A limitation of Electrical Submersible Pumps (ESPs) is the inability to handle significant volumes of gas. The implications of this limitation become even more critical if the fluid production rate is at or below the minimum rate required for cooling of downhole equipment. The oldest and most widely practiced method for forced convection cooling of the motor of an ESP system is to use a motor shroud. However, numerous field case studies have shown that even with the motor shroud in place, motor failure has been the primary cause of ESP failure in low-volume high-GOR wells.The optimal mitigation solution for low-volume high GOR cased-hole producers is to lower the ESP string below the perforations, with a shroud installed for cooling of the motor. For low-volume high-GOR ESP-equipped producers that are producing from an open-hole interval installation of the same conventional shrouding system would take care of the cooling of the motor but it will not function as a free gas eliminating or reducing device. The production strings of the ESPs producing from an open-hole interval usually include an inverted shroud intended to reduce the amount of free gas entering the pump. Such installations would not function as a motor cooling device.The large degree of production loss and the increased operating cost incurred by unplanned ESP shut-down and failure have been two of the major challenges faced by the asset teams of South Fuwaris (SF) and Humma (HUM) Fields in PNZ-Kuwait, in their efforts to maximize the uptime of low-volume high-GOR ESP-equipped open-hole producers. A customized shrouding system was needed to simultaneously resolve the issues of motor cooling and the reduction of the amount of free gas entering the pump. The dual functioning nature of a shrouding system composed of a conventional shroud combined with an inverted shroud was the main feature that had to be incorporated in the design of such system.Through the continuous efforts of the South Fuwaris and Humma asset teams, a novel dual-shrouding system has recently been developed to fulfill the requirements of cooling of the motor and reduction of free gas entering the pump simultaneously. Multiple customized versions of this system have been installed in critical low-volume high-GOR openhole producers since the 4th quarter of 2009. Examination of historical operating conditions of ESP strings equipped with the new shrouding system showed a significant reduction in the number of ESP shut-downs due to underload, overload or high motor temperature trips, and a dramatic drop in the number of ESP failures caused by overheating of the motor.This paper discusses the benefits of the newly-designed shrouding system and its built-in perforated tail pipe, specifically designed for low-volume high-GOR producers in South Fuwaris and Humma Fields, and actual results achieved from field implementation of this system.

The South Fuwaris and Humma Fields are located in the Partitioned Zone between Kuwait and Saudi Arabia. The South Fuwaris Field commenced production in 1963, with the majority of its production from the Lower Cretaceous Ratawi Limestone/Oolite reservoir. The Humma Field was discovered in 1998, and has the only PZ production from the early Jurassic Marrat Formation. 95% of the wells in South Fuwaris and Humma produce via electrical submersible pumps (ESP).The remote location of both fields requires all ESP systems to be powered by individual diesel generator sets located close to the well heads. Based on the requirements of the preventive maintenance program for these generators, each generator set is scheduled for lube oil/filter change every two weeks, at which time production is shut-in. The shut-ins result in a considerable volume of deferred oil.A recent Root Cause Analysis study of the historical failures of the downhole production assemblies of ESP-equipped South Fuwaris and Humma producers revealed that a significant number of failures could be directly or indirectly attributed to the produced solids settling back into the ESP after shutdown. When the well is shut down, the fluid column above the ESP drains back into the wellbore through the pump, causing produced solids to be deposited in the ESP. This causes high current draw during start up and eventually leads to motor or cable failure, in many cases resulting in complete seizure of the ESP shaft.To avoid the production loss and ESP failures that result from well shut in, the asset management teams in South Fuwaris and Humma have developed a method for keeping wells on line while generator sets undergo lube oil/filter change.The purpose of this paper is to demonstrate how the downhole ESP is kept running while its power generator undergoes scheduled preventive maintenance work. The paper also demonstrates the in-field applicability of the generator set synchronization technique to the oilfield operations, and how this technique has maximized ESP run time in Humma and South Fuwaris Fields, saving Wafra Joint operations greater than $10 MM annually. As more new wells are being drilled and produced, the annual dollar savings increase even further, through the use of a simple and cost-effective process.