title: Seismic geomorphology of shallow-water lacustrine deltas in the Paleocene Huanghua Depression, Bohai Bay Basin, eastern China

authors: Wang, Jiahao

subjects: Seismic geomorphology

abstract: The most important sedimentary facies comprising shallow-water lacustrine deltas are distributary channels, and these form abundant ribbon-shaped sand bodies that are excellent petroleum reservoirs. However, distributary channel sandstones are notoriously difficult to correlate and characterize in the subsurface based on well data alone. Here, we show how seismic geomorphology can be used to map lacustrine deltaic sedimentary successions in the First Member of the Kongdian Formation within the Zilaitun Oilfield, Huanghua Depression (China). Using core and wireline logs, this study identified distributary channels as the dominant sedimentary facies. Together with mottled gray-green or maroon mudstones and locally shingled progradational seismic reflection architecture, this indicates that deltas were built in a weakly-oxidized shallow-water lacustrine environment. Next, core observations were linked to seismic data to produce a successive series of stratal slices and root mean square amplitude attribute (RMSAA) maps. The RMSAA maps allowed distributary channel, mouth bar, and beach bar facies to be identified and mapped across the study area. Two patterns of distributary channels emerged from the data: (1) a distributive pattern with a lower concentration of distributary channels; and, (2) an anastomosing deltaic pattern with a high concentration of bifurcated distributary channels. Based on the seismic geomorphological analysis we show that the succession records three phases of delta evolution - retrogradation, aggradation, and progradation - which combine to form 3rd-order sequences. From a petroleum reservoir point of view, the distributive pattern yields narrower, thicker, and less connected sand bodies than the anastomosing pattern. This is consistent with observations from modern shallow-water lacustrine delta systems, providing independent support for the interpretation and highlighting the effectiveness of using seismic geomorphology.

text: Seismic geomorphology of shallow-water lacustrine deltas in the Paleocene Huanghua Depression, Bohai Bay Basin, eastern China The most important sedimentary facies comprising shallow-water lacustrine deltas are distributary channels, and these form abundant ribbon-shaped sand bodies that are excellent petroleum reservoirs. However, distributary channel sandstones are notoriously difficult to correlate and characterize in the subsurface based on well data alone. Here, we show how seismic geomorphology can be used to map lacustrine deltaic sedimentary successions in the First Member of the Kongdian Formation within the Zilaitun Oilfield, Huanghua Depression (China). Using core and wireline logs, this study identified distributary channels as the dominant sedimentary facies. Together with mottled gray-green or maroon mudstones and locally shingled progradational seismic reflection architecture, this indicates that deltas were built in a weakly-oxidized shallow-water lacustrine environment. Next, core observations were linked to seismic data to produce a successive series of stratal slices and root mean square amplitude attribute (RMSAA) maps. The RMSAA maps allowed distributary channel, mouth bar, and beach bar facies to be identified and mapped across the study area. Two patterns of distributary channels emerged from the data: (1) a distributive pattern with a lower concentration of distributary channels; and, (2) an anastomosing deltaic pattern with a high concentration of bifurcated distributary channels. Based on the seismic geomorphological analysis we show that the succession records three phases of delta evolution - retrogradation, aggradation, and progradation - which combine to form 3rd-order sequences. From a petroleum reservoir point of view, the distributive pattern yields narrower, thicker, and less connected sand bodies than the anastomosing pattern. This is consistent with observations from modern shallow-water lacustrine delta systems, providing independent support for the interpretation and highlighting the effectiveness of using seismic geomorphology.

year: 2020

title: Magnetic flux braiding: Force-free equilibria and current sheets

authors: Longbottom, A.W.

subjects: MHD-plasmas-sun

abstract: We use a numerical, nonlinear, multigrid magnetic relaxation technique to investigate the generation of current sheets in three-dimensional magnetic flux braiding experiments. We are able to catalog the relaxed nonlinear force-free equilibria resulting from the application of deformations to an initially undisturbed region of plasma containing a uniform vertical magnetic field. The deformations are manifested by imposing motions on the bounding planes to which the magnetic field is anchored. Once imposed, the new distribution of magnetic footpoints are then taken to be fixed, so that the rest of the plasma must then relax to a new equilibrium configuration. For the class of footpoint motions that we have examined, we find that singular and nonsingular equilibria can be generated. By singular we mean that within the limits imposed by numerical resolution, we find that there is no convergence to a well-defined equilibrium as the number of grid points in the numerical domain is increased. These singular equilibria contain current “sheets” of ever increasing current intensity and decreasing width; they occur when the footpoint motions exceed a certain threshold and must include both twist and shear in order to be effective. On the basis of these results, we contend that flux braiding will indeed result in significant current generation. We discuss the implications of our results for coronal heating.

text: Magnetic flux braiding: Force-free equilibria and current sheets We use a numerical, nonlinear, multigrid magnetic relaxation technique to investigate the generation of current sheets in three-dimensional magnetic flux braiding experiments. We are able to catalog the relaxed nonlinear force-free equilibria resulting from the application of deformations to an initially undisturbed region of plasma containing a uniform vertical magnetic field. The deformations are manifested by imposing motions on the bounding planes to which the magnetic field is anchored. Once imposed, the new distribution of magnetic footpoints are then taken to be fixed, so that the rest of the plasma must then relax to a new equilibrium configuration. For the class of footpoint motions that we have examined, we find that singular and nonsingular equilibria can be generated. By singular we mean that within the limits imposed by numerical resolution, we find that there is no convergence to a well-defined equilibrium as the number of grid points in the numerical domain is increased. These singular equilibria contain current “sheets” of ever increasing current intensity and decreasing width; they occur when the footpoint motions exceed a certain threshold and must include both twist and shear in order to be effective. On the basis of these results, we contend that flux braiding will indeed result in significant current generation. We discuss the implications of our results for coronal heating.

year: 1998-06

title: HIEMPA: Hybrid Instruments from Electroacoustic Manipulation and Models of Pütorino and Aquascape

authors: Whalley, Ian

subjects: music

abstract: The HIEMPA project combined a team of people with technical, artistic, environmental and cultural expertise towards an artistic outcome aiming to extend the New Zealand sonic art tradition. The work involved collecting audio samples from the aquascape of the Ruakuri Caves and Nature Reserve in Waitomo, South Waikato, New Zealand; and samples of a variety of pütorino – a New Zealand Mäori wind instrument. Following a machine learning analysis of this audio material and an analysis of the performance material, hybrid digital instruments were built and mapped to suitable hardware triggers. The new instruments are playable in realtime, along with the electroacoustic manipulation of pütorino performances. The project takes into account the environmental and cultural significance of the source material, with the results to be released as a set of compositions. This paper discusses the background research and process of the project.

text: HIEMPA: Hybrid Instruments from Electroacoustic Manipulation and Models of Pütorino and Aquascape The HIEMPA project combined a team of people with technical, artistic, environmental and cultural expertise towards an artistic outcome aiming to extend the New Zealand sonic art tradition. The work involved collecting audio samples from the aquascape of the Ruakuri Caves and Nature Reserve in Waitomo, South Waikato, New Zealand; and samples of a variety of pütorino – a New Zealand Mäori wind instrument. Following a machine learning analysis of this audio material and an analysis of the performance material, hybrid digital instruments were built and mapped to suitable hardware triggers. The new instruments are playable in realtime, along with the electroacoustic manipulation of pütorino performances. The project takes into account the environmental and cultural significance of the source material, with the results to be released as a set of compositions. This paper discusses the background research and process of the project.

year: 2008