Innovative Water Based Mud Design to Improve Formation Damage Results on Mariner Field

The Mariner Field consists of two shallow heavy oil reservoir sections: the deeper Maureen Formation and the shallower Heimdal Reservoir. Produced water is re-injected through stand-alone screens providing pressure maintenance for the aquifer support and producer well life longevity. The challenge is to design a drill-in fluid for the injectors to allow matrix injection across the sand face. This improves the longevity of the lower completion screens by reducing hot spot completion damage created by the injection fluid (Yildiz, 2004). It also improves the pressure support for the producing wells. Equinor is committed to using sustainable, environmentally sound drilling fluid options. Therefore, the preference was to utilize a water-based drilling fluid with the application of a breaker after the lower completion was in place. A significant formation damage study was performed using various designs of water-based fluids. Each formulation utilized a biopolymer to provide viscosity and rheological support. The sands were unconsolidated and sand packs had to be created to mimic the reservoir characteristics of the Maureen reservoir. This potentially impacted the formation damage interpretation. From the formation damage study, biopolymer was highlighted as a limiting damage mechanism. This prompted both Equinor and Schlumberger to look at alternative ways to provide rheological support without using biopolymers. A mono-valent biopolymer free reservoir drill-in fluid was designed specifically for this challenging high Darcy reservoir to mitigate the formation damage seen from coreflooding. This paper will detail the design, testing, diagnostic analysis of the formation damage mechanism and the new biopolymer free fluid. Together they showed a step change improvement in the formation damage testing. In addition, the paper will also detail the deployment of the new fluid on Mariner. Furthermore, it will describe how the laboratory design translated into large scale plant mixing with deployment at the rig site.