This original BMW cover plate fits into the engine splash panel / subframe reinforcement, and is removed when performing an engine oil service on E70 X5 3.5d, 35d (2009-2013).
This part is listed by BMW as BMW part number 51757173468 (51-75-7-173-468) and is described as Genuine BMW Access Cover for Subframe Reinforcement, E70 X5 35d.
BMW Fitments:
X5 Series
E70 X5 (07-13) > X5 xDrive35d (09-13)