Unlocking Hydrocarbon Potential of the Caribbean Plate with the New Deep Strata Survey Approach
Aleksandr Nikitin*, Nick Amelin*, Andrei Iakovlev (PhD)*
* Geology Without Limits, Horsham, West Sussex, United Kingdom
Structure and evolution history of the Caribbean Plate are very complex. Despite the big amount of studies conducted (James K.H. et al., 2009) the region is still remains being enigma for a scientific community. The upper part of sedimentary cover of the Caribbean Plate was mainly explored where giant oil and gas fields are located. Deeper parts of sedimentary cover and Earth crust structure were studied only along a limited number of seismic lines (Christensen G.L. et al., 2008). The main reason is that due to technical issues deep depth seismic surveys have been often considered as cost & time demanding and low efficient ones. To overcome this paradigm and break through technical limitations of present deep depth seismic surveys technique – a new approach should be evolved.
The new concept of deep depth seismic surveys is based on two specially developed tools: GWL LF Source™ – able to emit low frequency energy beneficial for deep penetration of seismic signal and GWL Seismobuoy™ – compact and easy to handle standalone unit to record ultra-long offset seismic data from deep buried structures. The first goal of the development was to design equipment suitable both for simultaneous use during conventional towed seismic streamer surveys as well as for separate deep strata surveys using small tonnage vessels of opportunity. The second, but not less important goal was to increase production rate of such kind of surveys and considerably reduce price per km of acquired data without any loss of data quality or operational integrity.
The pilot run of the new technology was done during the first phase of Scientific Program “Investigation of Lithosphere Deep Structure of the Caribbean Region by Seismic Methods”. The pilot survey line was running from the Atlantic Ocean into the Caribbean Plate interior crossing Lesser Antilles. The main goal was to test the new technology capabilities in a challenging geological environment. The simultaneously acquired 295 km of long-offset 2D seismic streamer data together with super-long offset data helped to reveal value that the new technology is able to add. 2D towed seismic streamer data was acquired with help of a 12 km streamer and a standard 7060 cu. inch air gun array. Free drifting recording units deployment spacing was 6 km and shot points spacing equaled to 50 m.
Reliable velocity model is highly essential for clear seismic imaging and proper time to depth conversion. Dominance of diffractions and ray bending associated with steep dips and irregular bedding reduced veracity of CDP velocity analysis causing CDP velocity model being “patchy” and non-geological. Presence of high-velocity igneous layers caused problems with energy penetration because of the large seismic impedance contrast. Thus, the main goals of seismic imaging and interpretation became challenging. Long-offset data recorded with help of the proposed acquisition technique and asserted into the processing routine helped to create geologically consistent velocity model along the 2D CDP seismic line. Pre-stack depth migration with an improved velocity model considerably enhanced wavefield quality in areas with complex geological structures. Therefore, the clarity of the seismic image, quality of reflecting horizons tracing and data interpretation were uplifted.
Our approach to simultaneously towed seismic streamer and super-long offset data acquisition proved its consistency and efficiency. Proposed technology has potential to make deep strata surveys both well-resolved and more affordable for academic community and oil & gas companies. Availability of a large amount of high quality deep data will help to resolve the long-standing debate on the Caribbean Plate origins and determine type of crust underneath each particular basin enclosed in the Plate. Which is the question of a huge importance because of the notion that the most part of giant oil and gas fields are located on continental crust.