Abu Dhabi Oil Co., Ltd.(ADOC) has been applying artificial lift with ESPs in Mubarraz Field, offshore Abu Dhabi, U.A.E., since 1975. In 1989, the authors published a paper which presented the trouble analysis, technical improvements and actual ESP Performance. Since then ADOC continued making efforts to increase the ESP Lifetime by applying technical improvements and countermeasure against ESP troubles. By this result, the average lifetime was increased from 2.1 years to 3 years. In particular, the longest lifetime reached is 3,617days, compared with the old record of 1,659days mentioned in the paper1).
Furthermore, detailed inspection of troubled ESPs and investigation on the new ESP units had been carried out. With intensive discussion between ADOC and the ESP manufacturer, the new ESP units were selected in 1995 and had been installed in the field.
This paper presents the technical improvement, countermeasures against the different ESP troubles including asphalten precipitation and corrosion protection, proper selection of new ESP units and actual performance of ESPs as a result of these improvements.
Mubarraz Field is located in the southern part of the Arabian Gulf about 56 km off the coast of Abu Dhabi, UAE. Field production commenced in May 1973. However, the production of some wells declined rapidly and artificial lift or other IOR (Improved Oil Recovery) methods became necessary to maintain a stable field production. After studying the application of artificial lift and other IOR methods, the ESP (Electrical Submersible Pump) was selected as the most suitable recovery method for the field for the following reasons:
The applications of other artificial lift would require more space for facilities. It would result that the construction costs would increase.
Oil production with high water cut is inevitable because drainage mechanisms of all main reservoirs are strong water drive. Therefore higher lifting energy would be required.
All of reservoirs in Mubarraz field are highly undersaturated with relatively low solution GOR. These properties are suitable for the application of ESPs.
And it was evaluated that gas supply would be short for the application of gas lift.
However, the only disadvantage of ESP application is higher operation cost caused by workover jobs due to ESP failures. Therefore, a long lifetime of ESP is economically essential for the application of ESPs in Mubarraz Field.
The first ESP was installed in March 1975. Two hundred and thirty-three ESPs were installed in 29 wells by March 2000.
Mubarraz Field is composed of two major anticlinal trends with three main structures, which are further separated into five sub-structures in total. Oil has been discovered in numerous subzones in Zones 2 through 6 in the Thamama group of Lower Cretaceous age at a depth of between 8,800 and 11,000ft. Subzones of Zones 2 through 6 consist of limestone and dolomite with a wide variation in thickness, porosity, permeability and other reservoir characteristics. The main features of the field and reservoirs are summarized as follows:
Mubarraz Field is not composed of one large structure with a few main reservoirs, it is a complex of five small structures with numerous thin reservoirs. Furthermore, there are two types of reservoirs: bottom water and edge water reservoirs. Drainage mechanisms of the main reservoirs are water drive, and some reservoirs without water influx are classified as solution gas drive.
Each structure has a low structural height with a low oil column. Therefore, OOIP of each reservoir is relatively low and the productive area of each reservoir is limited and narrow. Therefore, the number of wells should be properly controlled.
The reservoir depths are relatively deeper than other offshore oil fields in Abu Dhabi, which results in requiring a higher driving energy for the oil production. The reservoir temperature also becomes higher. This makes several problems more severe, such as corrosive environments, chemical stability and higher equipment specifications for high temperature use.