“山1盒8攻关”,SCP勇于尝试,探索未知

SCP is taking another new step to unblock the massive but challenging gas reserves of the Yanbei field for the resource holder and our collaboration partner, Yanchang Petroleum. Yanbei’s valuable resources are buried 3.5 km under the rolling hills of northern Shaanxi.

SCP正在采取新举措,助力资源方兼合作伙伴——延长石油,开采延北气田庞大且极具挑战的气藏。延北宝贵的资源,正埋藏在陕北绵延起伏的群山之下3.5km深处。


At these great depths, there exist fossilized 260-million-year-old river systems stacked on top of each other after repeated cycles of glaciation. Over the eons, the pressure from these overlying layers crushed buried vegetation into coal which, in turn, released natural gas which collected in the porous sandstones of these ancient riverbeds. Now it is our duty to drill down to produce this resource to the surface to benefit China’s energy supply.

这里,埋藏着两亿六千万年的石化河流体系,历经循环反复的冰川作用后,它们堆积交织在一起。亿万年来,这些重叠压覆的层位压力碾碎掩埋的植被,变成煤碳,进而释放出天然气,随后,天然气便在这些远古河床的砂岩孔隙中聚集。现在,我们肩负的使命是,钻井采气,把这些天然气资源开采出来,助力中国的能源供应。

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图:A general model of the original depositional environment

原始沉积环境的一般模式

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图:Examples of what the original rivers that made S1-H8 looked like

形成S1-H8的原始河流例子


But it takes technology investment and skill to locate these rock formations. And it is not enough just to drill a well into this rock, as it is so impermeable that no gas can flow through it unless we also create a network of small fractures spreading out from each well into the reservoir. These fractures open the rock pores and free the trapped gas so it can flow to the surface.

不过,找到这些岩层需要技术投资和技巧。而且,仅仅在一块岩石上钻一口井是不够的,因为岩石渗透率低,天然气无法渗透,除非我们在每口井与气藏之间创建一张由细小裂缝构成的网络,由这些裂缝打开岩石孔隙,释放出受困的天然气,流向地面。


This approach has been proven effective to develop a group of rock layers called S2-3, which contain nearly half of Yanbei’s gas. To fracture S2-3 layers and release the gas, we pump into each well, a slurry consisting of gum-thickened water and tiny ceramic grains at high pressure. Our engineers use advanced engineering software to determine the pumping pressure and fluid specifications. After a sufficiently large fracture network has been created, we stop the pumps and allow the natural rock pressure to try to clamp the fractures closed, but the closure process stops when it encounters the solid ceramic grains. Billions of these grains “prop” the crack open (hence they are called “proppant”) and allow the gas from the rock pores to flow past them into the wellbore and thence to the surface.

已证实该方法是有效,能用于开发山2-3层位,山2-3包含了延北近一半的气藏。为了压裂山2-3层位释放天然气,我们用高压泵注入粘稠水和陶粒砂混合而成的泥浆。我们的工程师使用先进的工程软件,来确定泵送压力和入井液规格。当一张足够大的裂缝网形成后,我们停止泵送,让岩石的自然压力去夹紧闭合裂缝,但当遇到固体陶粒砂时,裂缝闭合的过程会停止。数十亿陶粒砂“撑开”裂缝(因此陶粒砂也被称为“支撑剂”),使岩石孔隙中的天然气穿过支撑剂,进入井筒,到达地面。


Apart from S2-3, most of the rest of the Yanbei's gas lies in another group of rock layers called S1-H8 which was prehistorically formed from narrow, slow, meandering rivers, whose now-mineralised riverbeds comprise a mix of fine gas-bearing sand and other non-gas bearing rock.These geological factors make it much harder to extract gas from S1-H8 than from the cleaner, bigger sands of S2-3. In S1-H8, firstly, the non-gas bearing rock is indistinguishable from good sand on the seismic images that we use to locate the reservoir. Secondly, the narrow rivers that formed S1-H8, resulted in thinner, and therefore smaller, gas reservoirs. Thirdly, because the original rivers were sluggish, they allowed finer deposits to settle, leading to a less porous reservoir rock. As if that were not enough, inside S1-H8’s smaller rock pores (compared to S2-3), the individual tiny puffs of gas lack the momentum to overcome relatively massive water droplets glued to the rock by surface tension.

除了山2-3外,延北剩余大部分气储藏在另一组被称为山1盒8的层位中。山1盒8由史前狭窄、舒缓、蜿蜒的河道形成,现已矿化的河床由含气的细砂和其他非含气岩石混合而成。这些地质因素,使得从山1盒8中提取天然气,比从更清洁、更大块的山2-3砂体中提取,要困难很多。首先,山1盒8层位中的非含气砂岩,相较于地震图像上我们用于定位储层的优质砂岩,二者难以区分。其次,形成山1盒8的河道很狭窄,导致气藏更薄,也更小。第三,由于原始河流流速缓慢,允许更精细的矿物沉淀下来,导致储层岩孔隙更小。不仅如此,与山2-3相比,由于山1盒8的岩石孔隙较小,单个微小的一缕一缕的天然气缺乏势气,难以突破相对大量的因表面张力附着在岩石上的水滴。


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左图:Drilling patterns to reach the reservoir units

到达油藏单元的钻井模式

右图:Micrographs of the different rock qualities

不同岩石质量的显微照片


In any case, in 2014 at the start of the development drilling we, perhaps optimistically, tried the S2-3 frac design on some S1-H8 wells. With hindsight, the results, not surprisingly, were poor. Our investigation concluded that the high-water content slurry was flooding already-wetted rock pores and obstructing gas outflow.

2014年,钻井开发伊始,我们或许乐观地把山2-3的压裂设计,用在了山1盒8的气井上。事后看来,压裂结果不理想,似乎并不意外。调查结论显示,高含水的泥浆淹没了本已潮湿的岩石孔隙,阻碍了天然气流出。


After these initial results, SCP appointed a research taskforce to work on the S1-H8 problem in parallel with the main S2-3 development focus. The taskforce team surveyed the global state of the art for stimulating such reservoirs and concluded that there was no off-the-shelf solution to unlock this gas, and while many companies had tried elsewhere, the one-off success cases could not be directly applied to Yanbei.

得到这些初步结果以后,SCP组建了一支攻关小组,来攻克山1盒8难关,与主力层山2-3的开发齐头并进。该小组调查了全球现有的此类气藏的改造技术,得出的结论是,没有现成的解决方案可用来开采此类气藏,虽然许多公司已经在其他地方尝试过,但一次性的成功案例不能直接应用到延北项目上。


Consequently, the taskforce chose a step by step approach the progress into the unknown – choosing as its breakthrough attempt in 2017 a so-called “volume frac” design: It was hoped that by creating much bigger fractures they would propagate far enough to dissipate near-wellbore water blockage effects. Using water was a cost-effective way to increase the size of the fracture. However, the hopes for a breakthrough were dashed as severe water blockage re-occurred, and gas productivity remained low. Nevertheless, this was an important final attempt with water because the next logical step, moving away for water as the main fluid, would entail new challenges and costs.

因此,攻关小组采用了循序渐进的方法来探索未知。2017年,他们选择了一种称为“大规模压裂”的设计来作突破性尝试:希望压裂规模越大,裂缝延伸得足够远,井筒附近的水锁效应就会自然消失。用水来压裂是扩大裂缝的一种经济有效的方法。然而,攻关的希望破灭了,因为再次发生了严重水堵,天然气产量仍然很低。不过,用水来压裂的这次尝试也很重要,因为下一步的合理措施是,不再用水作为主要入井液,这又将带来新挑战,产生新成本。


In 2018, the taskforce’s post-trial review confirmed that the only way to achieve adequate gas flow rates was to reduce the slurry’s water content by adding a non-aqueous fluid. CO2 was selected because even though it is normally a gas, when pressurised it liquefies and so can be easily pumped. However, using 100% CO2 at -40C would have placed excessive thermal stresses on the equipment and would have been very expensive and logistically challenging on our small remote well pads. So, we settled for a 60/40 CO2/water mix instead.

2018年,攻关小组的试后评估证实,要获得足够的天然气流速,唯一的办法是使用CO2这种非水性流体来降低泥浆的含水量。之所以选择二氧化碳,是因为尽管它通常是气体,但加压后会液化,因此很容易泵送。 但使用零下40℃ 的 100% 纯 CO2 会给设备带来过大的热应力,并且对于我们小型偏远的井场而言,成本太高,后勤支持也会面临挑战。 因此,我们把二氧化碳/水的比率设定为60/40 。




图:Liquid carbon-dioxide frac operations

液态二氧化碳压裂作业


Happily, initial gas rates from this trial were many times higher than previous trials. It was a real step in the right direction to defeat our water block demon. However, the higher rates could not be sustained as long as required. So, this presented us with the next challenge - ie how to scale up the technique to achieve both high production rates and high ultimate recovery volumes.

欣喜的是,这次试验的初始气量比前几次试验高很多倍,标志着我们在打败水锁恶魔的正确方向上迈进了真正一步。 但高产量不能持续所需的时长。 因此,这给我们带来了下一个挑战——如何扩大技术规模,来实现高产量和最终的高采收率?


This brings us to the present day. A lot has happened in the interim in SCP. After successfully completing the technologically demanding execution and start up phases of the project, Schlumberger and Copower agreed to swap roles within their close partnership to give the lead to Copower’s entrepreneurial mindset, underpinned by Schlumberger’s world-class technology.

到目前为止, SCP 做了很多优化调整。成功完成延北项目高技术的建设与投产后,斯伦贝谢与长和实业同意,在其紧密的合作伙伴关系中互换角色,由长和实业来主导实施企业战略,由斯伦贝谢来提供世界一流的技术支持。


Now a reconstituted S1-H8 research taskforce, is harnessing the best of Schlumberger technology and domestic experience to make the next breakthrough. Experience in other basins has shown that multi-organisational collaboration is a must for breakthrough projects like this, and so we are also reaching out to research institutes and other companies.

现在,SCP重新组建了一支山1盒8 攻关小组,该小组正在充分利用斯伦贝谢技术和国内先进经验,来努力取得下一个突破。其他盆地的经验表明,多组织合作是此类项目取得突破的必要条件,因此我们正在与其他研究机构和企业接洽。


Currently the team has identified three focus areas: (i) productivity (ii) cost (iii) well targeting. The top S1-H8 priorities in 2021 remain (i) & (ii) - productivity and cost. Productivity is key because unless a well exceeds a critical gas rate, it will always need expensive nursing to avoid choking on its own water production. For the latest batch of trials we are applying lessons from the CO2 trials to minimise water content, and lessons from recent S2-3 well trials to maximise fracture size.

目前,攻关小组确定了三个重点领域:(i) 产量 (ii) 成本 (iii) 井位。 2021 年,山1盒8攻关的重点仍然是 (i) 和 (ii) ——产量和成本。产量是关键,因为除非气井产量超过了临界产量,否则一直需要采取昂贵的措施,来避免气井因自身出水而导致水堵。在当前批次的试验中,我们吸取了 CO2 压裂试验的经验,把含水量降至最低,也吸取了最近山S2-3试验的经验,使压裂规模最大化。

 

Cost is also critical to ensure the well is commercial and economic. So, to drive costs down we are also switching from CO2 to a cheaper and more environmentally friendly, nitrogen-based, design.

要确保气井具有商业性和经济性,成本控制至关重要。因此,为了降低成本,我们在压裂设计中,把二氧化碳替换成了更便宜、更环保的氮气。


The third research focus (“well targeting”) aims to push the boundaries of geophysical technology (eg seismic imaging) to accurately locate “sweetspots” – ie areas of bigger and better reservoir rock.

第三个攻关重点是“井位”,旨在突破地球物理技术(例如地震成像)的界限,以准确定位“甜点区”,即更大更好的储集岩区域。




左图:Identifying sweetspots using combined geophysical techniques

利用综合地球物理技术识别“甜点”

右图:Petrophysical logs of the rock properties


From now until 2022, we will write the next exciting chapter of this adventure story to break through the “S1-H8-barrier” and permit large-scale commercial development. There is risk for sure, but also a huge potential prize. We are confident that if it can be done, then SCP, Yanchang, Schlumberger and our committed supporters have the can-do mentality to do it. Stay tuned.

从现在到2022年,我们将为这个历险故事,续写激动人心的篇章。攻克“山1盒8壁垒”,实现大规模商业开发。风险肯定会有,但潜在回报也是巨大的。我们坚信,如果我们能做到,那么SCP、延长、斯伦贝谢及我们忠实的支持者们,都能以“能做到“的心态继续前行。

让我们拭目以待……


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