EXERCISE 6 Retell the text and discuss in dialogs with your group mates this theme

EXERCISE 7 Prepare a presentation about rotary drilling bits.

UNIT IV

SUPPLEMENTARY READING

Text 1

Read, translate the text "Oil Business" and make the annotation of it.

Oil Business

Part I

Nowadays speaking about all the activities connected with oil and gas business the petroleum experts use three terms: upstream, midstream and downstream. The term «upstream» means oil and gas exploration, drilling and production, «midstream» means transportation, storage, gas processing and «downstream» means refining, distribution, marketing.

To start the story of oil business one should know something about the origin of petroleum. Most geologists believe that oil is of organic origin, i.e. (that is), it originated from decomposition of mainly marine animals and plants buried under thick layers of mud perhaps as long as 400 - 500million years ago. These deposits rich in organic material became the source rocks (sedimentary rocks) for the generation of crude oil. High temperatures and pressures in the sedimentary rocks caused chemical processes that, in turn, resulted in the formation of a waxy substance called kerogen. When heated to a temperature above 100° С kerogen is separated into a liquid (oil) and gas (natural gas). The chemical composition of petroleum is principally hydrocarbons, although a few sulphur-, nitrogen-, and oxygen-containing compounds are usually present.

To look for and to find petroleum is the art of exploration. According to the theories of petroleum origin sedimentary basins are a prime aim for the oil hunters. In general, to form oil and gas pools the following conditions must be fulfilled. 1) The presence of a "source rock" which geologic history allowed the formation of oil. 2) Migration of the oil from the source rock to a «reservoir rock» that is thick, permeable and porous enough to hold a sizable accumulation of oil. 3) Entrapment. Waters and pressure of overlying layers pushed oil upward until it reached an impermeable layer of rock called a cap rock. A cap rock stops further migration of oil and oil is thus trapped in a reservoir. It is from these reservoirs that people began extracting oil and gas millions of years later.

It should be noted that successful exploration is based on accurate interpretation of the information to be provided by geological and geophysical surveys. Seismic prospect minimizes exploration risk and reduces finding costs. Using complicated tools geologists identify potential traps for oil and gas.

Drilling can prove the presence of oil after the geologists and gee-physicists have found a favorable location for the accumulation of oil. All wells drilled to discover oil and gas accumulations are "exploratory wells", commonly referred to as "wildcats". A successful wildcat is a "discovery well", while an unsuccessful one is a "dry hole".

After oil has been discovered the first wells to be drilled to establish the limits of the field are "appraisal wells". All subsequent wells are "development wells". To determine the reservoir and oil properties geophysical investigations (logging) are to be conducted in the wells. If the first wells "prove" an oilfield, the data from them are used in drawing up plans for the commercial development of the field.

Part II

Once oil is found it must be extracted. After the drilling site has been prepared the rig is to be constructed. The rig is known to consist of surface equipment and a derrick which houses drilling tools. The derrick is used to lift sections of pipe which are lowered into the hole made by the drill. To get oil and gas out of the ground is not easy.

Sophisticated techniques and equipment must be used to extract the most out of every oil and gas deposit. Experts consider oil recovery to depend in much on natural pressure. Under natural pressure oil flows freely and it is called the natural flow. It is the most economic period of a well life. If oil wells have too little energy to produce oil efficiently, additional energy must be supplied by pumps or other artificial means.

Crude oil must be transported from the fields where it is produced to the places where it is consumed. Pipelines are likely to be the main means of oil transportation. But tankers, barges, tank tracks, and railroad tank cars are thought to be of no less importance. The latest discoveries of welding methods, construction practices and new materials have extended pipeline transportation into harsh environments and deep waters. All the means of transportation carry oil from wells to storage tanks or directly to refineries. Pipelines also carry petroleum products from refineries to markets. Some of the largest pipelines are to carry more than a million barrels of oil daily.

The basic job of a refinery is to convert petroleum into useful products. As mentioned above, crude oil consists chiefly of hydrocarbons. Refineries are to separate oil into various hydrocarbon groups, or fractions, distillation being the first step of refining. The fractions are then chemically changed and treated with other substances. The refining processes may be classified as separation, conversion and chemical treatment. The latest improvements in refining maybe said to have saved billions of barrels of crude.

Distribution and marketing appear to be the final links in the petroleum industry chain that begins hundreds of meters below the ground and ends in your home.

Text 2

Read, translate the text "Creekology" and make the annotation of it.

Creekology

Finding oil and getting its products to market have intrigued us for about 150 years. The search, however, was not always as high-tech as it is now. Our industry began, of course, with Col. Drake and his famous well in 1859. The first wells were drilled near oil seeps because, obviously, oil was there. But after the oil seeps were covered, new methods of finding it had to be found. Some of the early "science" is worth looking at.

One of the first theories was that underground pools of oil ran parallel to creeks and rivers and that drilling in creek beds would yield the prize. I mink they called this «creekology». This theory led to Oil Creek and the Allegheny River in Pennsylvania (along with every stream leading into them) to be lined with operators. It was a very popular and successful method until one day in the late 1860s when Pennsylvania suffered very heavy rains and the industry was flushed away. Survivors began checking higher ground for oil.

Oil was everywhere and sometimes could be found by accident. One day, a fire broke out in the kitchen of a boarding house in a small oil-area town. Buckets of water were quickly brought from the nearest well. But the fire wasn't going out. In fact, the water seemed to be feeding the fire. The well was found to have several inches of oil in it. Water was brought from other wells nearby, but with the same result. This story is related in "Oil Region Reminiscences'', published in 1907. It doesn't give us the fate of the boarding house but does say that the town's residents were quite happy to find oil seeping into the water wells. All of them were scooping and bailing oil and dreaming of what to do with all the money they would be making. And then the pipeline company fixed the leak in its line that ran over the hill behind town.

Text 3

Read, translate the text "How are oil and natural gas produced?" and make the annotation of it.

How are oil and natural gas produced?"

Once an oil or gas reservoir is discovered and assessed, production engineers begin the task of maximizing the amount of oil or gas that can ultimately be recovered from it. Oil and gas are contained in the pore spaces of reservoir rock. Some rocks may allow the oil and gas to move freely, making it easier to recover. Other reservoirs do not part with the oil and gas easily and require special techniques to move the oil or gas from the pore spaces to a producing well. Even with today's advanced technology, in some reservoirs more than two-thirds of the oil in the reservoir rocks may not be recoverable.

Before a well can produce oil or gas the borehole must be stabilized with casing, which is lengths of pipe cemented in place. The casing also serves to protect any fresh water intervals that the well passes through, so that oil cannot contaminate the water. A small-diameter tubing string is centered in the well bore and held in place with packers. This tubing will carry the hydrocarbons from the reservoir to the surface.

Reservoirs are typically at elevated pressure because of underground forces. To equalize the pressure and avoid the "gushers" of the early 1900s, a series of valves and equipment is installed on top of the well. This wellhead, or "Christmas tree", as it is sometimes called, regulates the flow of hydrocarbons out of the well.

Early in its production life, the underground pressure will often push the hydrocarbons all the way up the well bore to the surface, much like a carbonated soft drink that has been shaken. Depending on reservoir conditions, this "natural flow" may continue for many years. When the pressure differentia! is insufficient for the oil to flow naturally, mechanical pumps must be used to bring the oil to the surface. This process is referred to as artificial lift. In the U.S., above-ground pumping units are often called "horse head" pumps because of their unique shape and movement.

Most wells produce in a predictable pattern called a decline curve. Production will increase for a short period, then peak and follow a long, slow decline. The shape of this decline curve, how high the production peaks, and the length of the decline are all driven by reservoir conditions. Some wells may stop producing in economic quantities in only a few years. In the U.S., 8 oil and gas fields have been producing for more than 100 years.

Engineers can do a variety of things to affect a well's decline curve. They may periodically perform an operation called a "work over", which cleans out the well bore to help oil or gas move more easily to the surface. They may fracture or treat the reservoir rock with acid around the bottom of the well bore to create better pathways for the oil and gas to move through the subsurface to the producing well.

As a field ages, the company may choose to use a technique called water flooding. In this case, some of the wells in the field are converted from production wells to injection wells. These wells are used to inject water (often produced water from the field) into the reservoir. This water tends to push the oil out of the pores in the rock toward the producing well. Water flooding will often increase production from a field.

In more advanced cases, the company may use more sophisticated techniques, collectively referred to as enhanced oil recovery (EOR). Depending on reservoir conditions, various substances [from steam to nitrogen, carbon dioxide to a surfactant (soap)] may be injected into the reservoir to remove more oil from the pore spaces and increase production.

Throughout their productive life, most oil wells produce oil, gas, and water. This mixture is separated at the surface. Initially, the mixture coming from the reservoir may be mostly oil with a small amount of water. Over time, the percentage of water increases. On average in the United States, oil wells produce 8 barrels of water for each barrel of oil. Some older wells may produce as much as 100 barrels of water for each barrel of oil. This produced water varies in quality from very briny to relatively fresh. In arid areas of the western U.S., produced water may be used for agricultural purposes, such as livestock watering or irrigation. Where it cannot be used for other purposes, this produced water may be reinjected into the reservoir — either as part of a water flooding project or for disposal (returning it to the subsurface).

Natural gas wells usually do not produce oil but do produce some amount of liquid hydrocarbons. These natural gas liquids are removed in the field or at a gas processing plant (which may remove other impurities as well). Natural gas liquids often have significant value as petrochemical feed stocks. Natural gas wells also often produce water, but the volumes are much lower than is typical for oil wells.

Once it is produced, oil may be stored in a tank and later moved by means of truck, barge, or ship to where it will be sold or enter the transportation system. Most often, however, it goes from the separation facilities at the wellhead directly into a small pipeline, which then feeds into a larger pipeline. Often, pipelines are used to bring the production from offshore wells to shore. Pipelines may transfer oil from a producing field to a tanker loading area for shipping. Pipelines also may be used to move oil from a port area to a refinery to be processed into gasoline, diesel fuel, jet fuel, and many other products.

Natural gas is almost always transported through a pipeline. Because of the difficulty in moving it from where it exists to where potential consumers are, some known gas deposits are not currently being produced. Many years ago, the gas may have been wasted as an unwanted by-product of oil production. The industry recognizes the value of clean-burning natural gas and is working on improved technologies for getting gas from the reservoir to the consumer. Gas-to-liquids (GTL) is an area of technology development that will allow natural gas to be converted to a liquid, transported by tanker. Some countries have installed facilities to export gas as liquefied natural gas (LNG), but the number of countries with facilities to use LNG is still limited

Text 4

Read, translate the text "Gas – Drive Reservoirs" and make the annotation of it.

Gas – Drive Reservoirs

In nearly all cases, oil in an underground reservoir has dissolved in it varying quantities of gas that emerges and expands as the pressure in the reservoir is reduced. As the gas escapes from the oil and expands, it drives oil through the reservoir toward the wells and assists in lifting it to the surface. Reservoirs in which the oil is produced by dissolved gas escaping and expanding from within the oil are called "Dissolved-Gas-Drive" reservoirs. This oil production process is generally considered the least effective type, yielding maximum recoveries indicated between 15 to 25 percent of the oil originally contained in the reservoir.

In many cases there exists more gas with the oil in a reservoir than the oil can hold dissolved in it, under the existing conditions of pressure and temperature in the reservoir. This extra gas, being lighter than the oil, occurs in the form of a cap of gas over the oil. Such a gas cap is an important additional source of energy, for, as production of oil and gas proceeds and the reservoir pressure is lowered, the gas cap expands to help fill the pore spaces formerly occupied by the oil and gas produced. Also, where conditions are favorable, some of the gas coming out of the oil is conserved by moving upward into the gas cap to further enlarge the gas cap. The "Gas-Cap- Drive" production process is substantially more effective that "Dissolved-Gas-Drive" alone, yielding indicated oil recoveries ranging from 25 to 50 percent.

The "Gas-Drive" production processes described are typically used with the limited or closed reservoirs. However, the natural energy is usually confined to a form of "Gas Drive" in any type of reservoir where the porous part of the formation is limited essentially to that actually forming the reservoir and containing the oil and gas.

Text 5

Read, translate the text "Range of explored depths" and make the annotation of it.

Range of explored depths

The range of explored depths in the earth's crust, which have to be dealt with when resolving various geological problems, starts from first two-three meters and proceeds to dozens of kilometers. Seismic exploration deals with the first meters when determining level of underground waters (a very important objective when searching for water in arid regions to design irrigation systems and implement melioration) or identifying thickness of crumbly sediments that must be removed prior to construction of large facilities and open-pit development of minerals. Seismic exploration also has to deal with dozens of kilometers when investigating the earth's crust and upper mantle.

The range of depths from 1000 to 6000 meters is typical for oil and gas searching, where seismic exploration is the key tool of exploration geophysics. Inaccuracy in determining location of any objects in the thickness of rocks in this case must not exceed 1 – 2% with several kilometers thickness of capping sediments. It should be noted that properties of rocks, as a rule, significantly change both vertically (with depth) and horizontally. Further, actual geological bodies significantly differ from ideal elastic bodies in their properties and have sufficiently complex structure.

All of this results in tremendous mathematical difficulties even at the stage of resolving direct problems - calculating field of displacements on the medium surface based on established location of elastic waves source. Differences in elastic properties, and first of all in the capacity to absorb elastic waves, enormous variety in combinations of rocks of different types, changeability of rocks in immediate proximity to the surface do not allow without appropriate experimental surveys answering the question, which capacity should the source of elastic waves have to ensure reaching the target exploration depth.

Text 6

Read, translate the text "Diamond bits" and make the annotation of it.

Diamond bits

Diamond bits are designed to crush nonabrasive rocks of medium hardness and hard rocks by abrasion (micro cutting). Diamond bit consists of steel housing with connecting toll-joint thread and shaped diamond-bearing head (matrix). Matrix is divided into sectors with radial (or spiral) flushing channels, which are connected to the bit housing cavity through flushing ports.

Diameters of diamond bits are 2 — 3 mm less than relevant diameters of roller-cutter bits. This is made to create conditions required for transition to drilling with diamond bits after roller-cutter bits, which, as a rule, are decreased in diameter with deterioration. Key advantages of diamond bits are good centralizing capacity on the well bottom and development of circular bottom hole (opposite to triangular bottom hole with rounded tops when drilling with roller-cutter bits).

Significant disadvantages of diamond bits include: first, extremely low mechanical drilling rate. Maximal mechanical drilling rate, as a rule, does not exceed 3 m/h. For comparison - maximal mechanical rate of drilling with roller-cutter bits is about 120 m/h. Second, diamond bits have small range of application (abrasive rocks are excluded) and third, higher requirements to preliminary preparation of well bore and bottom are set.

Text 7

Read, translate the text "Spontaneous well deviation" and make the annotation of it.