This is the second installment in this series of posts on Hydrofracking for oil and natural gas that is currently completely changing how we extract these resources from deep reservoirs.
The author lays out in detail how this is done in this segment. If you haven't read the 'Introduction to Fracking', please do so as it leads into the rest of the report.
(Part 2)
What is Hydraulic Fracturing?
by Darrell Mattheis
Hydraulic Fracturing is not a drilling process at all,
but rather is a separate process that
starts after the drilled hole is complete, and usually takes about four days.
What is called "fracking" is actually the
last part of a complicated series of
operations. Here I have attempted to outline the major steps involved in
accessing the natural gas from a 6-7,000 foot deep shale layer in the Marcellus
Shale.
The first step (4-8 weeks) a geological formation, that promises to hold
trapped methane and perhaps oil has been identified, all permits required by
state and federal laws have been obtained, the use of a drilling rig has been
secured, final tests conducted, and all required environmental analysis
completed.
The second step Rig Work. (2-4 -weeks) involves bringing in and setting up a drilling rig
capable of operating at the depth that the shale layer has been identified at.
The third step Drilling The Well.
As drilling commences, workers install a
series of protective steel and cement layers in the upper part of the well to
create an impermeable barrier between the well and ground water zones.
Well casings and cement layers ensure the
integrity of the well and protect against the release of drilling mud, hydrofracking
fluid and gas & oil into other parts of the geological formation.
The most critical area is generally the first 1000
feet, where virtually all water
bearing strata are found. As the drill
string goes deeper, special steel casing is used to isolate the natural gas
formations from surrounding areas. As
the drill gets closer to the desired geological formation, the drill string
must be angled horizontally to traverse the middle of the shale layer.
The fourth step in a conventional perforated
completion has holes being
punched through the horizontally oriented casing. Today the preferred process of perforating casing, "jet
perforating" requires small electrically-ignited charges lowered into the
well. These charges, when ignited, poke
tiny holes through the casing to the formation.
The fifth step has the drill rig and associated equipment removed and the site
modified for the hydraulic fracturing equipment and the hydrofracking equipment
setup.
The sixth step, Hydrofracture. (Generally this
takes four days)
The placement of hydraulic fracturing treatments
underground is sequenced to meet
the particular needs of the formation.
Each oil and gas zone is different, and requires a fracking design
tailored to the particular conditions of the formation.
Today, sophisticated computer programs are run to predict fluid efficiency, fracture
geometry and flow properties in three dimensions. Models currently in use can simulate the way
fluids move through the fracture, and the way the propping agent is
distributed.
Programs are
available to obtain a temperature
profile of the treating fluid during a fracturing treatment. These same programs can assist in designing
the concentrations of the gel, gel stabilizer, breaker and propping agent
during treatment.
The actual fracture, takes place in a sequence of pumping operations,
during which truck mounted, high-pressure pumps, move millions of gallons of
fracking fluids down the well at high pressure, (1000-20,000 PSI,). The
fracking fluid moves through the holes in the casing of the horizontal run, and
either enlarges pre-existing, or opens new fractures in the shale, and holds
them open. The hydrofracking fluid, contains the proppant (usually treated
sand) and 0.5%- 2% chemicals
Shale rock has gas trapped in pores smaller than the
width of a human hair, so a network
of small fissures in the rock must be created to release the gas.
FlowBack Water.
Once the high pressure in the drill
casing is released, the proppant will keep any fractures open and the lowered
pressure will allow the fracking fluid, (flowback) methane and/or oil to flow
back out.
This "flowback" water, contains the fracking
fluid, and proppant, and may also contain
salty water from the well. This "produced
water" must be contained and disposed of according to EPA waste water
disposal regulations.
The vast majority of FlowBack Water is disposed in
underground injection wells, whose
operation is regulated by the US EPA.
Underground injection is an expensive procedure as the fluid usually
must be trucked to regulated sites considerable distances away.
Over the last several years many companies have begun
recycling the Flowback fracture
fluid, finding that around 50% of the "load" water recovered could be
reused, resulting in significant reductions in trucking and disposal costs.
Well Completion - Producing Natural Gas
Once a well is drilled and
completed, a process usually taking a few months, it is ready for
production. Everything on the site is
dismantled except for a four-to-six foot well head and local processing
facilities connected to gas pipelines that run to national distribution
networks.
The Wellhead
Consists of the equipment
mounted at the opening of the well to manage the extraction of hydrocarbons
from the underground formation. It
prevents leaking of oil or natural gas out of the well, and also prevents
blowouts caused by high pressure.
If the well in question is
considered to be "high-pressure" the wellhead must be capable of
withstanding pressures up to 20,000 PSI.
The wellhead consists of three components; (1) The
casing head, (2) The tubing head, and (3) The "Christmas tree".
The casing head
consists of heavy fittings that provide a seal between the casing and the
surface, and serves to support the entire length of casing that runs all the
way down the well. The casing head
typically contains a gripping mechanism that ensures a tight seal between the
head and the casing.
The Tubing Head provides a seal between the tubing, which runs inside the casing, and
the surface. The tubing head is designed
to support the entire length of the casing, and, provides connections at the
surface which allow the flow of gas and liquids out of the well.
The Christmas Tree fits on top of the casing and tubing heads, and contains tubes and
valves that control the flow of hydrocarbons out of the well. The "Christmas tree" is the most
visible part of a producing well, and allows for the surface monitoring and
regulation of the gas and liquids from a producing well.
A normal, natural gas well, can continue to produce
gas for up to forty years, with
minimal attention, and is connected to a sophisticated monitoring network to
determine that everything is functioning as it should.
No comments:
Post a Comment