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.

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Crosswell electromagnetic (X-well EM) resistivity is emerging as an intriguing technology for reservoir surveillance. It provides a cross-sectional resistivity image between two wells and has the potential to provide fluid distribution at an inter-well scale. It can be used for identifying bypassed hydrocarbons, monitoring macroscopic sweep efficiency, planning infill drilling, and improving effectiveness of reservoir simulation. It can be deployed for one-time or time-lapse surveys. A crosswell EM technology trial project is being conducted in an Upper Jurassic carbonate reservoir, at the Ghawar Field in Saudi Arabia, to monitor the movement of injected water flood front and map the fluid distribution. The project site is in Ghawar's southern region, Haradh Field, and consists of three wells in the oil-water contact zone where peripheral injection water may have produced an uneven flood-front distribution. Significant drilling and well deepening were required prior to the deployment of tools in the three-well triangle. In fact, one new well was drilled and two other wells were deepened by more than 200 m, so that good volumetric coverage could be obtained at the oil- water contact zone. Extensive logs, core and formation tests were also acquired to provide deterministic saturation profiles at the near wellbore region. Formation evaluation in the project area indicates that one of the wells was fully swept while a second well, some 400 m away, was not. In July 2007, crosswell EM surveys were acquired across the three Haradh wells. In spite of the large well separations, the acquired EM data had good quality, and good stations repeatability. Preliminary processing has revealed a structure consistent with the background structure but a clear image of the oil-water contact is yet to be made. Introduction The Haradh Field is in the southernmost part of the greater Ghawar Field - the largest single oil field in the world (Figure-1). Arab-D is a 100-m thick, highly prolific, upper Jurassic reservoir comprising a carbonate sequence of grainstones, packstones, and wackestones 1. The original sedimentary textures have been altered in many places by leaching, recrystallization, cementation, dolomitization, and fracturing, which have caused a variety of pore types 2 to coexist in Arab-D. Flood-front movement can be uneven in some parts of the reservoir. Reservoir porosity ranges from less than 10% at the base to over 30% at the top while permeability ranges from few millidarcies to more than one Darcy. The Arab-D reservoir in Ghawar has historically been operated at relatively low depletion rates. Flank water injection is being carried out to maintain pressure and to improve sweep efficiency in this reservoir. With current inter-well spacing, about 1 km, determining fluid distribution behind the flood front is a key challenge to maximizing recovery from this reservoir. Traditional reservoir fluid monitoring techniques, e.g. pulsed- neutron logs (PNL) and resistivity logs, have investigation depths ranging from few inches, for PNL logs, to about 3 m for the deepest resistivity logs 3. Therefore, they cannot be used effectively for flood-front monitoring at the inter-well scale.

A new technique is developed for modeling 3D permeability distributions. The technique integrates all available data into a fluid flow simulation model. The integrated modeling process honors the essential aspects of the established reservoir descriptions as well as the geological facies model and engineering data. The added value of data integration of the fluid flow simulation is illustrated by the improved accuracy of the resulting well performance predictions and the decrease in time requirements for reservoir modeling history matching. The technique utilizes diverse data at different scales to condition reservoir models of facies, porosity, and permeability. Such data includes 3D seismic, well logs, core measurements, geologic facies distribution, flow meter logs, and pressure buildup tests. The model building process explicitly accounts for the difference in scale of the various measurements. The model calculates the porosity, facies, and permeability in the inter well volume using geostatistical techniques that are constrained by seismic impedance derived from the 3D seismic data. The use of engineering data in the permeability modeling constrains the results and decreases the history matching time requirements. A case study demonstrates the modeling technique. A reservoir model is developed for the Unayzah Formation in the Hawtah Field of Saudi Arabia. The Unayzah is a highly stratified clastic reservoir in a mixed fluvial and eolian depositional environment. Data integration provided more realistic reservoir model for this complex geologic setting than the conventional approach. Specifically, the integrated approach provide a reservoir model that captured the complex and highly stratified nature of the lithological units. Fluid flow simulation was carried out for both the new integrated reservoir model and the conventional reservoir model. Results show tremendous savings in history matching time and more accurate results for use in reservoir management production strategies when applying the new technique.