High stress, high near-wellbore pressure losses (NWBPL) and pressure-dependent leakoff (PDL) contribute to premature screen outs during some fracturing treatments in the Cooper Basin of South Australia and Queensland. In one case, an unsuccessful attempt to hydraulically fracture a well occurred because of limitations raised by completion design, insufficient stress data forewarning high-stress observations, and inadequate ability to counter high NWBPL and PDL effects.
We reviewed the current completion, hydraulic fracturing design and treatment execution practices and concluded that changes should be made in these areas: stress modeling/layering, completion design, perforating practices, hydraulic fracture design strategy, management of PDL and on-site treatment execution strategy. The largest departure from current practices was the use of 0- and 180-degree oriented perforating; thus, we describe the methodology chosen for this case, discuss current means to orient perforations and review alternative methods available.
The specific changes in hydraulic fracturing design and execution included: developing and calibrating log-derived rock-mechanical properties; incorporating PDL characteristics in the hydraulic fracturing treatment design; and applying specific job steps to reduce PDL and NWBPL. Our evaluation presents our frac implementation strategy and describes field fracturing treatments applying all these changes. Wherever possible, we will discuss the considerations that lead to our choice of actions and must be made when evaluating the potential applications of these technologies.