Enhanced definition of near-surface layers

Paul Boughton

Sean Ottewell looks at a new seismic survey technique which enhances palaeochannel mapping, oil sands and regolith characterisation.

Improvements to near-surface resolution and depth of exploration are continuous goals for exploration customers engaged in geological mapping and mineral exploration. Previously, customers were forced to choose a system which had been optimally tuned to achieve one of these goals while sacrificing some capability in the other.

Now CGG has launched MULTIPULSE, an innovative new near-surface and deep-penetrating electromagnetic (EM) survey technique which increases resolution and bandwidth.

The proprietary MULTIPULSE technology combines the benefits of the trusted CGG airborne time-domain EM products HELITEM, GEOTEM, MEGATEM and TEMPEST, by offering both a high-power pulse (half-sine wave) for depth of exploration, and a lower-power pulse (square wave) for near-surface resolution; both within one cycle, providing the value of two exploration techniques in one pass (Fig. 1).

MULTIPULSE technology can be applied on either CGG fixed-wing or helicopter time-domain systems, offering customers a cost-effective option for regional projects and a premium option providing maximum spatial resolution.

Exploration customers can expect to benefit from the enhanced definition of near-surface layers such as palaeochannel mapping, oil sands and regolith characterisation for engineering or agricultural applications as well as in mineral exploration for low-conductivity targets such as porphyry deposits, sedimentary exhalative deposits (SEDEX), volcanic-associated massive sulphide (VMS) and Mississippi valley type (MVT) deposits. In addition, better mapping of the weakly conductive alteration haloes around many deposit types can be obtained.

In other developments the company has successfully completed a second BroadSeis multi-client survey offshore Norway. The survey covers a 2300km2 area in the Barents Sea. Fast-track processing deliverables will be available by the end of 2013 and final processing products by August 2014.

This second BroadSeis 3D survey is located in the south eastern part of the Barents Sea adjacent to the recent eastward extension of Norwegian territory as a result of the border agreement between Norway and Russia. New data is required to assess the petroleum potential in this region.

The Barents Sea BroadSeis survey follows on from CGG's recent first BroadSeis multi-client survey offshore Norway which targeted the Halten Terrace. According to the company, the industry has shown strong interest in this new multi-client data and initial results just released show a significant improvement in the imaging of deeper targets.

Meanwhile, in Lebanon, the first shot has been acquired on Spectrum's multi-client land seismic survey. This initial line of acquisition is located in the Batroun region of the country, a symbolic gesture from caretaker energy minister Gebran Bassil who was born in the city of Batroun.

Spectrum holds a contract with the ministry of energy and water to acquire up to 500km of multi-client 2D land data. The first phase will carry on until the winter rain season. Phase two will commence early in 2014.

The survey covers an area which has never been seismically surveyed. The seven wells drilled in the region do show some hydrocarbon indicators in the Cretaceous or Jurassic sections and Spectrum says many analogues can be made with Syria's Palmyride Trough to the North.

The company has also announced mobilisation for the acquisition of an airborne gravity/magnetic/seep multi-client survey in the Barents Sea South East. The survey will cover the entire newly opened area with approximately 29,280km to be acquired.

The survey aircraft will also carry, on an experimental basis, the new GRAVEX high-sensitivity gravity sensing system that not only measures gravity but also gravity gradients. If successful, it will be the first time ever data from this instrument will be presented to the industry. Also the Seepfinder sensor, applied to detect oil-seeps from the sea floor into the water, will be introduced for the first time on the Norwegian continental shelf.

In another technological development, Wireless Seismic has made the first sale of its 3-channel RT System 2 seismic data acquisition system to a major oilfield service company. The system will be used on passive seismic monitoring projects, initially in the North American region.

The three-channel wireless remote unit (3D-WRU) operates without cables and with ultra-low power consumption, in the same manner as Wireless Seismic's 1-channel WRU. An extension to the company's proprietary 2.4 GHz radio technology has been developed that supports the transmission of seismic data from multiple channels housed within a single WRU and with geophones deployed at multiple depths. With the addition of the 3C-WRU, RT System 2 can be deployed with a mixture of 1C and/or 3C surface arrays and 3C near-surface buried arrays, at scale, all managed interactively from a single central control system.

Key factors in the selection of RT System 2 by the oilfield service company are its ease of deployment, efficient logistics, reduced HSE factors, and flexible geometries. Because no cables are involved, deploying the WRUs is faster, crew and transportation costs are reduced, productivity is increased, and the risk of injuries is lowered. Also, RT System 2 enables significantly more flexibility than cabled systems in deploying the complex recording arrays that are becoming popular in the passive monitoring market.

"This sale further confirms that RT System 2 is an ideal technology for passive monitoring projects," said Roy Kligfield, Wireless Seismic ceo. "We continue to add capabilities to RT System 2 to broaden its range of applications and to take advantage of its unique abilities to deliver real-time seismic data without the limitations of cables."

Field developments

WHL Energy is pushing ahead with exploration of its La Bella gas and condensate field in the Otway Basin, offshore Victoria, Australia, with the signing of a contract to acquire a key 3D seismic survey in mid-November.

AWE is funding 75 per cent of the cost of survey up to a cap of US$12 million (EUR8.8 million) to earn a 60 per cent stake in VIC/P67 while Tap Oil is paying 20 per cent of the survey cost up to US$2.95million (EUR2.2 million) for the option to acquire a 10 per cent equity interest.

Data from the 3D survey will assist with confirmation and definition of the La Bella gas and condensate resource and progress its development planning and commercialisation. It will also further define several exploration targets in the La Bella area that will be considered for drilling in early 2015.

La Bella is estimated to contain contingent resources of 114 petajoules of gas and 1.4 million barrels of condensate.

The field's commercialisation is expected to be quick given its proximity to gas pipeline and processing infrastructure and the growing Eastern Australian gas market.

In the USA TGS is to launch a new 3D multi-client onshore survey, Rush Creek, covering 161.5square miles in Roger Mills County, Oklahoma and Hemphill County, Texas, that will build on an existing 62 square miles 3D survey that it recently purchased. Once the volumes are merged, the Rush Creek survey will illuminate subsurface targets in the Granite Wash, Hogshooter, Cleveland Sands, Atoka and Tonkawa geological trends.

Acquisition has just begun, using a high channel count vibroseis crew. Data processing will be performed by TGS and final data will be available to clients in the second quarter of 2014.

Fasken Oil & Ranch selects SIGMA3 for fracture mapping

SIGMA3 Integrated Reservoir Solutions has been selected by Fasken Oil & Ranch to provide real-time microseismic fracture mapping, processing and interpretation for key assets in the Permian Basin.

"We have utilised several different companies to acquire microseismic surveys in both the Permian Basin and the Eagle Ford, but the company of choice for us is SIGMA3 due to the fact that they are able to acquire and process data from large-aperture, 40-level arrays," said Glenn Winters, chief geophysicist, Fasken Oil & Ranch. "This is more than twice the number of geophones as their competition, and in addition we believe their processing algorithms are the best in the industry."

"In unconventional reservoirs, it's all about designing and acquiring microseismic data that provides the highest level of confidence in real time and providing our clients with unprecedented insight to make critical business decisions," said Jorge Machnizh, SIGMA3 ceo. "We appreciate the opportunity to help the Fasken team enhance their ability to meet their production objectives and look forward to working with them on upcoming projects."

SIGMA3 offers technology, expertise and services ranging from reservoir understanding, field development planning to production optimisation. This integration of geoscience and engineering forms the foundation of SIGMA3 GeoEngineering solutions, including: earth modelling and imaging; seismic-driven reservoir characterisation and continuous fracture modelling (CFM); hydrofrac engineering design and microseismic fracture and field monitoring.

The company believes that smart use of fit-for-purpose technologies in a real-time dynamic modelling workflow gives E&P companies the power to implement the best solution and enhance production efforts, reduce drilling and completion costs, and drive profitability.

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