[编者注：本文最初发表于 2020 年 4 月版《E&P》。在这里订阅杂志 。]

在过去的十年中，在页岩地层（通常是低渗透性砂岩和碳酸盐岩地层）的开发方面进行了大量的工作。许多这些地层的基质孔隙度较低，但不同程度地自然破裂，这有助于提高地层内整体碳氢化合物的流动性。在压裂作业期间，这些天然裂缝被主要活动水力裂缝激活和/或交叉，并且还可能产生额外的小型水力裂缝（裂缝）。最初，这些微裂缝（天然的和水力的）提高了油井的产能，但最终随着油井的下降而在压力下封闭和关闭。

证明这一点的证据是，油井具有较高的初始产能（高于单独使用基质渗透率来表征的产能），随后在油井生产寿命几个月后产量急剧下降，这是页岩井的常见特征。微支撑剂的开发是为了进入这些微裂缝，支撑它们打开，这样它们就可以在油井的整个寿命期内有助于生产，就像​​无支撑的裂缝有助于一些页岩油藏的生产一样。

微支撑剂的进步
二氧化硅和陶瓷基微支撑剂已存在多年。不幸的是，微支撑剂总是难以融入压裂作业中，因为它们需要预混入胶凝泥浆系统，这增加了巨大的费用和后勤复杂性。因此，开发可干混的微支撑剂（类似于标准支撑剂）使得在任何阶段的任何压裂处理中掺入微支撑剂变得更加容易且成本更低。

任何新产品的开发通常都是从客户的要求开始，以解决某些生产挑战。在这种情况下，问题在于如何使用能够在油井生产寿命期间承受地层应力的产品来防止各种尺寸的微裂缝闭合。技术研究团队致力于开发一种制造小目陶瓷支撑剂的工艺。结果是平均粒径为 325 目 (45 微米)，约为标准 100 目支撑剂尺寸的 30%。此外，微支撑剂的设计主要范围在 150 至 635 目之间，可以支撑多种尺寸的微裂缝。

与沙子相比，微支撑剂具有更大的强度，因为它是陶瓷的。这使其能够保持开放式裂缝，特别是在部分单层设置中，这是当单个晶粒必须承受高应力并保持裂缝开放时实现的。因此，即使含有少量微支撑剂的微裂缝也会在井的使用寿命内保持开放。此外，微支撑剂设计为干泵送，现在大多数应用都使用当今的“牛”型支撑剂输送系统来部署。

对产量的影响
已发表的文章记录了微支撑剂导致产量增加了 15% 至 20%。由于产量增加，一些运营商已将微支撑剂纳入其标准完井中。由于狭窄的微裂缝所需的体积较小，因此增量成本并不显着。一些运营商还使用陶瓷微支撑剂来降低处理压力，这归因于更好的裂缝调节甚至减少了漏砂。

这导致更少的马力消耗或更短的压裂阶段时间，这两者都降低了压裂处理的成本。此外，小目尺寸的微支撑剂的沉降速率比100目支撑剂慢10至15倍。支撑剂可输送性的显着改善不仅适用于裂缝内，还适用于管道内，使微支撑剂能够输送到一个阶段中最远的射孔簇，清洁和调节射孔并建立水力裂缝。结果是流体和支撑剂更好地分布到所有簇中，这意味着所有簇都可以得到有效的增产。最近的管流研究表明，支撑剂物理特性可以显着影响通过多个射孔簇的流量分布。

与所有压裂处理一样，支撑剂需要放置在碳氢化合物产油区所在的位置，以及它将实现最大产量增长的位置。将微支撑剂放入微裂缝中也是如此。使用商用软件可以分析标准钻井数据，以估计沿横向的天然裂缝的大小。利用这些数据，可以针对油井的每个处理阶段设计微支撑剂的掺入，以最大限度地提高油井经济效益。

[Editor's note: This story originally appeared in the April 2020 edition of E&P. Subscribe to the magazine here.]

Over the last decade, there has been a significant amount of work performed in the development of shale formations, typically low permeability sandstone and carbonate formations. Many of these formations have low matrix porosity but are naturally fractured to varying degrees, which helps boost overall hydrocarbon mobility within the formation. During fracturing operations, these natural fractures are activated and/or intersected by the primary active hydraulic fractures, and additional small hydraulic fractures (fissures) also can be created. Initially, these microfractures (natural and hydraulic) enhance well productivity but eventually seal up and close under stress as the well is drawn down.

This is evidenced by wells that have high initial productivity (higher than can be characterized using matrix permeability alone) followed by steep production declines a few months into the well’s producing life—a common signature in shale wells. Microproppants were developed to enter these microfractures, propping them open so they may contribute to production over the life of the well, much the same as unpropped fractures contribute to production in some shale reservoirs.

Microproppant advances
Both silica and ceramic-based microproppants have been around for several years. Unfortunately, microproppants were always difficult to incorporate into fracturing operations because they required preblending into a gelled slurry system, which added a large expense and logistical complications. Therefore, the development of a microproppant that can be blended dry (similar to a standard proppant) makes it significantly easier and less expensive to incorporate microproppant on any fracture treatment at any stage.

The development of any new product usually starts with requests from customers to address certain production challenges. In this case, it was about how to prevent microfractures of wide-ranging sizes from closing with a product that can endure formation stresses during the productive life of a well. The technical research team worked to develop a process to make small mesh ceramic proppant. The result was a 325 mesh (45-μ) mean particle diameter, which is approximately 30% of the size for standard 100 mesh proppant. In addition, the microproppant was designed to range primarily between 150 and 635 mesh, allowing the propping of many sizes of microfractures.

Microproppant has greater strength compared to sand because it is ceramic. This enables it to maintain an open fracture, particularly in a partial monolayer setting, which is achieved when a single grain must experience high stress and hold the fracture open. Therefore, the microfractures that contain even a small amount of microproppant will remain open for the life of the well. In addition, the microproppant is designed to be pumped dry, with most applications now being deployed using today’s “box” type proppant delivery systems.

Effect on production
There have been published articles documenting 15% to 20% increased production that was attributed to microproppant. Several operators have incorporated microproppant into their standard completions due to the increased production. The incremental cost is not significant due to the low volumes required for the narrow microfractures. Some operators also have used the ceramic microproppant to obtain a reduction in treating pressure that is attributed to better fracture conditioning or even reduced screenouts.

This leads to fewer horsepower charges or shorter frac stage times, both of which reduced the cost of the fracture treatment. Furthermore, the small mesh size of the microproppant has a settling rate of 10 to 15 times slower than 100 mesh proppant. This significant improvement in proppant transportability not only applies within the fractures but also within the pipe, allowing the microproppant to be transported to the farthest perforation cluster in a stage, cleaning and conditioning the perforations and establishing a hydraulic fracture. The result is a better distribution of the fluid and proppant into all of the clusters, meaning all clusters can be effectively stimulated. Recent pipe flow studies have shown that proppant physical properties can significantly impact flow distribution through multiple perforation clusters.

As with all fracture treatments, the proppant needs to be placed where the hydrocarbon pay zone is located and where it will achieve the largest increase in production. This is also true of placing microproppant into the microfractures. Using commercially available software is possible to analyze standard drilling data to estimate the magnitude of natural fractures along the lateral. With these data, the incorporation of microproppant can be engineered for each treatment stage of the well to maximize well economics.