The obstructions generated by elastomers is one of the most common problems in the majority of the heavy oil fields producing with progressive cavity pump (PCP) in Venezuela. For this reason rehabilitation work are done constantly to clean wells with the objective of reactivating, or increasing their production.
Given that the application of conventional rehabilitation work done with service rig using wash pipe and shoe mill has not shown successful results because of lack of circulation in the well; arises the need for a new cleaning technique by using the cyclone bailer tool combined with coiled tubing unit.
The global procedure of this combination involve making runs with coiled tubing and the cleaning's BHA composed of: a shoe mill, collecting chamber, a flapper valve, a bottom filter, a high torque bottom motor, and a cyclone bailer which allows, by a suction effect, catching the residuals inside the collecting chamber. Once the collecting chamber is filled with elastomers and oil residuals, the tool is taken to surface for cleaning and this process is repeated until reaching the target depth and remove all obstruction.
As a consequence of applying this technique on the four wells studied, an average overall effectiveness of 85% was achieved in clearing blockages ranging from 363-817 ft in liners from 3-1/2 to 6-5/8 in, in an average of 8 runs in 7 days operational time per job, thereby achieving full production restoration at 769 BPD, which meant an average increase of 22% above the estimated production of 630 BPD.
The result of the application of the cyclone bailer tool to remove the cumulated rubber residuals in the liner showed more effective than cleaning with jets, or conventional motors with wicks used previously, this is due to compaction and the sizes of the elastomers residuals, which in several occasions reached up to 1.5 feets in length, too big to pass by annular space between inner diameter of liner and outer diameter of coiled tubing (CT) and the debris were too heavy to be lifted using fluids energized with nitrogen.
It is important to highlight that during the first run of well intervention with this technology, no further progress was observed due to flapper valve obstruction in the BHA due to the presence of large pieces of trapped elastomer, which prevented entry of other elastomers in the collecting chamber, making it difficult to reach full capacity and thereby causing lost time in the recovery of elastomers and well cleaning, so it was decided to try changing the BHA eliminating the flapper valve to allow free passage of elastomeric rubber clippings and so achieve greater debris collection by run, thus obtaining better results in the operation, due to their compaction and maintaining a low fluid pumping rate while pulling the CT to surface to prevent their return to the well.