Explosive are smooth; unlike a torn surface where



Explosive decomposition is also known as Gas permeation
occurs when gas; under pressure; enters the elastomer matrix and expands due to
a pressure drop. When the gas expands, it often results in blister or bubbles
forming within the elastomer. This pressure drop can be the results of the
event such as the fluid level equalizing in the wellbore after a shut down or
from the pulling of the pump.

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 The expanding gas
within the elastomer matrix can sometimes expand to the point that the
elastomer ruptures. This is called explosive decompression.  The rapidly decompressing of the gas
entrained within the elastomer matrix tears and chunks the elastomer when it




The word delamination contains the word lamination which
means “layer”. In elastomeric terms, this means that the elastomers had not
knit through its cross-section resulting in layer-like striation within the
elastomer. This is often the result of temperature during the injection
process. These lamination or layers create weak areas within the elastomers and
a prime location for gas that has permeated into the elastomers to gather. When
a pressure drop occurs, the gas has entered these laminated areas expands
thereby tearing these weak areas. Visually looking at the laminated areas, the
internal surface of the laminated are smooth; unlike a torn surface where the
surface are rough and jagged.   




Improper Rotor Spacing:


Improper rotor spacing is not a material or application
related failure but a failure due to improper installation procedure. For a
given set of well condition, the sucker rods will stretch a given amount. This
stretch is dependent upon the rod size, total dynamic head and the effective
cross-sectional areas of the pump. If the proper amount of stretch is not accounted
for, the rotor placement within the stator could either be too high or too low.
In either case, excess stresses are placed on the rotor and sucker rods and may
result in a torsional fatigue of the either the rotor or the sucker rods.

In case of not enough
space out:


Rotor runs on the tag bar, thus putting the rotor in
compression and potentially causing premature failure of the rotor and tag bar.


If a torque anchor is not used the additional torque of the
rotor running on the tag bar could result in the stator/tubing unscrewing.    


In case of too much
space out:


Reduced contact with the pump stages & over pressuring
of the pump or excessive unidirectional bending of the rotor causing it to


Dry run:


A pump that has run dry its elastomer hard, brittle and
extensively cracked. In an extreme run dry condition, the contour will be
completely gone.


Abrasive wear:


Abrasive wear occurs when the elastomer is worn from the
presence of abrasives in the produced fluids. As the percentage of abrasives
increases, the chances of prematurely wearing the seal lines that are formed by
the interference fit between the rotor and stator also increase. The hardness
and angularity of the pumped abrasive can also affect the wear rate.


The total differential pressure seen across the pump as
well as the pump’s rotational speed play a key role in how abrasive affect the
elastomer. As a result of the elastomer wearing, the slip within the pump
increases and as a result, the production will drop off. 



 The data and the
related case studies are mentioned below at page no.6 & 7.



coal particles flow with formation water then it stuck the CBM well. In
conventional oil wells, sand cleanout is usually operated by circulating the
cleaning fluid into the wellbore to bring sand particles to the surface.
However, when applied in CBM wells, this traditional hydraulic particles
hoisting technology would leak the working fluid into the formation, destroy
the coalbed formation structure and jam the formed channel of gas because the
bottom-hole pressure (BHP) is low.

CBM wells belong to the low reservoir pressure and absorption wells. The bottom
hole pressure (BHP) of CBM wells is very low, usually ranges from 1 to 5 MPa,
and the coal reservoir fracture characteristics are highly developed. In
principle, coal particles are dragged by the formation fluids, which are water
and gas, carried out through the formation fractures and settle down at the
bottom of the well. By the time the casing is full of the sedimentary solids,
the production zone becomes plugged and the down-hole pump gets stuck. Workover
activities have to be carried out to bring the well back into production. Frequently,
removal of wellbore fill is considered inadequate, leaving large quantities of
coal particles in the well, which often requires repeating well cleanouts in a
relatively short time interval. On average, the period between two cleanout
operations is 5 months for CBM wells. In addition, wellbore cleanouts are
extremely time consuming and costly, preventing timely return of wells to
production and increasing the cost of well maintenance.


Structure and Principle:

to the working area, the coal particles cleanout technology system is divided
into two subsystems: the surface subsystem and the Downhole subsystem. The
surface subsystem consists of a plunger pump, a separation tank, a gas recovery
facility, and flow meters etc., as shown in Fig. 1