre. A small amount of that light returns to the DAS unit through the process of Rayleigh backscatter, which the interrogator continually monitors. When sound and vibrations, caused by production activity or a leak, for example, disturb the fibre, the characteristics of that backscatter are changed. The DAS unit analyses the changes in backscatter to identify and locate the disturbance. This enables operators to ‘visualise’, locate and record what is happening downhole at every point of the well in real-time, adding a new layer of intelligence to the monitoring process.

DAS can not only be deployed on new wells, but also deployed in existing wells through various intervention methods such as Wireline, Slickline, Carbon Rod or Coiled Tubing. This means that it can enhance a number of downhole procedures, including well integrity, sand detection, production profiling and borehole seismic surveys:

Well integrity:
Since 2009, it has been estimated that poor well integrity has cost operators around the world more than $75 billion. Technologies such as DAS provide operators with a crucial monitoring tool that can support with all aspects of well management – from identifying potential integrity incidents at the earliest possible stage, to assisting with decommissioning. Crucially, DAS enhances traditional point sensors by providing coverage of the entire well simultaneously, rather than compelling operators to take multiple readings. That said, by having the fibre permanently installed, operators can benefit from a wealth of in-depth data captured through long-term monitoring.

Sand production:
Sand production is an extremely expensive problem for operators and has the potential to jeopardise the entire well if extreme sand makes it unserviceable. DAS can detect the moment a well starts to produce sand and pinpoint its exact location, enabling operators to manage the well and immediately lower the flow rate. By having a fibre permanently installed in the well, operators can benefit from a complete feedback loop. This enables them to optimise the flow rate as necessary to maintain optimum production levels, while mitigating against excess sand production.

Production & Injection profiling:
With a renewed focus on efficiency amongst operators, DAS’ ability to enhance recovery techniques is particularly important. For example, by identifying the different fluid phases that are present and their flow rates, operators can isolate water production to enhance the recovery of oil and gas. Whether it’s gas, water or polymers being injected to increase production, operators can monitor the effects in realtime and adapt their method if necessary.

Borehole seismic:
There are a number of instances where operators may want to run regular seismic operations to review how well a reservoir is producing. However, this is an extremely costly operation to run with traditional geophones as operators need to stop production for a period of time to conduct the survey. DAS can significantly improve the efficiency of reservoir management as the permanently-installed fibre allows operators to run surveys while the well is still producing and acquire seismic data across the entire wellbore with the minimum of vibroseis sweeps.

The key challenge for operators trying to improve efficiency is acquiring the right data and overcoming this relies on gaining immediate intelligence. DAS’ ability to deliver real-time monitoring and post-operation analysis means that it is a powerful well surveillance tool for operators. By having a fibre permanently installed in the well, DAS can act as a multi-tasking instrument to help enhance production efficiency and rapidly diagnose operational issues. That said, existing intervention techniques continue to evolve and therefore wells that do not have a permanent fibre can still benefit from DAS’ capabilities.

Although market conditions seem to be improving, it is still early days and things could change significantly at any point. With production cuts also coming into effect from January 2017, it is therefore paramount that operators invest in the most innovative tools available to them to maximise production levels and ensure the long-term profitability of their assets.

Fotech Solutions
Stuart LargeStuart Large is Sales & Product Line Director at Fotech Solutions. Established in 2008, Fotech Solutions specialises in the development and delivery of Distributed Acoustic Sensing or DAS based solutions. Operating primarily in Oil & Gas and pipeline sectors, Fotech has developed the Helios system, which converts an optical fibre up to 40km long into a solution that is equivalent to tens of thousands of individual vibration sensors.

For further information please visit: fotech.com