Shale gas sweet spot identification and precise geo-steering drilling in Weiyuan Block of Sichuan Basin, SW China

Based on drilling and production test data and the geological, geochemical, geophysical and rock mechanics achievements of Weiyuan Block of Sichuan Basin, “sweet spots” of shale gas were determined and geosteering technology was tested in drilling the sweet spots under complex structural background. The high quality Silurian Longmaxi Formation shale (with TOC≥2%) in the study area, thick (36.0−44.5 meters), is divided into four sublayers, from bottom to top, which differ widely in TOC (2.0%−8.1%), gas content (1.2−12.6 m3/t), porosity (0.66%−11.80%), and brittle mineral content (17.5%−98.5%). Considering gas content and fracability of shale, the layer Long 11a in Longmaxi Formation is the best “sweet spot” layer in vertical direction; horizontally, the areas with folding structure in shale reservoir have more natural fractures, and thus have better storage quality and permeability, are “sweet spots”. During drilling of the sweet spots, three-dimensional seismic and geological modeling was used to predict the depth of “sweet spot”, which was corrected in time with drilling data, and by controlling well trajectory this way, the drilling rate of “sweet spots” has been improved. Key words: Sichuan Basin, Weiyuan Block, Silurian Longmaxi Formation, shale gas, high quality shale, sweet spot, geosteering technology in drilling