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

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.

Synergizing Crosswell Seismic and Electromagnetic Techniques for Enhancing Reservoir Characterization

“…We further assumed that for each update step, the crosswell imaging was performed sequentially for the individual wells during a time frame of 1 to 2 months and therefore does not require a total halt of the field production. On the basis of a sensitivity analysis, we could conclude that the temporal differences over which the EM and seismic surveys are conducted only marginally affect the signals, and the data were history-matched at the same UT (Schlumberger Imaging Services Report 2009Marsala et al 2011;Schlumberger 2013). Attenuation effects for both crosswell EM and seismic imaging were taken into account, as outlined in the Full-Wave Acoustic-Wave Propagation Method and Full-Wave EM Method sections.…”

“…In contrast, EM data showed a strong dependence on the water-saturation changes, which is consistent with Archie's relation. EM data depend strongly on the water-saturation levels in the reservoir and therefore may more easily distinguish between heavily and less heavily waterflooded reservoirs (Marsala et al 2007(Marsala et al , 2011Lien 2013) that is rather challenging with seismic techniques. Furthermore, because of the strong salt-concentration dependence of the EM signal, EM techniques are further able to distinguish between water influx from an aquifer and the water that is injected from the surface (as outlined in the 3D case) because of the significant salt-concentration difference between the two fluids.…”

Applications of tomography in the oil-gas industry – Part 2

“…To better monitor movements of hydrocarbon fluid lying between wells at a reservoir scale, fluid-saturation surveys based on cross-well EM induction tomography have been performed Wilt et al, 1995;DePavia et al, 2008;Wilt, Donadille, AlRuwaili, Ma, & Marsala, 2008;Marsala et al, 2008. Surface-to-borehole EM uses an array of borehole receivers and a movable surface source, Pardo, Torres-Verdín, Marsala et al, 2011). The cross-well EM induction tomography approach produces a resistivity distribution between wells and offers a better resolution than surface seismic surveys .…”

Evaluation of Borehole Casing Sources for Electromagnetic Imaging of Deep Formations

“…The specificity of borehole to surface EM (BSEM), in respect to crosswell EM (Xwell EM), is that BSEM requires only one surveyed well to obtain an areal map of fluid distribution of a reservoir target layer, kilometers away from the transmitting well (up to 4 km, as demonstrated in Saudi Arabian pilots, Marsala et al 2011 and2013a). Xwell EM, on the contrary, allows higher resolution results, but it is limited to cross sections between two or more wells, close enough for EM propagation: about 1 km in open holes, less in cased holes (Marsala et al 2008).…”

“…The BSEM technology was first employed in the ex-USSR at the end of the last millennium and has been extensively improved in recent years in China, leading to positive field deployments and resulting in a commercial protocol, subsequently being developed and introduced by BGP (He et al 2012). Successful pilot studies of BSEM have been reported by Saudi Aramco, producing resistivity and IP images of oil-water contact at reservoir depth (Marsala et al 2011).…”