An Innovative Acid Stimulation Technique for Reviving Dead Wells in the Ghawar Field of Saudi Arabia - A Holistic Approach

Abstract

The Uthmaniyah field is one of the biggest sub fields and older producing sections in the giant Ghawar structure. A few wells have been dead for sometimes due to high water cut (60 to 80%). In all cases the target interval was only 5'-10' at the top of the dominating water producing zones. There was no scope of water shut-off and artificial lifting. The pilot stimulation comprised of trials in a number of such wells with similar reservoir producing conditions. Isolation of bottom intervals by conventional gel-plug method was not very suitable here because of very marginal target interval. Even slightest inaccuracy of the coil tubing depth meter or depth correlation could be detrimental due to very close water producing interval. The treatment involving the use of high viscous visco-elastic surfactant (VES) diverter technology and controlled bullheading placement was designed to achieve effective acid diversion during acid stimulation. Stages of high viscous VES was pumped as a diverter to temporarily plug the dominating water zones, followed by considerably low strength HCl acid to achieve shallow wormhole growth. All the wells responded to the treatment with sustained oil gain. Although water cut remained high, the well head pressure increased substantially to flow the well naturally. This paper discusses the planning and design processes leading to the successful implementation of the technique, the experience during the stimulation treatment execution and the excellent post-stimulation results. Considering no cases of matrix acid stimulation in high water cut wells in the field, this technique promises to deliver in similar wells here and elsewhere. The significance of the new well stimulation technique is to revive dead wells with very high water cut and also to enhance oil recovery from these wells in a cheaper, easier and effective way. Introduction Most oil wells drilled and completed in the world today produce water to a certain extent. In many cases it is almost like a necessary evil since it brings the oil along with this flow. In new wells the flowing well head pressures are high and these water cuts as a result have minimum consequences on the production of these wells. However as the wells age and the flowing well head pressures become lower the rate at which hydrocarbons flow is reduced ultimately leading to accumulation of water in the completion and production tubing shutting of and ceasing oil production from these wells. The Uthmaniyah area is one of the biggest and older producing sections in the giant Ghawar structure. Although most wells are prolific producers in this area, a few wells have been dead due to high water cut associated in these wells for some years and many strategies were deliberated among various teams to come up with possible solutions to liven these wells. This low flowing well head pressure (LFWHP) wells could not sustain production to gas oil separation plant GOSP. Artificial lift is not commonly used in this area as meticulous reservoir pressure maintenance helps sweeping the oil bottom up. In case of confirmed formation damage, simple matrix stimulation improves the communication between the reservoir and wellbore. But reviving the dead wells by matrix stimulation was a challenging task considering these wells were located in matured area. A pilot involving the use of a proven diverter technology designed to achieve effective acid diversion during acid stimulation was recently implemented. The pilot comprised of trials in four wells with similar reservoir producing conditions with very high water cut of 60 to 80%. In all cases the target interval was only 5'-10' at the top of Arab-D zone-2A.