Chapter 5 - Drilling and Completion: Onshore

Question 1

Each onshore well is sited within a what?

Answer 1

Drilling Spacing Unit (DSU)

Question 2

In recent historical practice, a DSU was a what? PAST.

Answer 2

A DSU was a square encompassing 40 or 80 acres, within which only one well was drilled

Question 3

Why was the DSU constraint established?

Answer 3

The DSU constraint was established in the 1930s in the United States to prevent exploitation of a field with excessive drilling and production rates.

Question 4

Based on advances in geologic evaluation and drilling technology, what has happened to the DSU?

Answer 4

Tighter spacing is being used, depending on such factors as formation permeability and heterogeneity, and drilling costs. A 10-acre DSU is not uncommon. In addition, operators can now drill as many as two dozen wells in a spoke pattern from a single surface location (pad).

Question 5

After the legal and environmental issues are settled, the crew goes about preparing the drill site. For an onshore site, this entails the following steps:

Answer 5

1) Land is cleared and leveled, and access roads are built if needed.
2) A water well is drilled if necessary to provide the significant volumes of water used in oil and gas drilling operations.
3) A reserve pit is dug and lined with plastic, to hold rock cuttings and drilling mud generated during the drilling process. In environmentally sensitive areas, the cuttings and mud are trucked off-site instead of being placed in the pit.

Question 6

Once the lad has been prepared, the crew digs several holes to make way for the rig and main hole. What is a cellar?

Answer 6

A rectangular pit, called a cellar, is dug around the point where drilling will take place. The cellar provides a workspace around the hole and room for auxiliary equipment that will be located below the floor of the pain drilling platform.

Question 7

For Onshore Drilling, define the main hole.

Answer 7

The crew then drills the main hole, often with a small drill truck rather than the main rig. The first part of the hole is larger in diameter than, and not as deep as, the main portion will be and is lined with a large-diameter conductor pipe.

Question 8

The first commercial oil well drilled in the United States-in 1859 at Titusville, Pennsylvania-used what type of rig?

Answer 8

Cable Tool Rig

Question 9

Define Cable Tool Rig

Answer 9

Cable tool rigs drilled all wells in all U.S. fields discovered during the 1800s, as recently as 1953. In simple terms, a cable tool rig repetitively raises and drips a solid steel rod (about 5ft long with a chisel point on its lower end) to pound, rather than drill, a hole into the ground. Progress was very slow with the Cable Tool Rig, about 25ft/day. Also, the inability to control subsurface pressure meant that blowouts were frequent.

Question 10

Define Rotary Drilling.

Answer 10

Virtually all oil and gas wells-onshore and offshore-are drilled using a system called a rotary drilling rig, which can drill several hundred to several thousand feet per day. This system turns a long length of steel pipe with a sharp bit on its lower end to cut the wellbore.

Question 11

A basic rotary drilling system consist of four groups of components:

Answer 11

1) Prime Mover (one or more engines)
2) Hoisting equipment
3) Rotating equipment
4) Circulating equipment

Question 12

In Rotary Drilling, define Prime Mover.

Answer 12

Most rotary rigs use from one to four diesel engines, generating as much as 3,000 horsepower. This prime mover powers the rotating equipment, the hoisting equipment, and the circulating equipment as well as associated lighting, water-pumping, and compression equipment.

Question 13

In Rotating Drilling, define Hoisting Equipment.

Answer 13

The hoisting equipment raises and lowers what goes into or comes out of the wellbore. The most visible part of the hoisting equipment is the derrick, or mast, a tower like structure up to 200 feet tall. The floor of the derrick is typically built on a framework that raises it 10-30 feet above the ground, to allow space for installation of wellhead equipment.

Question 14

In Rotating Drilling, of the Hoisting Equipment, define Drawworks.

Answer 14

A strong hoisting line (braided steel wire wound on a fiber or steel core) is spooled around a frame, called the drawworks, on the derrick floor. The prime mover drives the drawworks to wind and unwind the hoisting line.

Question 15

In Rotating Drilling, of the Hoisting Equipment, define Traveling Block.

Answer 15

From the drawworks, the line goes up to the top of the derrick and attaches to a set of large pulleys (bolting to the derrick) in a block-and-tackle arrangement. Below the block (called the traveling block) is a large hook, from which a swivel hangs. As the drawworks reels in or pays out the hoisting line, the equipment hanging from the hook moves up or down.

Question 16

In Rotating Drilling, of the Rotating Equipment, define Kelly, Kelly Bushing, & Rotary Table..

Answer 16

A key component-hanging directly from the hook described above-is a very strong pipe called the Kelly. Made of high-grade molybdenum steel, it is a standard length (40 or 54 feet) and has four or six flat sides. Those flat sides allow the kelly’s lower end to fit into (but slide up and down within) a special fitting (the Kelly bushing) that is attached to a circular device on the derrick floor called the rotary table.

Question 17

In Rotating Drilling, what is the configuration after the Rotary Table.

Answer 17

At the very start of a drilling operation, one section of round drill pipe is screwed tightly to the bottom end of the Kelly. That first section-with a shart drill bit attached to its lower end-is then lowered through the bushing and rotary table until the flat sides of the lower end of the Kelly are seated securely in the Kelly bushing.

Question 18

What is each drill pipe section called? Specs?

Answer 18

Joint. Made of heat-treated alloy steel, each section can be from 8 to 45 feet long (commonly 30 feet), with an outside diameter ranging from 3 to 5.5 inches.

Question 19

Define the Drill String.

Answer 19

Collectively, the downhole drill pipe, the bit, and related equipment comprise the drill string.

Question 20

Special sections can be added to the drill string to serve what functions?

Answer 20

Drill Bit, to add weight, vibration absorption, stabilization, changing drill pipe diameter and threads

Question 21

How large are Drill Bits?

Answer 21

Typically, range in diameter from about 4 to 26 inches.

Question 22

What is the most common drill bit?

Answer 22

The most common type is the rotary cone bit, and the general design that uses three rotating cones is called a tricone bit. As the drill string turns, the three cones also rotate, and teeth or buttons on the cones either flake or crush rock at the bottom of the well. Typical rotation speeds range from 50 to 100 rpm.

Question 23

Touch on tricone bit designs of drill bits.

Answer 23

There are hundreds of different tricone bit designs, generally classified as either milled-teeth or inset bits. The former are more suitability for rock of soft or medium hardness; the latter are more effective on hard rock.

Question 24

Touch on drill bits and the use of industrial diamonds.

Answer 24

A different drill bit design uses industrial diamonds to shear away the rock. Its metal cutters are studded with chips of diamond (rather than milled teeth or tungsten carbide insert buttons). The diamond drill bit has no moving parts (unlike the rotating cones in the tricone design). It simply turns at the same speed as the drill pipe to which it is attached.

Question 25

What is a common drill bit diamond configuration?

Answer 25

A common configuration is the polycrystalline diamond compact (PDC) drill bit. Although a PDC bit is expensive, it can last several hundred hours and drill more footage than other types.

Question 26

Touch on the lubrication and cooling of the drill bit.

Answer 26

The structure that connect a drill bit to the drill string above it contain channels. These enable the flow of drilling mud to lubricate and cool the drill bit and flush rock cuttings from the face of the bit.

Question 27

Touch on the weight of the drill string pressing down on the drill bit.

Answer 27

The weight of the drill string pressing down on the drill bit is controlled from above the drawworks and is hoisting line, as well as by the number of sections added to the drilling string. Typically, 3,000-10,000 pounds per square inch (psi) of pressure per inch of bit diameter is applied.

Question 28

Define ‘tripping’ during drilling.Define ‘tripping’ during drilling.

Answer 28

In a time-consuming process called tripping, drilling is halted while the entire drill string is pulled from the wellbore. The drill pipe sections are unscrewed in sequence (sometimes three sections at a time) and are stored temporarily on a special rack on the drilling platform.

Question 29

Define ‘bit breaker’ in drilling.

Answer 29

A device called a bit breaker is attached to the rotary table to grip and unscrew the bit when it reaches the surface.

Question 30

Touch on the pressure and temperature changes as we drill deeper.

Answer 30

As a drill bit moves downward, it encounters increasing temperature and pressure. On average, temperature rises by about 1-2F for every 100 feet of depth below the surface.

Question 31

In drilling define the ‘circulation system’, specifically ‘mud’.

Answer 31

The circulating system consists of a range of equipment that works together to move drilling fluid (called mud) into and out of the hole being drilled. This drilling mud serves several purposes: it cools and lubricates the drill bit; it flushes cuttings and debris away from the face of the drill bit; and it coats the walls of the well to stabilize them.

Question 32

What is a very critical function of drilling mud.

Answer 32

Another critical function of the circulating system is to help control pressure within the well. The weight of the drilling mud can be adjusted to exert greater pressure on the bottom of the well than the pressure exerted by the fluids (oil, gas, and water) in the surrounding rock. This control is necessary to prevent uncontrolled fluid flow into the well and to prevent the well walls from caving in, trapping equipment downhole.

Question 33

What common mixtures can drilling mud consist of?

Answer 33

- Water (fresh or saline) and clay (commonly bentonite) - Oil (diesel, mineral, or synthetic) and clay - Water with 10% oil, plus clay (emulsion) - A synthetic organic material and water

Question 34

Define the ‘annulus’ of a well.

Answer 34

The walls of the well

Question 35

What happens to drilling mud when it returns to the surface?

Answer 35

At the top of the well, the mud moves into the mud return line and then through a series of devices that remove well cuttings, sand, silt, and even dissolved gases. This “clean” mud goes back into the mud tanks, ready for recirculation into the well, while removed solids are directed into a reserve pit.

Question 36

What is done with the mud after a well has been drilled?

Answer 36

After a well has been drilled, the mud cannot be reused. If made with freshwater, the mud can be spread on nearby land to fertilize crops. Other types must be moved by truck or barge to an approved disposal site.

Question 37

What is a blowout during drilling?

Answer 37

A blowout is the uncontrolled flow of oil or gas up the drill string or wellbore annulus. This is triggered when the formation pressure (exerted by gas or oil in the formation around or at the bottom of the well) exceeds the pressure created by the drilling mud. A blowout can seriously injure workers and damage the drilling rig.

Question 38

What is a blowout preventer?

Answer 38

A BOP (blowout preventer) – designed and built to rigorous standards set by API – typically consists of several stacked components. At the top is an annular preventer – a rubber-and-steel doughnut that can be rapidly compressed hydraulically to close around the equipment of any size or shape still in the well. The aim is to completely seal the annulus.

Question 39

In a blowout preventer – what is a blind ram?

Answer 39

If the annular preventer cannot stop the flow-and if there is no drill string or other equipment in the wellbore-then a series of large still plates are rapidly pushed together to completely seal off the top of the well. The first of these is called a blind ram and is mounted immediately below the annular preventer.

Question 40

In a blowout preventer – what is a pipe ram?

Answer 40

If the blind ram is ineffective (or cannot be used), then a pipe ram (mounted below the blind ram) is activated. The pipe ram also is composed of two large blocks of steel, but each has a semicircular cutout in tis mating surfaces. These cutouts allow the ram to close around, but not damage, the drill string (in the same manner as the annular preventer) while simultaneously sealing the annulus.

Question 41

In a blowout preventer – what is a blind shear ram?

Answer 41

A blind shear ram consists of two sliding stell plates with intersecting blades. As the plates come together, the angled blades cut the drill string, then , the plates in which they are mounted move into place to seal both the drill string and the annulus.

Question 42

In a blowout preventer – what is a choke manifold?

Answer 42

A final BOP-related component is the choke manifold, a set of flow lines, valves, and chokes connected to the BOP stack. It is routinely used for nonemergency routing of drilling mud from the well to various onsite equipment. However, if the BOP has been activated, it can also be used to relieve well pressure and to circulate heavier drilling mud into the well.

Question 43

Why cant operators drill a straight well, expending the least amount of time and money to reach a subsurface target?

Answer 43

In reality, because of the physics of rotary drilling, a straight hole in relatively uniform ground typically has a slight corkscrew configuration, which the drill bit moving downward within a cone whose angle is as large as five degrees. In most cases, this digression from true vertical is acceptable.

Question 44

In many situations, however, it may be necessary or desirable to drill at a predetermined angle to avoid (or reach) specific rock formations or orientations or to hit a desired target. What is this called?

Answer 44

Directional or deviated drilling

Question 45

Define how in the deviation from true vertical occurs in directional drilling.

Answer 45

This deviation from true vertical can be initiated at the start of drilling or after a vertical well (or well segment) has already been drilled. In the latter case, special tools are used-such as a long steel wedge (called a whipstock), or a device that blasts drilling mud at high pressure at the desired angle against the wall of the wellbore-to redirect the path of the drill bit.

Question 46

Give an advanced method of directional drilling.

Answer 46

A more advanced method for directional drilling sends a stream of high-pressure drilling mud down through a pipe to power a specially designed downhole mud motor that has a drill bit attached. The pipe does not spin, only the drill bit, as a pilot ole is drilled at the desired orientation.

Question 47

In directional drilling, after the new angle is confirmed as correct, the original mud-motor system is replaced by what?

Answer 47

A more elaborate unit called a downhole steerable assembly. This assembly can maintain or further change the deviation angle.

Question 48

Give a notable example of Shell using directional drilling offshore.

Answer 48

One notable example is the Cognac platform, sited in 1978 by Shell Oil in the Gulf of Mexico. Workers on the Cognac platform put in place 62 wells, all of which used deviated drilling.

Question 49

When is directional drilling particularly valuable?

Answer 49

Offshore operations, particularly in deep water, a large production platform is typically constructed to drill several main wells, with many deviated or directional wells drilled out from each of those wells, at various depths and angles.

Question 50

Give an example of Shell doing precision drilling offshore.

Answer 50

Shell Oil (the U.S. subsidiary of Royal Dutch Shell) brought into operation its Perdido production platform in March 2010, located nearly 200 miles offshore in the Gulf of Medico, in water almost two miles deep. The company reported that operators on the Noble Clyde Boudreaux floating drilling rig, using advanced control systems, were able to guide and drill bits as much as two miles farther below the seabed to hit targets the size of a lid on a garbage can.

Question 51

Define Extended-Reach Drilling.

Answer 51

A specific type of deviated drilling is ER drilling. An ER well has just a single deviation from vertical and typically bottoms out thousands of feet horizontally from its point of origin. This technique can be particularly useful in drilling from an onshore site to a target lying below the seabed offshore or in tapping resources that lie beneath environmentally sensitive areas.

Question 52

What is the world’s longest well?

Answer 52

ExxonMobil and its international partners announced in February 2011 that they had drilled the world’s longest well, Odoptu OP-11, in Russia. This ER well set world records both for total measured depth (40,502 feet [7.67 miles]) and for horizontal reach (37,648 feet [7.13 miles]). Oduptu is one of three large fields five to eight miles offshore northeast Sakhalin Island, which lies of Russia’s Pacific Coast.

Question 53

Define a horizontal-drain well.

Answer 53

A horizontal-drain well is a deviated well with a long horizontal section that taps into a subsurface structure whose hydrocarbon-bearing zones are parallel to the surface of the ground. This approach is particularly effective in reservoirs with vertical fractures and in tight (low-permeability) formations.

Question 54

Define Laterals

Answer 54

Short horizontal branches drilled outward from a main vertical wellbore are called laterals. They allow operators to rap hydrocarbon-bearing zones at different depths.

Question 55

In drilling, define a ‘kick’

Answer 55

Unusually high pressure is encountered in a formation, overwhelming the pressure exerted by the drilling mud. This causes a kick-a rapid, unexpected flow of formation fluids into the wellbore-which could lead to a blowout.

Question 56

For production, what else can well testing do?

Answer 56

In general terms, these tests help to determine the rate at which the greatest amount of oil or gas can be extracted without harming the formation.

Question 57

For well testing, describe how they test pressure.

Answer 57

Pressure is a particulary important parameter. It is measured in the tubing, within the casing, and at the bottom of the well. It si often measured while the well is flowing, but it is sometimes measured after a well has been ‘shut in’ (i.e., flow has been deliberately stopped) for a day or so.

Question 58

For well testing, define decline rate.

Answer 58

The operator will typically make an intital estimate of the well’s decline rate. This parameter is an indicator of the expected drop in production rate as more and more oil or gas is extracted from a formation. Understanding the decline rate will guide decisions about the possible use of artificial lift to improve production.

Question 59

For well testing, what can be determined from tests?

Answer 59

- Potential (the maximum amount of oil and gas a well can produce in a 24-hour period) - Productivity (various production rates and their likely effect on well life). - Drawdown profile (change in bottom-hole pressure as a flowing well is shut in). - Absolute open flow (maximum flow rate of oil or gas into the well when the bottom-hole pressure is zero).

Question 60

In well testing, what is done if a decision is made to recomplete a well?

Answer 60

If a decision is made to recomplete a well (i.e., to tap a new zone above or below the original), a cased-hole log is commonly run to confirm the presence of oil or gas in the new zone. An instrument using a gamma-ray and neutron detector is typically used to assess the relative fluid content of the formation rock.

Question 61

Define Onshore Well Completion.

Answer 61

After an exploration well has been drilled and tested-and the presence of commercially producible hydrocarbons has been verified-the well must be completed, in preparation for drilling a development well. The completion process is sometimes called setting pipe.

Question 62

In onshore completion – define casing.

Answer 62

The first step in the completion process is to install casing-hollow steel pipe with relatively thin walls-from the surface to the bottom of the well. Casing can range from about 4-36 inches in diameter. Its outer diameter is at least 2 inches less than the diameter of the wellbore (which is generally wider at the top than at the bottom).

Question 63

What purposes does casing serve?

Answer 63

- prevents the sides of the well from caving in - prevents flow of oil, gas, and salty water (produced while drilling) into the underground freshwater reservoirs - prevents the flow of unwanted water and other fluids from the drilled formation into the gas and oil being produced.

Question 64

For casing, what are hangers?

Answer 64

Hangers suspend the casing string from the top of the well (so that it does not go all the way to the bottom of the well)

Question 65

For casing, what are centralizers?

Answer 65

Centralizers keep the string centered within the wellbore. Once the casing string is in position, a slurry of cement (Portland cement with various additives) is mixed and pumped into the casing.

Question 66

For casing, what is a cementing plug or wiper plug?

Answer 66

A cementing plug or wiper plug is put into place before cement is pumped. As the cement is pushed down into the casing, the plug moves ahead of it, wiping any material from the inner casing wall that might contaminate the cement slurry.

Question 67

For casing, describe the cementing process.

Answer 67

Movement of the cement displaces drilling mud downward. Equipment positioned at the bottom of the casing string prevents drilling mud from moving back up into the casing but allows the cement to flow out of the casing and then upward to fill the space between the casing and the walls of the well. The cement job is complete once the cement has hardened, after which the special tools are removed.

Question 68

For casing, describe a squeeze job.

Answer 68

A related remedial operation, called a squeeze job, is sometimes conducted to force additional cement into place around the casing. It is used to seal leakage paths detected after initial cementing, to isolate a segment of casing that has been perforated, or to repair damaged casing.

Question 69

For casing, define conductor pipe.

Answer 69

The largest-diameter casing string (30-42 inches)- also called conductor pipe-is typically several hundred feet long. It helps route drilling mud coming from the well back to the mud tanks, prevents the top of the well from caving in, and isolates an freshwater or gas zones that are near the surface.

Question 70

What are the levels of casing?

Answer 70

Conductor pipe Surface casing Intermediate casing Production casing Each with a smaller diameter than the casing above it.

Question 71

Define open-hole completion.

Answer 71

In an open-hole completion, the well is first drilled to the top of the hydrocarbon-bearing formation and casing is set. Then, drilling continues down into the formation, which leaves the bottom of the well uncased, or open.

Question 72

Define gravel-pack completion.

Answer 72

In softer formations, where the walls of the well might cave into the well, a gravel-pack completion can be used, placing coarse sand (either loose or hold within a special liner) a the bottom of the hole. This porous sand allows oil or gas, but not sediments, to flow into the well

Question 73

Define a set-through completion.

Answer 73

A common modern approach is the set-through completion. In this method, a liner or casing is cemented into the production formation and is then perforated, using small, shaped explosives to create holes through the casing, the cement, and the formation. Oil and gas can then flow out of the formation and into the well.

Question 74

In completions, define tubing.

Answer 74

A final element of downhole equipment on a development well is tubing. This is small-diameter pipe (typically 1-4 inches), designed to carry gas, oil, water and other produced fluids to the surface. Sections of tubing (each about 30 feet long) are threaded together and positioned down the center of the well, inside the casing.

Question 75

In completions, define a packer.

Answer 75

The tubing performs several other important functions. For example, a rubber doughnut called a packer-installed at the bottom of the tubing-fits tightly around the tubing, large enough in diameter to tightly seal the space (annulus) between the outside wall of the tubing and the inside wall of the casing.

Question 76

What is the purpose of a packer?

Answer 76

Besides centering the tubing string, packers prevent produced fluids from flowing up into the casing, where they could cause corrosion. Diesel oil or specially treated water is sometimes pumped into the annulus for added corrosion protection.

Question 77

In completions, specifically tubing, how do they separate pay-zones?

Answer 77

A special narrow-diameter segment of tubing installed near the bottom of the string serves to stop any equipment that may fall into the tubing. If two or three pay zones (layers) in a subsurface formation are to be completed, the operator can install as many as three separate tubing strings, packers, and associated equipment to segregate the produced fluids from each zone.

Question 78

Define a wellhead.

Answer 78

At the surface of the completed and cased well sits the wellhead-a large forged or cast steel fitting that is bolted or welded to the conductor pipe or surface casing.

Question 79

What are casingheads and tubingheads?

Answer 79

Equipment mounted above the wellhead called casingheads and tubingheads supports the downhole pipe strings and seals the annulus between the strings.

Question 80

Define Christmas tree.

Answer 80

Another typical unit is called a Christmas tree-an assembly of valves, fittings, pressure gauges, and chokes designed to manage fluid flowing from the well.

Question 81

Define Well Treatment.

Answer 81

Well treatment collectively refers to several techniques used to ensure the efficient flow of hydrocarbons out of a formation. These techniques are typically used to optimize production. However, they can also be used to repair formation damage-the blockage of pores in a formation by drilling mud, cement particles, corrosion products, or chemical buildup.

Question 82

In broad terms, what is Well Treatment?

Answer 82

In broad terms, well treatment involves the injection of acid, gases, or water into the well to open up the rock formation and allow oil and gas to flow through it (and to the wellbore) more easily. Among the most common well treatments are acidizing and fracturing (also called fracing).

Question 83

What are the two types of acidizing?

Answer 83

Acidizing | Matrix Acidizing

Question 84

In well treatment, define acidizing.

Answer 84

Acidizing is a process used to dissolve dolomite, limestone, or calcite cement between grains of sediment. Two types of acid are most commonly used-hydrochloric or hydrofluoric acid, sometimes mixed together-although acetic and formic acids are also used occasionally.

Question 85

In well treatment, define matrix acidizing.

Answer 85

Matrix acidizing is a well treatment used to enlarge the existing rock pores. In other cases, fracture acidizing is used, pumping the acid downhole under high pressure to both fracture and dissolve reservoir rock. Occasionally, an acid job is performed to clear away carbonate materials that can build up on the walls of the wellbore and inhibit oil and gas flow.

Question 86

Define Hydraulic Fracturing

Answer 86

As its name implies, hydraulic fracturing makes use of the force exerted by fluids (gases or liquids) under great pressure to crack open an underground rock formation, creating new fissures or expanding existing ones.

Question 87

Give a brief background to the origin of fracing.

Answer 87

Until the late 1940s, oil and gas well operators commonly used explosives to increase production, lowering nitroglycerin into a well and detonating it. The explosion fractured the rock, creating a large cavity. The cavity was then cleaned out, and the well was completed as an open hole.

Question 88

What is special about 1947 for hydraulic fracturing?

Answer 88

According to API, the first commercial use of hydraulic fracturing was in 1947, and it has been used on more than one million wells since then.

Question 89

What is special about 2006 for hydraulic fracturing?

Answer 89

Since about 2006, increased use of fracing has been instrumental in boosting production from gas-bearing shale formations in North America. The technique is also finding wider use in the exploitation of oil-bearing shales. Fracing is often used in combination with horizontal drilling to reach as much of the formation volume as possible.

Question 90

How has Energy in Septh, a group of U.S. oil and gas producers, asserted about hydraulic fracturing?

Answer 90

Energy in Depth, a group of U.S. oil and gas producers, has asserted that approximately 90% of the oil and gas wells in operation in 2011 had been fractured. And the National Petroleum Council estimates that 60%-80% of all oil and gas wells drilled in the United States from 2011 to 2020 will require fracturing treatment to remain viable.

Question 91

Describe the frac fluid.

Answer 91

A key ingredient is the frac fluid prepared for each job, brought in tanker trucks to the work site, where it is mixed and stored in large tanks. This fluid is typically water (though it can also be a gel, a foam, or a gas [e.g., nitrogen or carbon dioxide]), mixed with organic polymers and proppant—grains of quartz sand (sometimes resin coated), aluminum oxide pellets, or tiny ceramic beads. The injected fluid mixture is about 99% water and proppant.

Question 92

What does the frac fluid do?

Answer 92

When pumped into the ground under high pressure, the frac fluid pushes out into the rock formation, creating or widening existing cracks and crevices.The proppant props open the cracks after the pressure is reduced, enabling oil or gas held in the pores of the shale to flow more easily to the wellbore.

Question 93

How do they predict the exact geometry of a hydraulic fracture?

Answer 93

Predicting the exact geometry of a hydraulic fracture is complicated, so operators use a variety of tools to monitor fracture progress. In simple terms, the injected fluid is pressurized to a level greater than that imposed by the overlying rock.

Question 94

Define the fracture gradient.

Answer 94

The term fracture gradient is typically used to quantify the required minimum pressure. A gradient of 0.8 psi per foot of depth means that that at 10,000 feet, it would take 8,000 psi of hydraulic pressure to create or extend a fracture.

Question 95

Touch on how much sand and water is typically required for hydraulic fracturing.

Answer 95

Pumper trucks are used to create the desired downhole pressure. A small frac job can use 45,000 gallons of frac fluid and 35 tons of sand; an especially large job can require several million gallons of fluid and 1,500 tons of sand. Pumping pressure can reach 15,000 pounds per square inch, with fluid flow rates of 100 barrels per minute.

Question 96

How is frac fluid dealt with after production?

Answer 96

After the injection phase is completed, the fluid and any loose proppant are back-flushed out of the well so as not to impede production. A portion of the frac fluid is generally recovered and stored in pits or containers; then, it may be processed to allow reuse in later fracing operations. Some of the fluids are treated (cleaned) and then released to the environment, while some other residual material is placed in permanent deep-well storage.

Question 97

What are the results from hydraulic fracturing?

Answer 97

Experts estimate that hydraulic fracturing can increase a well’s initial production rate by 1.5–30 times, with the greatest increases seen in low-permeability (tight) reservoirs. In fact, some tight formations may produce for no more than a few months (or not at all) if not stimulated in this way.

Question 98

How many times can a well be fraced?

Answer 98

A well can be fraced several times during its life, and the technique may increase ultimate production by 5%–15%.This technique has been used with great success since about 2006 to increase gas production from shale formations across the United States, including the Barnett (Texas), Haynesville, and Fayetteville (southeast), and Marcellus (northeast).

Question 99

Due to fracing, how has the DOE report on shale gas changed?

Answer 99

In an April 2009 report, DOE reported shale gas production of only about 0.26 tcf in 1998.5 That figure jumped to 1.4 tcf in 2007, and DOE expected production of 4.8 tcf in 2020. DOE stated that shale gas production potential of 3–4 tcf per year may be sustainable for decades. (Roughly, 1 tcf is enough gas to heat 15 million homes for one year.)

Question 100

What happened in 2007 for hydraulic fracturing?

Answer 100

In 2007, engineers found they could use the method to extract oil from the large Bakken formation beneath North Dakota and Montana (fig. 5–21) by increasing the number of cracks in the rock and using different chemicals. In 2010, production there topped 458,000 b/d.

Question 101

How has hydraulic fracturing changed the size of some oilfields?

Answer 101

Fracing is now also being applied in the Eagle Ford oil shale formation of South Texas. By some estimates, the Bakken and the Eagle Ford are each expected to ultimately produce four billion barrels. That would make them the fifth- and sixth-biggest oil fields ever discovered in the United States.

Question 102

How have several foreign oil companies pursuing investment in the U.S. oil shale development?

Answer 102

Several foreign oil companies (e.g., Shell, BP, and Statoil) are pursuing investment in U.S. oil shale development. In particular, the China National Offshore Oil Corporation, China’s national oil company, signed two deals in late 2010 and early 2011 (together worth $1.5 billion) with Chesapeake Energy for stakes in shale projects in the Niobrara and Eagle Ford formations.

Question 103

Define the FRAC Act.

Answer 103

Federal legislation was proposed in 2008 and 2009 as the Fracturing Responsibility and Awareness of Chemicals Act (FRAC Act). Reintroduced in 2011, it would give the federal Environmental Protection Agency (EPA) the authority to regulate hydraulic fracturing in some states. However, as of February 2012, lawmakers had taken no action on the proposed law.

Question 104

How have several European countries responded to hydraulic fracturing?

Answer 104

Several European countries are also weighing the benefits and impacts of hydraulic fracturing. In May 2011, France imposed a moratorium on the practice, but a committee of the British parliament judged fracing to be acceptable. Poland, which may have Western Europe’s greatest shale gas reserves, had awarded dozens of concessions for development as of mid-2011, but was proceeding carefully.

Question 105

Comment on the studies released showing hydraulic fracturing did not pose a threat to drinking water supplies.

Answer 105

EPA released a study in 2004 that showed hydraulic fracturing did not pose a threat to drinking water supplies. However, in early 2011, the agency submitted a draft plan for further study to the agency’s independent Science Advisory Board for its review. EPA expects release of initial study results by the end of 2012.An additional report based on further research is planned for release in 2014.