Bounds for Viscoelastic Properties of Heavy-oil Rocks

Heavy oils exhibit viscoelastic behaviour which is strongly frequency- and temperature- dependent. Due to the viscoelastic rheology of heavy oils the common elastic bounding methods such as Hashin-Shtrikman bounds are not rigorous for heavy-oil rocks. In this paper, we demonstrate that viscoelastic bounds of Milton and Berryman for the effective shear modulus of a two phase three-dimensional isotropic composite can be used as rigorous bounds for heavy-oil rocks. The viscoelastic bounds provide an effective tool for testing laboratory measurements and theoretical predictions for heavy-oil rocks

Rigorous bounds for seismic dispersion and attenuation due to wave-induced fluid flow in porous rocks

The Hashin-Shtrikman (HS) bounds define the range of bulk and shear moduli of an elastic composite, given the moduli of the constituents and their volume fractions. Recently, the HS bounds have been ex tended to the quasi-static moduli of composite viscoelastic media. Because viscoelastic moduli are complex, the viscoelastic bounds form a closed curve on the complex plane. We analyze these general viscoelastic bounds for a particular case of a porous solid saturated with a Newtonian fluid. In our analysis, for poroelastic media, the viscoelastic bounds for the bulk modulus are represented by a semicircle and a segment of the real axis, connecting formal HS bounds that are computed for an inviscid fluid. Importantly, viscoelastic bounds for poroelastic media turn out to be independent of frequency. However, because the bounds are quasi-static, the frequency must be much lower than Biot’s characteristic frequency. Furthermore, we find that the bounds for the bulk modulus are attainable (realizable). We also find that these viscoelastic bounds account for viscous shear relaxation and squirt-flow dispersion, but do not account for Biot’s global flow dispersion, because the latter strongly depends on inertial forces

Predicting sea level variations with artificial neural networks at Hillarys Boat Harbour, Western Australia

In the present study, the artificial intelligence meshless methodology of neural networks was used to predict hourly sea level variations for the following 24 hours, as well as for half-daily, daily, 5-daily and 10-daily mean sea levels. The methodology is site specific; therefore, as an example, the measurements from a single tide gauge at Hillarys Boat Harbour, Western Australia, for the period December 1991-December 2002 were used to train and to validate the employed neural networks. The results obtained show the feasibility of the neural sea level forecasts in terms of the correlation coefficient (0.7-0.9), root mean square error (about 10% of tidal range) and scatter index (0.1-0.2)

The use of artificial neural networks to retrieve sea-level information from remote data sources

The knowledge of near-shore sea-level variations is of great importance in applications such as ocean engineering and safe navigation. It also plays an essential role in the practical realisation of the height reference surface in geodesy. In the cases of gaps in tide-gauge records, estimates can be obtained by various methods of interpolation and/or extrapolation, which generally assume linearity of the data. Although plausible in many cases, this assumption does not provide accurate results because shallow-water oceanic processes, such as tides, are mostly of a non-linear nature. This paper employs artificial neural networks to supplement hourly tide-gauge records using observations from other distant tide gauges. A case study is presented using data from the SEAFRAME tide-gauge sta-tions at Hillarys Boat Harbour, Indian Ocean, and Esperance, Southern Ocean, for the period 1992 to 2002. The neural network methodology of sea-level supplementation demonstrates reliable results, with a fairly good overall agreement between the retrieved information and actual measurements

Artificial neural networks in wave predictions at the west coast of Portugal

In coastal and open ocean human activities, there is an increasing demand for accurate estimates of future sea state. In these activities, predictions of wave heights and periods are of particular importance. In this study, two different neural network strategies were employed to forecast significant wave heights and zero-up-crossing wave periods 3, 6, 12 and 24 h in advance. In the first approach, eight simple separate neural nets were implemented to simulate every wave parameter over each prediction interval. In the second approach, only two networks provided simultaneous forecasts of these wave parameters for the four prediction intervals. Two independent sets of measurements from a directional wave buoy moored off the Portuguese west coast were used to train and to validate the artificial neural nets. Saliency analysis of the results permitted an optimization of the networks' architectures. The optimal learning algorithm for each case was also determined. The short-term forecasts of the wave parameters verified by actual observations demonstrate the suitability of the artificial neural technique

Long-term natural flow regime (spells) analysis for water treatment discharges

Conducting mineral extraction activities usually requires obtaining a set of permits for each of the activities planned to be undertaken. This directly concerns water management and discharges associated with any mineral extraction operations. In response to the growing demand for energy resources worldwide, the industry demand for permits relating to the extraction of coal seam (and shale) gas also increased dramatically. This was in turn accompanied by the growing community concerns in regard to fracking and wastewater management practices.&#x0D; To address these concerns, the state governments in Australia developed a strict framework and guidelines for the permit application process and provided terms of reference for the environmental impact assessments, where required. In accord with the guidelines, a liquefied natural gas mining operator was conducting a research to assess several facets of water releases from Reedy Creek Water Treatment Facility to Yuleba Creek in Queensland. The scope for the research was developed in line with such guidelines and included estimating the downstream extents of flows from several Water Treatment Facility discharge volumes over a period of planned discharges. More specifically, the purpose of the study presented in this paper was to assess flows in Yuleba Creek before and after the proposed releases of treated water from the Reedy Creek Water Treatment Facility, and how the planned change to flow parameters would satisfy the regulatory guidelines. The assessment was based on 41 years of data collected at the Forestry Station gauge.&#x0D; An analysis of the obtained results suggested that the historical maximum was 25,825 ML/d. An analysis of the median flows suggested that the years 1983, 1999, and 2010-2012 had the highest medians of around 15 ML/d, 10 ML/d, and from 9 ML/d to 12 ML/d respectively. The median flow values would exceed from 0.09 ML/d to 0.69 ML/d flows during the months of February and March only. The lowest 90th percentile flows were obtained for the months from April through to October. The highest flow estimates would be in the months from November through to March. An analysis of the flow duration curves suggested that the annually averaged flow of 0.08 ML/d in the Yuleba Creek would be present for around 48% of the time. Flows predictabilities were calculated; for the baseline flow records, the value of predictability was 0.50, and the constancy/predictability ratio was 0.89. The rates of streamflow rise and fall were estimated and analysed. The results suggested that the rate of streamflow rise varied within a range from 0.0 up to 320.0 ML/d per day. The rates of streamflow fall was up to 15.0 ML/d per day.</jats:p

Fluid substitution in heavy oil rocks

Copyright © (2008) by the Society of Exploration Geophysicists All rights reserved. Heavy oils are defined as having high densities and extremely high viscosities. Due to their viscoelastic behavior the traditional rock physics based on Gassmann theory becomes inapplicable. In this paper, we use effective-medium approach known as coherent potential approximation or CPA as an alternative fluid substitution scheme for rocks saturated with viscoelastic fluids. Such rocks are modelled as solids with elliptical fluid inclusions when fluid concentration is small and as suspensions of solid particles in the fluid when the solid concentration is small. This approach is consistent with concepts of percolation and critical porosity, and allows one to model both sandstones and unconsolidated sands. We test the approach against known solutions. First, we apply CPA to fluid-solid mixtures and compare the obtained estimates with Gassmann results. Second, we compare CPA predictions for solid-solid mixtures with numerical simulations. Good match between the results confirms the applicability of the CPA scheme. We extend the scheme to predict the effective frequency- and temperature-dependent properties of heavy oil rocks. CPA scheme reproduces frequency-dependent attenuation and dispersion which are qualitatively consistent with laboratory measurements and numerical simulations. This confirms that the proposed scheme provides realistic estimates of the properties of rocks saturated with heavy oil

Integrated marine monitoring for drilling discharges under mesotidal forcing

There is a range of hydrocarbon exploration and extraction industrial project activities taking place on the North West Shelf of the Australian Continent. The shelf is a diverse and important marine ecosystem, with a number of globally significant shallow coral reefs and marine protected areas, which are vital for survival of threatened and protected species. Some of the mentioned exploration and extraction activities, such as offshore drilling, may be permitted within few kilometres away from sensitive habitats extant near a project resource extraction area. The habitats may in some cases be presented by submerged shoal ecosystems of high biodiversity and thus high environmental/ecological value, due to the presence of either or both benthic biota and fish assemblages. As part of an environmental assessment program for the industrial activities, some of the offshore exploration operators examine the effects of drilling discharges on the marine ambience. This study describes such an assessment. For the assessment, a novel integrated marine monitoring approach was conceptually designed; the program was then executed in the field using bottom-mounted equipment and a remotely operated underwater vehicle with sensors mounted on it. This study focuses on assessing the wind conditions in the project area, sea level and current velocities, in situ water temperature, salinity, turbidity and acoustic echo intensity, over several stages of the drilling operations while the drilling cuttings and muds were discharged into the water column. The collected during the austral autumn months of April and May winds showed prevailing east-southeaserlies, which is aligned well with the general understanding of wind climatology of the area. Importantly, stronger than usual winds may have a defining impact on current speeds and directions, with the current speeds enhanced by such winds. On these occasions the water transporting a discharge material may pushed towards the sensitive habitat present in the area. Normally though the hydrodynamics in the project area are dominated by semi-diurnal tides. Both vertical current velocity and water temperature distributions indicated the presence of three layers within the water column over the project site. The vertical distribution of water salinity was rather homogenous throughout the entire water column. The monitored by an optical instrument turbidity and acoustic echo intensity from an ADCP (acoustic Doppler current profiler) showed that tracing discharge plumes with a remotely operated underwater vehicle is a viable technique, which could be implemented at other locations. Such independent parameters though need a thorough cross-calibration and inter-validation for the results to be fully understood.</jats:p