Abstract

Second offshore Gas Production Tests from the methane hydrate concentrated zone (MHCZ) of Daini Atsumi knoll, the eastern Nankai Trough was conducted in 2017. This production test results revealed production behavior on two production test wells (AT1-P2 and AT1-P3), and additional geological data was required. Plug and well abandonment (P&A) of production test wells and monitoring wells were carried out in 2018. During this P&A operation, data acquisition was made using two newly drilled wells (AT1-CW1 and AT1-CW2) nearby former production and monitoring wells (AT1-P2, AT1-P3, AT1-MT2 and AT1-MT3) which were drilled in 2017. Data acquisition in AT1-CW1 and AT1-CW2 included pressure coring and wireline logging. Two tools, pressure cores analysis and transfer system (PCATS) by Geotek Co. Ltd. and pressure-core nondestructive analysis tools (PNATs) by The National Institute of Advanced Industrial Science and Technology (AIST) were utilized for pressure coring. The HPTC-III that could take 2.5-meter core sample at each run with keeping in-situ pressure was used, and twenty-four cores from AT1-CW1 and twenty-five cores from AT1-CW2 were drilled out with average core recovery rates 71% and 75%, respectively. In addition, wireline logging tools such as combinable magnetic resonance (CMR), natural gamma ray, formation micro imager (FMI), high resolution latero-log array tool (HRLT), gamma ray neutron sonde (HGNS) and three detector lithology density (TLD) were acquired to obtain petrophysical properties to do correlation with log measurements of production and monitoring wells and other reservoir characterization studies. Onboard analyses of pressure cores are X-Ray transmission image, compressional wave velocity, gamma-ray density, and several intervals were selected and kept maintaining pressure without dissociation of natural gas hydrate for onshore analysis. Cores from residual intervals were degassed and analyzed onboard as the manner of conventional cores using multisensory core logger (MSCL). From those cores, anion, cation, chlorinity, alkalinity of interstitial pore water were also measured onboard. This study will report onboard analysis of core data and quick look well correlation of AT1-CW1 and AT1-CW2 with existing production and monitoring wells.

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