Implications of Geomechanical Analysis on the Success of Hydraulic Fracturing: Lesson Learned From an Australian Coalbed Methane Gas Field

摘要

Hydraulic fracturing is a widely used technology in the petroleum industry to increase production rates from lowpermeability reservoirs. It has also been successfully applied to coalbed methane gas development in many occasions. This paper presents an Australian field case of coalbed methane gas development where expensive fracture treatments did not yield the expected benefits. A comprehensive integrated geomechanical analysis was performed to understand the underlying causes for the failure. The geomechanical model consists of the magnitude and orientation of the three principal stresses, the pore pressure, and the rock strength. Fracture treatment data were used to estimate the least principal stress, vertical stress was determined from density logs, pore pressure was derived from direct field measurements, and rock strength values were determined from well logs and core measurements. The maximum horizontal stress (Shmax) magnitude was constrained by modeling the stress and pressure conditions consistent with the observation of wellbore breakouts in image logs. The relative magnitude of principal stresses corresponds to a transition between Strike- Slip and Reverse Faulting stress regimes (SV < Shmin < Shmax) with an overall Shmax orientation of NE-SW. Fracture propagation simulations using boundary element modeling showed that a complex fracture growth under the influence of the current in-situ stresses could be the main reason for the fracture treatment failure. The study recommended a number of alternative configurations for well orientations and fracture treatments in the field considering the existing in situ stress and the complex fracture network. Also the interactions between the coal seam and different fracturing fluids have been studied to evaluate the formation damage aspects to recommend the formation compatible fracturing fluid. Presentation of these results in this paper is expected to give a general framework for successful hydraulic fracture treatments and example of specific implementation issues with respect to an Australian coalbed methane gas field.