The Mukhaizna Heavy Oil Field

The Mukhaizna Heavy Oil Field A World Class Es-PCP Operation

Klaus Mueller, George Oppenhuizen, John Fraser, Nasser Omairy Petroleum Development Oman

Abstract

The Mukhaizna field is a giant heavy oil field in southern Oman which, although discovered in 1975, could not be developed cost effectively until 2000 due to technical challenges associated with lifting high viscous crude from a relatively deep reservoir at acceptable rates. Key enabling technologies were horizontal wells and electrical submersible progressing cavity pumps (ES- PCPs). Initial field appraisal and testing was carried out using vertical wells and surface driven PCPs. Production rates from these vertical wells were poor and long term tests were plagued by frequent rod breaks especially during well start-up. Whilst horizontal drilling technology was well established in Oman by the late eighties, it was not until the late nineties that ES-PCP technology could be considered as a potential lift system to produce heavy oil at high rates. Nevertheless, relying on ES-PCPs for the development of the field was a major out-step when the field development plan was prepared in 1998, as little was known about the long term reliability of these systems. However, with the correct design specifications, installation, operating, and work- over procedures, ES-PCPs have proven to be the right choice. Critical success factors were the use of down-hole pump and reservoir data recording and continuous remote monitoring systems, variable speed drive technology and specific pump installation and work-over procedures. To date, after three-and-a-half years of operations, outstanding pump run times have been achieved. It appears that pump speed and water cut are key factors influencing the pump mean time between failures.

The continuous quest to increase production and reduce cost has lead to a number of technical developments and improvements in conjunction with ES-PCP technology. One of these was the development of a slimmer ES-PCP gear box, which was initially intended for a slim well design, but has become the preferred choice for many small to medium size pumps due to it’s superior performance and lower cost. Another special development was a semi-selective completion using a surface operated hydraulic sleeve below an ES-PCP to enable testing of individual legs in dual lateral wells. For production optimisation purposes, pumps have also been run successfully in pump-off control mode governed by pump intake pressure.

Today Mukhaizna is the biggest single field ES-PCP operation world wide. Although future developments of the field may include reverting to surface driven PCPs in low rate wells in the more marginal areas of the field, further exciting technology challenges lie ahead in conjunction with ES-PCP lifting of heavy crude at elevated temperatures at the initial stages of the thermal development planned to take place in the central part of the field. This paper describes the initial ES-PCP lift system design, the teething problems encountered and lessons learnt, the technical development to further improve the pump design and reduce well cost, pump performance, as well as potential future developments to address changing production conditions with respect to both cold and thermal developments in the field.