An operator drilling a development well in the Sarawak field offshore Malaysia needed to confirm the actual depths of key targets to maximize reservoir contact of a planned sidetrack. Initially imaged with surface seismic technology, the intended targets needed to be confirmed with a full vertical seismic profile image. Obtaining a VSP image with wireline was not considered feasible because of the 60º inclination of the well. To ensure that the resulting image would be free of spatial aliasing artifacts, an alternate solution would need to meet a tool spacing criteria of 15 m [49 ft].
SLB recommended configuring a BHA with two seismicVISION seismic-while-drilling service tools to acquire a high-resolution image for real-time well placement decisions. The seismic tools would be placed 15 m apart to meet the spatial sampling distance required to qualify as a VSP image. This novel configuration would be the first-ever use of dual seismic LWD in the world.
To ensure accurate acquisition of the seismic data, SWINGS seismic navigation and positioning system was recommended for precise positioning of the vessel source. SLB also suggested using the EcoScope™ multifunction logging-while-drilling service to efficiently evaluate the formation. By transmitting gamma ray, resistivity, and neutron gamma density measurements from a single collar, the EcoScope service would minimize the length of the BHA. These measurements would then be correlated with seismic reflectors to determine the presence of hydrocarbons.
Using the VSP image produced by the seismicVISION service, the operator confirmed the actual depths of its targets while drilling the pilot hole. The processing of this high-resolution data was expedited during the casing break to provide the VSP image to the drilling team prior to drilling the next section.
This information lead the operator to alter the trajectory of a sidetrack by several hundred meters to maximize reservoir contact. The operator also saved 24 hours by eliminating the need to run wireline.
