Simulation of wax deposits formation in wells using electric submersible pumps

Abstract
The paper shows how parameters of the electric submersible pump installation infl e the conditions of formation of asphaltene, resin and paraffi deposits (ARPD) based on the model of high-wax oil moving along the well bore using the hydrodynamic analysis of the formation- well-pump system. Practical recommendations for the conditions under consideration were obtained.
Materials and methods
The paper used results of lab researches of physical and chemical properties of high- wax oil as well as the results of simulation of high-wax oil moving along the well bore equipped with ESP, carried out in PIPESIM software by Schlumberger.
Results
1. Using known physical-chemical characteristics and blend composition of the studied oil a high-wax oil model was built using the Multifl sh Wax module. It was used as a basis for a phase equilibrium diagram of a hydrocarbon system with a PT-profi e of fl moving from productive horizon to wellhead and to determine characteristic points of phase transitions. The wax appearance temperature was determined at 44°С; by 20°С its content reaches 27% of mass. 2. Nodal analysis was used to evaluate productivity of the well. Due to decrease in formation pressure during fi d development the productive horizon proved to be short of productive potential, not suffi ient to provide blowing. An electric submersible pump was handpicked and factors aff g the depth of organic deposits while using it were studied.
Conclusions
1. High convergence was established between the actual temperature log and the calculated temperature profiles of P.D. Lyapkov and I.T. Mischenko. This makes it possible to rely on these methods if field study results for temperature distribution in the well bore are not available. However, the closest value to the actual depth of initial organic deposits was produced from a complex mechanistic model of vertical multiphase flow OLGAS. 2. The nature of wax appearance temperature changes in the well bore was determined. Those changes were most prominent when creating a depression on the productive formation and increasing pressure in ESP. During degassing the wax appearance temperature increases due to lower content of light fractions. 3. To infl e on one of the main ARPD formation factors in the well - the temperature - it is recommended to use ESP nominal sizes with bigger productivity that required for the planned rate of fl w, which will result in hotter fl wstream. 4. The infl e of ESP rotation rate on depth of ARPD formation in well was estimated. Besides increased rotation, another way to infl e the fl wstream is to decrease the tubing internal diameter and add more steps, which would also lead to altered pressure and discharge characteristics of a pump. 5. The dependency of initial ARPD formation depth in the well on the water content of the high-wax oil was established. Decreased interval of ARPD formation in the well was caused by decrease in share of high-molecular hydrocarbons in the fl wstream during oil fi d development, hydrophilization of the tubing internal surface and slower cooling of the stream. 6. An area was identifi for effi ient choke restriction (buff ed pressure increase) as a way to fi ARPD formation. The positive eff is observed in case when deposits in a bore start to form after beginning of degassing. Otherwise the result is negative, and the increase of buff ed pressure leads to increase of wax appearance temperature and consequently to earlier formation of organic deposits in the well bore.