Filtercake Cleanup Techniques for Openhole Water Injectors with Sand Control: Lessons from Laboratory Experiments and Recommendations for Field Practices

Abstract

Many water injection wells in sand control environments are being completed as open holes because of the higher injectivities attainable with open-hole completions. The sandcontrol techniques used in these wells varies from standalone screens or slotted liners (including expandable screens) to gravel packing. In field practice, the drilling fluids used for injectors have also varied from water-based (either sizedCaCO3/Polymer or sized-salt/polymer) fluids to oil-basedsystems. Although a cake cleanup followed by a production period is typically desirable to maximize injectivity, often this is not feasible either due to limited storage capacity on the rigor requirement for artificial lift due to low reservoir pressure. These limitations therefore necessitate direct injection after thecompletion is installed, which is not trivial as a complete and uniform filtercake removal, including drill solids as well as thebridging agents and polymers, is essential to ensure uniform injection profile in addition to maximizing injectivity index. Although exceeding the fracturing pressure can establish injectivity through by passing of filtercake damage, this istypically not desirable from a sweep efficiency standpoint. In this paper, we present details of a series of experimentsconducted on core samples using both water-based and oilbasedreservoir drilling fluid systems and various cleanup techniques involving displacements and soaks in standalonescreen and gravel pack environments. It is shown that with theproperly selected and designed cleanup treatments, uniformand high injectivities without producing the well is achievable in long open holes. The results from the experiments are discussed in detail, along with the lessons learned and recommendations for field practice. Introduction Many water injection wells in sand control environments arebeing completed as open holes due to higher injectivities attainable in such completions. Although targeted flow rates may sometimes be achieved without any cleanup chemicals inproduction wells (granted that this may not be the bestpractice), injection wells require filter cake cleanup, especially in cases where:producing the well prior to injection is not feasible ordesirable, because of limited storage capacity on therig, or artificial lift requirements due to low pressure, in addition to associated disposal costs, andinjecting above frac pressure is either not feasible(e.g., very high frac pressures and pump limitations)or not acceptable (e.g., sweep efficiency, premature water breakthrough, etc.). It is therefore highly desirable to provide techniques that will allow high and uniform injectivity across long open holes, without requiring a production stage and without having to exceed frac pressure. Water injection above frac pressure has been discussed in the literature, and various models have been proposed for propogation of such fractures when the injection water is"dirty".1,2In fact, even in cases where injection is initiallydone below frac pressure, often the fracturing pressure is exceeded some time during the life of the well due to declining injectivity and the common practice of maintaining constant injection rate. To avoid exceeding frac pressure and maintain high injection rates, mud acids treatments can be periodically performed. The reasons for water injectivity decline have also been discussed and various models have been proposed.3,4

Openhole Gravel-Pack Case Histories Using Alternative Fluid Displacement for Synthetic-Based Mud

“…• It is easy to clean up its filter cake through simple protonation of the emulsifier and conversion of its filter cake from oil-wet to water-wet state, as is well documented in the literature (Dick et al 2003;Parlar et al 2002;Ali et al 2006).…”

“…Initially, inclusion of a cleanup chemical in the carrier fluid was considered to provide simultaneous gravel-pack and filter-cake cleanup, since the RSBM is in fact ideal for such an application (Parlar et al 2002;Ali et al 2006). However, additional testing indicated that the concentration of the breaker needed to achieve an efficient filter-cake cleanup had a negative effect on the particular VES fluid's gravel-suspension capability.…”