Hyne 12-98-2a

About the Author

Norman J. Hyne is Professor of Petroleum Geology at the University of Tulsa in Tulsa, Oklahoma. He is also president of NJH Energy, a company that owns and manages the operation of oil wells. Norman is well known for his "Basic Petroleum Geology for Non-Geologists" short course that he has taught through out the world. He is the author of "Non-Technical Guide to Petroleum Geology, Exploration, Drilling and Production" and "Dictionary of Petroleum Exploration, Drilling and Production" published by PennWell Books. Norman has also edited four books on the petroleum geology of the mid-continent.

Finding and Producing Oil and Gas

Contents:

Chapter 1 - Gas and Oil

Chapter 2 - Petroleum Geology

Chapter 3 - Petroleum Exploration - The Prospect

Chapter 4 - Land - Leasing and Site Preparation

Chapter 5 - Drilling the Well

Chapter 6 - Testing the Well

Chapter 7 - Completing the Well

Chapter 8 - Producing Gas and Oil

Chapter Five

Drilling a Well

Today, the well is drilled with a modern rotary rig (Figure 5-1). It is called a rotary drilling rig because there is a long length of steel pipe with a drill bit on the end suspended in the hole. The pipe is rotated from the surface to rotate the bit and cut the hole on the bottom. The rotating drillpipe and the bit is called the drillstring.

The most common bit is the tricone bit (Figure 5-2) with three rotating cones mounted on bearings on the bottom of the bit. On the cones are teeth that are designed to flake the rocks on the bottom of the well into well cuttings, small rock chips.

The drillpipe comes in thirty foot sections which are threaded on both ends and are called joints. As the well is drilled deeper, another joint of drillpipe must be added each thirty feet in an operation called making a connection. After an average of 24 to 48 hours of rotating, the drill bit becomes worn out. To change the bit, all the drillpipe must be pulled out of the hole (tripping out), the bit changed and all the drillpipe put back in the hole (tripping in). This procedure takes time, and the deeper the well, the longer it takes.

The power to the drilling rig is supplied by diesel engines located on the ground next to the drilling rig. They are connected to the drilling rig by a mechanical transmission. On some of the more modern, large land rigs and on all offshore drilling rigs there are still diesel engines but they drive a generator that makes electrical power. The electrical power is fed to the rig by electrical cable to drive electrical motors. It is called a dieselelectric system.

The hoisting system on a drilling rig (Figure 5-3) is used to raise and lower equipment such as the drillstring in the well. It includes a steel tower located directly above the well, called the derrick. On the drill floor is the drawworks which contains a reel of hoisting line made of braided, steel cable. The hoisting line goes through a series of wheels in a steel frame at the top of the derrick called the crown block and through another series of wheels in a steel frame being suspended in the derrick called the traveling block. Below the traveling block is a hook to attach equipment to be raised or lowered in the well such as the drillstring. When the hoisting line is wound back onto the reel in the drawworks, the traveling block goes up and the drillstring is raised from the well. When the hoisting line is let off the reel in the drawworks, the traveling block goes down and the drillstring is lowered into the well.

Drilling mud is made at the drillsite by mixing fresh water with dry clay called bentonite that comes in sacks. It is pumped down the rotating drillstring (Figure 54). The drilling mud jets out of nozzles on the bottom of the bit and picks the well cuttings off the bottom of the well. The drilling mud and well cuttings then flow up the well in the space called the annulus between the rotating drillstring and the sides of the well. On the surface, they flow through the mud return line and onto the shale shaker which is located on the mud tanks. Screens in the shale shaker separate the well cutting from the drilling mud which flows through the screens and into the mud tanks where it is stored. Pumps next to the mud tanks, called mud hogs, then pump the drilling mud back down the drillstring. The drilling mud is continuously being cleaned and repumped down the well by the mud circulating system.

The mud circulating system does three things. It removes the well cuttings from the bottom of the hole to preventing them from clogging up the bottom of the hole and stopping the drilling. Secondly, it cools and lubricates the bit. The drilling mud also prevents any water, gas or oil from flowing out of the rocks and into the well. This is because the weight of the drilling mud exerts a greater pressure on the drilling mud at the bottom of the well than the pressure of any water, gas or oil in the rocks. Therefore, instead of the fluids flowing into the well, some drilling mud is forced into the rocks surrounding the wellbore. As the mud is forced into the surrounding rock, the clay in the mud is plastered onto the sides of the wellbore. This forms a mud or filter cake which is as hard as cement and stabilizes the sides of the well. If gas or oil flowed out of the rocks and up the well onto the drill floor, it could catch fire. If water flowed out of the rocks into the well, the sides of the well could cave or sluff in. As long as the well is being drilled, the mud must be kept circulating.

Because a drilling rig is very expensive, it must be kept operating 24 hours a day. Three eighthour crews of workers called tours are used each day. On rigs in remote areas or offshore rigs, only two twelvehour tours are used each day. The drilling contractor is the company who owns and operates the drilling rig. The operator is the oil company who contracts for the drilling of the well. The one person who is ultimately in charge at the drillsite is called the tool pusher He is an employee of drilling contractor and lives at the rig site in a trailer. Each morning the tool pusher puts together the daily drilling or morning report. It is a summary of the last 24 hours on the drilling rig. The company man is an employee of the operator and works with the tool pusher to make sure the well is being drilled right. On the floor of the drilling rig, the driller gives the orders to the crew and operates the machinery. There are usually two to four roughnecks on the floor of the drilling rig who do the general work under the command of the driller.

A mud man periodically checks the viscosity and density of the drilling mud. The mud man conditions the mud by adding water and/or chemicals called additives.

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If you are having problems printing this article, click on a portion of the text of the document. Clicking on any portion of the text will make the "frame" active and printable.

"Lewis Mosburg's OIL & GAS NEWSLETTER"™ and "Lewis Mosburg's OIL & GAS PRIMERS"™ are trademarks of Lewis G. Mosburg, Jr.