On the Mfinda Oilfield there are a dozen-or-so opponents. It would be a good idea to eliminate the one-by-one, which will make extraction easier, after you sabotage the installation at the enemy base. This is not required, but if you do not want to kill the enemies, you need to move slower and take time to check the most immediate area more carefully. You can be substantially helped by D-Dog, while finding enemies.
It should be noted that at the base on the oilfield, there are traps, of a kind. These are dummies that are to pose as real enemies. In the course of your exploration, they are marked on the map as real enemies. Before you approach one of the enemies to knock him out, or to shoot him, try to make sure that it is a real enemy or just a decoy (as often as possible, use binoculars, zoomed-in to the maximum).
Inside the enemy base, you need to perform two acts of sabotage and there is a different mission objective for each one of them. The first primary objective is to disable the pump and to do this, you need to reach the room on one of the higher floors of the central building in the oilfield. If you have already secured the majority of the base, you can take the metal balconies to get to the place. If, on the other hand, the enemy forces still remain active and operating in this area, you need to take a look around for the window at the back of the building. Jump to reach it and climb across into the marked room. In both cases, you need to interact with the control panel.
The other primary objective assumes much more aggressive approach, because you need to destroy the big red tank inside the base. It is best to leave this objective for the end, because blowing up the tank not only alarms soldiers within the base, but also results in reinforcements being called in (to learn more, see the next page). There are many ways to destroy the tank, but I recommend that you pick one of the two following. You can reach the tank and attach a C4 explosive to it. Which you can then detonate from safety, or use the rocket or the grenade launcher from a long distance.