|Book Details :|
Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production 3rd Edition by Norman J. Hyne | PDF Free Download.
This book contains an enormous amount of useful information on the upstream petroleum industry. It is designed for easy reading, and the information is readily accessible. The introductory chapter should be read first.
It is an excellent overview that shows how everything in petroleum geology, exploration, drilling, and production is interrelated. Each subject has its own chapter that is well illustrated with figures and plates. The rocks, minerals, and seismic examples are in color.
Industry terms are defined in the text and shown in italics. All measurements are in both English and metric units. A useful index and extensive glossary are located at the back of the book, as well as an interesting list of petroleum records.
Both crude oil and natural gas occur naturally in subsurface deposits. Crude oil is a black liquid that is sold to refineries to be refined into products such as gasoline and lubricating oil. Natural gas is a colorless, odorless gas that is sold to gas pipelines to be transported and burned for its heat content.
There are many different types of crude oils and natural gases, some more valuable than others. Heavy crude oils are very thick and viscous and are difficult or impossible to produce. Light crude oils are very fluid, relatively easy to produce, rich in gasoline, and more valuable.
Some natural gases burn with more heat than others and are more valuable. Some natural gases also contain almost pure liquid gasoline called condensate that separates from the gas when it is produced.
Condensate is almost as valuable as crude oil. Sulfur is a bad impurity in both natural gas and crude oil. Sour crude oils contain sulfur, and sour natural gases contain hydrogen sulfide and are less valuable. Crude oil is measured by volume in barrels (bbl).
Natural gas is measured by volume in thousands of cubic feet (Mcf) and by heat content in British thermal units (Btu). In order for there to be a commercial deposit of natural gas or crude oil, three important geological conditions must be met.
First, there must be a source rock in the subsurface of that area that generated the gas or oil at some time in the geological past. Second, there must be a separate, subsurface reservoir rock that holds the gas or oil.
When we drill a well into that reservoir rock, the gas and oil are able to flow through the reservoir rock and into our well. Third, there must be a trap on the reservoir rock to concentrate the gas or oil into commercial quantities.
The crust of the earth in oil- and gas-producing areas is composed of sedimentary rock layers. Sedimentary rocks can be source and reservoir rocks for gas and oil. These rocks are called sedimentary rocks because they are composed of sediments that were formerly loose particles such as sand grains, mud, and seashells or salts that precipitated out of water.
Sedimentary rocks are millions of years old and were deposited when the sea level rose and covered the land many times in the past. These sediments are relatively simple materials such as sands deposited along beaches, mud deposited on the sea bottom, and beds of seashells.
Ancient sediments, piled layer upon layer, form the sedimentary rocks that are now sandstones composed of sand grains, shales composed of mud particles, and limestones composed of seashells. These are drilled to find and produce oil and gas.
The source of gas and oil is the organic matter—dead plant and animal material—that is buried and preserved in some ancient sedimentary rocks. The most common, organic-rich sedimentary rock and the source rock for most gas and oil is black shale.
It was deposited as organic-rich mud on ancient ocean bottoms. In the subsurface, temperature and time turn organic matter into crude oil. As the source rock is covered with more sediments and buried deeper in the earth, it becomes hotter and hotter.
Crude oil starts to form at about 150°F (65°C) at a depth of about 7,000 ft (2,130 m) below the surface of the land (fig. I–1). It is generated from there down to a depth of about 18,000 ft (5,500 m) at about 300°F (150°C).
The reactions that change organic matter into oil are complex and take a long time. If the source rock is buried deeper where the temperatures are above 300°F (150°C), the remaining organic matter can generate natural gas.
Gas and oil are relatively light in density compared to the water that also occurs in subsurface sedimentary rocks. After oil and gas form, they rise due to buoyancy through fractures in the subsurface rocks.
The rising gas and oil can intersect reservoir rock, which is a sedimentary rock layer that contains billions of tiny spaces called pores. A common reservoir rock is a sandstone, composed of sand grains like those on a beach.
Sand grains are like spheres—there is no way the grains will fit together perfectly. There are pore spaces between the sand grains on a beach and in a sandstone rock.
Limestone, another common reservoir rock, is often deposited as shell beds or reefs, and there are pores between the shells and corals. Because limestone is soluble, there can also be solution pits in the limestone.
Porosity is the percent of reservoir rock that is pore space, and it is commonly 10 to 30%. The gas and oil flow into the pores of the reservoir rock layer.
Because the reservoir rock also contains water, the gas and oil will continue to rise by flowing from pore to pore to pore up the angle of the reservoir rock layer toward the surface. The movement of gas and oil up the angle of the reservoir rock toward the surface is called migration.
The ease with which the gas and oil can flow through the rock is called permeability. Because of migration, the gas and oil can end up a considerable distance, both vertically and horizontally, from where they were originally formed (fig. I–1).
As the gas and oil migrate up along the reservoir rock, it can encounter a trap. A trap is a high point in the reservoir rock where the gas or oil is stopped and concentrated. One type of trap is a natural arch in the reservoir rock (fig. I–2) called a dome or anticline.
In the trap, the fluids separate according to their density. The gas is the lightest and goes to the top of the trap to fill the pores of the reservoir rock and form the free gas cap. The oil goes to the middle to fill the pores and form the oil reservoir.
The saltwater, the heaviest, goes to the bottom. To complete the trap, a caprock must overlie the reservoir rock. The caprock is a seal that does not allow fluids to flow through it. Without a caprock, the oil and gas would leak up to the surface.
Two common sedimentary rocks that can be caprocks are shale and salt. Most gas and oil deposits are located in basins where sedimentary rocks are relatively thick. Subsurface deposits of gas and oil are found by locating traps.
In some areas, the rock layers that crop out on the surface can be projected into the subsurface to discover traps (fig. I–3). Today, these surface rocks can be mapped using photographs from airplanes and satellites.
In the subsurface, the rocks in different wells that have already been drilled are matched by correlation to make cross-sections, and maps of the depths to the top of subsurface reservoir rocks and their thickness are drawn.
Seismic exploration is commonly used today to locate subsurface traps. The seismic method uses a source and detectors (fig. I–4). The source, such as dynamite, is located on or near the surface and gives off an impulse of sound energy into the subsurface.
The sound energy bounces off sedimentary rock layers and returns to the surface to be recorded by the detectors. Sound echoes are used to image the shape of subsurface rock layers and find traps.
The only way to know for sure if a trap contains commercial amounts of gas and oil is to drill an exploratory or wildcat well. Many wildcat wells are dry holes with no commercial amounts of gas or oil. The well is drilled using a rotary drilling rig (fig. I–5).
There can be thousands of feet of steel drill pipe with a bit on the end, called the drill string, suspended in the well. By rotating the drill string from the surface, the bit on the bottom is turned and cuts the hole.
As the well is drilled deeper, every 30 ft (9.1 m) drilling is stopped and another section of drill pipe is screwed on the drill string to make it longer. The power to the rig is supplied by diesel engines. A steel tower above the well the derrick or mast along with a hoisting line and pulley system is used to raise and lower equipment in the well.
An important system on the rig is the circulating mud system. Drilling mud, usually made of clay and water, is pumped down the inside of the drill pipe where it jets out of nozzles on the bit and returns up the outside of the drill pipe to the surface (fig. I–6).
The drilling mud removes the rock chips made by the bit, called well cuttings, from the bottom of the hole and prevents them from clogging up the bottom of the well. The well is always kept filled to the top with the heavy drilling mud as it is being drilled.
The pressure of the drilling mud prevents any fluids such as water, gas, and oil from flowing out of the subsurface rocks and into the well. If gas and oil flowed up onto the floor of the drilling rig, they could catch fire, causing a blowout.
Even if only water flowed out of the surrounding rock into the well, the sides of the well could cave in, and the well could be lost. As the well is being drilled, it can be drilled straight down, out at an angle as a deviated well, or out horizontally as a horizontal well through the oil and gas reservoir (fig. I–7).
Horizontal wells typically produce oil and gas at a greater rate than vertical wells. Offshore wells are drilled into sedimentary rocks on the ocean bottom the same way as on land.
For offshore exploratory wells, the rig is mounted on a barge, floating platform, or ship that can be moved. Once an offshore field is located by drilling, a production platform is installed to drill the rest of the wells and produce the gas and oil.
The production platform can be fixed with legs that sit on the ocean bottom or floating with anchors and cables to hold it in position.
Because drilling mud keeps gas and oil in the rocks, a subsurface deposit of gas or oil can be drilled without any indication of the gas or oil. To evaluate the well after it has been drilled, it must be logged, and well logs must be created.
A good log is a record of the rocks and their fluids in the well. A mudlogger is a service company that makes a mud log as the well is being drilled. The mudlogger carefully analyzes both the drilling mud and well cuttings for traces of crude oil and natural gas.
Another service company drives a logging truck out to the well after the well is drilled to make a wireline well log. A long cylinder containing instruments called a logging tool is unloaded from the truck and run down the well on a wireline (fig. I–8).
As the logging tool is brought back up the well, the instruments remotely sense the electrical, sonic, and radioactive properties of the surrounding rocks and their fluids. These measurements are recorded on a long strip of paper called a wireline well log (fig. I–9) in the logging truck and are also digitized, encoded, and sent by radio telemetry to a data center.
Well, logs are used to determine the composition of each rock layer, whether the rock layer has pores and how much is pore space, and what fluid (water, gas, or oil) is in the pores. Depending on the test results, the well can be plugged and abandoned as a dry hole or completed as a producer.
To complete the well, many sections of large-diameter steel pipe called casing are screwed together to form a long length of pipe called a casing string that is lowered down the hole. Wet cement is then pumped between the casing and well walls and allowed to set (fig. I–10) during a cement job.
This stabilizes the hole. The casing is done in stages called a casing program, during which the well is drilled, cased, drilled deeper, cased again, drilled deeper, and cased again (fig. 1–11). In order for the gas or oil to flow into the well, the well is either completed open-hole or with perforated casing.
In an open-hole completion (fig. I-11a), the casing string is cemented down to the top of the reservoir rock and the bottom left open. In perforated casing completion (fig. I-11b), the casing is cemented through the reservoir rock and the casing is shot with explosives to form holes called perforations.
A long length of narrow-diameter steel pipe called a tubing string is then suspended down the center of the well. The produced fluids (water, gas, and oil) are brought up the tubing string to the surface to prevent them from touching and corroding the casing string that is harder to repair.
An expandable rubber device called a tubing packer on the bottom of the tubing string keeps the tubing string central in the well and prevents the fluids from flowing up the outside of the tubing (fig. 1–11).
The tubing string is relatively easy to repair during a workover. In all gas wells, gas flows to the surface by itself. There are some oil wells, usually only early in the development of the oil field, in which the oil has enough pressure to flow up to the surface.
Gas wells and flowing oil wells are completed on the surface with a vertical structure of pipes, fittings, gauges, and valves called a Christmas tree, which is used to control the flow (fig. I–12a).
Most oil wells, however, do not have enough pressure for the oil to flow to the surface, and the oil will fill the bottom of the well only up to a certain level.
A sucker-rod pump or beam-pumping unit (fig. I–12b) is commonly used to lift the oil and water up the tubing string to the surface. A downhole pump on the bottom of the tubing string is driven by the surface beam-pumping unit.
A motor causes a beam on a pivot, called the walking beam, to pivot up and down. The walking beam is connected to a downhole pump by a long, narrow, sucker-rod string that runs down the center of the tubing string (fig. 1–12b).
The pump lifts the oil and water up the tubing string to the surface. On the surface, gas is prepared for delivery to a gas pipeline by gas-conditioning equipment that removes impurities such as water vapor and corrosive gases.
Valuable natural gas liquids, such as condensate, are removed from the gas in a natural gas processing plant and sold separately. The gas can then be sold to a gas pipeline. For oil, along vertical or horizontal steel tank called a separator is used to separate natural gas that bubbles out of the oil and the saltwater that settles to the bottom (plate I–1).
The oil is then stored in steel stock tanks until it is sold to a refinery. The production rate from wells can be increased by acid and frac jobs. Acid is pumped down a well to dissolve some of the reservoir rock adjacents to the wellbore during an acid job.
During a frac job, the reservoir rock is hydraulically fractured with a liquid pumped under high pressure down the well. Propping agents such as sand grains are pumped down the well with the frac fluid to hold the fractures open and allow the oil and gas to readily flow into the well.
Periodically, production from the well must be interrupted for repairs or to clean out the well during a workover. A service company drives out to the well with a production unit to do the workover.
As fluids are produced from the subsurface reservoir, pressure on the remaining fluids drops. The production rate of oil and gas wells and the whole field decreases with time on a decline curve. Ultimate recovery of gas from a gas reservoir is often about 80% of the gas in the reservoir.
Oil reservoirs, however, are far more variable and less efficient. They range from 5 to 80% recovery but average only 35% of the oil in the reservoir. This leaves 65% of the oil remaining in the pressure-depleted reservoir.
After the reservoir pressure has been depleted in an oil field, waterflood and enhanced oil recovery can be attempted to produce some of the remaining oil.
During a waterflood, water is pumped under pressure down injection wells into the depleted reservoir to force some of the remaining oil through the reservoir rock toward producing wells (fig. I–13).
Enhanced oil recovery involves pumping fluids such as carbon dioxide, nitrogen, or steam down injection wells to obtain more production. Recently, an enormous amount of natural gas has been produced from shales with a special technique.
Shale is a very fine-grained rock. Even though many shales contain gas, shale has no permeability and the gas cannot flow through the shale into a well.
Horizontal wells drilled into these shales, however, are used for a special frac job called a slickwater frac, which allows the gas to flow through the shale and into the well. After the well has been depleted, it is required by law to be properly plugged and abandoned to prevent pollution.
The cement must be poured down the well to seal the depleted reservoir and to protect any subsurface freshwater reservoirs. A steel plate is then welded to the top of the well and the well is covered with soil.
Download Nontechnical Guide to Petroleum Geology Exploration Drilling and Production in PDF Format For Free.