Dynamic analysis of horizontal wells with complex fractures based on a discrete-fracture model

Key words:  reservoir  dynamic analysis  complex fractures  fractured horizontal well  discrete facture model  finite element numerical method

Abstract:

In a hydraulically fractured horizontal well, a complex fracture system can be formed, in which inclined and bifurcated fractures can be generated, and their distribution is asymmetric. A numerical method was developed for the dynamic analysis of horizontal wells with complex fractures. Firstly, the mathematic models were established to describe micro-fractures in matrix and the complex fractures hydraulically generated respectively. The models were solved using a finite element method. Then based on a discrete-fracture model (DFM), the dimension of the fracture system was reduced from 3D to 2D, in order to reduce the load in numerical calculation. The accuracy of the new method was verified by comparing the results obtained using the Odeh and Zerzar analytical solution. Finally, a dynamic analysis for the flow in a horizontal well with the complex fractures system was conducted. The results show that radical flows within the fractures, along with the four common flow forms (i.e. line flow in fracture, radical flow in fracture, line flow in formation and radical flow in formation, not including flow from outside the simulated reservoir volume (SRV)), may appear at the early stage of the production. But the early radical flow in fractures will disappear when the well is restricted at a constant production rate, and the contribution to the productivity from the fractures outside the SRV increases. When the bottom hole pressure is kept constant, the productivity of the horizontal well can be greatly enhanced due to the branched fractures that can increase the SRV.