Brittleness Logging Evaluation of Shihezi Formation in Yanchang Gas Field in Ordos Basin Based on Rock Mechanical Characteristics

Abstract

Brittleness determines the effect of reservoir fracturing and is important for increasing the production of unconventional oil and gas. The reservoir of Yanchang gas field is characterized by low porosity, low permeability and strong heterogeneity, which make it difficult to produce industrial gas flow under natural conditions. Triaxial compression tests in sandstone samples of Shihezi formation in Yanchang gas field show that the main fracturing mode is multiple horizontal splitting, the main cracks are completely fractured, and the brittleness index ranges from 46.1% to 51.4%. After S-wave velocity model in the study area is established, the conversion relation of dynamic and static mechanical parameters could be obtained, that is,Es=0.4142Ed+10.769(R2=0.8387),and μs=1.1076 μd-0.068(R2=0.7366), according to which, the dynamic mechanics parameters calculated by well logging can be adjusted, and then the reservoir brittleness could be quantitatively evaluated. Combining with the brittleness index calculated by mineral component method, it can be concluded that the brittleness calculated by well logging is reliable and the brittleness of Shihezi formation in Yanchang gas field is high, which is beneficial for reservoir fracturing.