b'AEGC 2021Short abstractssignal-to-noise ratio. Data were gridded to highlight spatialunambiguous relation between negative voltages and IP features and modelled to create conductivity depth images.effects. Another deterrent was the high ground clearance, Supporting information included a frequency-domain EMexpected to make possible IP effect insignificant. The survey using Geonics EM-34 equipment, passive seismicrapidly accumulating experience on IP effects in helicopter data obtained using the Sara GeoBox, and information fromEM systems, however, warrants further research on fixed groundwater monitoring bores. wing EM and IP. With this work we therefore investigate the The results identified various laterally coherent zones withfixed wing EM systems sensitivity to induced polarization elevated electrical conductivities, some of which relatedeffects, presenting numerical experiments on the SPECTREM to or appeared to originate from the environmental pond.system. We carried out a great number of forward responses, Features of interest included a shallow clay layer, a likelyassociated with different combinations of Cole Cole parameters bedrock shear zone, and possible contamination. The Loupein both homogeneous halfspaces and 2 and 3 layered models. TEM data correlated well with EM-34 bulk conductivity values,The SPECTREM system resulted sensitive to the presence while passive seismic data provided useful supplementaryof chargeable material, in several Cole & Cole parameters information on bedrock depth. Groundwater sampling datadomains. These effects vary non monotonically with resistivity, did not always correlate with EM survey results, but withoutand become more marked varying the layering, i.e., adding a conclusive evidence as to the cause of the discrepancy. purely resistive basement under a shallower chargeable layer. Deep conductors responses can also be widely affected by shallow chargeable strata.112: The evaluation of alternatives to pre-acquisitionThe result demonstrate that IP effects are, at times, detectable positioning for land seismic surveys by the fixed wing EM systems. As for the helicopter EM systems, Dr Tim Dean1 and Mr Matt Grant taking IP into consideration during processing and modelling may increase the accuracy of both data and derived resistivities.1 BHPAccurate positioning for sources and receivers is a fundamental114: Impacts of minimum horizontal stress uncertainty requirement for land seismic survey acquisition. Theon wellbore stabilityintroduction of stake-less navigation systems, where the vibrator driver uses a GPS guided display to navigate intoMr Matthew Musolino 1, A/Prof Simon Holford2, A/Prof Rosalind position, has removed the need for source point surveying, butKing1 and Prof Richard Hillis1receiver positioning is still required. Depending on the receiver spacing this tends to take place either on foot or from a vehicle. 1 The University of Adelaide2 Australian School of Petroleum and Energy Resources, The latest generation of self-contained recording nodes includeUniversity of Adelaide, Australiaa GPS positioning capability that offers the potential to removeAccurate estimation of in-situ stress magnitudes is critical the need to accurately survey receiver positions prior to nodefor multiple subsurface exploration and development planting. There remains a requirement for accurate height,applications, including enhanced recovery and ensuring however, that standard GPS devices are not capable of meeting.wellbore stability. Unproductive time related to the Airborne Light Detection And Ranging (LiDAR) technology isaforementioned practices costs operators US $8 billion each now well developed and offers a simple way to measure groundyear globally. Predictive geomechanical models of stress elevation across large areas which may meet this requirement. are typically provided as estimates, and uncertainties are In this paper we use results from a recent high-density 3Drarely fully quantified. Based on data from the Cooper Basin, survey to determine the accuracy of node position and LiDARAustralia, our study examines uncertainty relating to estimates altitude measurements. Using these results we determine ifof minimum horizontal stress (Shmin) magnitudes through these measurements are capable of negating the requirement(a) leak-off test pressure-time curve interpretation and (b) for accurate surveying prior to layout, and how the layoutcalculation method of Shmin dependent on assumption process might change as a result. of tensile or shear failure. The magnitude of Shmin varies considerably at depths of ~900 m, within the Cretaceous Winton Formation. Based on the interpretation of 115 leak-off 113: AIP effects in airborne EM fixed wing systems: Atests, the range of estimates of Shmin magnitude is 9 MPa. We SPECTREM theoretical study identify a subset of 23 high-quality tests, which are associated with a narrower range of Shmin estimates (3 MPa). Leak-off Drand Reaviezzoli 1, Mr Francesco Dauti, Mrs Niroccatests outside the higher-quality subset were interpreted Devkurran2 and Mr Brad Pitts2 to suffer from engineering complications. Uncertainties in Shmin quantification also arise relating to interpolation, when 1 Aarhus Ge ophysics determining the data point indicating fracture initiation. Using 2 Spectrem Air different techniques to ascertain fracture initiation pressures IP effects can distort airborne EM data, usually producing fasterresulted in a difference of 0.34 MPa Shmin in the Moomba decays and, under certain conditions, changes in signal polarity.1well 45 and 0.86 MPa in Moomba 151 at a depth of 911 m. These effects, if not recognized and treated with a dispersiveTraditional methods for calculating Shmin magnitude do not resistivity model, often lead to artifacts in the resistivities recovered. allow for the interpretation of a reverse faulting regime. By applying a new approach for Shmin calculation, we observe Historically, the IP effects in fixed-wing AEM systems havea 2 MPa increase in the lower bound of Shmin compared to been put in the too hard basket. This was mainly due to theirtraditional methods at depths of ~900 m. Finally, wellbore geometric configuration (and its monitoring) that preventedbreakout models show that at reservoir depths of 2.6 km, AUGUST 2021 PREVIEW 80'