In this month's column, Wayne Nash challenges fellow drillers with some industry math problems. And as always, there's an anecdote.



I just got back from the Colorado Water Well Contractors Association Annual Conference in Colorado Springs a couple weeks ago. Great show, beautiful location and some of the sharpest drillers I've ever met. I guess when you have to drill so many different formations and face so many challenging conditions, it sorta weeds out the “wormy” drillers pretty quick.

A funny thing happened just after I arrived. I had flown into Denver and rented a car. Since I couldn't smoke on the plane or in the airport, as soon as I got on the road, I started chain-smoking Camels to get my nicotine levels back to normal. For some dumb reason, the rental car didn't have an ashtray so I rolled down the window, turned on the radio and really was enjoying the view when my phone rang.

It took a few rings to turn down the radio, roll up the window and answer. It was my bride and personal terrorist, a.k.a., bin-Lottie. She wanted to know what took me so long to answer the phone. I said, “I had to roll up the window.” She said, “Are ya still on the plane?” Like Bill Envall says: “Here's your sign!” I told her that the turn signals were out and the pilot wanted me to hang out my arm so we could land this thang! She immediately realized what she had said, but it was too late - it's been a while since Lottie was on a plane. She made me promise not to write this in an article, so forget I ever told you this story!

While in Colorado Springs, I got talking to the drillers about the different geology and conditions they encounter. I soon learned to keep my mouth shut and my ears open, 'cause those boys drill some downright interesting holes.

When I got home, I got an e-mail from a friend who is a petroleum engineering student at LSU. He sent me part of a homework assignment that one of his professors gave him. It's a little deeper than most of us drill, but the math is the same, regardless of depth. I fooled with it for a while and enjoyed the challenge; thought you might, too. Here goes:

1. A well that you are drilling is at a depth of 14,500 feet in an 8.5-inch hole with 14.2 ppg mud. The next sand to be drilled has a known bottom hole pressure of 10,980 psi, and will be encountered at 14,700 feet. What mud weight will be needed to provide an overbalance of at least 200 psi when the sand is drilled?

2. If you are drilling at 12.5 feet per hour, how much time do you have before you reach the next sand?

3. a. Calculate the volume of mud in the drill pipe, assuming a 8.5-inch hole and 16.60 lbs./ft. drill pipe, to a depth of 14,700 feet.

b. Calculate the volume of mud in the annulus, assuming an 8.5-inch hole from surface to T.D.

c. Calculate the total volume of mud in the system to be weighted up if the surface volume is 700 bbls.

d. You are pumping 420 gpm while drilling. Once the pits are weighted up to the new mud weight, how much time will it take to circulate the new mud through the hole?

e. How much barite will you need to weight up to the new mud weight?

f. Assuming 14.2 ppg mud, what would the shut-in pressure be on the drill pipe if you were unable to weight up the mud when you drilled the sand?

I found these to be interesting problems. They took me back to my oilfield days and, kinda like a riddle for drillers, entertained me for a while. If you get some answers, e-mail me and we'll compare notes. Hey, even if we screw up, have a blowout and burn down the rig, it's a virtual rig; we'll build a better one next time and get a better mud engineer!

By the way, after I left Colorado Springs, I went to Denver and spent the night with my sister, who I haven't seen in a few years. We had a delicious buffalo roast, some wine and great conversation until pretty late. I had a good time even though my sister is sort of a moon-bat. Matter of fact, if you met my whole family, you'd find out that I am the NORMAL one.

Now there's a scary thought!