A number of maximum reservoir contact (MRC) wells have been drilled and completed in various fields (sandstone and carbonate) in Saudi Arabia. The drilling fluid, water-based mud, consists of xanthan, starch, polyanionic cellulose polymers and bridging agents like sized calcium carbonate or salt particles. Cleanup of drilling fluid filter cake in long horizontal wells completed as an open or cased hole is a challenging task. The obstacles encountered are the difficulty to ensure contact of the treating fluids with the filter cake throughout the whole interval, as well as controlling the reaction rate between the breaker and the filter cake to ensure uniform removal of the filter cake.
Today, several chemical and mechanical systems are available to remove the polymeric and bridging agents in oil and gas producers and water injectors. Chemical means (oxidizers and acids) have limitations, which can adversely affect well performance. Oxidizers and acids are highly reactive and non-specific species. Reservoir heterogeneity complicates the cleaning process. There is a need for cleanup fluids that have a delayed effect on filter cake-integrity to obtain a uniform distribution over the horizontal interval.
Specific enzymes can degrade xanthan and starch polymers in the filter cake with lower removal rates. A low reaction rate promotes a more uniform cake cleanup and should result in higher production rates. Field results indicate that utilization of enzyme treatments is very effective technique in removing drilling mud filter cake. The production rate for treated wells reached the target value without the need to acidize the well.
High pressure water jetting technique has been utilized to mechanically remove filter cake. Field results obtained from many injectors indicate that this technology has several advantages such as simplicity of use, cost effectiveness, and high success rate. This paper will discuss field application of specific enzymes and water jetting in gas, oil, and water wells. It will also highlight the advantages and disadvantages of each method based on field data.