A Comparison of Clean-Up Efficiency of Multiple Fractured Horizontal Wells and Hydraulically Fractured Vertical Wells in Tight Gas Reservoirs

Abstract

Hydraulic fracturing is a well-established stimulation technique especially for unconventional reservoirs. However, sometimes its performance is less than expected due to poor cleanup of the injected fracture fluid. There are publications studying the clean-up efficiency of hydraulic fractures in vertical wells, however, there is little information in this area for multiple fractured horizontal wells, MFHWs.
This paper compares the fracture cleanup efficiency of a hydraulically fractured vertical well (VW) with that of multiple fractured horizontal wells (MFHWs) using numerical simulations and statistical approaches.
In these simulations, twelve parameters related to fracture and matrix relative permeability and matrix capillary pressure were varied simultaneously based on the two-level full factorial experimental design statistical method. Gas production loss (GPL), as the response term, was calculated and input into Response Surface Model. In each set, the correlation between parameters and GPL was established and compared to investigate the post-fracturing cleanup efficiency.
Results show that the direction of impact of parameters for VW and MFHW are similar except for the matrix permeability, Km. This difference is attributed to the flow geometry and how the well has been completed. This observation underlines that in MFHWs, the cleanup mechanism and the sequences of the importance of pertinent parameters could be different from those of the VWs.
Results also indicate that matrix Book’s type capillary pressure pertinent parameters are more important in the MFHW sets whilst Corey type relative permeability parameters are more important in VWs. These observations suggest that having a higher capillary pressure is more important in MFHWs because it results in more FF imbibition into the matrix and consequently less resistance to gas flow within the fracture. Several MFHW models with different number of fractures were constructed, which demonstrated that although the impact on well productivity is significant, its impact on clean-up performance was minimal.
These results improve our understanding of VWs and MFHWs clean-up and design of such costly operations.