Good Vibrations

The previous article in this two part series (" Least Squares Migration: 1 of 2 Articles ") discussed important similarities and distinctions between RTM (Reverse Time Migration), LS-RTM (Least Squares RTM), and FWI (Full Waveform Inversion). It was noted that traditionally, LSM does not update the velocity model. The discussion here describes an elegant process to recover high-resolution subsurface models of reflectivity, velocity and relative density from marine shot gathers with minimal pre-processing applied. The description here avoids mathematics and highlights the key breakthroughs that have enabled conventional FWI and data domain (LS-RTM to evolve into a methodology that can simultaneously recover several models of subsurface properties without significant leakage between parameters, make no assumptions about rock physics relationships, and bypass traditionally cascaded processing and imaging flows. Introduction Full Waveform Inversion (FWI) is a topic published and ...

I was inspired to write this short note by an online course by The Great Courses  that provided a few interesting insights into the process of decision making. The course uses many case studies to provide tangible insights into the myriad issues involved in the decision making processes in complex organisations. A key aspect of the lessons was an understanding how catastrophic errors can arise in decisions, and the post-mortems of such failures provide quite powerful insights into the interplay of the many issues involved.  Decisions by groups or individuals can be difficult to understand. Take for example, the countless failed investments in the airline business. The world would be very different without cheap and convenient airline travel, yet as a commercial enterprise the investment in airlines has generally been a disaster. A couple of quotes reinforce the point: It can be observed that the seismic service company business is not dissimilar to the airline business in a fe...

I briefly consider the nature of hydrocarbon saturation in reservoir pore spaces and how both seismic and electromagnetic data can characterize and quantify the nature of this saturation. Fluids in a Rock Oil or gas in a reservoir rock is not a simple case of a fluid occupying a space such that the fluid can occupy all the pore space (100% saturation) and then be completely replaced by water during reservoir production. Once a fluid migrates into a reservoir, it will never be completely removable. Hence, we talk about the ‘recovery factor’ determined from estimates of the residual oil/gas saturation after production and estimates of the original volumes of oil/gas in place. A brief insight is offered into the complexity of how fluids occupy pore space, and how this may affect the detectability of hydrocarbons on both seismic and electromagnetics (EM) data. As the following two figures schematically illustrate, a ‘water wet’ rock consists of some kind of rock matrix of varying grain siz...

I discuss the important similarities and distinctions between RTM (Reverse Time Migration), LS-RTM (Least Squares RTM), and FWI (Full Waveform Inversion), and also relate their fundamental reliance upon back-projection to Deep Neural Network training used in many machine learning pursuits. Least-Squares Migration (LSM) in Traditional Formulism Recorded seismic data is band-limited (in temporal frequency and spatial frequency, i.e., wavenumber), subsurface seismic illumination is highly non-uniform because of imperfect acquisition geometry and impedance heterogeneities in the subsurface, and seismic migration is not the mathematical inverse of modeling (see also below). Collectively, the images of the subsurface produced by conventional seismic migration do not recover the true reflectivity and resolution for known fundamental reasons. The two most common forms of Least-Squares Migration (LSM) are pursued in either the image domain or the data domain , and which have a diverse range of...

The history of deep-sea mining is rich with tales of international subterfuge, espionage and growing alarm at the imbalance of global access to critical metals and rare-earth elements—increasingly precious commodities. I briefly discuss the seabed distribution, elemental composition, and common uses of rare-earth elements. Metals, Metals Everywhere Any future transition to large-scale dependence upon electric vehicles and wind turbines will require significant volumes of special metals like cobalt (Co), lithium (Li), tellurium (Te) and neodymium (Nd), as well as base metals like iron (Fe), copper (Cu), lead (Pb) and zinc (Zn), and rare-earth elements. Global attention in recent years has turned to various elemental deposits that lie loosely on the seabed or buried shallowly in the sediment, and that can in principle, be recovered fairly easily using methods to harvest polymetallic nodules or materials dissolved in hot fluids ejected by seafloor hydrothermal vents. Manganese nodules are...