ExplosiveDecompression: Explosive decomposition is also known as Gas permeationoccurs when gas; under pressure; enters the elastomer matrix and expands due toa pressure drop.
When the gas expands, it often results in blister or bubblesforming within the elastomer. This pressure drop can be the results of theevent such as the fluid level equalizing in the wellbore after a shut down orfrom the pulling of the pump. The expanding gaswithin the elastomer matrix can sometimes expand to the point that theelastomer ruptures. This is called explosive decompression. The rapidly decompressing of the gasentrained within the elastomer matrix tears and chunks the elastomer when itexpands.
Delamination: The word delamination contains the word lamination whichmeans “layer”. In elastomeric terms, this means that the elastomers had notknit through its cross-section resulting in layer-like striation within theelastomer. This is often the result of temperature during the injectionprocess. These lamination or layers create weak areas within the elastomers anda prime location for gas that has permeated into the elastomers to gather. Whena pressure drop occurs, the gas has entered these laminated areas expandsthereby tearing these weak areas. Visually looking at the laminated areas, theinternal surface of the laminated are smooth; unlike a torn surface where thesurface are rough and jagged. Improper Rotor Spacing: Improper rotor spacing is not a material or applicationrelated failure but a failure due to improper installation procedure. For agiven set of well condition, the sucker rods will stretch a given amount.
Thisstretch is dependent upon the rod size, total dynamic head and the effectivecross-sectional areas of the pump. If the proper amount of stretch is not accountedfor, 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 mayresult in a torsional fatigue of the either the rotor or the sucker rods.In case of not enoughspace out: Rotor runs on the tag bar, thus putting the rotor incompression and potentially causing premature failure of the rotor and tag bar.
If a torque anchor is not used the additional torque of therotor running on the tag bar could result in the stator/tubing unscrewing. In case of too muchspace out: Reduced contact with the pump stages & over pressuringof the pump or excessive unidirectional bending of the rotor causing it tobreak. Dry run: A pump that has run dry its elastomer hard, brittle andextensively cracked. In an extreme run dry condition, the contour will becompletely gone. Abrasive wear: Abrasive wear occurs when the elastomer is worn from thepresence of abrasives in the produced fluids. As the percentage of abrasivesincreases, the chances of prematurely wearing the seal lines that are formed bythe interference fit between the rotor and stator also increase. The hardnessand angularity of the pumped abrasive can also affect the wear rate.
The total differential pressure seen across the pump aswell as the pump’s rotational speed play a key role in how abrasive affect theelastomer. As a result of the elastomer wearing, the slip within the pumpincreases and as a result, the production will drop off. The data and therelated case studies are mentioned below at page no.6 & 7. CONTINUOUS VACUUME CLEANOUT TECHNOLOGY:Whencoal particles flow with formation water then it stuck the CBM well. Inconventional oil wells, sand cleanout is usually operated by circulating thecleaning fluid into the wellbore to bring sand particles to the surface.
However, when applied in CBM wells, this traditional hydraulic particleshoisting technology would leak the working fluid into the formation, destroythe coalbed formation structure and jam the formed channel of gas because thebottom-hole pressure (BHP) is low.TheCBM wells belong to the low reservoir pressure and absorption wells. The bottomhole pressure (BHP) of CBM wells is very low, usually ranges from 1 to 5 MPa,and the coal reservoir fracture characteristics are highly developed.
Inprinciple, coal particles are dragged by the formation fluids, which are waterand gas, carried out through the formation fractures and settle down at thebottom 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. Workoveractivities have to be carried out to bring the well back into production. Frequently,removal of wellbore fill is considered inadequate, leaving large quantities ofcoal particles in the well, which often requires repeating well cleanouts in arelatively short time interval. On average, the period between two cleanoutoperations is 5 months for CBM wells. In addition, wellbore cleanouts areextremely time consuming and costly, preventing timely return of wells toproduction and increasing the cost of well maintenance.
