Method and application of fracture width calculation based on formation contrast variation index

ABSTRACT Accurate calculation of fracture width is essential for characterizing fractured hydrocarbon reservoirs. However, this remains challenging when relying on geophysical logging alone. The results of fracture width calculations vary considerably when the same fracture is evaluated using electrical imaging logging under different formation contrasts, which are defined by the ratio of mud resistivity to flushed zone resistivity. This makes it difficult to perform multi-well comparisons accurately for the evaluated fracture width in practical applications. A logging evaluation method for fracture width was proposed based on physical experiment studies. First, we constructed a physical model of a granite formation containing micrometer-scale irregular fractures that can be used to capture data with the electrical imaging logging instrument and measured the true fracture widths in the physical model. Due to experimental constraints, the fractures of the physical model are open fractures with a certain degree of roughness. Formation microscanner image logging data were acquired in the physical model under five different mud salinity conditions and were subsequently processed and analyzed. Finally, the fracture width evaluation method was proposed by introducing the formation contrast variation index, a new parameter that accounts for resistivity contrast effects. This proposed method can accurately calculate fracture width when drilling in different mud salinity conditions. Validation through experimental data and case studies demonstrates its robustness and practical applicability. This approach provides a reliable foundation for the objective calculation of fracture porosity and fracture permeability, thereby supporting more effective exploration and development of fractured hydrocarbon reservoirs.