Pore pressure prediction near the plate boundary fault in the Nankai Trough, southwest Japan: Insight from seismic interval velocity and well data

1A predrill estimate of pore pressure can be obtained from seismic velocities using a velocity‐to–pore‐pressure transform, but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes. For a deepwater Gulf of Mexico example, significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the Dix equation. These lead to significant differences in the predicted pore pressure. Parameters in the velocity‐to–pore‐pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells. The uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data. If calibration wells are not available, the ideas proposed in this paper can be used with measurements made while drilling to predict pore pressure ahead of the bit based on seismic velocities.

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Initial pore pressures under the Lusi mud volcano, Indonesia

Interpretation ◽

10.1190/int-2014-0092.1 ◽

2015 ◽

Vol 3 (1) ◽

pp. SE33-SE49 ◽

Cited By ~ 16

Author(s):

Mark Tingay

Keyword(s):

Pore Pressure ◽

Mud Volcano ◽

Prediction Methods ◽

Pressure Gradients ◽

Modern Times ◽

Fine Grained ◽

High Magnitude ◽

Pore Pressures ◽

Pore Pressure Prediction ◽

Well Data

The Lusi mud volcano of East Java, Indonesia, remains one of the most unusual geologic disasters of modern times. Since its sudden birth in 2006, Lusi has erupted continuously, expelling more than 90 million cubic meters of mud that has displaced approximately 40,000 people. This study undertakes the first detailed analysis of the pore pressures immediately prior to the Lusi mud volcano eruption by compiling data from the adjacent (150 m away) Banjar Panji-1 wellbore and undertaking pore pressure prediction from carefully compiled petrophysical data. Wellbore fluid influxes indicate that sequences under Lusi are overpressured from only 350 m depth and follow an approximately lithostat-parallel pore pressure increase through Pleistocene clastic sequences (to 1870 m depth) with pore pressure gradients up to [Formula: see text]. Most unusually, fluid influxes, a major kick, connection gases, elevated background gases, and offset well data confirm that high-magnitude overpressures also exist in the Plio-Pleistocene volcanic sequences (1870 to approximately 2833 m depth) and Miocene (Tuban Formation) carbonates, with pore pressure gradients of [Formula: see text]. The varying geology under the Lusi mud volcano poses a number of challenges for determining overpressure origin and undertaking pore pressure prediction. Overpressures in the fine-grained and rapidly deposited Pleistocene clastics have a petrophysical signature typical of disequilibrium compaction and can be reliably predicted from sonic, resistivity, and drilling exponent data. However, it is difficult to establish the overpressure origin in the low-porosity volcanic sequences and Miocene carbonates. Similarly, the volcanics do not have any clear porosity anomaly, and thus pore pressures in these sequences are greatly underestimated by standard prediction methods. The analysis of preeruption pore pressures underneath the Lusi mud volcano is important for understanding the mechanics, triggering, and longevity of the eruption, as well as providing a valuable example of the unknowns and challenges associated with overpressures in nonclastic rocks.

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Characteristics of Slow Slip Event in March 2020 Revealed From Borehole and DONET Observatories

Frontiers in Earth Science ◽

10.3389/feart.2020.600793 ◽

2021 ◽

Vol 8 ◽

Author(s):

Keisuke Ariyoshi ◽

Takeshi Iinuma ◽

Masaru Nakano ◽

Toshinori Kimura ◽

Eiichiro Araki ◽

...

Keyword(s):

Pore Pressure ◽

Crustal Deformation ◽

Nankai Trough ◽

Pressure Sensors ◽

Plate Boundary ◽

Volumetric Strain ◽

Time History ◽

Pressure Change ◽

Plate Interface ◽

Deformation Component

We have detected an event of pore pressure change (hereafter, we refer it to “pore pressure event”) from borehole stations in real time in March 2020, owing to the network developed by connecting three borehole stations to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) observatories near the Nankai Trough. During the pore pressure event, shallow very low-frequency events (sVLFEs) were also detected from the broadband seismometers of DONET, which suggests that the sVLFE migrated toward updip region along the subduction plate boundary. Since one of the pore pressure sensors have been suffered from unrecognized noise after the replacement of sensors due to the connecting operation, we assume four cases for crustal deformation component of the pore pressure change. Comparing the four possible cases for crustal deformation component of the volumetric strain change at C0010 with the observed sVLFE migration and the characteristic of previous SSEs, we conclude that the pore pressure event can be explained from SSE migration toward the updip region which triggered sVLFE in the passage. This feature is similar to the previous SSE in 2015 and could be distinguished from the unrecognized noise on the basis of t-test. Our new finding is that the SSE in 2020 did not reach very shallow part of the plate interface because the pore pressure changes at a borehole station installed in 2018 close to the trough axis was not significant. In the present study, we estimated the amount, onset and termination time of the pore pressure change for the SSE in 2020 by fitting regression lines for the time history. Since the change amount and duration time were smaller and shorter than the SSE in 2015, respectively, we also conclude that the SSE in 2020 had smaller magnitude that the SSE in 2015. These results would give us a clue to monitor crustal deformation along the Nankai Trough directly from other seafloor observations.

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A Plate Too Far: Lessons Learned and Insight Gained from scientific and operational achievements during IODP Expedition 358 in the Nankai Trough.

10.5194/egusphere-egu2020-20880 ◽

2020 ◽

Author(s):

Adam Wspanialy ◽

Sean Toczko ◽

Nobu Eguchi ◽

Lena Maeda ◽

Kan Aoike ◽

...

Keyword(s):

Real Time ◽

Nankai Trough ◽

Drilling Fluid ◽

Plate Boundary ◽

Accretionary Prism ◽

Lessons Learned ◽

Hole Drilling ◽

Fault Mechanics ◽

Boundary Fault ◽

Novel Concept

IODP Expedition 358 planned to access and sample the subducting plate boundary at the Nankai Trough, Japan, and commenced on 7 October 2018, and ended on 31 March 2019, marking the ultimate stage of the NanTroSEIZE project. The goal was to drill down to the plate boundary fault, about 5 km below the ocean floor, where >8M earthquakes occur regularly at every 100&#8211;150 years. The successful completion would have represented the deepest borehole in the history of scientific ocean drilling and ultimately greatly deepen our understanding about fault mechanics, earthquake inception and tsunami generation processes.The IODP Expedition 358 intended to access the plate boundary fault zone system through deepening the previously drilled and suspended C0002P hole. The original operational objective of the Exp 358 was to reach a total depth of 7267.5 mbrt (+/- 5200 mbsf) in 4 drilled sections. Previous major riser drilling efforts during the IODP Expeditions 338 and 348 advanced the main riser hole at Site C0002 (Hole C0002F/N/P) to 3058.5 mbsf meters below sea floor (mbsf). Extensive downhole logging data and limited intervals of core were collected during those expeditions.Due to the nature of the drilling operation and the anticipated challenges ahead, JAMSTEC adopted oil & gas industry drilling standards and performed two detailed Drilling Well on Paper (DWOP) workshops as part of the very rigorous preparatory stage. Great deal of time was spent on selecting new and state-of-the-art drilling/circulating techniques, logging tools, bits and drilling fluid formulation including a new mud sealant additive &#8220;FracSeal&#8221; to make sure borehole integrity issues can be minimized as much as possible. Drilling stages seen implementation of a novel concept of near real-time geomechanics to continuously monitor and assess borehole integrity.The challenges born from side-tracking near the bottom of the previously drilled Hole C0002P (2014 Exp. 348), proved greater than the multi-disciplinary teams expected and the overall objectives set for Exp.358 were not achieved. Nevertheless, despite the significant problems seen during several attempts, the hole was deepened 204 m. This is a minor success and it is believed, once away from the highly damaged area of the C0002P hole, drilling can produce a high-integrity hole following excellent communication and recommendations between drilling and scientific teams during complex drilling operations, especially in complex environments such as the Nankai Accretionary Prism.Despite not achieving the ultimate goal of the expedition, the implemented industry drilling standards, real-time surveillance system, real time geomechanics, improved and strict communication protocols, and integrating both scientific and drilling teams have demonstrated their value and should become standard practice during future IODP/ICDP operations.

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