Petrological facies calibrations were performed on shale of horizontal wells in Fuling

Sichuan Basin

based on geological and well-logging characteristic marks

and specialized petrological facies.In accordance with the three key marks (lithological combination

calcareous content and siliceous content)

the whole set of 89-meter-thick shale interval in the typical pilot wells of the Lower Silurian Longmaxi Formation in Fuling were divided into nine different types of petrological facies.The No 1

3 and 6 petrological facies were identified as specialized petrological facies based on geological marks like marker beds

carbon dyes and silty laminae as well as logging marks such as logging response anomaly

the types of logging curve shape

excavation effect and pseudo excavation effect.We compared the results of projected well-logging information through horizontal section-based vertical projection with characteristic marks and specialized petrological facies in typical pilot wells to determine the top and bottom boundaries of the petrological facies and accomplished the calibrations.The relationship between petrological facies and the post-fracturing tested productivity was used to identify the petrological facies in prolific horizontal wells.It was found that the petrological facies with high calcareous and silica contents (No.1 and 3 facies with) have the greatest productivity potential

thus were determined to be the best petrological facies.Based on the principle of the best petrological facies

we suggest the best trajectory of horizontal well or landing point of target window be between the No.1 and 3 facies.Application of the calibration method to Fuling shale gas field were positive

with the coincidence rate between the predicted and tested productivities being more than 80%

proving it a potential method for optimizing well trajectory design and increasing single-well production.