Reservoir Characterization, Bridging the Scale from Micro to Macro

Abstract

This paper describes the reservoir characterization of a carbonate formation using acoustic and borehole imaging log in a novel way. Interpretation of the interplay between stratigraphic and structural reservoir elements allows additional understanding of the hydrocarbon trapping mechanism and informs decisions on the well testing program and future well placement. High-resolution Borehole Images (BHI) have historically been one of the most widespread geological evaluation tools and they continue to be a cornerstone for providing precise data on the facies and fractures intersected by the well. The shallow depth of investigation of wellbore imaging tools can now also be usefully augmented by the acoustic, Dipole shear processing. Patented Deep Shear Wave Image (DSWI) methodology allows identification of geological interfaces with a depth of investigation up to 110 feet away from the borehole. The processed data bridges the gap between wellbore images and field scale seismic data and so can guide meaningful reservoir descriptions and fracture characterization at the geo-cellular mode scale. Combination of the two separate imaging measurements compensates for the limitation of each logging tool's capabilities and helps increase the range of feature detection from near borehole to as much as 110 or more feet away from the well. The statistically rich borehole imaging data can be used to help confirm the detailed characteristic of these features and how the facies/lithology affect the fracture properties. BHI also calibrate the DSWI features true azimuth, while the DSWI data can help confirm fracture hierarchies and fracture bed interaction away from the borehole. The current study highlighted that the different scales of measurement allow additional quantified analysis of the fracture hierarchy and leads to proposal of conceptual fracture models that recognize bed-bound and non-bed-bound fractures sets. The reservoir itself is highly stratified with intercalations of limestone, mudstone and evaporite. Hydrocarbon (HC) presence, defined by an acoustic derived HC Index (but validated with conventional resistivity logging), suggests that oil is preferentially trapped in successive porous layers, but enhanced in some intervals by the additional presence of fractures. The Reservoir pressure points have indicated that only main faults-oriented NNW-SSE could potentially compartmentalized the reservoir. Additional wells and data integration are needed to confirm it. The DSWI is also useful to calibrate the poor to moderate seismic data in this field by detecting sub-seismic features that have an impact on the reservoir and helps in updating the geological and reservoir model.