Entry Pressure Measurement of Unconsolidated Sediments, Sampled from Methane Hydrate-bearing Zones near NE-Nankai Trough, for Capillary Pressure Analysis

摘要

Natural gas hydrate is a potential future energy resource, and itsrndevelopment is now realistic; however, it is not clear how methanernhydrate reservoirs accumulate. Few data are available on capillaryrnpressure around gas hydrate reservoir, which is commonly used forrnreservoir characterization, because of the difficulty measuring it.rnWhereas conventional oil and gas reservoirs involve solid rocks, thernlayers containing concentrated gas hydrate consist of unconsolidatedrnsediments, which are easily deformed during measurements.rnThe pore-size distribution of Nankai Trough unconsolidated sedimentsrnwas measured using mercury injection, which is commonly used tornmeasure capillary pressure. After many measurements, the relationshiprnbetween the injection pressure and injected volume of mercury wasrndetermined. The pore size at the time of injection was calculated fromrnthe mercury injection curves. After the measurements, we observed thernmicrostructure of the sediments using field emission scanning electronrnmicroscopy (FE-SEM) and clarified the pore size. The pore sizes ofrnsediments were compared to eliminate inferior data caused by samplerndeformation. We ultimately measured 99 pieces of unconsolidated sand,rnsilt, and mud. The results of the entry pressure measurements of NankairnTrough sediments will help to determine the mechanism of methanernhydrate storage in sediments and will contribute to methane hydraternresearch and development. The entry pressure that is an indicator ofrncapillary pressure data will also be important reference data onrnunconsolidated sediments for assessing carbon dioxide capture andrnstorage (CCS).