EnergyBC

Surveying/Exploratory Drilling (more on basin modelling...)

Deep-echo sounding or seismic reflection surveys (attached pdf) are done by a ship towing a compressed-gas airgun array and long strings of sound receivers (hydrophones) several kilometers in length. As the ship travels over the area of interest, the array emits short bursts of sound at specific intervals. Sound travels down through the water and into the subsurface, reflecting back off of the various rock layers. The hydrophones record the sound coming back up, and the time it takes the sound to travel down and back up is then recorded by a computer. This data can be compiled to form an image of the rock layers and geological structures below the sea floor. The data collected as the ship travels from one point to another gives a two-dimensional (2D) picture, like a single slice though an apple. By collecting many lines close to each other a three-dimensional (3D) picture can be produced.

Geophysicists use powerful computers to process the data collected by seismic surveys. By filtering extraneous noise and enhancing the desired signals, computers can image different rock layers and structures. Computer-assisted interpretation can create a 3D rendering of the sedimentary features below the surface. This image contains important information about the location and shape of underground rock layers that could hold crude oil and natural gas. The seismic images are used to identify structures that would either merit more detailed seismic surveying or would warrant exploratory drilling.

Lithologic interpretation of seismic data.

Computed liquid hydrocarbon saturation and expulsion from Jurassic marine source rocks in the Ghost Creek and Sandilands formations. Colours refer to liquid saturation which has a maximum possible value of 98%. Siltstone beds (effective hydrocarbon seals) are coloured light purple.

Click on image above to view model of basin for past seventy-five million years

New geophysical surveys in the Queen Charlotte Basin would fill in gaps in bathymetric data and improve imaging of the subsurface for assessment of potential petroleum reserves. The last survey of the region to image regional structural style was performed in 1988, and technology to acquire and analyze data have progressed significantly since then. Sonar and related technologies must be employed in order to fill gaps in bathymetric (water depth) data for much of the QCB (JWEL 2001). Seismic surveys would typically be conducted over many years by different companies. The initial goal of surveys would be to improve data quality and explore for likely areas of resource deposits. If successful and development proceeded, surveys may also be required during production to help determine reserve depletion rates (RSC 2004; JWEL 2001).

Areas that have been explored in the Queen Charlotte Basin

Click here for information on Basin Modelling

Some credit from above text to Review of Offshore Oil and Gas Development by Simon Fraser University, 2004 and Royal Roads University: BC Offshore Oil and Gas Socio-Economic Papers, 2004