Frontier seismic work can require site-specific programs

The need to discover new hydrocarbon reserves is pushing frontier exploration into the world's more remote and challenging regions.

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Equipment adaptions tailor surveys for success 

Kelly Richard
WGP

The need to discover new hydrocarbon reserves is pushing frontier exploration into the world's more remote and challenging regions. Such frontier operations have seen WGP obtaining 2D seismic data offshore Greenland and Somaliland for TGS-Nopec, and more recently operating a Portable Modular Source System (PMSS) in the Arctic for ION, and undertaking a vessel conversion for 2D seismic acquisition on a lake in Africa for Surestream Petroleum.

New challenges were found in the company's recent venture with Surestream Petroleum, an independent, UK-based exploration and production company with interests in sub-Saharan Africa, and specifically on Lake Tanganyika in Burundi, the longest fresh water lake in the world and the second deepest after Lake Baikal in Russia. The operation involved conversion of theTanganyika Explorer fisheries vessel originally designed for environmental and pelagic zone studies into a 2D seismic vessel for data acquisition projects for Surestream, which has been awarded licenses for blocks B and D on the lake.

Deepwater lake seismic acquisition

Surestream contracted WGP in 2010 for a feasibility study in preparation for the project.

"Over the last 18 months, we have seen rejuvenation in interest in the lake systems associated with the Great Rift Valley in East Africa," said Mark Burnett, CEO of WPG. "Each lake will have its own specific physical conditions (water depth, level of infrastructure, constitution of the shoreline, etc.) coupled with often fickle and complex geo-political situations. As a consequence, and the Surestream project is a case in point, each lake acquisition project necessitates individual review and bespoke solutions developed to ensure the both the clients' requirements are fulfilled without compromising protection of the sensitive natural environments upon which indigenous populations are so reliant."

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Lake Tanganyika survey off Burundi survey area. Surestream Petroleum has blocks B and D.

Members of the company's operations team embarked on an investigatory visit to Lake Tanganyika to assess the conditions on the lake as well as to research local infrastructure and logistics. Procurement for the project began August 2011, and the vessel will be upgraded to meet all accepted marine and geophysical operating standards and requirements. The conversion includes vessel stability works and seismic outfitting, with the final objective of achieving a vessel capable of acquiring 2D reflection seismic with a 3,000-m (9,842-ft) streamer and 500 cu. in. source. First acquisition is projected for 2Q 2012.

The first challenge will be lifting the vessel out of the water for stability works. Fortunately, the Tanzanian government recently upgraded the slipway at Kigoma including upgrading the slip and lifting equipment. Modifications also have been made to the port facilities and surrounding access which will facilitate the conversion phase of the project.

Security

Burundi is trying to stabilize after decades of civil war and whilst there is a reduced security threat for work being carried out on the lake it needs to be assessed, continuously monitored, and response plans developed. Working with the client and having access to its experience dealing with security in the region, has resulted in a detailed security plan.

Baffin Bay challenge

In 2007, WGP was awarded a contract with TGS-Nopec to acquire 15,000 km (9,321 mi) of seismic offshore Greenland in Baffin Bay. The survey stretched from the east coast of Canada to the west coast of Greenland, the majority of its 692,000 sq km (267,183 sq mi) surface area deep within the Arctic Circle, prone to temperatures below -28°C (-18°F) and dense iceberg fields from the Arctic pack ice. The company vessel was the first commercial 2D seismic boat to attempt a survey campaign off Baffin Bay. This challenge also included the most northerly commercial marine seismic ever recorded at the time.

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Baffin Bay is prone to temperatures below -28o C (-18o F) and dense icebergs.

Ambitious survey targets were met with the help of adaptations to the source system to enable consistent performance in freezing conditions. Adaptations primarily focused on eliminating moisture from the high-pressure air fed to the seismic air guns and maintaining working deck temperatures to both reduce the freezing of air guns when exposed to sub-zero air temperatures and to minimize the personnel safety risk. With these modifications and highly trained crew, the operation overcame high seas, hazardous adverse weather, and erratic movement of icebergs. An average of more than 100 km (62 mi) of full fold data was acquired per day; over the course of two seasons 15,571 km (9,675 mi) was acquired without incident.

Mitigating HSSE risks in tough environments offshore Greenland proved to be an advantage in 2008 when the company and TGS performed a 2D project offshore Somaliland in the Gulf of Aden without a safety or security incident. The survey, although acquired away from the main areas of potential piracy, required a comprehensive risk review exercise and mitigation plan with the client and security contractor. The operational presence in the area necessitated coordination with the national coast guard and fisheries agency as well as additional security considerations.

An additional safety vessel equipped with fast response craft was engaged and security professionals worked with personnel from the Somaliland costal authorities. The vessel was mobilized to ensure the well-being of the crew, equipment, vessel, chase boat, and survey. WGP's seismic vessel was modified for the survey with upgraded door locks and creation of a "lock down" secure area.

The operation also warranted the presence of an onshore liaison officer who followed the survey along the cost and engaged with the local communities to explain the purpose of the survey and to mitigate potential disruption from fishing. The chase boat not only was used to intercept errant vessels but also to record and monitor water depths as existing charts for the Gulf of Aden were out dated and not reliable. This was an additional operational necessity as the client required a complete, as practicably possible, near shore full fold data set.

WGP successfully acquired 5,143 km (3,196 mi) of full fold data (99.5% of the pre-plot program), at an average of 85 km (53 mi) per day. The 2D seismic survey was successfully completed in four months, including the pre-preparation time for the security plan implementation, and resulted in sufficient data being acquired to allow exploration blocks to be licensed by the Somaliland Ministry of Water and Mineral Resources.

The company returned to colder waters in August 2011 to assist ION GeoVentures with a proprietary survey in the Russian sector of the Arctic. WGP provided the source array, recording office, and source workshop components of the Thalassa Energy Services-owned PMSS in addition to the technical crew for the seismic program.

The vessel used for the operation by ION was selected on its ice-class and research capability. As a non-seismic vessel, it was recognized early that a custom umbilical winch would be required. WGP's Engineering Department designed a solution and subsequently installed it under the supervision of the field crew. The PMSS's self-recording office and gun workshop were quick and efficient to install. The PMSS systems were originally were designed and constructed to target the permanent reservoir monitoring market. However, the flexibility of the equipment allowed it to be modified to produce a custom source solution for ION.

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