ASEG Extended Abstracts - 1st Australasian Exploration Geoscience Conference – Exploration Innovation Integration, 2018

The fluvio-deltaic Triassic Mungaroo Formation, North West Shelf (NWS) of Australia, hosts vast resources of hydrocarbons. However, the mechanisms that generated its 4-6 km monotonous infill architecture (colloquially known as layer cake stratigraphy) remain elusive. The vertical fluctuation between fluvial and shallow marine deposits indicates that accommodation was created simultaneously with deposition. This seems to suggest that the stratigraphic style of the Mungaroo formation was significantly controlled by the isostatic compensation of the sediment load. To test this we use a basin and landscape dynamics model, BADLANDS that combines fluvio-deltaic processes (erosion and sedimentation) with flexural isostasy. To drive our simulations we use dimensions, gradient, water discharge and sediment flux from seismic and scaling relationships extracted from the Mungaroo Formation and different lithospheric elastic thickness (Te) to account for the effect of dissimilar lithospheric rigidities and flexural isostasy. Results show an increase in delta size and decrease in sediment thickness as the lithospheric elastic thickness increases. These models help explain how thick deltaic sequences can be generated in a lithosphere with low Te values. Future research will focus on comparing the synthetic stratigraphy extracted from the models with the stratigraphic record. This study provides a valuable quantitative approach for understanding how the isostatic compensation of the sediment load can control the architecture of fluvio-deltaic deposits, which has implications for reservoir modelling.

Unconventional shale reservoirs are characterised by their extreme low permeabilities and their high in-situ stresses. Multi-stage hydraulic fracturing therefore plays a key role in developing such reservoirs. However, depending on the in-situ stress magnitude and/or regime, breakdown pressures can be too extreme to achieve, given the available surface horsepower capabilities. The local principal stresses surrounding perforation tunnels dictate the required breakdown pressure to induce enough stress to exceed the rock tensile strength.

This paper presents a newly developed model to predict the breakdown pressures in cased and perforated wells. Given an arbitrary azimuth and inclination of the wellbore and the in-situ stress magnitude/regime, the model calculates the local stresses around the perforations and consequently predicts the perforations’ breakdown pressure and the initial fracture plane orientation. The results from the model indicate as to which perforation initiates first, creating a mini-fracture that extends to create a dominant fracture. This dominant fracture would be the only fracture extending, due to the induced stress shadowing on other mini-fractures and increasing the respective in-situ principal stresses. The model also aids cluster and well placement for highly deviated wells to better identify sweet spots where breakdown pressures are minimal, resulting in maximum hydrocarbon accumulations possible. If the perforations clusters are placed in zones with extreme local principal stresses, the near wellbore fracture widths would be too small to admit any proppant, leading to early proppant screenout. The results from the model shows a critical perforation phasing angle that should be avoided, as the local principal stresses maximise, increasing breakdown pressures.

The model aims to advance the current understanding of fracture initiation in highly deviated wells in shale reservoirs. It can also assist engineers to better select sweet spots for well and cluster placement to avoid excessive breakdown pressures and/or potential early proppant screenout.

There are several ways to estimate overburden cover thickness. One of the non-invasive and inexpensive ways to rapidly estimate the cover thickness is the Horizontal-to-Vertical Spectral Ratio (HVSR) of the ambient seismic noise method. This approach utilises a broadband three-component sensitive seismometer to record ambient noise (or microtremor) induced by the wind, ocean waves and several anthropogenic activities. These microtremors are mainly composed of Rayleigh Waves which propagate in the surface layer.

The Tromino^® seismometer, which works on the HVSR principle, is a very light and portable instrument that records seismic noise in the frequency range of 0.1 to 1024 Hz, and is capable of estimating overburden cover up to 100’s of metres depth, depending on the ambient noise strength and geological setting of the survey area.

The ratio of the horizontal-to-vertical (H/V) component of the shear wave (Vs) spectrum is used to calculate the peak resonance frequency at a particular survey station, which is used to estimate the overburden thickness by using one or more existing drill holes in the area, 1D modelling, or local geological knowledge about the overburden to get velocity information for calculating depth. This paper discusses different methods used to calculate the overburden thickness, which includes calculations using a hybrid approach and a regression equation.

This paper shows the results of a Tromino^® HVSR survey in North West Zambia and comparison of estimated overburden thickness using different methods. The results were further compared with those determined from Audio-MagnetoTellurics (AMT) and drilling data. Tromino^® successfully estimated the overburden thickness and mapped the bedrock topography with reasonable accuracy.

There has been a significant growth in exploration activity for rare earth element (“REE”) deposits since the firming of prices began in 2003. Numerous deposits have been subject to detailed evaluation, though during this period only one new western-world operation at Mt Weld, Western Australia is in production. One older operation at Mountain Pass, USA, reopened in 2012 but, due to low rare earth prices, shut down in 2015. Chinese production dominates the world rare earth industry, accounting for approximately 80 - 85% of the world’s annual production of ~125,000 tonnes, from numerous deposits in five provinces. It is reported that in excess of approximately 45,000 tonnes per year of total Chinese production is illegal.

Resource estimation of REE presents no special difficulties provided care is taken to avoid over-domaining and definition of domains based on rigid grade-based criteria that are close to the lower reporting cut-off grades. These are likely to result in overstated grades and understated tonnages. Primary and supergene copper resources are natural analogies for the estimation of non-alluvial REE deposits.

Rare earth deposits are typically hosted by carbonatite, alkali- intrusives and supergene-enriched mineralisation developed on REE-enhanced substrate. An important type of heavy-enriched REE mineralisation, first recognised in southern China, has been described as an Ionic Adsorption Deposit (“IAD”) and typically is hosted by secondary clays. REE in these deposits are relatively easy to recover using low cost leaching techniques based on lixiviants or eluants consisting of simple electrolytes such as ammonium sulphate and sodium chloride. Current practice in China is to use in-situ leaching (“ISL”), vat or tank leaching or heap leaching to extract the REE.

The Mt Weld deposit, in Western Australia, was put into production after a 30 year exploration history and was only successfully drilled after 1991 once the regolith that hosts the mineralisation had been de-watered. This enabled the recovery of samples that had not suffered from the loss of fines. Its first reported resource estimates in 2002 achieved close reconciliations within a few percent of actual mined material.

In general, cut-off grades used to report resources for many REE deposits of a similar style are unrealistically low and significantly less than those used by the only two recent Western operations. These cut-offs result from over-optimistic assumptions mainly relating to the use of:

• notional values applied to all the REE
• projected metal prices from periods of unstable price hikes and
• unrealistic low costs associated with production and sales.

Basins along the northern margin of the Yilgarn Craton developed in response to extensional and compressional processes during the Paleoproterozoic. Early extension resulted in the formation of the Yerrida Basin as a large single basin over the northern Yilgarn Craton. Subsequent rifting led to voluminous volcanism in the northern part of the basin, within two depositional centres - the c. 2.03 to 1.96 Ga Bryah and Mooloogool Sub-basins. Cu-Au VMS deposits formed in the Bryah Sub-basin. Yilgarn Craton crust can be mapped using gravity and magnetic data beneath the Yerrida Basin, and Mooloogool Sub-basin. However, the Yerrida Basin can’t be mapped below much of the Bryah Basin, implying the formation of an ocean in this region. The degree of rifting of the Yilgarn Craton, and resulting architecture influenced subsequent basin development, and deformation in the region. For example, in areas where Yilgarn Craton crust can’t be mapped beneath basin sediments deformation is pronounced with the formation of disharmonic folds, refolded folds, and anastomosing shear zones. The southern part of the Yerrida Basin and the Earaheedy Basin formed shallow depositional centres over the Yilgarn Craton, and subsequent deformation in these regions is less intense. Base metal mineralisation in the region can, in part be related to the presence of deep crustal scale structures that initially developed in the Archean, and were re-activated during the Proterozoic. However, the location of c. 1800 Ma orogenic Au mineralization in the Bryah Sub-basin may not have been influenced by localisation of fluid flow around deep crustal-scale faults that formed as 200 Ma earlier, or even as early as the Archean.

CGG Multi-Client & New Ventures have undertaken new interpretation and modelling, including stratal slicing and attribute analysis on the Schild Phase 2 3D located 170km off the north-west coast of Australia within the Caswell Sub-basin. The key objectives of the interpretation were to enhance understanding of prospectivity, paleogeographic settings and produce new insights into deeper Mesozoic - Paleozoic plays based on broadband imaging of up to 20km of sedimentary section. The following is a discussion on 2 key focus elements of the interpretation derived from the attribute analysis, comprising the identification of extensive vertical fluid / gas migration features, and fluvio-deltaic and submarine channel complexes at multiple stratigraphic levels.

Hydrocarbon production from unconventional reservoirs is often associated with hydraulic fracturing operations. In many cases however, the high in-situ stresses and complex natural fracture network hinder an effective stimulation process. Therefore, different strategies are adopted to increase the success chance of stimulation. These strategies are in many cases field dependent and thus cannot be extended to other fields. In this study, we demonstrate a new work flow to ensure a successful stimulation process in an unconventional gas field in Pakistan. Well Rizq-01 was drilled as an exploration into challenging PAB formation which is tight sandstone with 0.3mD permeability but highly fractured. Exploration wells in offset fields were drilled and stimulated in the same formation and resulted in screening-out and inability to place enough proppant due to fracture complexity and high in-situ-stresses. To overcome these challenges, extensive petrophysical and geomechanical analysis were performed to introduce a new workflow for stimulation of the formations with similar characteristics. The workflow includes a) Extract extensivewell log information for better understanding of stress barriers, stress magnitude and orientation, Young’s Modulus, formation fluid information, other essential petrophysical properties, b) Sensitivity analysis on the hydraulic fracturing treatment including the proppant size, type and volume, and fluid systeme.g. the design was based upon geomechanical and petrophysical interpretations of the openhole log data, and c) Redesign of fracturing treatment process utilizing a first-of-its-kind onsite pre-frac test results, showing its helpfulness in the absence of bottom-hole gauge. The study therefore summarizes the challenges, the work flow implemented, and the lesson learnt for successful stimulation job in Rizq Field.

Current gamma-ray detectors, based upon scintillation, are not likely to perform well in narrow diameter logging-while-drilling (LWD), such as NQ diamond drilling. The normally used halide scintillators of NaI, CsI are considered to not have sufficient resolution to compensate for a lack of stopping power in PGNAA applications. Whereas, BGO, a robust oxide scintillator performs so poorly with respect to resolution, light output, and temperature sensitivity that the higher density and stopping power does not compensate fully for its limitations.

We have evaluated several novel halide and oxide scintillators that might improve the viability PGNAA in small diameter LWD application. Specifically, we have looked at CsI, SrI, BGO, CWO, CeBr, GAGG, LaBr, YAP scintillators, and find that CeBr and CWO may be a useful alternative to LaBr in PGNAA applications. Our modelling and analysis indicates that very dense scintillators such as CWO, with moderate resolution capability, or moderate density with high resolution, such as CeBr and LaBr, are the best candidates for measuring line spectra from PGNAA with small, less than 50 mm diameter, detectors. However, none of the newer scintillators are a panacea as the penetrative nature of the PGNAA process means that a high background of scattered gamma rays will obscure many weak elemental peaks even with a “perfect” detector.

The Southern Thomson Project aims to advance understanding of tectonic history and mineral prospectivity of basement rocks of the southern Thomson Orogen beneath extensive Mesozoic and Cenozoic cover. The project area in northwestern New South Wales (NSW) and western Queensland is considered underexplored, with poor definition of structural corridors and mineral systems in the Palaeozoic rocks. This collaborative project between Geoscience Australia, the Geological Survey of New South Wales (GSNSW) and the Geological Survey of Queensland is acquiring and interpreting new geoscience data, including geophysical, geochemical, and isotopic investigations. Geophysical data interpretations and models have been tested through a program of stratigraphic drilling to provide basement cores for studies of petrology, geochronology, geochemistry, petrophysics and mineral systems. Downhole geophysical logging of the drillholes also aims to characterise the cover sequences and define depth to basement.

Interpretation of regional aeromagnetic and gravity data and synthesis of existing mineral, water-bore and petroleum drillholes created a geological map of basement lithologies and structures. Stratigraphic drilling has targeted areas with no data to constrain lithologies or their ages, with four key areas selected for drilling in far northwestern NSW. Information on the thickness of cover sequences over resistive basement interpreted from AEM inversion models has proven useful during the selection of drilling locations.

Seven stratigraphic drillholes were completed within NSW using a combination of mud rotary and diamond drilling. All holes penetrated surface regolith, as well as sedimentary rocks of the Eromanga Basin, to achieve approximately 50 metres of basement core for analyses. Resulting improvements to geological understanding and development of exploration techniques will be a keystone to progress future investigations in the southern Thomson Orogen.

The drainage of New Guinea has evolved rapidly since Pliocene time. Relief growth initiated in accreted oceanic terranes in the north and migrated into the Australian margin interior over time. The present-day drainage retains inherited elements of an ancient fluvial system that routed sediments from these northern terranes through the Central Highlands into foreland flexural basins, epicontinental seas, and deep oceanic basins. The rise of the Highlands and of the Papuan Peninsula spurred drainage reorganization, such that today little of the oceanic terranes still drains through the mountain range. This evolution has strongly affected the composition of the clastic sediments delivered to the shelves.

The topography retains the memory of some of the most recent changes. Most of the relief of the Papuan Peninsula formed during the past 5 Ma, driven by tectonic removal of the load of the peninsular ophiolites, accompanied by contractional collapse along the Aure-Pocklington trough. In the eastern Central Highlands, rapid drainage reversal results from flexural back-tilting under the load of the colliding Huon-Finisterre Range. Northward reversal is also observed at the western end of the Highlands. In the south, the Fly platform has experienced recent, widespread, non-tectonic and non-flexural uplift of deep origin that will ultimately close the Torres Strait.

The Quaternary drainage evolution will be used to calibrate the Badlands software developed by the Basin Genesis Hub, as a first step for simulating the evolution of topography and sediment delivery to the Australian shelf and Gulf of Papua in earlier times.

New high resolution geochemical information was acquired for fluids from recent Canning Basin wells and interpreted in context with previous work on fluid typing and correlation by Geoscience Australia (GA). Ungani field oils are interpreted to be derived from the same/very similar clastic source rock, comprising bacterial and marine algal matter deposited under anoxic to sub-oxic conditions, and generated within the peak oil window for a high quality marine source rock. Observed low GOR’s are the consequence of both source rock type and gas removal. Liquids from the Yulleroo field are derived from a similar source to the Ungani oils, with the addition of dry gas from a higher maturity and/or more gas prone source, and generated and expelled at slightly higher maturity. The current lean gas condensate phase is the result of the addition of dry gas combined with minimal water washing. In nearly all aspects the Ungani and Yulleroo liquids resemble the L4 family previously attributed by GA to a probable Carboniferous age source. Gas-condensate from the Valhalla North-1 field was derived from a more mature source rock deposited in an oxic environment and containing more gas prone (terrigenous) organic matter. Map based modelling incorporated eleven 1D models in the Ungani-Yulleroo and Valhalla-Asgard region, and a map based burial history and maturity model. The source rock model was derived from the liquid geochemistry results rather than the poor quality source rock potential data gathered to date. Burial history modelling and maturity modelling at the top of the Lower Laurel Carbonate shows maturity for gas expulsion in the main trough and oil to light oil expulsion on the flanks of the basin. Maximum burial in the basin took place immediately prior to the Fitzroy Uplift, resulting in the main phase of oil generation and expulsion taking place around 200Ma.

A database of over 10,000 wells with open hole logs, of which over 600 wells are dedicated surveillance wells with whole core, time lapse Carbon/Oxygen, Neutron, and Temperature data being used for evaluating Adrok’s deep penetrating radar system.

Kern River (California) is on its way to recovering 90% of its OOIP and surveillance is playing a significant role in achieving such a world class milestone. Future growth for development of the field and surveillance technologies still exist as well. To that end, we are looking at the possibly of surface only acquisition for Chevron’s surveillance needs.

Significant time and effort was spent on dielectric logging in the 1970’s - 80’s by operators and service companies. Adrok’s Atomic Dielectric Resonance (ADR) scanning technology claims to interact with the subsurface in the same region of the electro-magnetic spectrum as di-electric logging, but from surface measurement. First Principles predicts a rise in dielectric constant as temperature rises. Fieldwork was conducted during 2014 to 2016. The surveys were divided up into two groups, one for training (full access to database) and one for blind testing (no access to database). Surprisingly, the blind tests could detect the presence or absence of a single zone steam chest by a rise in dielectric constant at the correct space-time.

Atomic Dielectric Resonance (ADR) is a patented investigative technique (Stove, 2005) which involves the measurement and interpretation of resonant energy responses of natural or synthetic materials to the interaction of pulsed electromagnetic radio-waves from materials which permit the applied energy to pass through the material. Radiowaves (typically in the frequency range of 1MHz to 100MHz) are continuously pulsed into the ground from an ADR transmitter antenna and the responses from the ground are gathered at the ground surface by an ADR receiver antenna. The resonant energy response can be measured in terms of energy, frequency and phase relationships. The precision with which the process can be measured helps define the unique interactive atomic or molecular response behaviour of any specific material, according to the energy bandwidth used. ADR is measurable on a very wide range of hierarchical scales both in time and space. Time scales may range from seconds to femtoseconds, and spatial scales from metres to nanometres. The technology has been applied to help mining and petroleum companies in their search for subsurface natural resources, some of which are described in this contribution.

The body of the oral presentation describes in greater detail the technology, field experiments and results to date for Chevron. Results from onshore geothermal heat exploration at a number of sites in New Zealand are also presented.

The scope and principal objectives of this paper are to improve our understanding of the industrial minerals sector, especially regarding project evaluation and business profit drivers. Information and discussion is aimed to stimulate debate and hopefully assist towards a more professional approach in development of industrial mineral projects.

Industrial minerals are often misperceived by the community, education and research organisations, industry professionals and Governments. They are best defined as mineral products used and consumed in industrial, manufacturing and agricultural applications. Production of industrial minerals may enhance or up-grade their chemical and physical properties, though the mineral remains largely unchanged by chemical processing. Examples include iron ore, potash, borates, ilmenite, silica sand, gypsum and kaolin.

Industrial minerals are commonly underrated as the poor cousin to precious metals, base metals, light metals and energy minerals. To the contrary, many small and large industrial mineral companies are highly profitable with long-term 15-30% EBIT / Sales margins and strong returns on capital employed.

Successful evaluation and development of industrial minerals must recognise the principles of “Value in Use”. This involves a dynamic interplay between technical, market and commercial factors, including resource characterisation, geo-metallurgy, application tests, process optimisation, customer trials and primary market surveys. Industrial mineral products require consistency of physical and chemical properties, leading to performance in the customers’ application.

Keys to profitability include technical understanding, market knowledge, QA / QC discipline, and customer relationships. Success is rarely about having the biggest or cheapest operation, it’s more about consistency, rarity, functionality, market structures, barriers to entry and, ultimately, price leverage.

“New Age” raw materials to supply the electronic, battery and sustainable energy industries are considered, including lithium, cobalt, graphite, indium, manganese, scandium, and high-purity quartz.

Principal conclusions from this paper are that industrial minerals can be very profitable businesses if managed professionally with an understanding of industry drivers, opportunities and risks.

We have developed an algorithm and released open-source code for the 1D inversion of magnetotelluric data. The algorithm uses trans-dimensional Markov chain Monte Carlo techniques to solve for a probabilistic conductivity-depth model.

The inversion of each station employs multiple Markov Chains in parallel to generate an ensemble of millions of conductivity models that adequately fit the data given the assigned noise levels. The trans-dimensional aspect of the inversion means that the number of layers in the conductivity model is solved for rather than being predetermined and kept fixed. Each Markov chain increases and decrease the number of layers in the model and the depths of the interfaces as it samples.

Once the ensemble of models is generated, its statistics are analysed to assess the posterior probability distribution of the conductivity at any particular depth, as well as the number of layers and the depths of the interfaces. This stochastic approach gives a thorough exploration of model space and a more robust estimation of uncertainty than deterministic methods allow.

The method’s application to cover thickness estimation is discussed with synthetic and real examples. Inversion of complex impedance tensor and also derived apparent resistivity/phase data are both demonstrated. It is found that the more pronounced layer boundaries allow more straightforward interpretation of cover thickness than that from deterministic smooth model inversions. It is concluded that thickness estimates compare favourably with borehole stratigraphic logs in most cases, and that the method is a useful addition to a range of cover thickness estimation tools.

Exploring for the Future is a four-year programme of the Commonwealth Government that aims to boost Australia’s attractiveness as a destination for investment in resource exploration. A significant component of the data acquisition component of the programme is the AusAEM Airborne Electromagnetic (AEM) Survey. This survey will focus on wide line-spaced acquisition as a regional mapping tool to gather new pre-competitive data and information, on extents never previously attempted. The objectives are to map, at a reconnaissance scale:

• trends in regolith thickness, character, and variability
• variations in bedrock conductivity
• the continuity of key conductive bedrock (lithology-related) conductive units under cover
• the groundwater resource potential of the region.

The first AEM survey of this programme, when completed, will cover an area of over one million square kilometres (more than the areas of France and Spain together), at a nominal line spacing of 20 km with infill surveys in selected areas for subscription companies.

In order to have the greatest impact the survey targets greenfield areas where the resource potential is unknown. The AEM data will contribute to estimating features and character of the cover material. To maximize industry collaboration on the project GA sought, and received, expressions of interest from industry subscribers for infill flying on the regional survey for lines spaced at 200 or 400 meters.

Regional AEM surveys improve geological understanding in areas with little or no outcrop. The processed data enables informed interpolations of conductivity between sparse drill-holes and estimates on the depth of the basement-cover interface from geophysical modelling. The modelling results are used to inform follow-up exploration activities thereby reducing exploration risk. The new data will be released to the public domain at regular intervals to promote future activity by the government, exploration and research sectors.

In a collaboration between Department of Agriculture and Food, Western Australia (DAFWA) and CSIRO, funded by the Western Australia Government’s Royalties for Regions Program and the Gascoyne Foodbowl Project, the Gascoyne River AEM Aquifer and Groundwater Characterization Project was established with the aim of determining whether airborne electromagnetic (AEM) data can be employed to better map attributes of the unconfined alluvial aquifer beneath and adjacent to the ephemeral Gascoyne River.

One major aspect of the project was to produce drilling targets, based on interpretation of AEM data, for groundwater production. In this presentation, we briefly recapitulate our method and discuss the result of the drilling campaign that ensued. We show that our exploration targets have resulted in overwhelming success in the conversion of exploration wells to production bores; and that the production wells produce greater yields of better quality groundwater than previous campaigns that were conducted through step-out drilling.

We show that interpretation of the AEM inversions allowed us to map the aquitard layers that define the bottom of the Gascoyne River Old Alluvium aquifer system, determine the extent of the saltwater intrusion from the nearby Indian Ocean, and to calculate the overall volume of the aquifer system. These calculations allow us to provide estimates of total groundwater volume contained in the aquifer for sustainable production.

In October-November 2012 a geophysical mapping and dredging campaign in the eastern Coral Sea was conducted on the RV Southern Surveyor during voyage ss2012_v06 (ECOSATI). Part of this campaign was focussed in northernmost Zealandia where volcanic seamounts and uplifted portions of the Lord Howe Rise were targeted to determine the age and location of the northern portion of the Lord Howe Seamount Chain. Geophysical and geological analysis of the dredge sites from the southernmost South Rennell Trough and Chesterfield Plateau confirm the extension of the Lord Howe Seamount Chain ~200 km northward than previously identified, with an age-progression extending to ~27-28 Ma. These new samples, together with previously published samples from the youngest part of the chain, show consistency with both Indo-Atlantic and Pacific hotspots. The average magma flux rate of the Lord Howe hotspot is estimated at 0.4 m³/s, which is similar to the rates of crustal production at the South Rennell Trough, A peak in magmatism along the trail in the late Oligocene may be related to a slowdown in the motion of the Australian plate sometime between 27-23 Ma. The results of the geophysical and geological sampling and estimates of magma flux from the Lord Howe Seamount Chain will assist in thermal history modelling in the sedimentary basins of northern Zealandia and will help provide a geological framework for frontier resource exploration in this region.

Core supported study of the heterogeneous Ungani dolomite reservoir architecture is driving development drilling and upgrades to field resource estimates. Vuggy connected and macro non-connected pore space was directly measured over a 70m continuous core using 3D structural analysis of CT-scans. Plug density measurements indicate non-connected or sub-140 micron resolution contribution of around 1% to 2.5% (pu) for the tight matrix, but all remaining porosity potentially contributes to oil production. The high resolution core porosity data is vertically repositioned and upscaled to calibrate neutron-density and sonic petrophysically derived porosities which are inadequate to resolve productive zones using conventional reservoir cut-offs. Conditioned resistivity image data correlated exceptionally with directly measured connected porosities. Reservoir properties were extrapolated to all wells across the Ungani field giving field net/gross estimates of up to 63% and porosities over 30% pu in some vuggy and brecciaed zones. The heterogeneity and prolific nature of the uppermost 17m of reservoir had not been previously recognised due to poor log data coverage and access at the casing points. Recent re-analysis of this section at Ungani-3 with Chemostrat ICP-OES-MS analysis of ditch cuttings was instrumental in proposing additional drilling to re-target this zone. Mineralogy analysis is used to calculate rock grain densities and help calibrate neutron-density derived porosity logs over the Ungani field. Up-scaled core porosity correlates well with density and sonic porosity logs. Resistivity logs adjusted for minerology can also be used to predict porosity and support the use of resistivity image logs to identify vuggy zones and estimate porosity at a higher resolution than conventional logging tools. A field static model was populated with three facies distributed over vertical zones according to the distribution encountered in the core porosity analysis and well logs, and iteratively matched to the dynamic pressure data and field production history which exhibits field scale multi-Darcy horizontal permeability and protection from vertical water cut. Further drilling and downhole artificial lift is planned to extend field production rates to 3000 bbls/day. Increased confidence in this regionally developed reservoir is supporting further exploration of undrilled prospects in this immature and under-explored trend

A vertical seismic profile (VSP) survey involves placing sensors in a borehole to record the passage of energy transmitted using a source of seismic energy placed on the surface. The sensors are usually contained within sondes that are coupled to the borehole wall using mechanical clamps. Existing VSP acquisition systems are generally unsuitable for acquisition using the wireline units typically used for minerals logging. In this paper we describe a new multis-sonde VSP acquisition system specifically designed for acquiring high-resolution VSP surveys in hard-rock environments.