Method of estimating the effective fracture volume of shale gas wells using flowback data and its application

The fracture network parameters of multiple-fractured horizontal wells in shale gas reservoirs are usually obtained by interpretation of gas production data. However, it is difficult to obtain the effective fracture volume. In order to quickly obtain the effective fracture volume of shale gas wells, a fracturing fluid flowback model for multiple-fractured horizontal wells in shale gas reservoirs was established. Combining the water phase material balance equation and seepage equation, the expression for the effective fracture volume of multiple-fractured horizontal wells in shale gas reservoirs was derived. Analyzing the model solution, it was found that when water flowing enters the boundary dominated flow stage, the curve of the rate-normalized pressure and material balance time is a unit slope line in the double logarithmic coordinate. By using the rate-normalized pressure and material balance time data at this stage, the effective fracture volume of shale gas wells can be estimated. Based on this, a method for estimating the effective fracture volume of shale gas wells using fracturing fluid flowback data was proposed. The application examples showed that: (1) the fracturing fluid flowback model for multiple-fractured horizontal wells in shale gas reservoirs can quickly and reliably estimate the effective fracture volume of shale gas wells, and the results are credible; (2) the fracturing fluid flowback data during the gas testing period should be considered when estimating the effective fracture volume of shale gas wells, otherwise the results would be smaller than the actual results; (3) the proposed method can also be a means of recognizing and quantifying the fracturing interference effect of adjacent wells on the effective fracture volume of shale gas wells. The research results provide a new method for estimating the effective fracture volume of shale gas wells, and also provide a new idea and method for recognizing the fracturing interference of adjacent wells in oilfields.