Ketil Hokstad

Ketil Hokstad
Equinor

PhD

About

102
Publications
22,936
Reads
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825
Citations
Introduction
Working on multigeophysical inversion and machine learning, with applications to petroleum, geothermal and mineral exploration
Additional affiliations
September 2009 - present
Norwegian University of Science and Technology
Position
  • Professor (Associate)
May 1992 - September 2001
SINTEF
Position
  • Researcher
September 2001 - present
Statoil ASA
Position
  • Geophysicist
Education
January 1996 - December 1999
Norwegian University of Science and Technology
Field of study
  • Applied Geophysics
September 1987 - May 1992

Publications

Publications (102)
Conference Paper
Full-text available
Seismic imaging of the salt structures in the Nordkapp Basin is extremely difficult due to weak primaries, strong multiples and diffractions. The Uranus well was drilled on a conceptual salt tectonic model. The well penetrated more than 2000m of salt, and was terminated inside salt. The failure of the Uranus well triggered large geophysical efforts...
Article
Full-text available
The target of the RN-15/IDDP-2 well at Reykjanes is geothermal resources at supercritical temperatures. The drill site has been mapped by electromagnetic and gravimetric surveys. Here, a method for subsurface temperature prediction by multigeophysical inversion is presented and demonstrated on the IDDP-2 drill site. Using resistivity from magnetote...
Article
Full-text available
Understanding heat flow and its lateral variability is important for petroleum prospecting. We present a methodology and workflow for estimation of radiogenic heat production in the crust and heat flow from geophysical data. The surface heat flow is determined by three main components: heat from Earth's interior, heat produced in the crust, and hea...
Article
The aim of the Iceland Deep Drilling Project is to drill into supercritical geothermal systems and examine their economic potential. The exploratory well IDDP-2 was drilled in the Reykjanes geothermal field in SW Iceland, on the landward extension of the Mid-Atlantic Ridge. The Reykjanes geothermal field produces from a <300 °C reservoir at 1 to 2....
Conference Paper
Full-text available
A method for multigeophysical inversion for geothermal systems is presented. Datasets and models input to the inversion may include one or more of the following geophysical parameters: resistivity, magnetization, density and seismic P-wave and S-wave velocities, or /-ratio. Rock physics models relating geophysical parameters to temperature and poro...
Article
Full-text available
Harvesting geothermal energy often leads to a pressure drop in reservoirs, decreasing their profitability and promoting the formation of steam caps. While steam caps are valuable energy resources, they also alter the reservoir thermodynamics. Accurately measuring the steam fraction in reservoirs is essential for both operational and economic perspe...
Patent
Full-text available
A method of estimating a polymetallic nodule abundance is provided. At least one acoustic parameter of the seabed is provided and the method compromises inverting the at least one acoustic parameter to estimate the polymetallic nodule abundance of the seabed. The at least one acoustic parameter may be determined at least partially from multi-beam e...
Patent
Full-text available
A method of estimating a mineral content of a seabed geological structure is provided wherein there is provided at least one geophysical parameter of the geological structure. The method includes inverting the at least one geophysical parameter to estimate the mineral content of the geological structure.
Conference Paper
Full-text available
The green shift and energy transition will lead to increased need for metals and minerals. New onshore mines tend to have low grades, and the opening of new mines can be politically and socially controversial. Also, there is a geopolitical aspect of mineral supply. Deep-sea minerals may be of future importance to secure mineral supply for European...
Conference Paper
This paper presents preliminary results from a subset of work carried out as part of a multinational research project entitled DErisking Exploration for multiple geothermal Plays in magmatic ENvironments (DEEPEN). One objective of DEEPEN is to develop a customized approach to exploration for superhot geothermal plays in magmatic systems. This paper...
Article
This special section featuring Europe aims to promote the importance and value creation of data integration for subsurface characterization and to share the learnings across the various disciplines and industries. Geoscience activities in Europe have a long track record in various industries with diverse targets and challenges. This special section...
Patent
Full-text available
Title: : SEISMIC ACQUISITION SYSTEM AND METHOD FOR SEABED MINERAL EXPLORATION Abstract: A seismic survey system for prospecting for sub-sea minerals comprising: a first vessel 2 1towing a first seismic source 22 and a seismic detector 23; and a second vessel 24 towing a second seismic source 25. The seismic detector 23 is arranged to receive acous...
Patent
Full-text available
Title of the Invention: Method of calculating temperature of a geological structure Abstract Title: Inverting a magnetic parameter to calculate the temperature of a geological structure A method of calculating the temperature of a geological structure comprises inverting a magnetic parameter of the geological structure to estimate its temperature....
Article
Full-text available
Rock magnetism and magnetic potential field data are influenced by many factors, including mineral composition, hydrothermal alteration, faults, and past and present temperatures. Laboratory measurements on rock samples from Reykjanes show that mid-oceanic ridge basalts possess large remanent magnetization and have two or three different Curie temp...
Article
Full-text available
The subsurface temperature is of major interest for assessment of the petroleum prospectivity of a sedimentary basin. A key parameter in modeling the thermal structure of the subsurface is thermal conductivity. The information about lateral variation of this parameter is usually sparse. We propose a simple linear relationship between thermal conduc...
Article
Full-text available
The measured electromagnetic field in magnetotellurics (MT) is composed of the natural source field and its subsurface response. Commonly, the data are represented as impedances, the complex ratio between the horizontal electric and magnetic fields. This measure is independent of the source distribution because the impedance-tensor estimation conta...
Conference Paper
Full-text available
The Aru region is located offshore West Papua, Eastern Indonesia. This region is a tectonically complicated area and close to an active tectonic plate boundary. It is a frontier exploration area with very limited well information. One of the main challenges in this frontier area is to estimate the heat flow in order to estimate petroleum generation...
Conference Paper
Full-text available
The spatial and temporal distribution of subsurface temperature is of major importance for the petroleum prospectivity of a sedimentary basin. The thermal history controls the maturation of source rocks and the quality of reservoir rocks. The porosity loss associated with quartz cementation is directly dependent on temperature (Walderhaug, 1996). T...
Article
Full-text available
The Nordkapp Basin is an intra-continental basin with complex salt structures such as diapirs and possible traps/sealing mechanisms for oil reservoirs at Carnian level. The study presents 3D Simultaneous Joint Inversion (SJI) in three possible workflow configurations, used for cascade modelling and imaging of the deep salt base in Nordkapp basin. T...
Article
Full-text available
The seismic imaging of salt diapirs in the Nordkapp Basin gave rise to considerable problems in defining their shape and volume. Independent information was added by integrating the interpretation with high resolution gravity and magnetic data. We developed a novel, iterative workflow, separated into sub-categories: sediments, salt structures, base...
Article
Full-text available
A method has been developed to link present-day well or seismic measurements through rock-physics temperature and net-erosion variations caused by past tectonic events within a sedimentary basin. An ambiguous and intricate link among physical rock properties, temperature history, and burial history is demonstrated by modeling examples. Net-erosion...
Article
Full-text available
If the orientation of a seafloor electromagnetic (EM) instrument is unknown, it has to be estimated afterwards, relatively early in the processing. Here we present a method to estimate the horizontal and vertical orientation of seafloor electromagnetic receivers. Three component magnetic recordings of the naturally occurring magnetotelluric field a...
Article
Full-text available
We evaluated a joint contrast source inversion scheme for marine controlled-source electromagnetic (mCSEM) and magnetotelluric (MT) data based on a scattered field formulation. The scheme considered only contrasts in electric conductivity, and it allowed the medium to be transversely isotropic with a vertical symmetry axis. The method was based on...
Article
Full-text available
We present an integral equation framework for 2.5D frequency domain EM modelling in conductive media, i.e. in media which are assumed invariant in one direction. Furthermore, we consider media which are transversely isotropic in the vertical direction (TIV), thus allowing the horizontal and vertical conductivities to differ. The integral equation f...
Article
Full-text available
The paper presents a new approach for modeling important geological elements, such as reservoir, trap, and source, in a unified statistical model. This joint modeling of these geological variables is useful for reliable prospect evaluation, and provides a framework for consistent decision making under uncertainty. A Bayesian network (BN), involving...
Conference Paper
Summary Seismic imaging can be challenging in basalt regions, and we consider how EM methods can be used to enhance understanding in exploration. For a synthetic basalt model, we consider the sensitivity and inversion of CSEM and MT data, and discuss the dependence on anisotropy and water depth. Our inversion results demonstrate how the combination...
Article
Full-text available
We present a 3D contrast source inversion scheme for electromagnetic data in conductive media. We consider only contrasts in electric conductivity but allow the medium to be transversely isotropic in the vertical direction. This has applications in, for instance, inversion of marine controlled-source electromagnetic data. The contrast source invers...
Article
Full-text available
Reflection seismic investigation of salt diapirs may have - as in the Nordkapp Basin in the Norwegian Barents Sea - considerable imagining problems to define the shape of salt structures. To improve salt imaging, joint interpretation of full-tensor gravity gradiometry data (FTG), high-resolution magnetic data, controlled-source electromagnetic data...
Article
To apply a broad spectrum of signal frequencies for a marine electromagnetic survey (0.01 Hz to 500 Hz) is a unique way for detailed mapping of geology in conjunction to hydrocarbon exploration. We present results from a demonstration research survey over the Uranus salt structure (Nordkapp Basin, Barents Sea) involving purpose built broadband rece...
Conference Paper
Full-text available
Salt Imaging in the Nordkapp Basin with Electromagnetic Data, by K. Hokstad, E. A. Myrlund, and B. Fotland; #90096 (2009) The Nordkapp Basin is an intra­continental salt basin with approximately 30 complex salt structures. The salt is of Early Permian age, and was mobilized by Early Triassic sedimentation. Tertiary uplift and erosion removed 1200­1...
Conference Paper
We present a framework for 2.5D EM modeling in conductive TIV media based on integral equations. The method is developed for mCSEM purposes, thus assuming inline polarization of the source and crossline invariant media. The framework is tested numerically
Conference Paper
Full-text available
Interferometry is used to reconstruct surface data from Walkaway VSP data. Together with a common receiver gather of a WVSP experiment we formulate a data-driven surface demultple scheme for WVSP data. The theory will be presented together with real data examples from the Nordkapp basin in the Barents Sea, an area well known for its complex geologi...
Conference Paper
We present an inversion scheme for controlled source electromagnetic (CSEM) data to picture anomalies in conductivity on a geophysical scale. The method is based on the scalar diffusion equation corresponding to the approximation of the vector wave equation governing electromagnetic wave propagation in conductive media in the ultra low frequency do...
Article
Full-text available
Remote sensing techniques record variations in subsurface petrophysical parameters, such as seismic, electromagnetic, and potential-field properties. Seismic is by far the most common technique, using acoustic and elastic waves to map boundaries between buried strata with contrasting pressure (P) and shear (S) wave velocities. High-resolution data...
Article
Techniques to estimate the Green's function between two measured points using wavefield correlations and/or crosscorrelations are classified as seismic interferometry. In this paper we provide a unifying framework for understanding a broad class of interferometric techniques using Green's theorem. This framework and foundation allows spurious multi...
Article
Full-text available
The basic theory of surface-related multiple elimination (SRME) can be formulated easily for 3D seismic data. However, because standard 3D seismic acquisition geometries violate the requirements of the method, the practical implementation for 3D seismic data is far from trivial. A major problem is to perform the crossline-summation step of 3D SRME,...
Article
Full-text available
We study seismic traveltime measurements acquired in the borehole, including vertical seismic profiling, seismic measurements while drilling, and drill-bit noise generated data. These traveltime data are used to assess informative parameters, including drill-bit position, distance to drilling target, and parameters of the velocity model. First, we...
Conference Paper
Apex-shifted multiples in CMP gathers are difficult to suppress and can seriously degrade seismic imaging results. To address this problem, we present a high-resolution Radon transform based on shifted hyperbolae with an additional apex-shift parameter. This transform allows focusing of apex-shifted events with a wide range of shapes, leading to a...
Conference Paper
Surface-related multiple elimination (SRME) can predict and attenuate all multiples generated by the air-water interface. Earlier SRME schemes for walkaway VSP (WVSP) data involve a model in order to generate primaries recorded at the air-water surface which are not recorded in a WVSP experiment. In this paper, we generate surface data from the WVS...
Conference Paper
We present a transversely isotropic depth migration scheme for marine controlled-source electromagnetic (MCSEM) data, based on Claerbout's well-known 45 degree equation from seismic imaging. The proposed scheme is applicable to MCSEM data acquired with a 2-D geometry, and is numerically very efficient. We show examples from field data acquired offs...
Article
We present a simple method for estimating an effective source wavelet from the first arrival in marine vertical seismic profiling (VSP) data. The method, which utilizes the free-space Green's function of the Helmholz equation, is simple and very computer efficient. We show examples from synthetic and real offset and walkaway VSP data. In the synthe...
Article
Full-text available
The principle of the marine controlled-source electro-magnetic (CSEM) technique used for remote detection of hydrocarbons (HC), is described by Ellingsrud et al., (2002). A horizontal electrical dipole (HED) emits an ultra-low frequency (0.1–5 Hz) electromagnetic (EM) wavefield into the underlying seabed and downwards into the subsurface. EM energy...
Article
The use of controlled source electromagnetics (CSEM) in the marine environment has grown rapidly in the past few years from a simple anomaly fluid-hunting technique used in geologically simple environments to a modeling and inversion based technique applied in structurally and lithologically complex environments (Carazzone et al., 2005). The tool s...
Article
We present a method that predicts water bottom primaries at near offsets. The concepts of limited aperture migration and inverse scattering are combined to develop a data driven theory for data reconstruction. Data extrapolation can be particularly challenging in s hallow water, where early events of the recorded wave-field are mainly in the postcr...
Conference Paper
Full-text available
Electromagnetic diffusive fields and and seismic wave fields can both be propagated in smooth background media using Helmholz-type equations. Consequently, many seismic migration methods operating in the frequency-space space domain can be adapted for controlled-source electromagnetic (CSEM) data. We present and demonstrate 3-D frequency-wavenumber...
Article
Since the processing and data transfer capacity is highly limited in while drilling operations, it is important to evaluate the information content of different data sources. We focus on the analysis of seismic traveltime data acquired in the borehole, in particular the use of traveltime picks for well geosteering. The Bayesian methodology that we...
Article
Full-text available
Compensation for geometrical spreading is important in prestack Kirchhoff migration and in amplitude versus offset/amplitude versus angle (AVO/AVA) analysis of seismic data. We present equations for the relative geometrical spreading of reflected and transmitted P- and S-wave in horizontally layered transversely isotropic media with vertical symmet...
Article
Full-text available
Vector fidelity is an important issue in applications of oceanbottom seismic (OBS) data that involves shear-wave splitting, azimuthal anisotropy and amplitude analysis. Here, we discuss characterization and compensation for vector infidelity. Two component (2C) vector infidelity, involving only the horizontal components of the OBS data, can be char...
Article
Full-text available
We present an implementation of three-dimensional dynamic ray tracing in anisotropic elastic media. The geometrical ray approximation is extended through Maslov uniform asymptotics, and is employed in the calculation of Maslov canonical operators describing the transmission of waves between two points in the background medium.
Article
Dr. Tygel demonstrates that the factor [Formula: see text] introduced in equation (B‐15) is zero. There is no doubt that the proof is correct. I thank Dr. Tygel for bringing this result to my attention.
Article
Full-text available
This paper presents a method for elastic and viscoelastic imaging of multicomponent seismic data. The method is based on Claerbout's survey-sinking concept and the (visco) elastic Kirchhoff integral for the displacement field. Assuming a multishot and multireceiver experiment, the migration process is formulated as a wavefield reconstruction proble...
Article
Full-text available
We demonstrate the applicability of the Dirac equation in seismic wavefield extrapolation by presenting a new explicit one-way prestack depth migration scheme. The method is in principle accurate up to 90 degrees from the vertical, and it tolerates lateral velocity variations. This is achieved by performing the extrapolation step of migration with...