Petrobras pre-salt discovery is a huge hydrocarbon reserve located below an extensive layer of salt at about 5000 m depth. So far, the wells drilled at this scenario found light oil in highly heterogeneous carbonates reservoirs. The formation permeability varies more than four orders of magnitude. Some fields have most of the permeable zone with values ranging from 1 to 10 mD and this scenario requires stimulation in order to maximize productivity. This article will present the first multi-fractured sub-horizontal well constructed in the pre-salt reservoir.
In this stimulation operation 8 acid fractures were created in a sub-horizontal open hole well. This article will show the completion selected that permitted to register the bottomhole data above and below the zone where the fracture was being created. This record allowed the interpretation if the fractures were really created in the zones selected or if there were communication between zones. The article will present the calibration tests results, the fracturing data of all intervals and some insights regarding fracture orientation due to temperature behavior.
The reservoir depth and the proximity of the salt layer bring many challenges regarding hydraulic fracturing operations. This operation and other field results have shown minimum in situ stresses in the magnitude of 0.7 psi/ft and fracture propagation pressure that exceeds the estimated overburden. The records of the bottomhole pressure during this operation showed that there were some communication between zones. After the stimulation operation, a formation test was done measuring the well productivity and collecting samples of the reservoir fluid. The samples collected were analyzed and the tracers used during the stimulation were identified, indicating which fracture was contributing to production. The data registered during this operation is a huge lesson learned about doing multi-acid fractures in a carbonate reservoir for all the industry.
