A portable automated unit for determination of an annulus free volume of an annulus volume in a riser, the annulus volume being defined as the volume between an outer sheath of the riser and an inner pressure barrier of the riser, and the annulus free volume being defined as the volume that is not occupied or filled with liquid, which portable automated unit comprises: - a portable container having a riser outlet/inlet configured to connect the container with the annulus volume, - at least one flow arrangement for flow measurement, wherein the flow arrangement is situated in line with a gas flow direction between the riser outlet/inlet and an outlet/inlet of the portable automated unit, wherein the at least one flow arrangement is further configured to introduce a pressure into the annulus volume via the riser outlet/inlet for pressurization of the annulus volume, - at least one valve connected between the annulus volume and the flow arrangement for pressurization and/or depressurization of the annulus volume, - at least one pressure instrument connected between the annulus volume and the at least one valve, and - at least one logic unit, wherein the at least one flow arrangement, the at least one valve, the at least one pressure instrument and the at least one logic unit are fitted within the portable container; and wherein the at least one logic unit is configured to read off the at least one pressure instrument, to read off and control the at least one valve and to read off the at least one flow arrangement, and wherein the at least one logic unit is configured to calculate the annulus free volume based on the introduced pressure difference in annulus volume and the amount of gas added or removed from the annulus volume; and wherein the portable automated unit is configured to automatically perform a determination of the annulus free volume when connected to the annulus volume and a test sequence is initiated. which portable automated unit comprises: - a portable container having a riser outlet/inlet configured to connect the container with the annulus volume, - at least one flow arrangement for flow measurement, wherein the flow arrangement is situated in line with a gas flow direction between the riser outlet/inlet and an outlet/inlet of the portable automated unit, wherein the at least one flow arrangement is further configured to introduce a pressure into the annulus volume via the riser outlet/inlet for pressurization of the annulus volume, - at least one valve connected between the annulus volume and the flow arrangement for pressurization and/or depressurization of the annulus volume, - at least one pressure instrument connected between the annulus volume and the at least one valve, and - at least one logic unit, - a portable container having a riser outlet/inlet configured to connect the container with the annulus volume, - at least one flow arrangement for flow measurement, wherein the flow arrangement is situated in line with a gas flow direction between the riser outlet/inlet and an outlet/inlet of the portable automated unit, wherein the at least one flow arrangement is further configured to introduce a pressure into the annulus volume via the riser outlet/inlet for pressurization of the annulus volume, - at least one valve connected between the annulus volume and the flow arrangement for pressurization and/or depressurization of the annulus volume, - at least one pressure instrument connected between the annulus volume and the at least one valve, and - at least one logic unit, wherein the at least one flow arrangement, the at least one valve, the at least one pressure instrument and the at least one logic unit are fitted within the portable container; and wherein the at least one logic unit is configured to read off the at least one pressure instrument, to read off and control the at least one valve and to read off the at least one flow arrangement, and wherein the at least one logic unit is configured to calculate the annulus free volume based on the introduced pressure difference in annulus volume and the amount of gas added or removed from the annulus volume; and wherein the portable automated unit is configured to automatically perform a determination of the annulus free volume when connected to the annulus volume and a test sequence is initiated.