This dataset presents X-ray microtomography data of 23 Neogloboquadrina pachyderma tests recovered from a methane seepage area in the Sea of Okhotsk (station LV 50-05). Specimens were selected from four sediment intervals (20–25 cm, 120–125 cm, 210–215 cm, and 470–475 cm) to capture a range of diagenetic alteration intensities (minor, moderate, and major) associated with methane-derived authigenic carbonate (MDAC) precipitation. For each specimen, the following volumetric parameters were determined using SkyScan 1272 microtomography and CT Analyser software: total sample volume (Vsample), test volume (Vtest), solid phase volume (Vsolids), porosity (void volume fraction), and the volume fractions of shell and inclusions. X-ray density values (gray values) were measured for both the carbonate test and solid inclusions. The data enable quantitative assessment of morphological alterations in foraminiferal tests resulting from authigenic carbonate precipitation. These measurements support the interpretation of diagenetic overprints in fossil foraminifera from methane-influenced environments and provide a basis for distinguishing between primary biogenic and secondary authigenic carbonate phases.