PDO "ejects" smoky flares for a cleaner future

Petroleum Development Oman (PDO) is one of the first companies to apply a technology normally found at an oil refinery to the oil field, where it will be used eliminate smoky flares and reduce overall gaseous emissions. The technology, known as an ejector, allows the gas that emanates from crude oil in surge tanks to be recovered.

Ejectors work by using the flow of a high-pressure gas to suck low-pressure gas into a chamber. In PDO's application of the technology, the high-pressure gas is the natural gas that is often injected into oil wells to lighten the well liquids so that they can rise to the surface. This high-pressure "lift gas" is directed through the ejector unit, where it reaches supersonic speeds. The increase in flow velocity lowers the pressure in an attached suction chamber that then draws the gas from the surge tank into the production station's gas system.

Smoky flares are more than just an eyesore. Their black smoke - the result of incomplete combustion - is emitted with large amounts of gases that contribute to global warming and acid rain. With the introduction of the ejector technology, PDO thus contributes to the conservation of the environment: gas recovered from the surge tanks can be used rather than burned whilst gaseous pollutants are eliminated. Whatever little gas remains to be flared (for reasons of safety) can be done so completely and therefore smokelessly.

Senior Project Engineer Ali al Wardy has been overseeing the project to install ejectors at the production stations at Yibal. "Ejectors are simple in theory, because they have no moving parts", he says. But their main attraction is their cost-efficiency. As al Wardy further explains: "Ejectors pay for themselves within a year with the gas they recover. They cost $1 million to install, but you recover half a million dollars' worth of gas in 12 months! Had we refurbished the production station and installed new flare stacks to burn the gas, the cost would have been in the region of $3.6 million."

The actual installation of the ejectors at Yibal, however, was not a simple matter. Construction supervisor Hamed al Siyabi, who was responsible for the installation, said: "The tie-in involved working on 20- and 24-inch pipes, and the anticipated shutdown for the tie-ins was 22 hours. However, the careful planning and excellent team work of PDO with contractors Galfar, ATI and Arabian Industries enabled the actual shutdown time to be reduced to 13 hours. This was an achievement by itself!"

The application of ejectors is now also being considered for other PDO production stations in view of the company's commitment to completely eliminate the flaring of gas by 2008.

Another World first for PDO: Taking the temperature of a producing well along its entire length

Petroleum Development Oman (PDO) is testing a distributed temperature sensor (DTS) system for measuring the temperature of a well, metre by metre, along the well's entire length in order to gauge its "health" as well as that of the oil reservoir. This application of the DTS system - at a well in Marmul, south Oman - is the world first in a horizontal injector.

The DTS system works by detecting subtle changes to pulses of laser light that travel down and back up an optical fibre in the well. Changes in the nature of the returning light pulses provide an accurate measurement of the temperature at one-metre intervals along the well. From such temperature readings it is possible to determine precisely where the temperature unexpectedly changes along the wellbore. These changes can mark the presence of fractures, faults and can confirm into which zones the injected water is flowing. Because it continuously and accurately measures the temperature along the wellbore in real time, the DTS system could provide information that would enable the productivity of some wells to be increased by 10-20%.

"The main advantage of the DTS system is that it works in real time," says PDO Technology Manager Joe Straccia. "Although we have been able to take temperature readings along the wellbore before, we had only been able to do this by logging the well. And that meant shutting off the well, thereby foregoing valuable oil production. The readings we obtained were also not as accurate as those from DTS system."

"The real-time DTS data will enable us to make intelligent decisions about what to do to optimise a well's performance," says Production Technologist Ahmed al Kharusi. "The fact that PDO has hundreds of wells in which the DTS technology can be applied makes this an exciting development. It remains our aim to get proven technology into the ground, where it can add value to the business. So far, the signs are very good indeed that DTS system will prove its worth."