Time-Lapse 3D CSEM for Reservoir Monitoring Based on Rock Physics Simulation of the Wisting Oil Field Offshore Norway.

The marine controlled-source electromagnetic (CSEM) method has been used in different applications, such as oil and gas reservoir exploration, groundwater investigation, seawater intrusion studies and deep-sea mineral exploration. Recently, the utilization of the marine CSEM method has shifted from petroleum exploration to active monitoring due to increased environmental concerns related to hydrocarbon production. In this study, we utilize the various dynamic reservoir properties available through reservoir simulation of the Wisting field in the Norwegian part of the Barents Sea. In detail, we first developed geologically consistent rock physics models corresponding to reservoirs at different production phases, and then transformed them into resistivity models. The constructed resistivity models pertaining to different production phases can be used as input models for a finite difference time domain (FDTD) forward modeling workflow to simulate EM responses. This synthetic CSEM data can be studied and analyzed in the light of production-induced changes in the reservoir at different production phases. Our results demonstrate the ability of CSEM data to detect and capture production-induced changes in the fluid content of a producing hydrocarbon reservoir. The anomalous CSEM responses correlating to the reservoir resistivity change increase with the advance of the production phase, and a similar result is shown in anomalous transverse resistance (ATR) maps derived from the constructed resistivity models. Moreover, the responses at 30 Hz with a 3000 m offset resulted in the most pronounced anomalies at the Wisting reservoir. Hence, the method can effectively be used for production-monitoring purposes.

Sensing whales, storms, ships and earthquakes using an Arctic fibre optic cable.

Our oceans are critical to the health of our planet and its inhabitants. Increasing pressures on our marine environment are triggering an urgent need for continuous and comprehensive monitoring of the oceans and stressors, including anthropogenic activity. Current ocean observational systems are expensive and have limited temporal and spatial coverage. However, there exists a dense network of fibre-optic (FO) telecommunication cables, covering both deep ocean and coastal areas around the globe. FO cables have an untapped potential for advanced acoustic sensing that, with recent technological break-throughs, can now fill many gaps in quantitative ocean monitoring. Here we show for the first time that an advanced distributed acoustic sensing (DAS) interrogator can be used to capture a broad range of acoustic phenomena with unprecedented signal-to-noise ratios and distances. We have detected, tracked, and identified whales, storms, ships, and earthquakes. We live-streamed 250 TB of DAS data from Svalbard to mid-Norway via Uninett's research network over 44 days; a first step towards real-time processing and distribution. Our findings demonstrate the potential for a global Earth-Ocean-Atmosphere-Space DAS monitoring network with multiple applications, e.g. marine mammal forecasting combined with ship tracking, to avoid ship strikes. By including automated processing and fusion with other remote-sensing data (automated identification systems, satellites, etc.), a low-cost ubiquitous real-time monitoring network with vastly improved coverage and resolution is within reach. We anticipate that this is a game-changer in establishing a global observatory for Ocean-Earth sciences that will mitigate current spatial sampling gaps. Our pilot test confirms the viability of this 'cloud-observatory' concept.

The plane-wave primary reflection response from an impedance gradient interface.

A weak scattering model that allows prediction of the one-dimensional acoustic plane wave primary reflection response from an impedance gradient interface is described. The velocity and density gradient profiles are represented by a smooth approximation to the Heaviside function of the Fermi-Dirac distribution type. The profiles are described by the velocities and densities at minus and plus infinity, the reference depth of the gradient interface, and its smoothness. The primary response is derived by using the Bremmer series to reduce a generally complex reflection problem to the simpler one of the primary reflections which is a valid solution for small impedance contrasts. The reflection response can be expressed in terms of the Appellian hypergeometric functions of two variables of the first kind and Gaussian hypergeometric functions. When the reflection response is evaluated at sufficiently large distance above the reference depth, the Appellian functions are reduced to Gaussian hypergeometric functions. In the Born approximation, the reflection response simplifies. In the limit of zero frequency, the reflection coefficient in the small impedance contrast approximation can be related to the classic reflection coefficient for two impedance layers in welded contact.

Source level and vocalizing depth estimation of two blue whale subspecies in the western Indian Ocean from single sensor observations.

The source level (SL) and vocalizing source depth (SD) of individuals from two blue whale (BW) subspecies, an Antarctic blue whale (Balaenoptera musculus intermedia; ABW) and a Madagascar pygmy blue whale (Balaenoptera musculus brevicauda; MPBW) are estimated from a single bottom-mounted hydrophone in the western Indian Ocean. Stereotyped units (male) are automatically detected and the range is estimated from the time delay between the direct and lowest-order multiply-reflected acoustic paths (multipath-ranging). Allowing for geometric spreading and the Lloyd's mirror effect (range-, depth-, and frequency-dependent) SL and SD are estimated by minimizing the SL variance over a series of units from the same individual over time (and hence also range). The average estimated SL of 188.5 ± 2.1 dB re 1µPa measured between [25-30] Hz for the ABW and 176.8 ± 1.8 dB re. 1µPa measured between [22-27] Hz for the MPBW agree with values published for other geographical areas. Units were vocalized at estimated depths of 25.0 ± 3.7 and 32.7 ± 5.7 m for the ABW Unit A and C and, ≃20 m for the MPBW. The measurements show that these BW calls series are stereotyped in frequency, amplitude, and depth.

Storage of Carbon Dioxide in Saline Aquifers: Physicochemical Processes, Key Constraints, and Scale-Up Potential.

CO2 storage in saline aquifers offers a realistic means of achieving globally significant reductions in greenhouse gas emissions at the scale of billions of tonnes per year. We review insights into the processes involved using well-documented industrial-scale projects, supported by a range of laboratory analyses, field studies, and flow simulations. The main topics we address are (a) the significant physicochemical processes, (b) the factors limiting CO2 storage capacity, and (c) the requirements for global scale-up.Although CO2 capture and storage (CCS) technology can be considered mature and proven, it requires significant and rapid scale-up to meet the objectives of the Paris Climate Agreement. The projected growth in the number of CO2 injection wells required is significantly lower than the historic petroleum industry drill rates, indicating that decarbonization via CCS is a highly credible and affordable ambition for modern human society. Several technology developments are needed to reduce deployment costs and to stimulate widespread adoption of this technology, and these should focus on demonstration of long-term retention and safety of CO2 storage and development of smart ways of handling injection wells and pressure, cost-effective monitoring solutions, and deployment of CCS hubs with associated infrastructure.

Acoustic signals in air and water generated by very shallow marine seismic sources: An experimental study.

When a marine seismic source, like an airgun, is fired close to the water surface the oscillating bubble interacts with the water-air interface. The main interest for seismic applications is how this effect impacts the acoustic signal propagating into the water. It is known that the sound transmission into air is abnormally strong when the sound source is very close to the sea surface relative to the emitted wavelength. Detailed insight into how the acoustic signal changes when the source depth is changed is useful in seismic data analysis and processing. Two experiments are conducted in a water tank with two different types of seismic sources. In experiment A the source is a small cavity that is sufficiently far away from the water-air interface so that it can be assumed that no interaction between the cavity and water surface occurs. In experiment B the source is a larger air bubble that is very close to the water-air interface, and hence interaction between the bubble and water surface occurs. The effects on the water surface, oscillating bubble, and emitted acoustic pressure into air are discussed. It is demonstrated that the moving surface contributes significantly to the acoustic signal measured in air.

Deep electrical imaging of the ultraslow-spreading Mohns Ridge.

More than a third of mid-ocean ridges have a spreading rate of less than 20 millimetres a year1. The lack of deep imaging data means that factors controlling melting and mantle upwelling2,3, the depth to the lithosphere-asthenosphere boundary (LAB)4,5, crustal thickness6-9 and hydrothermal venting are not well understood for ultraslow-spreading ridges10,11. Modern electromagnetic data have greatly improved our understanding of fast-spreading ridges12,13, but have not been available for the ultraslow-spreading ridges. Here we present a detailed 120-kilometre-deep electromagnetic joint inversion model for the ultraslow-spreading Mohns Ridge, combining controlled source electromagnetic and magnetotelluric data. Inversion images show mantle upwelling focused along a narrow, oblique and strongly asymmetric zone coinciding with asymmetric surface uplift. Although the upwelling pattern shows several of the characteristics of a dynamic system3,12-14, it probably reflects passive upwelling controlled by slow and asymmetric plate movements instead. Upwelling asthenosphere and melt can be traced to the inferred depth of the Mohorovicic discontinuity and are enveloped by the resistivity (100 ohm metres) contour denoted the electrical LAB (eLAB). The eLAB may represent a rheological boundary defined by a minimum melt content. We also find that neither the melt-suppression model7 nor the inhibited-migration model15, which explain the correlation between spreading rate and crustal thickness6,16-19, can explain the thin crust below the ridge. A model in which crustal thickness is directly controlled by the melt-producing rock volumes created by the separating plates is more likely. Active melt emplacement into oceanic crust about three kilometres thick culminates in an inferred crustal magma chamber draped by fluid convection cells emanating at the Loki's Castle hydrothermal black smoker field. Fluid convection extends for long lateral distances, exploiting high porosity at mid-crustal levels. The magnitude and long-lived nature of such plumbing systems could promote venting at ultraslow-spreading ridges.

Acoustically induced cavity cloud generated by air-gun arrays-Comparing video recordings and acoustic data to modeling.

For seismic air-gun arrays, ghost cavitation is assumed to be one of the main mechanisms for high-frequency signal generation. Ghost cavitation signals are weak for seismic frequencies (<300 Hz) and do not contribute to seismic reflection profiling. In the current experiment, the ghost cavity cloud is monitored by a high-speed video camera using 120 frames per second. This is, as far as the authors know, the first convincing photographic evidence of ghost-induced cavitation. In addition to video recording, acoustic signals were recorded with a sampling rate of 312.5 kHz using broadband hydrophones suspended 17 m below the array. The pressure drop around the source array is estimated using air-gun modeling followed by a phenomenological modeling of the growth and collapse of each vapor cavity. The cumulative effect of cavity collapses is modeled based on linear superposition of the acoustic signals generated by individual cavities. The simulated acoustic ghost cavitation signal and the corresponding cavity cloud show good agreement with the field data.

Acoustic generation of underwater cavities-Comparing modeled and measured acoustic signals generated by seismic air gun arrays.

Underwater vapor cavities can be generated by acoustic stimulation. When the acoustic signals from several air guns are reflected from the sea surface, the pressure drop at some locations is sufficient for cavity growth and subsequent collapse. In this paper the generation of multiple water vapor cavities and their collapses are numerically modeled and the results are validated by comparing with field data from a seismic air gun array test. In a first modeling attempt where cavity interaction is neglected, a correspondence between measured and modeled data is found. Then, this correspondence is improved by assuming that the acoustic signal generated by the other cavities changes the hydrostatic pressure surrounding each cavity. This modeling can be used to estimate the amount and strength of high frequency signals generated by typical marine air gun arrays, given that a calibration step is performed prior to the modeling.