Long Exposure Chelating Acid Treatment to Release ESP Stuck Pump

In October 2019, electrical submersible pump (ESP) XY-107 experienced an overload shutdown. Troubleshooting actions have been conducted such as reverse rotation, used rocking method, voltage boost, inject gas through the annulus, and even fluid circulation, yet still failed to reactivate the well. Pump stuck condition was suspected and urgently need a solution. A study was performed to determine the cause of pump stuck. XY-107 is produced from limestone formation, therefore suggesting possibility of scale deposit formation in this well. Upon physical inspection inside the well's flowline, lump of deposit was recovered and suspect similar material could have occurred inside the pump. Rig intervention is a common solution for the ESP pump stuck condition. However, it required high cost (around 80,000 USD) and a longer well service job period up to 5 days. With scale deposit as the suspect, an unconventional solution was proposed to soak the well with acid to dissolve stuck-material by rigless operation. It was much cheaper than rig intervention (only about 4,000 USD) and with a shorter time of 1 day. Yet, acid selection is critical to avoid material damage during operation. Since conventional acid system is known to be corrosive to the metal components, hazardous, and difficult to handle; chelating acid was chosen as an alternative since it is known as a metal-friendly and able to dissolve carbonate and iron deposit. Treatment to address pump stuck situation was executed in March 2020. The chemical treatment was injected by pumping and circulating chelating solution from tubing to the annulus. ESP then soaked for 48-hours long. The treatment has successfully revived the well. It produced with no significant issue for 8 months and even double the oil production. This successful treatment proves chelating technique is safer for ESP and able to regain well production. Significant cost saving up to 76,000 USD was realized by avoiding rig intervention and shortening time of well services. Detailed study, laboratory testing, treatment procedure, and further analysis are discussed in this paper. Chelating acidizing is an uncommon acid system to stimulate carbonates and sandstone in our operating area. Since its successful performance during the trial, more acid campaign using chelating was conducted to enhance oil production. However, this acid system was never been tried as a solution treatment for pump stuck condition and the case of well XY-107 was the first time in the company's history.

On precipitation of struvite (MgNH4PO4.6H2O)

Excessive input of N and P into water bodies causes eutrophication which leads to deterioration of aquatic evironments and has adverse effects naturally and economically. It is therefore urgent to remove N and P from wastewater prior to disposal into inland and coastal waters. Among the various removal methods, controlled struvite precipitation is preferred. Struvite (MgNH4PO4.6H2O) precipitates uncontrollably under the specific conditions producing a scale deposit causing persistent problems in industries and wastewater treatment plants. The scale deposit clogs the piping system and impair plant equipment. On the other hand, thanks to its composition and properties, struvite is a potential fertilizer. In medical field, struvite is a common component of kidney stones. A number of process parameters govern the struvite precipitation. This paper briefly presents these parameters: pH, molar ratios, temperature, mixing, and presence of foreign ions. pH level is considered as the most important variable affecting the precipitation of struvite and the pH level: 9.5 to 10.5 is seen as the optimum. For an effective precipitation the molar ratios of the struvite components, i.e. Mg:N:P should be at least unity. With regard to struvite solubility, the effect of temperature, in the range of 21oC to 49oC, is conflicting, which is probably due to different experimental conditions. Whilst agitation is not regarded as a decisive parameter, the influence of foreign ions, notably divalent metal ions, on struvite morphology and change of crystal phases is significant.