Dead Space 2

Another great way to get this is in Chapter 6 when you return to the main concourse where the Lightspeed Boy is (the giant spinning purple teletubbie statue) and just before you meet Ellie for the first time.

When you first enter the room, two enemies will constantly spawn on the other side of the room and charge towards where Ellie has the security door down and she'll blow them away. If you aim the launcher right, you can place a mine right in the path of one of the spawn points and the point where Ellie will blast away the necromorphs. If you have enough mines, the enemies will just keep running into them and you'll get the achievement to pop. I needed 10 more to get the achievement, had like 20 mines and got it easy with plenty of mines to spare.

Notes: Incase you miss a proper path point, you can just click RB to close the mine and then kinesis the mine back over to you.

Also, if you go far enough into the room where you get attacked by a crawler, the enemies will stop respawning and it won't work.

This one is rather easy. Chapter 3 where the little pack necromorphs are will easily net you 7 or 8 kills depending where you place your mines. The detonator is also very effective at killing stalkers when you progress further into the game. When you get to an area with stalkers back up into a corner and put down a perimeter of detonator mines and wait for the stalkers to run into them. When one trips one mine put up another one in the same spot and repeat. The end of the school fight is a good place to rack up kills with this weapon as well.

The way I did this was when I first encounted a Guardian, which are the whiny necromorphs that hang on the walls and shoot little pods on the ground. This part is located in Chapter 6, right after you fight your first Brute. When you get there, just keep making the Guardian produce pods and make sure you aim the mines on the wall (low as possible), so that the sensor beams are horizontal. Do this twenty times or less and move on to better things.

*Note*
Be careful when you approach a pod when it's dead, it sometimes explodes. I hope this helps :]

at the very very final segment of the game, right before "the escape" you have to fight "an enemy" that constantly spawns "shadows" if you will. i didn't use the mine weapon up until this part and i was able to take out around 5 enemies at a time with one mine

This is to improve Stronger's suggestion. Right when you enter the room with the light boy turn to your right. Aim the mines directly above, the shoot the necros come out of, preferably in between the letter C O N, due to the arc of the trajectory the mine literally attaches right below the opening where the necros spawn from, and they get blown away. The only thing I caution is the fact that if they sit to long they seem to explode, so get the timing and area down, and if you mess up just restart checkpoint, incidentally also restart after the achievement to keep your ammo.