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Unconventional wisdom

Published:  06 April, 2016

The oil and gas industry is renowned for pushing sealing technology to its limits while chasing deeper and previously uneconomic wells with increasingly arduous conditions. As conventional wells are depleted, unconventional wells are becoming financially viable, meaning seals must cope with higher temperatures and pressures previously unimaginable, leading to new challenges and opportunities. ODEE reports.

Conventional wells, where oil and gas stored in pores can flow freely along permeable fractures through the rock, such as sandstone or carbonates, are largely already accessed and many are being depleted. Conversely, unconventional wells exploit deeper and higher pressure reservoirs or low-permeability sources and fine grained, organic-rich sediments, such as shale or coal deposits. Though these rocks are frequently as porous as conventional deposits, very small pore sizes and low permeability make extraction difficult. New techniques within directional drilling and hydraulic fracturing, originally designed for shale production, but now utilised to enhance conventional recovery rates, have led to an upward trend in production, particularly in the U.S. with regards to shale gas and tight oil formations.

“Conventional” and “unconventional” however are not fixed definitions, and can be categorised in different ways with no universally accepted definition. Part of the difficulty of defining what is conventional and what isn’t, is that current reserves are estimated using what is accessible through present technology. Traditional oil reserves are nearly all well established and are more easily "mapped" to discover their full potential. Today's challenge is to maximise the recovery of these reservoirs and reduce overall costs. Unconventional deposits, such as those in shale, are notoriously difficult to measure accurately and lack the historical data to give geologists a high degree of reliability in estimations. Additionally, concerns over how easily the rock can have its permeability increased to allow extraction become as important as quantity.

As time and technology advance, previously uneconomic deposits become financially feasible, and what today is thought of as “conventional” was once thought of as being impossible to extract. Changes in the production and extraction techniques though, lead to changes in the operating conditions for seals.

“As an example of the kind of changes the industry is undergoing, temperatures for downhole tools a few years ago were between -20 °C to +120 °C/-4 °F to +248 °F with pressures of 69 MPa/10,000 psi. Now temperatures can be anything up to +200 °C/+392 °F with the pressures doubled or tripled to 207 MPa/20,000 or 30,000 psi,” says Eric Bucci, Segment Manager Oil & Gas Americas for Trelleborg Sealing Solutions. He continues: “As you can imagine, this has made a significant difference to the seals needing to be specified. We’ve been leading developments of new designs and materials that can cope with and provide additional concrete benefits to operators working in these kinds of challenging environments.”

Though more costly, extraction from unconventional wells is trending upwards and is significantly increasing oil production globally, potentially becoming the norm rather than the exception. The correct sealing systems are paramount to effective recovery, increasing efficiency and safety, and enabling companies to reduce production costs while increasing output.

James Simpson, senior account manager for Trelleborg Sealing Solutions, explains: “The seals within valves and downhole tools are absolutely critical to effective operations, especially for directional drilling, where motorised tools are employed. They are the primary barrier to system fluid loss and ingress of contaminants. This isn’t just about performance – hydrocarbon leakage is a major concern for environmental and worker safety.”

Bucci concludes: “Moving with the industry and keeping abreast of upcoming trends is a core principle of our developments, not only with operating conditions, but with approvals such as NORSOK M-710 and the latest fluids being employed in the field. The kind of revolution that we’re witnessing within the industry is redefining the way both we and operators think about our approaches.”

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