Unsuccessful hydraulic fracturing cases in Australia:Investigation into causes of failures and their remedies

摘要

This paper presents the results of investigations into two field cases in Australia where expensive fracture treatments did not yield expected benefits.Field-1 contains a thin gas reservoir in which more than 20 vertical wells were drilled and hydraulically fractured.The post-frac well tests yielded low production rates prompting to a comprehensive study.Among other reservoir properties,the in-situ stresses were characterized and found to be in the reverse faulting stress regime.Through 3D mixed-mode simulation of hydraulic fracture propagation,the first part of this paper shows that the vertical fracture initiated from the vertical wellbore would turn and twist to be horizontal during propagation and would require extremely high treatment pressure and leave very little conduit for flow.These were the main reasons for multiple screen-outs during treatments and post-frac low production rates from the reservoir.A number of potentially effective hydraulic fracture treatments have been recommended for the reservoir.Field_2 contains a tight-gas reservoir,which a number of operators have attempted to develop by hydraulic fracturing over the last 30 years.After every attempt,the post-frac flow rate was lower than the pre-frac rate and therefore the well was plugged and abandoned.The second part of this paper presents the results of a comprehensive investigation into the field.The investigation has established the inadequacy of the treatment carried out in the reservoir to achieve the expected production rate,and demonstrated how more effective treatments could be designed by using a constrained hydraulic fracturing optimization model.