AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
The Use of Passive Adsorbents for the Assessment of Hydrocarbon Charge in the Shallow Waters around Bahrain
(1) Survey Products Group, W.L. Gore & Associates, Inc., Elkton, MD.
(2) The Bahrain Petroleum Company, Manama, Bahrain.
(3) Occidental of Bahrain (Offshore), LLC, Manama, Bahrain.
This document will summarize the efforts to assess hydrocarbon charge in the shallow waters around Bahrain.
Shallow water presents a challenge for the exploration and prospect development of hydrocarbon reserves. The surf zone is a high-energy environment that is frequently avoided due to the expense of seismic acquisition in these water depths.
To help overcome the exploration uncertainty presented by these shallow transition areas, divers deployed over eight hundred passive devices in the sediment for the collection and assessment of geochemical data as part of this reconnaissance survey. The passive adsorbents were embedded in the sediment to a depth of 10 - 20 cm, and left in place for an average of 17 days.
Samples were deployed in four separate areas with an average distance between points of approximately 1 km. The water depths ranged from less than 1 meter to approximately 20 meters in the deepest block. Many of the samples were embedded near living coral reef with no disturbance to this sensitive habitat; supporting the premise that this technique is environmentally neutral and does not significantly affect even the most highly sensitive habitats. Samples were also placed around select analog wells in order to provide a means of comparing a known geochemical signature to the unknown areas.
The geochemical signature acquired by each sample was qualified and quantified using thermal desorption followed by gas chromatography and mass selective detection (GC/MS). A broad range of compounds from ethane (C2) to octadecane (C18) were reported from each sample including normal alkanes, iso-alkanes, cyclic alkanes, aromatics and alkenes as well as biogenic and alteration compounds. In total there were 85 compounds reported from each sample.
The data were processed and evaluated using standard signal-to-noise elimination and advanced statistical processing specifically developed for use with these adsorbents. The data interpretation yielded an assessment of the hydrocarbon charge that otherwise would have been impossible or very costly to acquire. Geochemical anomalies have been identified for further consideration and have provided a means for narrowing the search for hydrocarbon charge. In one of the areas surveyed, a possible correlation is recognized between interpreted gas chimneys on 3D seismic data and a cluster of small geochemical anomalies in map view.