- Home
- A-Z Publications
- First Break
- Previous Issues
- Volume 35, Issue 9, 2017
First Break - Volume 35, Issue 9, 2017
Volume 35, Issue 9, 2017
-
-
Reservoir quality prediction with CSEM
Authors Daniel Baltar and Neville BarkerCSEM sensitivity to buried resistors is a function of the area, thickness, and resistivity of the resistive body. CSEM information in an exploration process will therefore generally imply changes to one or more of a prospect’s area, thickness, and resistivity expectation. Changes in the area and thickness lead to changes in the expected recoverable volume and risk assessment (Baltar and Barker, 2015). To date, any change in reservoir resistivity expectation has typically been used, at most, to impact the saturation expectation (Loseth et al., 2014). Such an approach overlooks material information regarding reservoir flow capacity, a property that directly influences the producibility, and therefore value, of a field. In this paper, we outline an interpretation framework within which this additional information-value may be realized. We first detail a suitable rock physics framework for relating the CSEM resistivity measurement to reservoir properties, then consider the information conveyed by the change in the reservoir resistivity expectation. We illustrate how this information can be interpreted with both synthetic and real-life examples, and consider its impact on the value of a prospect.
-
-
-
Continental-scale joint inversion of Alaska and Yukon gravity and magnetic data
Authors Martin Cuma and Michael S. ZhdanovThe 3D inversion of potential field data constitutes an increasingly important method of interpretation of geophysical data. A generalized inversion method first discretizes the 3D earth models into cells of constant density, susceptibility, or magnetization vector. In the case of continental-scale geophysical data collected by a combination of land, airborne and satellite measurements, the survey area may cover thousands and even millions of square kilometres, which makes the size of the inversion domain and the number of inverse model parameters extremely large. It is well known that for potential field data the computational complexity increases linearly with the size of the problem. Even a small-sized 3D inversion of huge amounts of data to 3D earth models with hundreds of thousands of cells can exceed the memory available on a desktop computer. In the case of several millions of discretization cells, the memory requirements may exceed the capacity even of the PC clusters. The second obstacle is the amount of CPU time required to apply a huge, dense matrix of the forward modelling operator to the data and model vectors, even using parallel computing.
-
-
-
Transient electromagnetic surveys for highresolution near-surface exploration: basics and case studies
Authors M.V. Sharlov, I.V. Buddo, N.V. Misyurkeeva, I.A. Shelokhov and Yu.A. AgafonovTransient electromagnetic (TEM) surveys have been used broadly in Russia and worldwide for engineering geology, groundwater prospecting, and other near-surface applications (Bucharsky et al., 1986; Plotnikov and Kozhevnikov, 2004; Agafonov et al., 2013; Ranieri et al., 2005; Shaaban et al., 2016, etc.), as well as for petroleum and mineral exploration (Mandelbaum et al., 1983; Korolkov, 1987; McNeill, 1980). Voltage decay patterns are highly sensitive to the presence of conductors associated with ore bodies, water saturation, clay, etc. Another advantage of the method is that it does not need galvanic grounding and works in any climate and terrain. The resolution of shallow transient electromagnetic (sTEM) data has improved greatly in the past two decades due to breakthrough in micro-electronics providing advanced facilities for data acquisition and processing (nanosecond sampling rates, high-resolution ADC, etc.). Extensive sTEM surveys at a density reaching 33 points per km2 have demonstrated high performance in solving diverse problems of geosciences from structural mapping to environmental monitoring within a range of depths from 10 to 500-600 m.
-
-
-
Public domain satellite gravity inversion offshore Somalia combining layered-Earth and voxel based modelling
Authors Gaud Pouliquen, Gerry Connard, Hannah Kearns, Mohamed Gouiza and Douglas PatonAt the end of 2016, Spectrum Geo released two long offset seismic reflection profiles across the Somalian rifted margin, in the Juba Lamu and Obbia basins respectively – part of two larger 2D surveys acquired in 2014 and 2015/16 (Stanca et al., 2016; Figure 1). In frontier areas, potential field data interpretation, in particular public domain satellite-derived gravity, can play a key role in the early stages of exploration by identifying basement structure, sediment thickness, and the continental-oceanic crust transition (COT) or continental-oceanic boundary (COB), and hence indirectly contribute to the understanding of thermal history and the hydrocarbon system. This is particularly relevant over the Somalia margin, where geophysical surveys have been extremely sparse until very recent years. A high-gradient in the gravity is often used as a marker of the COB along passive margins (see Pawlowski (2008) for a review), expressing laterally contrasting physical properties between the continental and oceanic crusts. However, at magma-poor rifted margins, such as the Somalia margin, the lithosphere undergoes a progressive thinning/stretching process and the transition between unaltered continental crust and oceanic crust becomes gradual (Manatschal, 2004). Crustal hyper-extension, serpentinization, embrittlement, and exhumation of mantle peridotites can precede accretion of true oceanic crust, which in turn can blur the simple transitional model between a dense and highly magnetized oceanic crust and a weakly magnetized and lighter continental crust. Along a magma-poor margin, analysis of potential field data can distinguish the different rifting domains and quantify crustal thinning (Stanton et al., 2016; Cowie et al., 2015). In offshore Kenya and Somalia, the image is further complicated by thick sedimentary cover.
-
-
-
Understanding the tectonic history offshore Southern Gabon with high resolution seismic, gravity and magnetics
Authors Marianne Parsons, Pedro Martinez Duran, Wolfgang Soyer and Gregor DuvalHaving produced oil since 1957, Gabon has several proven petroleum systems, both onshore and offshore. Over the last decade interest has moved towards the deep offshore area where a number of early exploration wells have been successful in finding hydrocarbons, but also highlighted the need to answer questions about trap formation, source maturation and timing of charge in this new area. Following this exploration trend, and aiming to answer these key questions, a recent 3D broadband seismic survey was acquired in conjunction with shipborne gravity and magnetic data in the southern deep offshore area of Gabon. Understanding the tectonic evolution of the basin and its impact on the petroleum systems, requires the integration of seismic with the concurrently acquired gravity and magnetic data. Potential fields data provide deep crustal information where it may be challenging for seismic to resolve deep geological features, and vice versa for the shallower sedimentary section. One of the key objectives of the potential fields study was to model crustal types and thicknesses for input into basin modelling. Upper and lower crust ratios, as well as the crustal characteristics and processes in the continental-oceanic transition zones, are important for understanding the temperature regimes undergone by potential source and reservoir rocks. Knowing the distribution of lower- or higher-density crust, and zones of higher susceptibility, provides insight into the characteristics and timing of formation/deformation of the crust along the margin.
-
-
-
Total hydrocarbon volume in place: improved reservoir characterization from integration of towed-streamer EM and dual-sensor broadband seismic data
Authors Zhijun Du, Ghazwan Namo, Joshua May, Cyrille Reiser and Jonathan MidgleyUnderstanding reservoir characteristics, such as porosity, water saturation, thickness and the lateral extension of the reservoir is key for the characterization of a reservoir. These parameters are important because they serve as veritable inputs for reservoir volumetric analysis, i.e. estimating the total volume of hydrocarbon in place. Seismic data provide high-resolution images of the subsurface structure, but attempts to map fluids from seismic data may be misleading due to the ambiguity between lithology-fluid and lithology effects. In contrast, CSEM (Controlled Source Electromagnetic) data constrains subsurface resistivity – a physical property that strongly correlates with the fluid content and saturation of hydrocarbon reservoirs. By carefully integrating complementary information from both types of data, the limitations of each method can be overcome and the strength of each exploited. Used together, they help to better understand the prospect and the reservoirs characteristics, ultimately de-risking exploration, and the further applications in field development and reservoir management.
-
-
-
Qualitative analysis of seismic amplitudes for characterization of Pliocene hydrocarbon sands, eastern offshore India
More LessA comparative study of amplitudes of near- and far- stacks with prestack can be a simple and effective way for characterization of Pliocene hydrocarbon channel sands in offshore India. Synergetic studies of amplitude analysis constrained with well logs and testing data make it possible to predict quality of reservoir sands, the pore fluid content and their production potential. The amplitude studies can also help in taking decisions for testing doubtful zones in drilled wells. An example of a seemingly genuine high amplitude seismic anomaly is authenticated by AVO but testing water is also discussed as an example of seismic pitfall.
-
-
-
Adaptive techniques and other recent developments in aeromagnetic compensation
Authors Gerardo Noriega and Andre MarszalkowskiAeromagnetic compensation, an integral part of most airborne geophysical exploration programmes, has received considerable attention throughout the last few decades. Advanced compensation systems, rooted in the original model which accounts for aircraft interference from permanent, induced, and eddy-current sources, have led to significant advances fueled by research in the areas of modelling, algorithms, sensors, performance analysis, implementation issues, and emerging applications. This paper focuses on two important recent developments. Adaptive compensation allows a fundamentally different approach by using a recursive algorithm to solve the underlying least-squares problem. The system continuously ‘learns’ from inputs, dynamically adapting solution coefficients for optimum compensation with each new set of measurements. Factors affecting its performance are analysed, and it is shown that regular use of adaptive compensation along simple trim-manoeuvre segments, much less demanding than conventional full-calibration flights at high altitude, can maintain the goodness of fit of a solution near optimal levels. Secondly, real-time dynamic compensation of on-board electronic (OBE) systems is discussed. Electric currents from avionics, hydraulics, and other instrumentation, generate interference which is not accounted for by the conventional compensation model. OBE compensation technology provides robust tolerance of such sources, simplifying both operational and data processing requirements.
-
Volumes & issues
-
Volume 42 (2024)
-
Volume 41 (2023)
-
Volume 40 (2022)
-
Volume 39 (2021)
-
Volume 38 (2020)
-
Volume 37 (2019)
-
Volume 36 (2018)
-
Volume 35 (2017)
-
Volume 34 (2016)
-
Volume 33 (2015)
-
Volume 32 (2014)
-
Volume 31 (2013)
-
Volume 30 (2012)
-
Volume 29 (2011)
-
Volume 28 (2010)
-
Volume 27 (2009)
-
Volume 26 (2008)
-
Volume 25 (2007)
-
Volume 24 (2006)
-
Volume 23 (2005)
-
Volume 22 (2004)
-
Volume 21 (2003)
-
Volume 20 (2002)
-
Volume 19 (2001)
-
Volume 18 (2000)
-
Volume 17 (1999)
-
Volume 16 (1998)
-
Volume 15 (1997)
-
Volume 14 (1996)
-
Volume 13 (1995)
-
Volume 12 (1994)
-
Volume 11 (1993)
-
Volume 10 (1992)
-
Volume 9 (1991)
-
Volume 8 (1990)
-
Volume 7 (1989)
-
Volume 6 (1988)
-
Volume 5 (1987)
-
Volume 4 (1986)
-
Volume 3 (1985)
-
Volume 2 (1984)
-
Volume 1 (1983)