Injectivity as a Critical Factor in The Performance of Water Flooding Operation

Abstract

Petroleum exploration, development and operation usually involves large capital investments that requires maximum reserves be recovered, so as to compensate for initial investment efforts. To achieve such a goal, where the natural drive mechanism is inadequate, water can be injected into the reservoir to supplement reservoir energy and improve sweep efficiency in conventional oil fields. The knowledge of key factors that could negatively affect the effectiveness of water injection in oil reservoirs is of great importance. Water injectors experiencing injectivity decline significantly impact recovery. Injectors are susceptible to impairments, which may end in gradual injectivity decline and catastrophic failure. Therefore, robust field management and business planning require an honest understanding of the impairment mechanisms of water injectors. The water-flooding concept depends on several elements that could affect the overall project value; water quality requirements, well placement, inherent formation quality and relative permeability characteristics are some examples. This translates into economic failures, the need for costly workovers and recompletions on a regular basis to facilitate injection operations.This work is a review of the various factors that can lead to the degradation of water injectivity in a reservoir. The factors include: repetitive shut-in of a well; crossing flow from low permeability layers; unconsolidated reservoir; simultaneous flow of sand with the producing hydrocarbons, production from different sand layers in the same time, water with many chemical contaminants, cold water bank near an injector, weak reservoir formation, presence of clay in reservoir rocks, residual oil around the injector, H2S deposition, bacteria presence, cold water injection, water quality, suspended solids, corrosion products, skim/carryover oil, scales, precipitates, emulsions, oil wet hydrocarbon agglomerates. It also illustrates how application of surveillance and 9 monitoring principles is vital to understanding reservoir performance and identifying opportunities which will improve ultimate oil recovery.A comprehensive review of field cases has been carried out, followed by analysis of causation factors. Thereafter, screening criteria was developed and suggestions for improving injectivity are provided. Most of the water injectivity decline is due to the migration of suspended particles in injection water or the injection water/reservoir fluid incompatibility. Advancements in Science and Technology has resulted in identifying other causation factors, such as sand mobilization (sand particulates separate from rock matrix and move into deep formation), injection pressure, injection rate, water hammer, microbial activities, permeability anisotropy etc.