Paralana-2 South Australia, Micro-Seismic Monitoring During Stimulation

Abstract

On 3 January 2011 the Paralana JV carried out a stimulation experiment on the Paralana-2 (P2) borehole in South Australia injecting +14,668l at a depth of 3,679-3,685mRT and 8,700psi. Over 125 Micro-earthquake (MEQ) events were recorded by the monitoring network and located in an area about 100m x 220m with an average depth of 3,850m. The largest event, ML1.4, occurred at the end of the frac test just after shut-in. Between 11 and 15 July 2011 P2 was stimulated with +3,040,000l of fluid being injected at pressures up to 9,000psi. Over 10,000 MEQ events were recorded by the monitoring network with only about ½ of these events being locatable due to their small size. The maximum event, a ML2.6, occurred near the beginning of the test with several others of equal size occurring throughout the stimulation. No events triggered the “Traffic Light” safety system imposed by PIRSA.

Over 850 of the larger MEQ events, ranging in size between ML-0.5 and ML2.6 were handpicked, located and plotted on site to provide Petratherm an image of the fracture created and guide the stimulation. Post processing of the data yielded another 1,025 high quality events down to ML-1.5 in size and helps provide the final picture of the fracture. Results show that fracturing occurred in three swarms. Swarm one occurred near the well and deepened from 3.7km to over 4.1km. Swarm two occurred as a circular patch extending a few hundred meters east of the 1st swarm. Swarm three occurred after shut-in and extends downwards to the NNE and reaches a depth of 4.4km. All events formed along an NE trending structure steeply dipping to the NW. A total length of over 900m and width of 400m to 600m was achieved. Total seismic moment estimations for the injected volume measures ML3.2. Recorded total moment measured ML3.15.