New Artificial Lift System Using Coiled Tubing and Reciprocating Downhole Pumps for Heavy and Viscous Oil

摘要

The use of coiled tubing as an artificial-lift mechanism has been very popular for lifting oil wells as velocity strings (siphon strings) and also removing water and condensate from gas wells. The effect of reducing the effective flowing area, increasing fluid velocity and therefore unloading the well is no longer the only lifting mechanism for this particular application. Reciprocating movement provided by a surface hydraulic operated unit is transmitted by the coiled tubing to a down-hole pump to assist in the lifting process. Therefore for low productivity wells in which the fluid velocity is significant below the minimum or critical velocity to prevent a well from loading up, the down-hole pump will achieve the flowing condition. Utilizing coiled tubing as the motion transmitter to the down-hole pump increases the benefits already explored by the use of continuous rod for SRP applications, by also providing a flow path from surface to bottom. Through this flow path, chemical injection down the coiled tubing, and returning by the annular space between the coiled tubing and the 2 7/8” tubing string can be achieved while pumping the well. Chemicals pumped can be either viscosity reducers, corrosion inhibitors or any other needed to achieve optimum production. Also this flow path can be used to wash out sand or debris present inside the tubing string in an easy, fast and economical way. Also the potential use of pumping up through the inside of the coiled tubing or the back side (annular space between the coiled tubing and the production string) has been investigated with satisfactory results in this application. The system has been successfully tested in four oil wells in North Mexico (two of them in the Chicontepec project) with densities up to 13.9 °API and viscosities up to 6464 centipoises. System components, selection criteria, design, execution, evaluation and lessons learned during this first time application are discussed in this paper. Based on the observed results, this technology is being considered as a technical and economical alternative to develop the heavy and viscous oil wells in the area.