Vaca Muerta formation in the Neuquén Basin, Argentina, is being exploited as an unconventional reservoir with horizontal wells targeting different benches considering the thickness of the organic rich interval. One of the uncertainties that impact in the Vaca Muerta reservoir modeling is the role of the natural fracture system and its spatial characterization. Well bore imaging tools are used to identify natural fractures in the well but, due to several reasons, an additional wireline trip is not always a suitable option to run conventional tools.
A new logging-while-drilling technology for borehole imaging with dual physics measurements was deployed to assess its capabilities and applications in two laterals drilled in two different landings vertically separated by around 10 m and running opposite to each other azimuthally. The pad, located in the Central-North area of the basin, includes a vertical pilot well with wireline borehole images. The new borehole imager is unique for its two different measurements simultaneously from a short sub (∼15-ft), namely apparent resistivity and ultrasonic while drilling to acquire high resolution azimuthal images of the borehole wall, providing real-time data for decisions related to geosteering and completion planning.
The apparent resistivity images were found to be more sensitive to the facies boundaries and associated variations, whilst the ultrasonic images were more sensitive to fractures and drilling-related features on the borehole wall. The subtle facies variations manifested on the real-time apparent resistivity images ensured that the narrow geosteering window identified on the vertical pilot is honored for easterly and westerly dipping sub-horizontal layers traversed by the two laterals. A comparison with legacy gamma ray images from different LWD services is provided in the wells drilled with oil-base mud, where they remained the only chemical source-less images prior to the advent of unique borehole imager deployed in the field. Also, different intensity of fracturing was observed in the two sub-layers drilled with two laterals; with the well drilled towards northerly azimuth showing high definition of fractures striking ENE-WSW. Advanced borehole interpretation apps were used to map the facies variation and characterize the fracture distribution.
The LWD image data from two laterals were compared with the wireline images of resistivity and ultrasonic acquired in vertical pilot well to assess the consistency of the new technology.
The new technology imager helped a great deal in understanding the fracture networks, facies variations in long laterals with images acquired while drilling, thereby providing key-decision making data for real-time steering and subsequent interpretation, without the need of wireline runs.