Stig Lyngra

Fluid Distribution Inter-Well Mapping in Multiple Reservoirs by Innovative Borehole to Surface Electromagnetic: Survey Design and Field Acquisition

Borehole to Surface Electromagnetic (BSEM) technology was conceived in the former Soviet Union and fine-tuned by the Chinese Bureau of Geophysical Prospecting (BGP). Saudi Aramco recently deployed the first BSEM pilot test outside of China (Marsala et al., 2011). This paper describes a new world first innovative electromagnetic borehole to surface survey in a well completed with multiple casings. The objective was to deploy a single BSEM survey to map the oil-water distributions in two separate reservoirs. This BSEM survey was conducted in a mature Saudi Arabian oil field composed of two main naturally fractured carbonate reservoirs, separated by a thick nonpermeable zone. The Upper reservoir is prolific, while the Lower reservoir is relatively tight and highly fractured. The reservoir pressure data from the early production period confirmed communication between the two reservoirs through several large scale fractures crossing the nonpermeable zone. In the Lower reservoir, well log observations show a variable oil-water distribution. No direct measurements of fluid saturations are available in the inter-well areas. The BSEM survey was designed to fill this data gap. In June 2012, a very challenging BSEM field acquisition was successfully completed with zero downtime and no accidents, obtaining very good data quality. Electromagnetic (EM) signals were transmitted at multiple frequencies from four source locations placed in a single vertical transmitting well that cross through both reservoirs and received by more than 1,000 surface stations, located in a grid at distances up to 3.5 kilometers away from the transmitting well. Multidisciplinary teamwork and independent peer reviews are undertaken to guarantee the optimal benefit from this pioneering technology. The business impact is to increase recovery by maximizing sweep efficiency and optimize well placements.