Production logging is difficult in complex well designs such as horizontal multilateral (ML) wells with jagged level-two exits. The ML exits can obstruct the access of logging tools due to damage around the milled windows. Once inside a low-flow high-water cut reservoir, the challenge becomes measuring an oil inflow profile in stratified flow.
The access issue is worse in sub-hydrostatic wells completed with artificial lift. Horizontal gas lifted wells are easily choked by the presence of coiled tubing (CT). Y-Tools can be deployed in electrical submersible pump (ESP) wells to provide bypass tubing for logging strings necessary to log while pumping, although the system has not been successful in low rate wells due to re-circulation across the dynamic seal in the Y-Tool. This recirculation invalidates the log data and overheats the motor. As in gas lift completions, the low rate ESP completions also suffer rate reduction caused by the presence of CT.
This paper describes the methods used to overcome these access and production logging challenges in North Oman. A new tool configuration that comprises a vertical array of mini spinners and fluid type sensors was used to detect a 2% oil hold-up in a stratified flow. It has a surface controlled collapsible spinner cage that makes the tool slick to maneuver around obstructions in the well. This has overcome some of the level 2 bypass problems in ML wells. A temporary ESP and Y-tool upper completion has been used to log a 3-leg ML backbone successfully. To fix the recirculation problem, a modified Y-tool plug was designed to reduce the fluid leakage in the dynamic seal. A variable speed drive (VSD) at surface controlled the ESP motor speed, adjusting the pump rate to compensate for the rate reduction caused by the presence of the CT. Wireline conveyed tractors have overcome some of the choking limitations of CT in gas lifted wells. Openhole completions remain a challenge.