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Integrated Seismic-Log-Core-Test Fracture Characterization and Modelling, Barra Velha Formation, Pre-Salt of Santos Basin

Abstract

Discontinuities such as faults and fractures are important heterogeneities that must be investigated during characterization process and usually confer to reservoir distinct flow behavior when compared to reservoirs that produce only from matrix. These discontinuities must be considered during geological modelling process to assure robustness of production forecast obtained from these models and assess production development plans. Located in Santos Basin, Brazil, the Barra Velha Fm. is the most important reservoir unit for Santos Basin Pre-Salt oil fields. High permeability (up to 10 Darcy) was verified in wells drilled in geological features known as carbonatic mounds, inside Barra Velha Fm., mainly due to high fracture intensities and dissolution encountered in these regions, firstly identified through resistive and acoustic image logs. Several subsequent wells brought new information over this fractured reservoir through extensive core data, well tests and good quality well logs confirming large presence of fractures and outstanding reservoir productivity. The objective of this work was to integrate all the available data of logs, cores and seismic into the fracture modelling process, providing a reliable input for double-porosity/double-permeability modelling for field production forecast. The method initiates by interpreting all fractures features in borehole image logs and building fracture intensity logs (P32) for each well. The available 166m of cores had their structural features classified in types (joints, veins or shear fractures), attitude and opening. To extrapolate measured fracture intensity data to other regions far from boreholes, seismic attributes were employed, acting as secondary variable for co-krigging in 3D simulation of fracture intensities through the field. In addition, based on seismic facies and conceptual model, a discrete 3D property was built to determine regions with similar fracture behaviour. Each of these regions were populated with fracture intensities and attitudes of closest wells, honouring data from borehole as an input for the discrete fracture network model (DFN) process. After the construction of the DFN, fracture permeabilities were upscaled to grid using Oda Method (Oda, 1985) and adjusted to flow capacity observed in well tests. The results of this study were used for productivity assessment on the area.