Tight times

Seismic field work being carried out by Saudi Aramco.
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With trillions of cubic feet of gas tied up in low permeability reservoirs, tight gas production has become the hot topic. Schlumberger’s Lee Ramsey talks to ArabianOilandGas.com.

Around the world there are trillions of cubic feet of gas that could be used to supplement the world’s energy supplies. However, much of this abundant resource is difficult to produce because the gas is held in tight reservoirs where the permeability of the reservoir rocks is extremely low.

Producing tight gas is challenging, yet considering the quantities available and the long-term producability of this resource, such non-conventional gas is now being regarded as a significant energy resource for the future. Tight gas could help to address the predicted deficit between energy supplies and demand in the coming decades.

To understand the economic viability of the complex, unconventional gas developments of tomorrow, Middle East operators must focus on new solutions today.

A concerted technological effort to better understand tight gas resource characteristics and to develop solid engineering approaches is necessary to deliver significant production increases.

Schlumberger has risen to the challenge, and through real collaborative efforts with Saudi Aramco and its international oil company partnerships, its Tight Gas Center of Excellence
in Dhahran, is delivering bona fide leaps in reservoir understanding.

Lee Ramsey, manager of the Tight Gas Center of Excellence (TGCoE), tells Oil & Gas Middle East that the exciting developments are important steps to a real game changing approach to the tight gas conundrum.

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The permeability of rock formations is essentially what governs how easily gas held within will flow. High permeability carbonate formations have higher porosity and often have natural fractures through which gas will easily flow, and are typically prolific producers without the need for technically sophisticated approaches.

“In the Middle East people are accustomed to working with carbonates which have a very high permeability that will produce naturally or, if the wellbore is damaged, a matrix stimulation with a little bit of acid,” explains Ramsey.

“However, tight gas fields (today Schlumberger has a working definition of 0.1 millidarcy and below as tight gas), will usually not flow with a simple perforation. It requires a much deeper understanding of the reservoir and accurately tailored solutions that fit, as well as specialist treatment fluids and techniques,” he adds.

“What we are advocating is that the decision of whether to use a well for production should not be made exclusively on initial flow appraisals. With improved understanding of the reservoir characterisation, better informed decisions could be made.”

Indeed, obtaining commercial flow rates is a crucial factor when drilling and completing tight gas wells. In the Middle East, tight gas wells are typically deeper and hotter than other gas wells, making them more expensive to complete.

“On the surface of things it would seem simple to transfer the technology and knowledge from experiences in North America. However, because we can be working at depths of 18 000ft – 20 000ft and temperatures approaching 350 degrees Farenheit in Saudi Arabia, the wells in North America do not share the same high temperature and high pressure characteristics, as they are typically between 6000ft and 12 000ft so we find that the toolbox is
much smaller.”

This hostile environment becomes additionally challenging when the highly specialist equipment needed is rarely the sort that sits in inventory. “These pieces of kit tend to have long lead times; a good example would be 15K packers, sliding sleeves, upper and lower downhole completion equipment, which are essentially made to order,” says Ramsey.

An additional benefit which has come from the concentrated learning environment is that the research is highlighting crucial gaps in the technology – and the feedback from Dhahran to research centres throughout the Schlumberger regional and global network is helping to address these. To add to the already significant challenges, the fields in question are often remote from existing facilities and operating bases.