MechChem Africa March 2017

March 2017

•

MechChem Africa

⎪

Petrochemical industries, oil and gas

⎪

How hydraulic fracturing works:

Edited from an OilPatch CopyWriter article by Cyndee Davis.

Awellbore is drilledusing a drill pipe andbit.

Mud is pumped down to the drill to cool and

lubricate the drill pipe and bit. This helps to

stabilize the wellbore and helps carry rock

fragments to the surface.

Drilling continues way past groundwa-

ter levels and typically, over 500 m of rock

separatestheshalereservesfromthelowest

groundwater reservoirs.

The drill pipe and bit are removed and a

steel tube called surface casing is set inside

the well. The tube stabilises the sides of the

well, creating a protective barrier between

the well stream and any underground fresh

water reservoirs. Cement is then pumped

into the well, through and out of the casing,

displacingremainingdrillingfluidsandsecur-

ingthecasinginplacepermanently.Fillingthe

gapbetweenthecasingandwellborecement

creates a protective seal, keeping outside

materials from entering the well flow.

The casing is pressure-tested to make

sure hydrocarbons and other fluids do not

seep out as they are brought to the surface.

Drilling continues and another layer of

casing and cement are set in place to cre-

ate a second permanent protective barrier.

These multiple layers of casing and cement

are critical for safewell construction and to

protect drinking water.

At about 150 m above the hydrocarbon

shale formation a specific drilling motor

with sophisticated measuring instruments

begins drilling at an angle to create a hori-

zontal path into the targeted layer of gas or

oil bearing shale. The casing and cementing

process continues through the entire length

of the now horizontal wellbore.

A perforating tool is inserted into the

well, creating holes in shale layers to allow

the hydrocarbons to enter the well stream.

Once the perforating tool is removed, a

fracturing fluid made up of water, sand and

small percentages of a chemical solution,

is pumped into the well, opening up tiny

fractures deep into the shale.

Once the water is removed, the sand

remains, holding the fractures open. This

makes it possible for gas or oil to travel from

the shale out into the well.

Bridge plugs are inserted, allowing the

fracturing process to continue across the

whole length of the horizontal well. After

the fracturing process is completed, all the

bridge plugs are removed, allowing the gas

or oil to flow freely to the surface.

On average it takes four to eight weeks

to prepare a site for drilling and a further

four to five weeks during which the casing

and cementing occurs. Hydraulic fractur-

ing, itself, only takes between two to five

days, making the entire process fracking

from start to finish, a total of seventy to a

hundred days.

Following the establishment of a well by

fracking, the facility can typically produce

energy for 20 to 50 years. Trucks, pumps

and equipment are removed, leaving only a

production valve and collection equipment

on the land surface.

The establishment of a shale oil or gas well by fracking typically takes only eight to 12 weeks, with the hydraulic fracturing only taking two to five days. After

this time, a well can produce oil or gas for 20 to 50 years.