Prad Thiruvenkatanathan reveals how distributed acoustic sensing technology could revolutionise oil exploration and production

The oil & gas sector has always been invested in boosting efficiency – but the stakes are higher now. Pressures exerted on oil prices by the ongoing pandemic have driven a new wave of innovation in the search to limit expenditure.

We can already see a push by many leading companies to reduce capital expenditure on production, with an increased focus on using technology to ensure assets are producing as efficiently and sustainably as possible. Still, the crux of their challenge is this: how can these companies ensure a consistent pipeline of production while establishing new, productive assets?

Drilling new wells can be expensive – costing as much as several hundred million dollars in deep-water and can take years to come online. Crucially, it’s a venture that offers no guarantees – wells can be less productive than anticipated, or beset by issues such as sand ingress, poor inflow performance or water.

So how can the industry end this cycle of speculative investment? How can operators gain more certainty on the placement of new wells within their fields? The answer can be found in downhole distributed fibre optic sensing and the real-time well and reservoir surveillance insights derived from the data it generates.

How do fibre optic cables work with oil wells?

Fibre optic cables are nothing new, even in oil & gas. They’ve been used globally by the industry for decades, both for telecoms and to deliver information about the state of wells, for example by monitoring gas ingress through distributed temperature sensing.

Fibre optic cabling installed in wells can also be used for distributed acoustic sensing (DAS). DAS records the sound made by water, oil, gas and sand movement, and the sound of the well itself, within the subsurface. Each of these subterranean events has a distinctive acoustic signature, the raw data of which is picked up by sensors along each fibre optic cable.

The next step is to analyse the vast quantity of data generated. This is where the real challenge lies, as the greatest advantage of fibre – the terabytes upon terabytes of data it generates – is also what has held its industry-wide uptake back. Fibre optic cables produce more data than most operators can ever effectively analyse, let alone analyse quickly enough to inform timely operational decisions.

This is why, to extract a high-resolution, dynamic view of the subsurface that operators can use to inform their operational decisions, we must remove all unnecessary data from the equation and then apply cutting-edge machine learning algorithms – supplemented by physics and industry expertise – to the critical data that remains.

By matching the raw data collected at the well site to an extensive library of acoustic ‘fingerprints’ via cloud computing, critical information on the zonal productivity of the rock and the flow of oil, water and gas through it can be delivered as it happens.

What does this mean for oil well placement?

Having visibility of the production profile and the ability to ascertain changes in flow behaviour provides a massive advantage. It gives far better clarity around which zones are the most productive and which zones are prone to issues such as sand or even gas/water production. This enables cross-well learning helping make more informed decisions around which zones to drill. The fibres can also be used for borehole seismic profiling, giving further visibility of the rock strata in the vicinity of the well – all with a cable of tiny fibres only a human hair in width. These insights can result in savings of millions of dollars through improved production performance and decreased exploration time.

Using the current methods – typically interventions to run logs – it can take multiple days and millions of dollars for an operator to confirm what’s in the well and how productive it might be. And, since the technology now exists to circumvent this previous lack of information, those multiple days and millions of dollars are simply wasted time and money.

The insights delivered through analysis of data collected from fibre optic cables allows operators to monitor well health and deliver instantaneous diagnoses if issues occur, and as they occur. Instead of relying on lengthy, costly interventions to investigate a drop in production, the problem can be spotted even before it emerges. This circumvents the need for a halt, and therefore a deferral, in production.

Likewise, these insights show an engineer exactly how much water, oil, gas or sand is entering each zone of the well, when this happens, and how the dynamics of the wells change through time. This gives engineers all the information they need to optimise the well with its particular production risks front of mind, meaning that they can tailor how the well is operated down to the minute.

Take the prevention of erosion caused by sand ingress as an example. By matching acoustic data collected along the full length of a fibre optic cable with a library of acoustic ‘fingerprints’, it is now possible for an operator to recognise exactly which zone sand is coming from, how much is coming and when. This allows the engineer to optimise drawdown pressures to manage sand related risks during well ramp, patch issues accurately the first time, and ensure operations are run safely and efficiently.

The oil & gas sector has sometimes been reticent to embrace new technologies, but firms no longer have a choice. The industry must embrace innovation and improve the efficiency and sustainability of production. Supporting the industry transition and maximising opportunities available enhances energy efficiency and allows for responsible management of energy assets for the future.