What’s new in exploration

 Vol. 233 No. 9

Frontier basins require broad-brush exploration tools: regional seismic, gravity and magnetic surveys. Gravity measurements provide a direct estimate of mass and can distinguish density anomalies in the subsurface. Gravity gradiometry is used to measure subsurface density by measuring variations in acceleration.

In 2009, researchers at Lockheed Martin and Intrepid Geophysics estimated that 2.5 million line-km of gravity surveys have been run worldwide for hydrocarbon and mineral exploration. Recent gravity (and seismic) programs in the Greenland Sea are in preparation for two upcoming licensing rounds.

Gravity tensors. Scalars are described by individual numbers, vectors by 2D arrays and tensors by multidimensional arrays. Tensors provide a mathematical framework to represent correspondences between sets of geometrical vectors. Full-gravity tensors have six components: G_xx, G_xy, G_xz, G_yy, G_yz and G_zz. Multiple tensor components are used in density inversions to help determine the presence and orientation of geological anomalies. For instance, full-tensor gravity gradiometry (FTG) has been used with seismic in the Gulf of Mexico to image the base of salt.

FTG. Cambridge, England-based ARKeX recently completed an airborne FTG survey covering 50,000 sq km off northeastern Greenland, the largest single offshore FTG survey ever performed. According to ARKeX developer Gary Barnes, typical bandwidths in FTG data range up to 0.4 Hz, equivalent to 75-m half-wavelengths at airborne survey speeds. In other words, FTG has a much higher bandwidth and delivers a higher-resolution image than conventional gravity surveys.

Ion Geophysical is jointly interpreting the new gravity data with its 2D Northeast GreenlandSPAN seismic program, expected to be completed in September. Joe Gagliardi, Ion’s director of Arctic solutions and technology, said that linking the regional 2D seismic data with full-tensor gravity gradiometry data allows oil and gas companies to “bypass… the recon 3D phase to focus directly onto their prospects of interest.”

TGS-NOPEC Geophysical completed its seventh airborne gravity survey over Greenland in 2011, collecting 42,000 km of data. TGS has accumulated more than 311,000 km of airborne data, predominantly off western Greenland. TGS is also expanding its 2D seismic coverage in northeastern Greenland, currently shooting the NEG12 survey with the M/V Akademik Shatskiy supported by the icebreaker M/V Viking Balder.

GRACE geodesy. Measurement and study of the Earth’s gravitational field is known as geodesy. The GRACE project (gravity recovery and climate experiment) is based on twin satellites launched in March 2002, making detailed measurements of Earth’s gravity field over time. The satellites should remain in orbit until 2016.

Scientists at University of Texas at Austin and University of Colorado at Boulder used monthly GRACE gravity fields from 2002-2006 to estimate linear trends of ice mass redistribution in Greenland. UT-Austin researchers calculated that Greenland lost 57 cu mi of ice annually from 2002 to 2005. CU-Boulder researchers calculated that Greenland lost roughly 164 cu mi of ice from April 2004 to April 2006.

Greenland’s potential. In August 2007, the U.S. Geological Survey released its estimate for undiscovered oil and gas resources in the East Greenland Rift Basins Province: 31.4-billion-boe potential.

Greenland’s Bureau of Minerals and Petroleum (BMP) announced the North East Greenland licensing rounds on Dec. 1, 2011. The total area on offer covers 49,948 sq km, divided into 19 blocks. Two successive rounds are planned.

The Kanumas project is a regional seismic program that began in 1989 and acquired 6,839 km of seismic in northeastern Greenland (1991-95), and 4,071 km in northwestern Greenland (1992). Members of the Kanumas Group include Exxon Mobil, Statoil, BP, Japan National Oil, Chevron and Shell. Publicly owned Nuna-oil A/S is a carried partner and operator.

The deadline to submit bid applications for exploration and exploitation licenses in the pre-round is Dec. 15, 2012. The ordinary round will open on June 15, 2013, with prequalification applications due by July 1 and license bids due by Oct. 15, 2013.

International interest. Shell Chief Executive Peter Voser said earlier this year that the company’s Arctic interests are in Greenland, as well as Alaska. Edinburgh-based Cairn Energy is the largest acreage holder and most active operator off Greenland, with 11 blocks in four basins (combined area 102,000 sq km). Cairn acquired 85,000 km of 2D seismic in 2011 and completed two 3D surveys. The company drilled three wells in 2010 and five wells in 2011, with two basins yet to be tested. Cairn will partner with Statoil for a future test.

The most recent licenses were awarded in December 2010, in northwestern Greenland’s Baffin Bay area. ConocoPhillips and Dong Energy hold the Qamut Block. Shell, Statoil and GDF Suez work the Anu and Napu Blocks. Maersk Oil holds the license for the Tooq Block. Cairn received licenses for the Pitu, Napariaq and Ingoraq Blocks, through its subsidiary, Capricorn Energy.

DNV’s Allu Block. In 2011, ten graduate students in DNV’s summer program focused on developing a comprehensive concept for drilling in the “complex, rough and challenging” conditions around the northeastern coast of Greenland. Their concept, named “Allu,” from the Greenlandic words for “hole in the ice,” is a plan for year-round exploration and drilling. They predicted that working in the Arctic off Greenland could be up to four times as expensive as drilling in the North Sea, although the cost differential could be reduced through economies of scale and innovative technology.