Structural Problems When Drilling

Finally, structures in the earth can give the PG many challenges.   Look at this diagram.  Imagine you first drilled the hole on the left into the green layer which represents a nice oil and gas-bearing rock.  YES!  You have a great well, producing lots of oil and gas!

Then you drilled your second hole to the east (right) of the first one.  What happened to that hole? (answer below)

Answer:  The oil reservoir has been split in two by the fault, which is nothing but a place in the earth where rock layers break in two.   The arrows on the diagram show that the rocks moved DOWN on the LEFT side of the fault and UP on the RIGHT side of the fault.   This created a GAP in the oil field……right where you drilled your second hole!  Incredibly bad luck!  Or, bad seismic!  Your second hole is a DRY HOLE.

Only after drilling you should do the well completion:

• Choose the type of well completion (1. Open hole completion; 2. Cased hole (perforated) completion; 3 Liner completion);

• Choose tubing-casing configuration and tubing design;

• Determine tubing size, tubing grade and weight;

• Complete the perforation operation and well stimulation operation;

• Control the quantity of sand and make remedial cementation.

Who are the people in a typical drilling crew?

Roustabouts	The youngest people in a drilling crew. They clean, maintain and move equipment and help to other workers.
Roughnecks	They are like roustabouts but more skilled, they work on the drilling floor. They connect heavy drill pipes and put them into the hole, or they disconnect the pipes as they come up out of the hole.
Derrickman (rigger)	He works high up on the monkey board about 25 metres above the floor. He guides the top part of the drill pipe. At other time he helps the mud engineer (or a mud man)
Mud man	He checks the mud and maintains the pump. The mud must not be too thick or to thin, and the pump must keep working.
The driller	He supervises and trains the drilling crew and he controls the drilling equipment: he operates the motor that lifts the drill pipes; he controls the speed of the drill, which must not be too fast or too slow. On the modern rigs, the driller sits in special driller`s chair.
Rig manager (or toolpusher)	He is the most senior person in the drilling crew. He makes sure the crew has all the right equipment; he is responsible for their safety and for paperwork.

Below you find a test that will help you to understand: “Is drilling a job for you?”

Question 2. Non-hydrocarbons impurities.

For completeness, we should mention that other types of nonhydrocarbon compound occur in crude oils, gases and refinery streams. Most important are the following:

• Sulfur compounds

• Nitrogen compounds

• Oxygen compounds

• Metallic compounds

Sulfur Compounds. In addition to the gaseous sulfur compounds in crude oil, many sulfur compounds have been found in the liquid phase in the form of organosulfur. These compounds are generally not acidic. Sour crude oils are those containing a high percentage of hydrogen sulfide. However, many of the organic sulfur compounds are not thermally stable, thus producing hydrogen sulfide during crude processing.

The following sulfur compounds are typical:

1. Mercaptans (H–S–R): For example, butyl mercaptan (H–S–C₄H₉) is responsible for the unusual odor of the shank.

2. Sulfides (R–S–R): The hydrogen sulfide may be removed by heating and may be separated by using amine solutions.

3. Polysulfides (R–S–S–R): These are more complicated sulfur compounds and they may decompose, in some cases depositing elemental sulfur. They may be removed from petroleum fractions, similar to the sulfides, by hydrotreating.

Nitrogen Compounds. Nitrogen compounds in crude oils and gases are usually low in content (about 0.1–0.9%) and are usually more stable than sulfur compounds.

It has to be stated that the presence of nitrogen in petroleum is of much greater significance in refinery operations than might be expected from the very small amounts present. It is established that nitrogen compounds are responsible for the following:

1. Catalyst poisoning in catalytic processes

2. Gum formation in some products such as domestic fuel oils

Oxygen Compounds. Oxygen compounds in crude oils and gases are more complex than sulfur compounds. However, oxygen compounds are not poisonous to processing catalysts. Most oxygen compounds are weakly acidic, such as phenol, cresylic acid and naphthenic acids. The oxygen content of petroleum is usually less than 2%, although larger amounts have been reported.

Metallic Compounds. Many metals are found in crude oils; some of the more abundant are sodium, calcium, magnesium, iron, copper, vanadium, and nickel. These normally occur in the form of inorganic salts soluble in water—as in the case of sodium chloride—or in the form of organometallic compounds—as in the case of iron, vanadium, and nickel. The occurrence of metallic constituents in crude oils is of considerably greater interest to the petroleum industry than might be expected from the very small amounts present. The organometallic compounds are usually concentrated in the heavier fractions and in crude oil residues. The presence of high concentration of vanadium compounds in naphtha streams for catalytic reforming feeds will cause permanent poisons. These feeds should be hydrotreated not only to reduce the metallic poisons but also to desulfurize and denitrogenate the sulfur and nitrogen compounds. Hydrotreatment may also be used to reduce the metal content in heavy feeds to catalytic cracking.