If you saw a lot of sludge, I would personally perform another oil change. Drive your X3 until it is fully up to temperature. Then let it cool and change it again.
Do another change around 4k miles since you don't drive your X3 far based on your mileage/times between changes. hat alone can build up sludge. Try to get it out for a good drive weekly if possible!
My garage: 2007 BMW Z4 3.0si Manual, 2007 BMW X3, 2006 BMW 530xi
Retired: 1998 BMW Z3
Member of BMWCCA!