微震技术在二氧化碳储存领域取得新突破

微地震技术已证明其在非常规井中的价值,新的应用可以监测封存的二氧化碳促进地热能的开采。

一辆 FracStar 监测卡车正在监测现场收集的数据。(来源:Microseismic)

当彼得·邓肯 (Peter Duncan) 在 2003 年初宣布他要推出 MicroSeismic 时,不可否认的是,大家的反响并不热烈。

这位首席执行官兼创始人回忆起他的同事问过他:“你疯了吗?微地震监测是什么?这能做生意吗?”

人们从未听说过它,但邓肯决心重新定义石油和天然气行业的地下监测方式,将曾经的小众学术概念转变为商业强国。

早期,大多数从业者认为,要捕捉微震事件,必须在井下放置检波器,靠近地震活动源。但邓肯采取了一种新方法。

“你不需要钻到地底,只要在地表放置检波器,就能听到那些事件,”他说,“过去,他们只在地表放置检波器,而且只放置单个检波器,他们听了却听不到任何声音。信号太弱了。”

Duncan 和 MicroSeismic 决定在地表上散布多个检波器,并利用“堆栈的力量”来克服信噪比问题并产生更清晰的数据。他把这比作在足球比赛中使用碟形麦克风——从远处收集声音可以产生比将麦克风放在声源附近更清晰的结果。

尽管邓肯的方法最初遭到同行的嘲笑,但他的方法却让公司提供了有价值的服务,并成为微地震行业的先锋,尽管他并不愿意因此而居功。

清晰观察井下图像

Duncan 表示,新增的检波器提高了可视性,让 MicroSeismic 能够更清晰地了解井下作业情况。通过识别微震事件的震源机制(岩石相互滑过),该团队提高了数据准确性,从而能够更好地解释水力压裂结果,而不再需要使用老式的“盒子里的点”显示方式。

“我们实际上可以放入一个小平面元素,这个平面元素的大小与我们看到的大小成正比,我们可以从中判断事件是像这样移动还是那样移动。所以,现在我们对裂缝的地质情况有了更好的了解,”他说。

这一发展将微地震数据转化为详细的离散裂缝网络,并为 FracRx 奠定了基础,FracRx 是一种实时监控系统,可帮助工程师在水力压裂作业期间做出决策。

“我们开始使用这些数据进行实时监测。我们将预测碳氢化合物的含量,并使用外推法,并说‘好吧,如果你继续水力压裂半小时,你就会得到这么多的碳氢化合物,’”邓肯说。

“我们将帮助您做出有效的决策,不是由别人来决定如何压裂——而是帮助您更有效地决定何时完井、应该抽水多长时间、应该抽水多少水等等。”

随着行业面临挑战,尤其是在 COVID-19 疫情期间,运营能力急剧下降,这种能力变得更加重要。

在适应新挑战的同时,该公司还开拓了更多市场。其中一项重大进展涉及二氧化碳封存,旨在监测地下储存的碳,以确保安全并防止泄漏。

“能源部 (DOE) 发出了一份一般通知,称他们正在寻找在碳封存时监测碳的方法,以确保碳不会引发地震,并确保碳留在封存的碳库中。我们说,‘嗯,我们认为我们可以听到小地震,这是大地震的前兆。我们认为我们可以听到碳是否开始从碳库中泄漏。’我们实际上已经这样做过一次,”邓肯说。

邓肯说,这导致了CO2SeQure技术套件的问世,该套件包括 BuriedArray 系统,类似于二氧化碳储存的高科技安全系统

BuriedArray 系统是一个地下传感器网络,可持续监测二氧化碳储存,跟踪二氧化碳运动,检测小地震事件并将数据发送到中央处理设施。

在二氧化碳注入开始之前,该阵列会测量基线地震活动。注入期间,它会监测可能表明盖层问题或区域断层滑动的地震事件,并使用“顶灯系统”在超过某些临界水平时提醒操作员。

MicroSeismic 还涉足先进的地热业务。邓肯说,这一举措使公司的技术得以全面发展,因为该流程基于原有的 FracRx 解决方案。

“在像加州这样的地方,热岩接近地表。你可以钻进去,让水在岩石中循环,加热水,然后收集热量用于发电,”他说。地热系统将这个过程带入了不同的境界。“增强型地热系统的全部内容是钻入非常热的深层基岩,以产生超临界蒸汽,并能够将更多的能量带到地表,从而使其更具商业价值。”

邓肯认为增强型地热系统 (EGS) 有潜力重塑能源格局。通过借鉴水力压裂的经验,他相信分布式声学传感 (DAS) 等技术可以促进更高效的地热能源开采。

DAS 又称为分布式光纤传感,是一种创新技术,利用激光实时检测光纤电缆上的声音。将 DAS 装置连接到标准光纤的一端,可将光纤转变为分布在数公里范围内的数千个振动传感器或麦克风。此设置无需额外的电子设备或硬件,是一种高效的方式来监测远距离的声音和振动。

MicroSeismic 目前正在与澳大利亚公司 Terra15 合作,提供基于 DAS 的微地震解决方案,以增强公司的监测能力。

Duncan 表示:“我希望 AS 技术能够实现比检波器更高分辨率的信号。但作为一般应用,它目前还达不到这个程度。DAS 的功能有限,我们仍在努力。但我希望它能取代我们的传统检波器。”

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Microseismic Tech Breaks New Ground in CO2 Storage

Microseismic technology has proved its value in unconventional wells, and new applications could enable monitoring of sequestered CO2 and facilitate geothermal energy extraction.

A FracStar monitoring truck set up to monitor data collected in the field. (Source: Microseismic)

When Peter Duncan shared his decision to launch MicroSeismic in early 2003, the response was, admittedly, unenthusiastic.

The CEO and founder recalls his peers asking him, “Are you crazy? What is microseismic monitoring? Is there a business?”

People had never heard of it, yet Duncan was determined to redefine how the oil and gas industry approached subsurface monitoring, turning what was once a niche academic concept into a commercial powerhouse.

In the early days, most practitioners believed that capturing microseismic events required geophones placed downhole, close to the source of seismic activity. But Duncan took a new approach.

“You don’t need to drill down; you can place geophones on the surface and still hear those events,” he said. “In the past, they put their geophones—just single geophones—on the surface of the earth, and they listened and they didn’t hear anything. The signals were too small.”

Duncan and MicroSeismic decided to scatter multiple geophones across the surface and use “the power of the stack” to overcome the signal-to-noise problem and produce clearer data. He likened this to using a dish microphone at a football game—where gathering sounds from afar can yield clearer results than placing a microphone close to the source.

While initially laughed off by his peers, Duncan’s method allowed the company to provide a valuable service and spearhead the microseismic industry, although he does not like to take credit for that.

Bringing the downhole picture into focus

The better visibility created by the added geophones allowed MicroSeismic to create a clearer picture of downhole operations, Duncan said. By recognizing the focal mechanisms of microseismic events—how rocks slip past each other—his team enhanced data accuracy, allowing for better interpretation of fracking results, no longer having to use the old-fashioned “dots in a box” display.

“We can actually put in a little planar element where the size of the planar element is proportional to the magnitude that we see and where we can tell whether the event moved like this or like that. And so, now we’ve got a much better geologic picture of how the frac looked,” he said.

This development transformed microseismic data into detailed discrete fracture networks and laid the groundwork for FracRx, a real-time monitoring system that helps engineers make decisions during fracking operations.

“We started to use that [data] to monitor in real time. We’re going to predict the hydrocarbons, and we’re going to use an extrapolation and say, ‘Well, if you keep fracking for another half-hour, you’re going to get this much more hydrocarbons,’” Duncan said.

“We’re going to help you make efficient decisions about not how to frac—someone else is deciding where to drill the well—but we’re going to help you make more efficient decisions about when you complete that well, how long you should pump, how much you should pump into it, and more.”

This capability became even more critical as the industry faced challenges, especially during the COVID-19 pandemic, which saw a dramatic decrease in operational capacity.

As the company adapted to new challenges, it also explored additional markets. One significant development involved CO2 sequestration, aiming to monitor carbon stored underground to ensure safety and prevent leaks.

“The DOE (Department of Energy) sent out a general notice that they’re looking for ways to monitor carbon when it’s been sequestered to make sure that it’s not causing earthquakes, and to make sure that the carbon is staying in the reservoir where you put it. And we said, ‘Well, we think we could hear little earthquakes that are the precursors to big earthquakes. We think we could hear if it starts to leak out of the reservoir.’ We’d actually done this once,” Duncan said.

This led to the advent of the CO2SeQure suite of technologies, which includes the BuriedArray system, which is similar to a high-tech security system for CO2 storage, Duncan said.

The BuriedArray system is a network of underground sensors that continuously monitors CO2 storage, keeping track of CO2 movement, detecting small seismic events and sending data to a central processing facility.

Before CO2 injection starts, the array measures baseline seismic activity. During injection, it monitors for seismic events that could indicate caprock issues or regional fault slippage, using a “stoplight system” to alert operators if certain critical levels are exceeded.

MicroSeismic also is venturing into the advanced geothermal business. This initiative brings the company’s technologies full circle, as the process is based on the original FracRx solution, Duncan said.

“In places like California, hot rocks are close to the surface. You can drill in and circulate water through the rocks to heat the water and then harvest the heat for electricity,” he said. Geothermal systems take the process into a different realm. “What enhanced geothermal systems are all about is drilling down into the deep basement rocks that are very hot to make supercritical steam and be able to bring more energy up to the surface so that it becomes more commercial.”

Duncan sees potential for enhanced geothermal systems (EGS) to reshape the energy landscape. By applying lessons learned from fracking, he believes technologies such as distributed acoustic sensing (DAS) can facilitate more effective geothermal energy extraction.

DAS, also known as Distributed Fiber Optic Sensing, is an innovative technology that uses lasers to detect sound in real time along an optical fiber cable. Connecting a DAS unit to one end of a standard optical fiber transforms the fiber into thousands of vibration sensors or microphones spread over many kilometers. This setup requires no additional electronics or hardware, making it a highly efficient way to monitor sound and vibrations over large distances.

MicroSeismic is currently working with Australian company Terra15 to offer a DAS-based microseismic solution to enhance the company’s monitoring capabilities.

“DAS is a technology that I’m hopeful will come to bear to be able to get higher-resolution signals than we can get with geophones. But, as a general application, it’s not there yet,” Duncan said. “There are limitations on what the DAS can do, and we’re still working on that. But, I’m hopeful that will be something that replaces our conventional geophone.”

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