Published: 06/25/2015
Published: 06/25/2015
High-quality VSP data was needed to accurately position the trajectory of a deepwater development well offshore Angola on the surface seismic survey. The operator also wanted to improve efficiency and reduce risk for the logging operation, which is conventionally pipe conveyed in highly deviated wells.
The UltraTRAC all-terrain wireline tractor delivers the farthest reach in the industry by combining the highest tractor force available with reverse tractoring, dynamic suspension, and active traction control. In addition to its low sensitivity to well conditions, the UltraTRAC tractor is customized for the number and configuration of drive sections, which are fitted with wheel diameters and proprietary designs optimized for the well geometry and borehole conditions. By eliminating routine deployment on coiled tubing and drillpipe conveyance in both open and cased holes, the UltraTRAC tractor simplifies and streamlines wireline operations to reduce cost, time, and risk.
Schlumberger job planning integrated geophysical and operational parameters to determine that configuring the UltraTRAC all-terrain tractor with eight drives was the most efficient approach to conveying four VSI imagers for recording a walkabove VSP survey. The VSI imagers' shuttles were aligned and conveyed downhole with stiff bridles, and a triple G-Gun source deployed from a support vessel was positioned and controlled using the Q-Borehole integrated borehole seismic system, including the SWINGS seismic navigation and positioning system and the in-sea TRISOR acoustic source control element. Perfect synchronization of the vertical-incidence shots above the optimally coupled VSI imagers enabled recording wideband 5- to 120-Hz data at the reservoir level with excellent vector fidelity. The measured direct seismic wave incidence angles at the triaxial sensors of the VSI imagers accurately matched the well deviation, confir- ming the vector fidelity of the VSI imagers' sensors in this configuration.
The accurate time-depth data obtained with the precise walkabove geometry was used to produce a VSP corridor stack and high-resolution 2D VSP image below the wellbore. This information was key for positioning the well on the surface seismic survey in time. Robust well-to-seismic tie analysis was conducted, and previously undetected faults and other stratigraphic features were identified.
Challenge: Efficiently record high-quality triaxial vertical seismic profile (VSP) data in both the open- and cased hole sections of a well deviated up to 86°
Solution: Convey multilevel configuration of VSI versatile seismic imagers by using the UltraTRAC all-terrain wireline tractor to record a walkabove VSP survey that accounts for the geometry of the deviated well
Results: Accurately tied the well to surface seismic surveys and mapped faults and stratigraphic features on the basis of the accurate time-depth data, corridor stack, and high-resolution VSP images obtained efficiently and at lower risk with UltraTRAC tractor conveyance
