This invention relates to a movable collecting device (1) for downhole separation and removal of particulate matter (8) from a petroleum well, the collecting device (1) having a first end portion (11) and a second end portion (12), an exterior and an interior; the collecting device (1) comprising an outer wall (4) extending axially from the first end portion (11) and to the second end portion (12), a portion of the wall (4) surrounding a collecting chamber (5); a nose (2) at the first end portion (11) comprises at least one external inlet (23), the external inlet (23) being in fluid communication with the collecting chamber (5); a drive unit (3) positioned at the second end portion (12); and a means (6) for transporting the particulate matter (8) from the exterior of the collecting device (1) to the interior of the collecting device (1) through the external inlet (23), and a portion of the wall (4) comprises a screen in fluid communication with the collecting chamber (5) and the collecting device's (1) exterior. Use of a screen (40) to form at least a portion of a wall (4) surrounding a collection chamber (5) in a movable collection device (1) is described as well.