A comparative study of flowback rate and pressure transient behavior in multifractured horizontal wells completed in tight gas and oil reservoirs

Abstract

Tight reservoirs stimulated by multistage hydraulic fracturing are commonly characterized by analyzing the hydrocarbon production data. However, analyzing the available hydrocarbon production data can best be applied to estimate the effective fracture–matrix interface, and is not enough for a full characterization of the induced hydraulic fractures. Before putting the well on flowback, the induced fractures are filled with the compressed fracturing fluid. Therefore, analyzing the early-time rate and pressure of fracturing water and gas/oil should in principle be able to partly characterize the induced fractures, and complement the conventional production data analysis.We construct basic diagnostic plots by using two-phase flowback data of three multifractured horizontal wells to understand the physics of flowback. Analysis of flow rate plots suggests three separate flowback regions based on the relative values of water and gas/oil flow rate. In the first region, water production dominates while in the third region gas/oil production dominates. In the second region, water production drops and gas/oil production ramps up. The cumulative water production (CWP) plots show two distinct water recovery periods. Before gas/oil breakthrough, CWP linearly increases with time. After breakthrough, CWP increases with a slower rate, and reaches to a plateau for the oil well. We also develop a simple analytical model to compare the pressure/rate transient behavior of the three flowback cases. This work demonstrates that rate and pressure, carefully measured during the flowback operations, can be interpreted to evaluate the fracturing operations and to complement the conventional production data analysis for a more comprehensive fracture characterization.