In this work the authors have focused on analysis of causes for scale formation on pumps and downhole equipment in wells producing heavy oil. Thirty-three scale samples recovered from wells with downhole pumps failures have been analyzed. Various factors can contribute to emergency situations: carbonate salts may precipitate because of high mineralization of produced formation water and high temperature at the inlet of downhole pumps, or because of clogging of pump parts with formation particles, or solids. So, the problem must be addressed differently in each case.
The first step is to determine why certain scale is formed on downhole equipment of SAGD-wells. To do this, pump inlet must provide for temperature sensors and solids sensors to detect solids content in produced water. Also, produced water quality must continuously be analyzed for physicochemical properties and composition. Then, parameters that characterize produced water saturation with carbonate salts are calculated. If these parameters are critical, salting inhibitors are injected into downhole equipment and bottomhole formation zone.
If scale source is formation rocks, which is the case in unconsolidated rock, formation fines will enter the wellbore even at low differential pressure. In this case, gravel packs can be a useful tool to control scale formation. Also, this problem can be addressed by injecting polymer or hydrophobic systems into formation bottomhole zone, or at least, the well can be circulated with large volumes of aerated fluid. Of course, all these methods come at a cost; however, workover operations because of electric submersible pumps failure and the resultant well shutdown are translated eventually in much higher loss of profits.
References
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2. Non-plugging exploitation: complication control of mechanical impurities (In Russ.), Inzhenernaya praktika, 2010, no. 4, pp. 43-54.
3. Musin R.R., Povyshenie effektivnosti ekspluatatsii skvazhin v oslozhnennykh geologo-promyslovykh usloviyakh (na primere OAO “Var'eganneftegaz”) (Increasing the efficiency of well operation in complicated field geological conditions (for example, Varioganneftegaz)): thesis of candidate of technical science, Ufa, 2014.
4. Kashchavtsev V.E., Mishchenko I.T., Soleobrazovanie pri dobyche nefti (Salt formation during oil production), Moscow: Orbita Publ., 2004, 432 p.
