Numerical investigation of a low-efficient hydraulic fracturing operation in a tight gas reservoir in the North German Basin

In this paper, a hydraulic fracturing operation in the tight gas reservoir LZN in the North Germany Basin was numerically investigated to find out the reason for the weak productivity after the fracturing operation. For the investigation, a self-developed numerical model was used, in which rock formation, pore and fracture systems are coupled together. The hydro-mechanical coupling effect, the proppant transport and settling as well as their influences on the fracture closure and contact were fully considered. In the numerical modeling of the in situ operation, the whole process of the data and the main fracturing including fracture propagation, closure, contact and proppant transport were simulated. The modeling was based on the history matching of the derived bottom hole pressure (BHP) from the measured treating pressure. According to the final placement of the proppant and the width distribution after 1500 min, it was found that the middle part of the fracture around the perforation was fully closed after shut in. It indicates that the operation is unsuccessful for the production enhancement; because the connection between the borehole and the created fracture is weak. If the perforation would have been set 15 m lower, then a successful operation with a better connectivity between the borehole and the propped fracture would have been achieved. The precondition to move down the perforation is that the lower fracture barrier must be thick and has a much higher minimum horizontal stress to prevent the fracture going through it. This requirement is also fulfilled in the case study. (C) 2014 Elsevier B.V. All rights reserved.