Satellite-derived gravity data for efficient hydrocarbon exploration

Summary of the Impact

Research carried out at the University of Leeds has been used to develop data sets that are now routinely used in offshore oil exploration to identify prospective areas faster, and with reduced cost. New techniques applied to satellite altimeter data have been used to compute gravity anomalies in marine areas with increased accuracy and reliability relative to earlier products. These anomalies have been developed during the REF period in association with a University of Leeds spin-out company (Getech) into a global data set, which has been sold and licensed extensively within the hydrocarbon exploration industry. The global data set has delivered economic and reputational benefits to Getech, and has been employed by oil companies in more than 50 exploration projects per year. Shell values the improved gravity data at $2.5M per project.

Underpinning Research

By the mid-1990s, the use of marine gravity data sets derived from satellite altimeter data had become well established for offshore hydrocarbon exploration, as well as for general geological studies and for the development of global geoid and gravity models. However, although satellite altimeter data with good coverage were available (~4 km track spacing over most of the oceans), the resolution of the derived gravity grids was significantly worse, particularly in coastal regions. In consequence, the potential applications of satellite gravity anomalies were limited in scope by the available data.

Between 1996 and 1998, Leeds researchers Derek Fairhead, Chris Green, and Stefan Maus (Researcher, 1996-1998) developed an improved method of detecting marine gravity anomalies using satellite altimeter data. Their approach was to use the most basic altimeter data available – the raw waveforms transmitted from and recorded by the satellite. This relatively large data set required sophisticated processing, and a range of new techniques were developed to pick the exact return time of the radar echoes, and to test the robustness and accuracy of the retrievals. The results demonstrated a significant improvement over previously-available along-track data, enabling the production of improved gravity anomaly grids [1].

Subsequent research (1997-1998) by Green and Fairhead in association with Getech reviewed the whole process of generating satellite gravity data. By modifying the details of the various techniques, it was shown that the improved along-track satellite altimeter data could be processed to provide improved gravity anomaly grids. Paper [2] and report [5] describe these techniques and demonstrate that the improvement in results compared with gravity data from other sources is better than 10% (see also corroboration [B, C]). These new techniques were later (2002-2004) applied by Getech to develop a new gravity data set for the continental margins of the world [6]. Paper [3] looks at a specific area of interest and quantifies the improvement achieved by applying the new techniques.

Sustained collaboration between Getech and the University of Leeds has driven further advances in the technology. In 2008, Fairhead led research on the effectiveness of combining gravity data sets derived from different satellite missions, resulting in the production of Getech’s new Trident marine gravity product with improved resolution and reliability [4]. In 2012, Green and Fairhead initiated a joint research collaboration with Leeds to maintain their industry-leading position by incorporating the latest generation of interferometric satellite altimeter data. This project has now evolved into a major 3-year oil industry sponsored study (2013-2016) to improve, yet further, the resolution of the data.

The impact of the research has been achieved via Getech, primarily through the sale of gravity data products, which are used by oil companies in hydrocarbon exploration.

Key researchers

Derek Fairhead, Lecturer and Professor (now Emeritus) (1973-present) of Applied Geophysics in the School of Earth and Environment, University of Leeds; Managing Director (1991-2011) and President (2011-present) of Getech
Chris Green, Research Assistant (1983-1992), Teaching Assistant (2010-2016) and Lecturer (2016-present) in the School of Earth and Environment, University of Leeds; Scientist (1992-2010) at Getech

References to the research

This list includes both academic references and commercial reports as both are important in the dissemination of the research.
Academic references
1. Maus, S., Green, C.M. and Fairhead, J.D. (1998). Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms. Geophysical Journal International, 134, 243-253. doi:10.1046/j.1365-246x.1998.00552.x.
Paper describing the research that led to the impact.
2. Fairhead, J.D., Green, C.M. and Odegard, M.E. (2001). Satellite-derived gravity having an impact on marine exploration. The Leading Edge, 20, 873-876. doi:10.1190/1.1487298.
3. Bansal, A.R., Fairhead, J.D., Green, C.M. and Fletcher, K.M.U. (2005). Revised gravity for offshore India and the isostatic compensation of submarine features. Tectonophysics, 404, 1-22. doi:10.1016/j.tecto.2005.03.017.
Commercial reports
4. Fairhead, J.D., Williams, S.E., Fletcher, K.M.U, Green, C.M and Vincent, K. (2009). Trident – A New Satellite Gravity Model for the Oceans. Extended Abstract, 71st EAGE Conference and Exhibition, Amsterdam.
5. Towards the Ultimate Resolution of Satellite Gravity. Confidential Getech report G9815. May 1998.
Commercially funded R&D project.
6. Global Continental Margins Gravity Study (GCMGS). Confidential Getech report G0411. June 2004. Industry funded R&D and processing project leading to a near-global gravity grid.

The research described in [1], [2] and [3] is of international significance as approaches similar to those described have been used in recent satellite gravity data sets produced in both Europe and North America. The work reported in [4] is the best publically-available description of the Trident development. Commercial reports [4], [5], and [6] have led to significant sponsorship of follow-on studies and sales of the products developed.