Injectivity Monitoring & Evolution for Water Injectors in a Deepwater Turbidite Field

V. Onwuchekwa, M. Usman, P. Wantong, V. Biu, Jed Oukmal
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Abstract

Water injection is one of the key improved recovery techniques used for pressure maintenance and sweeping. Throughout the life of a field, changes in injectivity can have an effect on reservoir pressure management and sweep efficiency which both have a direct impact on production. This study aims to present an original methodology to analyse the performance of water injectors in a deepwater turbidite field and evaluate the evolution of their injectivity over time. An injectivity monitoring tool was developed by incorporating injection flowrate and pressure data with the following analytical techniques: (i) Instantaneous Injectivity Index, (ii) Hearn Plot or Reciprocal Injectivity Index, (iii) Hall Plot, (iv) Derivative Hall Plot and (v) Pressure Transient Analysis. The injectivity monitoring tool was able to capture subtle changes in injectivity and demonstrate the long term trend of stable injectivity in this field, even in situations where only wellhead pressure and injection flowrate were available. The resulting analysis showed that there is very good injectivity for all water injectors in this field with little or no degradation over time. One of the key drivers for the good injectivity is the water injection process philosophy in this field. This process consists of injecting deaerated seawater with biocides in order to prevent bacterial growth which causes near wellbore plugging. Another contributing factor to the good injection performance is the presence of injection valves which enable each injector to perform downhole shut-ins to stop migration of fines and curtail any possible water hammer effect when intermittent injection shut-ins required. It was furthermore found that there was no significant difference in injectivity that could be associated to deviation angle or completion type (Stand Alone Screens (SAS) or Expandable Sand Screens (ESS)). Injectors completed with SAS however appeared to exhibit increased injectivity with increasing screen length but no such correlation was apparent between screen length and injectivity for injectors with ESS.
深水浊积岩油田注水井注入能力监测与演化
注水是提高采收率的关键技术之一,用于维持压力和扫井。在油田的整个生命周期中,注入能力的变化会对油藏压力管理和波及效率产生影响,这两者都直接影响到产量。本研究旨在提出一种新颖的方法来分析深水浊积岩油田的注水井性能,并评估其注入能力随时间的变化。通过将注入流量和压力数据与以下分析技术相结合,开发了注入率监测工具:(i)瞬时注入率指数,(ii)赫恩图或倒数注入率指数,(iii)霍尔图,(iv)导数霍尔图和(v)压力瞬态分析。即使在只有井口压力和注入流量的情况下,注入能力监测工具也能够捕捉到注入能力的细微变化,并显示出该油田稳定注入能力的长期趋势。分析结果表明,该油田所有注水井的注入能力都非常好,随着时间的推移几乎没有退化。在该领域,良好的注入能力的关键驱动因素之一是注水工艺理念。该工艺包括注入含有杀菌剂的除氧海水,以防止细菌滋生,从而导致井筒附近堵塞。注入性能良好的另一个因素是注入阀的存在,它使每个注入器能够进行井下关闭,以阻止细颗粒的运移,并在需要间歇注入时减少可能的水锤效应。此外,井斜角度或完井类型(独立式筛管(SAS)或扩张式防砂筛管(ESS))对注入能力没有显著影响。然而,用SAS完成的注入器似乎随着筛长增加而增加注入性,但筛长与ESS注入器的注入性之间没有明显的相关性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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