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ViaLogy – making use of seismic noise

Monday, July 19, 2010 in Feature Articles

US company ViaLogy is developing new seismic data processing techniques – which actually use the noise to try to get a better understanding of the signal, leading to better decision making - rather than just try to strip the noise out

ViaLogy, a US company listed on the UK’s Alternative Investment Market (AIM), is developing new technologies to exploit noise in geophysical datasets to de-risk prospects and help find more oil and gas.

It is also developing techniques to analyse subsurface fluids by how they attenuate seismic waves, and get better predictions of rock porosity.

To date, ViaLogy's QuantumRD technology has been deployed to characterize porosity in complex onshore stratigraphic formations that exhibit fracture and structural changes below seismic acquisition resolution.

The system is being used to get a better understanding of the subtleties of geological variations within proven resource basins such as the Permian, Haynesville and Bakken in the US.

The technology is being used to detect productive depositional geologies, map their fluid distribution and porosity using 3-D and multi-component seismic.

In February this year, ViaLogy said that its technology helped to successfully identify a good place to drill a 170 bopd well in the Strawn Field of the central Texas Permian basin – a region where 18 wells had been drilled previously, 15 of which turned out to be dry.

The company was funded by a UK investment trust in 2001, this NASA’s Jet Propulsion Laboratories, operated by California Institute of Technology spin-off focused on commercializing technologies originally developed for use in defense and space. In Summer 2008, the company launched new services to the energy industry.

Separating noise and signal

The core technology, tradenamed QuantumRD, uses “Quantum Resonance Interferometry (QRI)” to detects “weak signals” as a disturbance to noise, not the other way around, as it is usually done.

Unlike conventional signal processing, QRI does not filter out coherent and incoherent information, and low and high frequency noise.

Instead it analyzes noise variations to assess how the noise distribution across a target formation has been impacted by variations in rock matrix and lithology.

The variations in noise are extremely subtle and often order of magnitude below the noise amplitude itself, and well below the signal amplitudes used by conventional processing.

QRI uses a “noise-injection” protocol, or a nonlinear mechanism of adding synthetically designed noise to further amplify these subtle changes.

The process can be customized to accommodate drilling criteria and risk-reduction attributes of interest to the drilling operator.

The company claims that the technology is 10-100 times more effective at detecting signals in noisy environments than standard passive signal processing techniques.

Another technique is to examine the noise itself to try to find more of the signal. With weak signal processing, the signal can be as little as a tenth or a hundredth of the noise, he says. But then you reach a point where the signal causes changes to the noise.

The company spent many years developing algorithms to pick out weak signals, focusing initially on genomics, drug discovery, mass spectrometry, security and surveillance applictions.

In particular the company looks at low frequency noise (3-10 Hz) and high (80-200 Hz).

Dr. Sandeep Gulati, Chief Technical Officer, believes that in seismic processing, a lot of the useful information information is often removed from the signal in the efforts to reduce noise.

While this simplifies structural interpretation, this process removes subtle features that could be strongly correlated to porosity, lithology and fluid distribution attributes, thereby limiting the use of seismic information.

Other technologies

The company is also developing technologies to work out what fluids you have in the reservoir by looking at how much the material absorbs different frequencies of wave.

In a study conducted by the company, they showed that based on well control the difference in how much energy is absorbed can be as little as a 0.01 per cent, between hydrocarbon bearing rocks and non-hydrocarbon bearing rocks, whole the noise could be 3%-4%.

A further focus is trying to get better predictions of porosity is the deconstruction of large 3D seismic volumes into volume cells or “voxels” which can be processed individually for reservoir properties.

Based on geological understanding of prospects of interest, the company decomposes seismic time/depth reflection amplitude volumes or raw gather blocks into discrete “voxels”.

These can be very small in areal extent and depth – for example 20"X20"X6 feet or 20"X20"X 1ms.

In fields where porosity is 6 per cent at best or changes rapidly, being able to calculate porosity down to 1-2 per cent resolution is essential.

For each voxel, ViaLogy uses the seismic reflection spectrum to predict porosity and porosity changes away from the well-bore.

It re-uses the same seismic spectrum differently to detect variations in lithology and sense for fluid presence. The resulting porosity, lithology and fluid attributes are combined to develop net-pay distribution for stratigraphic reservoir mapping, spawning out “sweet spots” or drilling targets.

Strawn Prospect

ViaLogy successfully used its technology to develop a limestone Strawn field in Andrews County, Texas.

The company was tasked to find "sweet spots" in the strawn stratigraphic platform with more than 4% porosity and natural fracturing that matched a productive geological deposition.

The company pinpointed a location for multiple wells. The first drilled well had shows in multiple clastic and carbonate zones, and the Strawn zone yielded an initial production of 170 barrels of oil per day, Dr. Gulati said.

Prospect acreage assigned to ViaLogy has 18 wells on it – of which only 3 are Strawn producers. The 3 producers were all drilled in the 1960s – the next 15 were drilled more recently using conventional seismic technology and turned out to be unproductive in the Strawn.

Before agreeing to drill using ViaLogy’s analysis, the client asked ViaLogy to show that they had a technique which would have shown that the 3 successful wells would be successful and the 15 dry wells would be dry.

However with a well in the right place “you can produce for 30-40 years,” he said.

ViaLogy's test area included 15 miles of 3D seismic shot in 2002 by CGG Veritas. Since then it has been reprocessed by a number of different companies and leading geophysics research groups. “So it has gone through a fairly rigorous analysis,” he said.

The reservoir is 11,000 feet deep and porosity of between 1 and 5 per cent – with about 90 per cent of the reservoir having porosity of under 3 per cent.

“The client said, ‘if you find regions of porosity of more than 4 per cent then I’ll drill’”, Mr Gulati said. But the company did analysis of the existing wells and “we found that’s not enough,” he said.

Porosity prediction is at the heart of discriminating potentially productive carbonate bodies.

Unlike structural faulted traps (e.g., conventional normal/reverse faulted sandstone reservoirs), Strawn platform is a stratigraphic formation with enigmatic discontinuities over small areas.

Because of the broad-spectrum of diagenesis (chemical, physical, or biological change undergone by a sediment its initial deposition) that affects carbonate rocks, the final porosity in these carbonates may or may not be related to the depositional environment.

Basin geology models provide limited insight to positioning of individual wells and offsets, as formation properties change unpredictably.

Also, unlike other lithologies, the original primary porosity in carbonates may be totally destroyed during diagenesis and significant new secondary porosity may be created. So to get a successful well, it was important to find a certain pattern of natural fracturing and high continuous porosities from 3D seismic.

The company is currently deploying its technologies to develop Wolfcamp, Strawn, Devonian, Ellenburger and other stratigraphic formations.

In addition to de-risking new drilling locations, ViaLogy is working in developing a systematic, automated approach to redeveloping under-performing or abandoned wells that could be sitting near porosity pockets within resource horizons or near-pay zones that may have just been missed.

Associated Companies
» Vialogy

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