First Borehole to Surface Electromagnetic Survey in KSA: Reservoir Mapping and Monitoring at a New Scale

Abstract

Abstract The first Borehole to Surface Electromagnetic (BSEM) pilot field survey in the Kingdom of Saudi Arabia (KSA) was successfully executed to identify oil and water bearing reservoir layers in a carbonate oilfield water injection zone. Maximizing recovery factor by means of detailed mapping of hydrocarbon accumulations in the reservoirs is a key requirement for oil producing companies. This mapping is done routinely by accurate measurements of fluid distribution at the wells’ locations, but a knowledge gap exists in the inter-well volumes, where typically only density-based measurements are available (seismic and gravity). Such technologies are not always effective to discriminate and quantify the fluids in the porous space (especially when difference in fluid densities is small, such as oil and water). On the contrary, when high electrical resistivity contrasts exist between hydrocarbons and water, electromagnetic (EM) based technologies have the potential to map the distribution of the fluids and monitor their movement during the life of the field, hundreds of meters or kilometers away from the wellbores. The objective of a BSEM survey is to obtain fluid sensitive resistivity and induced polarization maps. These are based on an acquisition grid at the surface, a few kilometers around the EM transmitting well, which reveal oil and water bearing zones in the investigated reservoir layers. In this pilot field test, BSEM showed the potential to map water-front movements in an area of about 4km from the single well surveyed, evaluate the sweep efficiency, identify bypassed/ lagged oil zones, and eventually monitor the fluid displacements, if surveys are repeated over time. The data quality of the recorded signals is highly satisfactory. Fluid distribution maps obtained with BSEM are coherent with production data measured at the wells’ locations, filling the knowledge gap of the interwells area. Three key R&D objectives for this BSEM pilot are achieved. Firstly, the capability to record at the surface EM signals generated in the reservoir, secondly, the capability of BSEM to discriminate between oil and water saturated reservoir zones, and finally obtain resistivity maps and a fluid distribution estimate plausible and coherent with the information obtained from well logs, crosswell EM, production data and reservoir models. In addition to reservoir monitoring, BSEM can be very useful in non-diagnosed areas like exploration fields for hydrocarbon exploitations.