非常规/复杂油藏

未来十年页岩油 EOR 前景依然黯淡,但专家呼吁持续投资并保持乐观

尽管试点项目和论文很多,但页岩油行业却没有值得一提的大型提高采收率项目。这种情况可能只能维持一段时间。

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资料来源:Getty Images。

自上个十年中期以来,大规模提高石油采收率(EOR)的想法在非常规领域一直只是海市蜃楼,而且在下个十年的剩余时间里,这种状况似乎仍将持续。

埃克森美孚公司的油藏技术开发专家 Ed Wanat 说:“从经济角度来看,只要一级油田面积仍然存在,它就可能总是胜过气体吞吐 [EOR] 技术。”

他补充说,随着未钻井库存的减少和致密油田显示出更多严重枯竭的迹象,页岩 EOR 的商业案例可能需要 5 到 10 年的时间才能巩固。

瓦纳特是一位油藏工程师,负责埃克森美孚非常规 EOR 试点项目,他在最近于休斯顿举行的非常规资源技术会议 (URTeC) 的一个小组讨论会上发表了讲话。

他对更广泛采用时间表的看法得到了 URTeC 专家组的一致赞同,该专家组成员包括来自西方石油公司 (Oxy)、雪佛龙以及美国第二大私营生产商 Ascent Resources 的其他油藏专家。

Ascent 油藏工程和企业储备总监 Raki Sahai 解释说,“这与重复压裂技术所面临的情况相同,即新井可能会获得更好的回报——60%、70% 到 80% 的回报,而且回报速度更快。”

除了新井位的吸引力之外,页岩 EOR 还存在一个问题,即它并没有达到人们的预期。尽管它被认为是一种技术上行之有效的方法。

除少数例外,油业一直专注于注入相对廉价的天然气来开采额外的石油,即吞吐技术。

Sahai 指出,总部位于休斯顿的 EOG Resources 在德克萨斯州南部 Eagle Ford Shale 进行了开创性的 15 口井吞吐试验,该试验于 2016 年宣布后引起了整个行业的关注。最初预计这组井的产量将比初始产量高出 30% 至 70%。然而,Ascent 的油藏工程师表示,最近的公开数据显示,它们的实际增量采收率仅为 10% 至 40%。

“我们从中了解到,天然气注入不是问题;我们可以注入,我们可以看到压力积聚。问题是采收率远低于 2016 年实际宣传的水平,”他说。

在鹰福特和其他地方,飞行员多次未能击中目标都是由于注入的气体控制问题造成的。

如果过多的气体从一口井流向另一口井,或者通过广泛的裂缝/断层网络逸出到储层远区,优化作业的所有希望都可能化为泡影。因此,遏制被广泛视为页岩 EOR 的主要技术挑战。

好消息是,操作员小组成员看到了一些有希望的解决方案。其中包括雪佛龙最近公布的方法,即在检测到大量天然气突破时关闭与注入器偏移的油井。

雪佛龙公司天然气提高采收率和碳封存技术顾问周登根表示,多井注入策略可以提高实现足够压力积累的机会,从而使气体能够调动滞留石油。

但对于页岩 EOR 而言,情况是这样的,一个难题解决了,另一个难题就随之而来。

对于许多美国和加拿大的生产商来说,最明显的问题之一就是,特别是那些规模较小的生产商,他们缺乏一种具有成本效益的来源,来获取启动吸入式 EOR 项目所需的大量天然气。

Oxy 公司非常规技术增产与采收主管谢雪英列举了其他瓶颈。其中包括,用于注入天然气的工业级压缩机多年来一直处于少数制造商的缺货状态。

她补充说,阻碍页岩 EOR 更广泛应用的其他较少被提及的障碍涉及土地和监管问题。“这些地区的统一化需要很多年,而许可证发放是另一个挑战,”她说。

发言者还强调,上述问题不应阻碍行业、特别是管理层向前发展。

周指出,尽管雪佛龙等运营商在未来十年将专注于钻探新井,但这种关注并不妨碍他们同时进行前端研究。

“据我所知,现在大多数决定都与试点有关,因为我们必须开发这项技术,”他解释道,并强调,“这方面非常紧迫。”

埃克森美孚公司的瓦纳特指出,该公司领导层最近公开设定了目标,要将非常规采收率从 10% 左右提高一倍至 20%,他表示,要实现这一目标无疑需要页岩 EOR 等新技术。

瓦纳特认为,技术专业人员的任务是“向管理层传达我们现在需要采取的愿景,以确保我们拥有这些技术,并确保他们了解其中存在的挑战”。

Wanat 随后表示,没有哪个页岩 EOR 项目能够一次成功。因此,管理层必须耐心等待,才能获得回报。

另一个有助于事情进展的缺失因素是行业内的合作。除了技术会议和其他非正式聚会之外,运营商几乎没有途径将数十名不同飞行员的经验教训结合起来。

瓦纳特承认大型运营商天生不愿意共享专有数据,但他表示支持成立联合行业项目,旨在解决页岩 EOR 的最大痛点。

他说道:“如果我们共同努力,我们就能以更快的速度加快进步,甚至可能打消一些担忧。”

原文链接/JPT
Unconventional/complex reservoirs

Shale EOR Prospects Remain Dim This Decade, Yet Experts Call for Sustained Investment and Optimism

Pilots and papers are plentiful, but the shale sector has no big enhanced oil recovery projects to speak of. It may just have to stay that way for a while.

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Source: Getty Images.

Since the middle of the past decade, the idea of large-scale enhanced oil recovery (EOR) has been a mirage in the unconventional sector and it appears likely to remain so for the rest of this decade.

“Economically, as long as that tier one acreage still exists, it’s probably always going to beat gas-huff-and-puff [EOR],” said Ed Wanat, a reservoir technology development expert at ExxonMobil.

He added that it could reasonably take 5 to 10 years for the business case to solidify around shale EOR as those undrilled well inventories shrink and tight oil fields show more signs of significant depletion.

Wanat, a reservoir engineer who leads ExxonMobil’s unconventional EOR pilot program, was speaking during a panel at the recent Unconventional Resources Technology Conference (URTeC) in Houston.

His view on the timeline to wider adoption was echoed across the URTeC panel that included other reservoir experts from Occidental Petroleum (Oxy), Chevron, and the second-largest private producer in the US, Ascent Resources.

“It’s the same thing that happened with refracs and with what that technology is facing, which is that you have new wells that are probably going to get better returns—60, 70 to 80% returns—as well as a quicker payout,” explained Raki Sahai, the director of reservoir engineering and corporate reserves at Ascent.

Beyond the attractiveness of new well locations, there is also the problem that shale EOR has not lived up to the hype. This is in spite of it being considered a technically proven approach.

With few exceptions, the industry has been focused on pumping in relatively cheap natural gas to pump out extra barrels of oil, i.e., the huff-and-puff technique.

Sahai pointed to Houston-based EOG Resources' groundbreaking 15-well huff-and-puff pilot in the Eagle Ford Shale of south Texas that sparked sectorwide interest when it was announced in 2016. Uplift from the group of wells was initially projected to be between 30 to 70% above initial production. However, the reservoir engineer from Ascent said recent public data show their actual incremental recoveries are on the order of only 10 to 40%.

“What we learned from this is that gas injectivity is not a problem; we can inject and we can see pressure buildup. The issue is that recovery is significantly lower than what was actually touted back in 2016,” he said.

Many of the missed targets with pilots in the Eagle Ford and elsewhere have been attributed to problems with containing the injected gas.

If excessive volumes of gas flow from well to well or escape into the reservoir’s far field through an extensive fracture/fault network, all hope for an optimized operation may be lost. For this reason, containment is widely regarded as the primary technical challenge in shale EOR.

The good news is that the operator panelists see promising solutions emerging. They include Chevron’s recently revealed approach which calls for wells offsetting an injector to be shut in if a major breakthrough of gas is detected.

Dengen Zhou, a technical advisor for gas EOR and carbon storage at Chevron, suggested that the multiple-well injection strategy improves the chances of achieving a pressure buildup adequate enough for the gas to mobilize stranded oil.

But with shale EOR, it is the case that as one challenge is ironed out, there’s always another wrinkle.

One of the most obvious for many US and Canadian producers, especially on the smaller end of the spectrum, is that they lack a cost-effective source for the large volumes of natural gas required to launch a huff-and-puff EOR project.

Xueying Xie, the director of unconventional technology stimulation and recovery for Oxy, listed other bottlenecks. Among them are that the industrial-sized compressors used to inject the gas are chronically on backorder from a small number of manufacturers for several years out.

She added that other less spoken of hurdles to the wider uptake of shale EOR involves land and regulatory matters. “The unitization of these areas takes many years and the permitting is another challenge,” she said.

The speakers also stressed that the issues listed above should not dissuade the industry, and especially management, from pushing forward.

Zhou noted that just because operators like Chevron are concentrating on drilling new wells over the next decade, this focus does not prevent them from conducting front-end research in the meantime.

“Most of the decisions right now are as I understand are around the pilots since we have to be developing the technology,” he explained, emphasizing, "there’s a lot of urgency there."

Wanat from ExxonMobil noted that the leadership of his company recently set a public goal to double its unconventional recovery factor from around 10 to 20%, a feat he said will undoubtedly require new technologies such as shale EOR.

The task for technical professionals according to Wanat “is going to be selling [management] on the vision that we need to get going now in order to make sure that we have these technologies and to make sure they understand that there are challenges.”

Wanat followed up by saying that no shale EOR project will get it right the first time. Management must, therefore, be patient in order to reap the rewards.

One other missing element that would help things along would be collaboration within the industry. Outside of the technical conference circuit and other informal gatherings, there are few avenues available for operators to combine the lessons learned from dozens of disparate pilots.

Wanat acknowledged the natural reluctance of large operators to share proprietary data, yet he expressed support for the formation of a joint industry project designed to address shale EOR's biggest pain points.

“We can accelerate progress at a lot faster rate if we work together, and perhaps, belie some of those fears,” he said.