Lecture 2

Common question: drilling

Related question: mechanical impurities

Special question: ideal gas mixtures

1 Drilling

A drilling engineer develops, plans, costs and supervises the operations necessary for drilling oil and gas wells. They are involved from initial well design to testing, completion and abandonment. Look at the figure 1 below and remind the main part of the drilling process.

Figure 1 – Typical drilling process

The main part is drill bit. Drill bits rotate and drill through the rock. They are connected to the end of the drill string (or a drill pipes). The drill pipes stand on pipe rack before they go into the hole. Derrick or rig is the tallest thing that supports all lifting equipment and drill string. The rotary table helps to rotate the drill string.

What is the mud? Mud (or drilling fluids) is the composite of water, clay, weighting material (some polymers), and chemicals.

The mud pump pumps mud from the mud tank into the top of the drill string. The mud flows down inside the drill string to the bit. It cleans and cools the drill bit. Then it flows up the holes and carries rock cuttings up with it. The mud and the cuttings go to the mudscreen. The mudscreen separates the cuttings from the mud. The mud flows through to the mudtank below.

The mud pump is one of the largest and heaviest parts of a drilling rig, and one of the most difficult parts to transport.

Figure 2 – Mud pump transportation

Here are four traps.  The anticline is a structural type of trap, as is the fault trap and the salt dome trap.

The stratigraphic trap shown at the lower left is a cool one.  It was formed when rock layers at the bottom were tilted, then eroded flat.  Then more layers were formed horizontally on top of the tilted ones.  The oil moved up through the tilted porous rock and was trapped underneath the horizontal, nonporous (cap) rocks.

Four Types Of Structural and Stratigraphic Traps

This hole has been drilled into a sandstone that was deposited in a stream bed.  This type of sandstone follows a winding path, and can be very hard to hit with a drill bit!  The plus is that old stream beds make excellent traps and reservoir rock, and some of these fields are tens of miles long!

This type of sandstone is usually enclosed in shale, making this a stratigraphic trap.

Just because you drill for oil or gas does not mean that you will find it!  Oil and gas reservoirs all have edges.  If you drill past the edge, you will miss it!  This might explain why your neighbor has a well on his land, and you do not!

 

Stratigraphic Problems When Drilling

When you drill, you may find a producing reservoir very near the surface. But many other things can happen:

You might drill into a reservoir that has been depleted (all the oil and gas removed) by another well.  There may be a new infill reservoir between two wells that could be developed with a third well.  Or one that was incompletely drained.  Maybe if you drill a little deeper you might hit a deeper pool reservoir!  You might be able to back up and produce a bypassed compartment.  The petroleum geologist has to think of all these things when planning a new well!