Polymers and Polymer-Based Gelants for Improved Oil Recovery and Water Control Applications in Naturally Fractured Chalk Formations

摘要

Water flooding of naturally fractured carbonate (NFC) formations always poses several challenges related to formation sweep, oil recovery efficiency and rate of extraction from matrix blocks, and water management. The presence of natural fractures decreases formation sweep, delays oil recovery rates, and often yields high injector/producer conductive paths which increase produced water cuts with undesirable impacts on fluids production from technical point of view (ranging from lifting difficulties to well stop flowing) as well as economic one (produced water separation, cleaning, and re-injection). Downhole and deep-reservoir fluids management becomes important to addressing or reducing negative oil production effects in NFC formations. Injected fluid diversion away from well-established high-conductivity flow paths will be extremely beneficial to (a) sweep previously unswept formation regions, (b) reduce circulation of injected water, and (c) improve the oil recovery rate and ultimate recovery factors. Injected fluid diversion gels, used in such applications, are normally based on a polymer/crosslinker mixture designed to gel at a given distance /location away from a treated well. However, HSE regulations and/or surface facilities requirements may not permit in certain occasions the use of such chemical systems that have been tested and successfully field-applied previously. In this work, existing commercial polymer and polymer-based chemicals that could be used for water management is NFC reservoirs are screened and evaluated in the laboratory. Several testing bulk- and core-based techniques have been used to achieve this goal with the selected chemicals undergone thorough investigation of their filterability, injectivity, gelation time, gel strength, gel shrinkage, and impact on oil production. Injection of high and low molecular weight HPAM polymers into fractured cores does not hinder the oil production mechanism in chalk formations yielding a lower oil recovery rate but comparable ultimate recoveries with water injection. The environmental friendly polymer (Polymer B) gelant is "inconsistent" related to the formation of gel; when it gels, the quality of the formed gel is poor and provide no resistance to a post-treatment water injection. The non-environmentally friendly polymer (Polymer A) gelant worked consistently concerning gelation and yielded good quality, strong gels that can withstand post-treatment applied pressures during water injection.