doi:10.16186/j.cnki.1673-9787.2023020074

Received:2023/02/27

Revised:2023/10/10

Published:2024/05/15

Theoretical model of injection flow rate influencing hydraulic fracturing effects

WANG Li1, HU Wenheng1, CAO Yunxing2, SHI Bin2, NAN Yakun1

1.School of Civil Engineering，Henan Polytechnic University，Jiaozuo  454000，Henan，China 2.School of Resources and Environment，Henan Polytechnic University，Jiaozuo  454000，Henan，China

Abstract:Hydraulic volumetric openings（HVO），which are referred to as the total volume increment over the original pore volume in the reservoir formation in the process of hydraulic fracturing，are direct measures of hydraulic fracturing effects.  Objectives In order to evaluate the HVO quantitatively，in this paper， Methods a new Finite Element Method （FEM） based on the HVO model defined on the RVE scale is established within the framework of the seepage-damage coupling Finite Element Method. This method involves establishing the controlling equations and parameter representations based on the RVE HVO model， and recognizing the damage evolution state based on the principle of energy conservation.  Results The novelties of the new method lie in that the results can output both the increments of pore volume and fracture volume and their temporal evolutions；and that the damage evolution parameters are determined not by the anhydrous tests，but by the coupling between the fluid load and the characters of rock breakdown damage evolution，which indicates the difference between the hydraulic fracturing and anhydrous fracture.The example is to perform a numeric simulation of hydraulic fracturing of a horizontal well for CBM.The calculation program is developed on the ANSYS platform.Firstly，the finished hydraulic fracturing project is simulated，which is used to verify the proposed method.The verification shows that the change of computed horizontal well pressure is basically conformed to the monitored casing pressure curve，and the computed fracturing zone is basically conformed to the spatial distribution of micro tremors，which shows the validity of the proposed method.Then，a series of simulations are performed at varied cluster spaces on the same numeric models.The results show that the fracturing area，HVO，and fracturing efficiency decrease following negative power laws with cluster space increasing，and the small cluster space is inclined to produce stress disturbances thereby improve the fracturing efficiency.  Conclusions The proposed method opens up a new prospect for damage FEM in hydraulic fracturing and supplies more exact theoretical guidance for hydraulic fracturing design.

Key words:hydraulic fracture;injection flow rate;volumetric opening;damage;fracture network