NOV公司另辟蹊径，开发出可部署在海床上的水处理设备。Seabox模块具有极高的灵活性与可靠性，可提高采收率，降低投资成本，完美解决边际油田开发成本高的困局。 作者丨二丫 在油田开发初期，工程师们需苦心研究地层特性，以确保适当的油藏与注水管理。注水是最常用的二次采油方法，也是提高采收率（EOR）的一种手段。但注水通常会引起作业者的担忧，因为优质的水是优化采油的必要条件。注入劣质水，例如未经处理的海水，会对地层产生不利影响，包括储层堵塞、结垢、腐蚀以及储层酸化等。在平台上安装水处理设备可解决作业者的缺水之痛，并能避免上述负面影响，但水处理设备的设计受到平台承重与空间的限制。 二次采油的有效性会因以下原因而变得复杂：*）注入水与地层水之间的相容性；*）可用注水井的数量有限，限制了驱油效率；*）注入水到达油藏的位置。此外，越来越多的边际新发现迫使油气行业重新思考现有技术，以改善二次开采技术，提高边际油田的开发利润。 海底水处理 为了解决水质问题，******（NOV）开发出Seabox技术，将水处理转移到海床，就可摆脱平台的种种束缚。由于不依赖于配套的平台设施，海底系统使水处理更加有效并降低了成本。该系统固有的灵活性使作业者可以大显身手，无论何时何地，都能够执行水处理作业。 该模块由三大部分组成：*）底座；*）静止室；*）处理装置，如图*。每个组件在系统中各司其职。该模块占地面积为**×**×*m，由纤维增强复合材料（FRP）构成，可抵抗腐蚀。它每天能够处理四万桶未经处理的海水，但在某些应用中可以增加到每天六万桶。水处理装置中存在寿命较短的组件，需要每四年进行一次维护，包括系统电源与控制模块，以及对水处理至关重要的电极。底座是模块的基础结构。静止室是一个沉淀池，用于氯浸泡与固体沉降。 图* 静止室的横截面可观察到蜂窝结构，延长停留时间可实现有效的氯浸泡与固相沉降。 处理过程 在水处理装置的入口处，未经处理的海水直接流过电解氯化反应池。当反应池的正负极与海水反应时，会产生次氯酸钠，如图*所示。这是一种常用水消毒法。海水停留在静止室内，水处理模块可提供足够的时长，确保对未经处理的海水执行最佳的消毒与抗菌。静止室内的停留时间为*至*小时，具体取决于通过静止室的流道。静止室及其内部蜂窝状结构的次要用途是沉淀固体。 图* 海底模块拥有两个处理过程，都位于装置内部，可产生次氯酸钠与羟基自由基。 海水从静止室返回到处理装置，当消毒后的海水进入生成羟基自由基的反应池时，在那里，它会进行第二道处理过程。该系统利用掺杂硼的金刚石电极生成羟基自由基，羟基自由基具有极高的活性，可用于进一步分解有机物质，或杀死细菌，分解死去的有机物。通过这些处理过程，海底模块在注水点附近提供高质量的水，以提高驱油效率，或作为预处理，为基质驱油、低矿化度或低硫水应用持续调整水质。 提高采收率 水驱作为二次采油方法用于世界各地，通常是提高油气采收率的首选方案。一般来说，水处理设施占地面积大，需要大量的前期投资，而且还需要持续投入额外的运营成本。海底水处理方案与平台设施分离，并可根据油藏的需求逐步进行水处理，更加灵活，而不是将整个提高采收率方案建立在几口探井的基础上。 Seabox模块可部署在**米至****米的水深范围内，可以集成到任何对采油有积极影响的应用中。对于未开发区块以及老油田，水质要求与集成设施是不同的，需要提供独立的方案以提高驱油效率。 在迫切需求注水的油田中，该模块可与现有的平台处理设备相结合，以确保注入的水质比现有方法的水质更好。控制现有平台处理设备的供水口，将水注入Seabox模块的消毒与固体清除系统进行处理。无需过多调整平台设施，就可以优化现有设备处理后的水质。该模块还可安装在平台设施的底部，以增加水处理能力。 提高经济效益 随着边际油田的数量不断增加，必须设计新技术，使边际油田的开发在经济上更具可行性。改善边际井的一种方法是回接，这可以延长现有采油设施的使用寿命。对于开发新油田而言，回接技术变的愈发重要，海底处理模块是一种经济高效的解决方案，适用于需要注水的回接应用。 在此应用中，模块唯一需要与平台连接的是通信与电源。无需利用高压长管道将水泵入井中，也无需注入化学药剂。得益于该模块与平台基础设施分离，因此它可部署至离平台更远的位置，使二次采油更加灵活。它还降低了水中的固相含量，并为储层提供消毒后的水。 NOV公司还在开发一种针对低盐度和/或低硫酸水的整套海底解决方案。通过将整个水处理过程移至海底，注水方案可完全独立于平台设计与平台限制。 现场测试 ****年*月，在水深***米的挪威Stavanger海岸安装了首个全尺寸装置，如图*所示。通过***米长的管道将水泵至平台，处理后又排放到海里。安装该设备的两个主要目标是在三个月的测试中获取作业经验，并验证模块的处理能力。根据石油行业的实际情况制定了测试程序，并由第三方进行采样与分析。目的是验证消毒与固相清除能力的理论计算。海底水处理模块平均清除了**%的固相颗粒，这还仅是依靠沉降。 图* 在Stavanger海岸准备进行安装的全尺寸测试模块 普通异养细菌与硫酸盐还原菌的测量结果已经低于可检测限度，这表明通过电化学产生的次氯酸钠，加上足够的停留时间，以及生成的羟基自由基，完全杀死了水中的细菌。在整个测试期间，水处理模块表现出优异的稳定性与一致性，无论处理何种水质的海水，都具有稳定的固相去除与消毒能力。 ****年*月，该公司将一套全尺寸设备安装于北海油田，以进行现场测试。该模块已成为北海作业者评估项目的一部分，目的是研究该模块是否有能力延长油田生产寿命，并提高开发边际油田的可行性。该模块于*月份在水深**米处投入使用。计划于****年第二季度完成该测试。根据API **N标准，Seabox模块现已被评定为技术就绪级别(TRL) *。 价值 Seabox海底水处理技术为作业者提供了优化油藏管理的能力。该模块不受平台空间的限制，利用无限的海底面积，可显著减少平台基础设施的占地面积，并且作业者将获得更大的灵活性，以整合适用于特定油藏的水处理方案。该模块通过减少平台维护以及海上作业人员数量，来降低水处理相关的运营成本，并且可以实现向无人平台的转变。 海底水处理过程没有添加化学品。次氯酸钠与羟基自由基都是基于电化学反应产生的，其中化学反应过程可溶解于海水中，不会对环境造成影响。该模块的功率低于**kW，比具有相同处理能力的类似水处理地面设备少约**倍。该模块固有的灵活性使油田开发的前期投资更少。它避免了调整现有设施而产生的不必要开支。Operators are faced with water-related challenges early in the field development phase, with engineers investigating formation characteristics to ensure proper reservoir and waterflood management. Water injection is the most commonly applied method for secondary recovery, and a tool for improved oil recovery (EOR). But water injection often causes concerns among operators, because good-quality water is necessary to optimize oil recovery. Injecting poor-quality water, such as untreated seawater, can have detrimental effects on the formation, including reservoir plugging, scale formation, corrosion-related issues, and reservoir souring. Installing topside processing equipment enables operators to meet water specifications and avoid these negative effects, but the design for treatment facilities is restricted by weight and space limitations. The effectiveness of secondary recovery is complicated by: *) compatibility between injected water and formation water; *) limited number of wells available, hindering sweep efficiency; and *) where injected water can reach in the reservoir. In addition, an increasing number of marginal new discoveries have forced the industry to re-think existing techniques to improve secondary recovery and make marginal field development more profitable. SUBSEA WATER TREATMENT To solve the water delivery issues, National Oilwell Varco (NOV) developed Seabox technology to move water treatment to the seabed, where it is unconstrained from typical topside restrictions. The subsea system makes water treatment significantly more effective and reduces costs, because there is no dependence on supporting infrastructure. The system’s inherent flexibility enables a new approach to implementing water treatment where, and when, required. The module consists of three major components: *) a tray; *) a still room; and *) a treatment unit. *. Each constituent serves a unique purpose in the system’s setup. The module, which has a footprint of ** × ** × * m, is constructed of fiber-reinforced polymer (FRP) to resist corrosion. Its raw seawater treatment capacity is **,*** bpd, but this can be increased to **,*** bpd in certain applications. The treatment unit contains components with a shorter design life and will require an intervention interval every fourth year. Components requiring maintenance include the system’s power and control modules, as well as electrodes, which are essential to the treatment processes. The tray is the module’s base structure. The still room is a sedimentation tank for efficient chlorine soak and solids settling. At the inlet of the treatment unit, the raw seawater flows through electro-chlorination cells. Sodium hypochlorite is generated, as the cell’s anodes and cathodes react with seawater. This is a common method for disinfecting water. The water treatment module will allow the sodium hypochlorite time to react, due to the residence time within the still room, ensuring optimal disinfection and antimicrobial effect on the raw seawater. The residence time inside the still room ranges from * hr to * hr, depending on the water path through the still room. The secondary purpose of the still room, and its internal honeycomb structure, is to settle out solids. The seawater returns to the treatment unit, where it is exposed to the second treatment process at the outlet, when the disinfected water is exposed to a hydroxyl radical generator cell. The system uses boron-doped diamond electrodes to electrochemically generate hydroxyl radicals, which are extremely reactive and used to further decompose organic matter—or to kill bacteria and decompose dead organic matter. Through these treatment processes, the subsea module provides high-quality water near the injection point for increased sweep efficiency, or as a pre-treatment for continued tailoring of water qualities for matrix flooding, low-salinity, or low-sulfate water applications. ENHANCED OIL RECOVERY Waterflooding as a secondary recovery method is used in fields all over the world and is often a prerequisite to optimize hydrocarbon recovery. Traditionally, water treatment is acreage-intensive and requires a significant up-front investment, followed by additional ongoing operational costs. The subsea water treatment solution is decoupled from topside infrastructure and provides greater flexibility toward phasing in water treatment according to reservoir requirements, rather than basing an entire EOR program on a few exploration wells. The module can be deployed in water depths ranging between ** m and *,*** m and can be integrated into virtually any application where water could have a positive effect on oil recovery. These scenarios include greenfield and brownfield applications, where water quality specifications and infrastructure integration vary from module integration with existing topside processing facilities, to stand-alone solutions for improved sweep efficiency. In fields with an urgent need for an improved flooding regime, the module can be combined with existing topside processing equipment to ensure that the water injected is of higher quality than what is available with the existing method. Control of intake water on existing topside processing equipment, can be processed through the module’s disinfection and solid removal systems. This optimizes output of injection water from the existing processing equipment without major topside modifications. The module will perform as an add-on pre-treatment step to an operator’s existing infrastructure, or to increase total water treatment capacity when installed at the foot of a topside facility. The module’s pre-treatment processing of raw seawater disinfects the fluid after suspended solids, greater than **μm, have typically settled out. The treated water is then fed to a topside filtration system, significantly reducing the risk of biofouling. This technique enhances the performance of topside filtration units, reduces downtime, and increases the duration between maintenance intervals. The module’s integration flexibility makes it well-suited for brownfield applications, where operators need a solution for water treatment to be implemented quickly with only minor topside modifications. IMPROVING ECONOMICS New technologies must be designed to make marginal developments more economically viable, particularly as the number of borderline discoveries continues to increase. One approach to improving marginal wells is using tie-backs, which extend the life of existing production infrastructure. Tie-backs are becoming more important to developing discoveries, and the subsea treatment module is a cost-effective solution for tie-back applications in need of water injection. In this application, the module’s only topside connection requirement is for communication and power. This eliminates the need for long, high-pressure pipelines to transfer water to the well, in addition to the requirement for chemical injection. Being decoupled from topside infrastructure also makes longer step-outs and secondary recovery more feasible. It reduces particle content and provides completely disinfected water to the reservoir. The Seabox module, as a stand-alone unit, provides high-quality water for injection. In many waterflooding regimes, the control of sediment levels down to **μm is sufficient to improve reservoir sweep efficiency. However, operators have developed specific, injected, water quality specifications. To be capable of meeting such specifications, the module can be integrated with existing topside processing equipment. NOV also is developing a full subsea solution for low-salinity and/or low-sulfate water. By moving the complete water treatment process subsea, the water injection strategy can be fully decoupled from typical platform design and constraints. FIELD TESTING The first full-scale unit was installed off the coast of Stavanger, Norway, in February ****, at a water depth of *** m, Fig. *. Water was drawn topside through a ***-m pipeline via a submerged pump and discharged to sea. The two primary objectives of this installation were to gain operational experience during a three-month test program and to verify the treatment capabilities of the module. The test program was set according to oil industry practice, and sampling and analysis were provided by a third party. The aim was to confirm the theoretical calculations regarding disinfection and solid removal capabilities. The subsea water treatment module removed, on average, **% of all particles using sedimentation only. NOVOS software enables automation of repetitive drilling activities, allowing drillers to focus on consistent process execution and safety. The scalable system can be expanded to full closed-loop automation. An imported well plan describes desired drilling parameter ranges, enabling the system to optimize the performance within the given set of parameters based on the well plan. Users can set parameters to meet requirements, including circulation and WOB. The result of the general heterotrophic bacteria and sulphate-reducing bacteria was below detectable limits, demonstrating complete bacteria kill through the exposure of electrochemically produced sodium hypochlorite, residence time, and hydroxyl radical generation. Throughout the test period, the water treatment module showed stable performance with high regularity, providing treated water with a consistent solid removal and disinfection capability, despite fluctuation in raw seawater quality. North Sea field installation. In August ****, the company installed full-scale production units in a test project on a real-field application. This module is now a part of an operator assessment program in the North Sea, to investigate the module’s ability to prolong field life and make marginal discoveries more feasible. The module was made operational at a **-m water depth in September. The test program is scheduled to complete during second-quarter ****. The Seabox module is now accepted as a Technology Readiness Level (TRL) *, according to the API **N standard. With the completion of an ongoing joint industry project for development of a subsea low-salinity processing plant, NOV will bring its SWIT technology for subsea low salinity and/or sulfate removal to TRL * during ****. VALUE PROPOSITION The Seabox subsea water treatment technology provides operators with the ability to optimize reservoir management. The module is not restricted by the existing capacity of topside infrastructure and can increase availability on water injection. By exploiting the unlimited acreage of the seafloor, the footprint of topside infrastructure can be reduced significantly, and the operator will gain greater flexibility toward the integration of a water treatment solution adapted to specific reservoir requirements. The module can drive down operational costs connected to water treatment by reducing topside maintenance and offshore personnel requirements, and can enable a move toward unmanned platforms. The subsea water treatment process has no added chemicals. The sodium hypochlorite and hydroxyl radicals generated are produced electrochemically in situ, where the chemical processes are dissolved in seawater without creating an environmental footprint. The module typically requires less than ** kW, approximately ** times less than similar surface water treatment plants with the same capacity. The module’s inherent flexibility requires a smaller upfront investment on field developments. It avoids unnecessary expenditures of rebuilding existing infrastructure to meet water injection needs. SUMMARY Flexibility. Water injection philosophy can be decoupled from topside processes to provide advantageous flexibility in drainage strategy. Improved recovery. There is an ability to tailor an injection, based on reservoir behavior and the possibility to inject any quality water in otherwise inaccessible areas of the reservoir. Reduced capex. There are lower overall investments and increased net present value by deferment of cost. Lower opex. There is lower power consumption, compared to topside units. Long periods exist between required intervention intervals. Offshore personnel requirements are reduced. High reliability. There are no rotating or moving parts, combined with built-in system redundancy.