Abstract:

The 3D lattice based method was used to model hydraulic fracture initiation from perforation, including the stress concentrations due to excavation of the wellbore and perforation. The fracture propagation process and the associated BHP history was modeled for both vertical and horizontal wells. For the configurations presented here, the models show that fracture propagation is initially almost uniform from all perforation tunnels. Fractures then propagate preferentially from some perforations to gradually coalesce and form the hydraulic fracture while fractures from the remaining perforations stop propagating.

The near-wellbore fracture system can result in a large pressure drop and may also prevent proppant from entering the main body of the fracture.

The results demonstrate the capability of modeling complex fractures with this lattice based method. The model is also capable of modeling the true 3D hydraulic fracture propagation and interaction with natural fractures.

Introduction

Hydraulic fracture initiation and near wellbore tortuosity i s of great importance to the interpretation of bottom hole pressure (BHP) during hydraulic fracturing treatments. It is generally believed that near-wellbore tortuosity greatly contributes to the abnormal BHP often seen in the field, which can be one order of magnitude higher than theoretical predictions based on classic hydraulic fracture models. However, the stress concentration and complex fracture geometry near the wellbore can be very challenging to model.

In this paper, we used a newly developed 3D lattice based method [1] to model fracture initiation from perforation tunnels. The model is fully coupled hydro-mechanically, and can represent detailed geometries at a wide range of scales, ranging from small laboratory samples (e.g. [2]), to multi-well field-scale models. In the work presented here, the geometry of perforation tunnels and the wellbore are captured in details for two cases, namely a vertical well and a horizontal well.

Modeling Method

The lattice method used in this paper is a simplified form of the particle based bonded-particle method (BPM) [3] with the discrete element method (DEM) [4]. The lattice is a quasi-random 3D array of nodes with masses connected by springs, as shown in Figure 1. It is analogous to the configuration of particles connected by contacts in BPM but with significantly improved computational efficiency.

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