Page 217 - A Practical Companion to Reservoir Stimulation

PRACTICAL COMPANION TO RESERVOIR STIMULATION

P-7 pump in addition to the main treating line. The pressure rating
of the wellhead should be checked to make sure it exceeds the
Equipment Hookup
treating pressure. If the wellhead has a lower pressure rating
than the anticipated treating pressure, a tree saver will be
Assembling the equipment in a safe, organized and efficient necessary to isolate the wellhead from this pressure level.
manner is extremely important for the success of a fracturing The pretreatment safety meeting is the principal means of
treatment. Thorough pretreatment planning is essential to the communication where final instructions to all personnel can
organizational process of coordinating equipment hookup. be given. A well-organized safety meeting helps ensure the
An inspection of the location prior to the actual treatment treatment is an operational success without being a threat to
allows diagrams to be made that can optimize the use of human safety.
available space.
Many steps of the organizational procedures are driven by P-7.1.2: Controlling Wellhead Pressure
common sense. Yet, small problems can easily be overlooked To ensure that well control is always maintained, the valve
in the rush to get things ready. Pretreatment planning can arrangement at the wellhead should consist of at least two
eliminate many small problems that have the potential to valves. A “frac” valve or “master” valve should be installed
develop into problems which may ultimately jeopardize the above the main wellhead valve. If one valve fails to hold the
success of the treatment.
pressure, the other valve can quickly be closed to control the
P-7.1: Safety Considerations well. It is preferable to have the main wellhead valve flanged
At no time should the safety aspects of a treatment be com- to the casing head, rather than having a threaded connection.
promised. Safety guidelines have been developed from ex- If a threaded connection is necessary, the condition of the
threads must be thoroughly inspected for thread wear and
periences derived from previous incidents. Many of these proper taper.
incidents have had great potential to seriously injure personnel
or destroy valuable equipment. The inherent risks of dealing P-7.1.2.1: Tree Saver
with high pressures can be greatly minimized by following Specialized isolation tools, or tree savers, can protect a
simple safety procedures. Hydraulic fracture treatments can Christmas tree from damage and possible failure that results
never be considered a success if an accident results in de- from exposure to high pressure, corrosive fluids or abrasive
struction of equipment or injury to personnel.
proppant-laden fluids. Often, the pressure rating of a wellhead
P-7.1.1: Safety Meeting is less than the pressure required to pump a stimulation
The pretreatment safety meeting ensures that all personnel on treatment. Replacing the existing tree with one having a
higher pressure rating is expensive and requires killing the
location are aware of specific dangers and required procedures well with potentially damaging fluids. Even if the existing
relative to the treatment. Each person on location should tree has a sufficient pressure rating, exposure to high pressures
clearly understand his or her role during the treatment as well and the treating fluids may leave it in an unsafe condition.
as his or her responsibility during emergency situations. A The tree saver can be mounted on the existing Christmas
head count must be taken to account for everyone on location. tree. A mandrel is then extended through the valves on the
An escape route and meeting place should be agreed upon . tree and into the tubing. The mandrel has a rubber cup
where all personnel will gather in the event of an emergency assembly that seals to the walls of the tubing and prevents
situation. Personnel who are not directly involved in the fluid or pressure from directly reaching the tree. Once set, the
treatment should have limited location access during the tree saver can extend the working pressure of the wellhead up
actual pumping operations. to 20,000 psi. Figure P-61 shows the tree saver mandrel set in
Everyone should be aware of the unique dangers of each
treatment. Some locations may be in an area of H*S, or pos- the tubing. Once the stimulation treatment is completed, the
mandrel is pumped back out of the Christmas tree, and the
sibly the fluids being pumped are highly flammable. As many wellhead valves can be closed.
of the possible safety problems or concerns as possible should
be brought to the attention of everyone. P-7.1.2.2: Check Valves
Maximum pressure limits should be set at this time, and
every high-pressure pump operator must be aware of this A check valve should be placed in the treating line, on the
ground, as close to the wellhead as practical. This valve
limit. Instructions for pressure testing the treating iron will allows flow in one direction; therefore, it can be pumped
also be covered. The high-pressure treating line, up to the through but automatically closes once pumping stops. This
wellhead valve, should be tested to slightly above the antici- isolates well pressures to the closed side of the check valve
pated fracturing pressure. A properly tested line will test each
and prevents flow of well fluids. This type of valve is essential

P-56