January 2021 /// Vol 242 No. 1)
Fracturing and the environment
One of the industry’s premier experts says hydraulic fracturing actually reduces the environmental impact of oil and gas production by increasing the productivity of each well.
Over the last few years, there has been a lot of public debate about the environmental impact of hydraulic fracturing, as well as advocacy by some of our civic and political leaders for banning the process as a way of improving environmental quality. This article makes an in-depth analysis of the subject and the advisability of such action.
The environmental impact of oil and gas is usually discussed under a single umbrella. But careful and learned examination of the subject teaches us that the proper way to analyze the topic is to break it into its two main separate and independent parts—its production, and its use/consumption. The activities falling under the production heading include drilling, completions (including fracturing), and lifting the produced fluid to the surface. The use/consumption portion covers its many industrial applications.
Oil and gas are the primary fuels for power generation, transportation, heating, petrochemicals, and many other uses for our essential individual and social activities. Consumption of oil and gas has a vastly bigger impact on the environment than its production. Historical oil and gas consumption statistics show continuously increasing demand, reaching over 95 MMbopd in 2019.
The overall emphasis of governments, and general consensus of the public, is to reduce the need for oil and gas by replacing it with other less environmentally harmful alternatives such as solar, wind, geothermal, and nuclear energy, as well as use of electric cars, etc. The effect of these replacements is to reduce the percentage contribution of oil and gas in the overall energy picture. But since the general global need for energy is increasing continuously, the actual need for production of oil and gas is projected to increase in absolute terms, even though, and while, its relative contribution will be decreasing subsequent to the above replacements. Thus, production of more oil and gas will continue to be an important source for satisfying the energy needs of the future.
Let us now shift our focus to the environmental aspects of oil and gas production, and the effects of its various phases, such as drilling, completions (including fracturing), and production operations. Meeting our present and future oil and gas needs requires drilling and completing a certain number of wells. The actual number of required wells depends on their individual productivity; the higher the productivity of each well, the fewer the required number of wells. Thus, any operation that increases the productivity of wells will reduce the need for drilling more wells, and consequently reduce the environmental impact of production operations.
At the present time, the dominant method for enhancing well productivity is hydraulic fracturing. As a matter of fact, the vast majority of all wells take advantage of some form of fracturing for starting or enhancing their production. Thus, the more effective the fracturing operations are for increasing well productivity, the less the need for drilling more wells to meet our production objectives. In fact, this is the reason for the huge financial and intellectual effort of the industry to improve effectiveness of fracturing operations by reducing their size and intensity to get the required production enhancement. Any improvement in fracturing effectiveness will also reduce the overall environmental imprint of production operations.
Thus, as long as the world needs access to oil and gas for its energy supply, use of fracturing and improving its production effectiveness is going to be essential for improving environmental quality. The consequence of banning fracturing is to ban our ability to get better production from oil and gas wells. The net effect is removal of many of our marginal reservoirs which will become uneconomic to produce from, thus scarcer sources of oil and gas and higher prices, and a need for more drilling, which also will result in more environmental impact and higher prices. In summary, the environmental consequences of banning fracturing are very different than what is recognized by a casual or emotional review of the subject.
This author’s exposure and involvement in hydraulic fracturing started more than 50 years ago, while a graduate student at the University of Minnesota, with the job of preparing samples and helping with fracturing experiments for a classmate who was researching the subject for his PhD thesis. That very modest beginning was continued and expanded to include laboratory research on various technical aspects of the subject, developing simulators for engineering design of the different applications of the process, and extensive review of the results of these applications for better understanding of what happens in the mysterious underground when we fracture wells in oil-and-gas-bearing formations.
Increasing use of horizontal wells for production from ultra-low-permeability reservoirs (such as the U.S. unconventional shales) has added a new dimension to the widespread use and technical complexity of hydraulic fracturing. A common practice for production from these reservoirs includes drilling long horizontal wells (often close to, and sometimes in excess of, 2-mi-long horizontal sections), mechanically dividing the horizontal segment into multiple isolated sections, and simultaneously creating multiple fractures within each isolated section during each fluid injection stage.
The ability to perform these complex operations has been made possible by the development and integration of many advanced mechanical components into a coherent and functional system. Without these advancements, the contribution of U.S. unconventional reservoirs to our energy needs would have been close to negligible!
Over the years, many of us in the fracturing community have been witnesses to, and participants in, the industry’s growing interest in the various technical and operational aspects of the subject, and infusion of many advanced technologies for this purpose. These have included mapping the location of the hydraulic fractures within the formation by detecting micro-seismic signals caused by a growing fracture, and deployment and detection of electromagnetic particles injected inside the fracture. Other advanced technologies deployed in the process include use of fiber optic lines inside the wellbores for detection of changes in ground deformation and temperature caused by fracturing; use of various types of chemicals for tracing fracturing fluid movement within the fractured formation; and measurement and analysis of small pressure changes detected in adjacent wellbores caused by an approaching hydraulic fracture.
Use of each of these technologies, and analysis of their results, has been supported by a group of highly capable scientists and specialists in this subject. The results of these investigations have been published in many technical papers. In fact, there are more technical papers on hydraulic fracturing than any other subject within the oil and gas industry. Multiple dedicated technical conferences discuss the continuous evolution of the subject and improvements in our understanding of the technology while improving its effectiveness. It is fair to say that the industry is very much aware of the positive impact of hydraulic fracturing on the productivity of reservoirs and supporting ways of enhancing its effectiveness.
The level of increase in well productivity depends on reservoir properties, and especially on its permeability; the lower the permeability, the higher the level of production increase resulting from proper fracturing. Drilling and completion operations cause substantial reduction in the formation permeability of the near-wellbore region, and consequently in well productivity. Nearly all wells drilled today require some level of fracturing before they are ready for production.
Furthermore, without fracturing, some of the low-permeability reservoirs would not contribute to world energy needs at all. Most notable among these are the U.S. unconventional shale formations which are a major contributor to energy needs in this country.
CHANGES IN PRACTICES
To demonstrate the environmental benefits of present industry practices for production of unconventional reservoirs, let us review the effects and contributions of changes in prevailing practices over the last two decades. Horizontal wells have mostly replaced vertical wells for production of these reservoirs. This has substantially reduced the required number of wells. A 10,000-ft horizontal section, at a depth of 10,000 ft, has a total well length of less than 20,000 ft, and is drilled during one continuous operation. It replaces the need for drilling eight to 10 vertical wells—each 10,000 ft deep—which would have a combined length of 80,000 to 100,000 ft and are drilled over a much longer period of time, with separate surface set-ups for each well.
It is obvious that the shorter horizontal well will have a much smaller environmental impact than the several vertical wells that it replaces. With a similar analogy, one also can appreciate the environmental benefits of creating multiple fractures during a single operation in a horizontal well, compared to multiple set-ups for fracturing multiple vertical wells. The main components of this advancement, drilling horizontal wells, dividing them into multiple segments, and continuous fracturing of these segments, are essential parts of the entire operational package that need to be practiced together to get their beneficial results.
Another important point for consideration is the quality of the oil being produced—the lighter the oil, the less its environmental impact during its use. For example, the fluid produced from U.S. unconventional reservoirs is a light crude. Its use produces less environmentally harmful by-products than heavier crudes. Fracturing these reservoirs is essential for producing from them. Banning fracturing will practically stop production from these reservoirs within a few years, which then forces its replacement by heavier imported crudes that will have higher environmental impacts during their use.
Some of the negative public reaction to fracturing is likely to be related to the increasing intensity of these operations during the last decade. These changes have, in fact, reduced the environmental impact of fracturing during completion operations. Some of the horizontal wells drilled for production from unconventional reservoirs are fractured a few hundred times during a continuous operation. The concentrated execution of these operations reduces their environmental impact per unit of produced fluid.
Another change has been drilling multiple horizontal wells from a single pad, which has substantially reduced the footprint of drilling activities. Fracturing these wells is then undertaken during a single continuous period, as it progresses and moves alternately between adjacent wells, starting from their toes and moving toward their heels. While the entirety of these operations may take two to three weeks of continuous fracturing and assembly of large surface pumping and storage facilities, the net overall effect is, in fact, a reduction in the environmental impact of the operations per barrel of produced fluid.
Figure 1 provides a typical case history of the efficiencies that have resulted from use of horizontal well drilling and fracturing. The horizontal well in this case was nearly 2 mi long. It was subdivided into 53 segments and fractured during a single continuous operation that took 17 days. For comparison, separate preparation and fracturing of each of the 53 segments would have taken more than one full day.
The graph also shows the data collected in an adjacent offset well, using a new technology known as Frac-Driven Interaction (FDI) for better evaluation of the created hydraulic fractures. This easy-to-use technology gives very valuable information about the size and orientation of fractures created in this reservoir. In this specific example, it shows that the previous fractures in the offset well had extended very close to the location of the new well and farther than initially anticipated. The data open the option of using less fluid in future fractures in this reservoir and in shorter time, all of which reduce every aspect of the environmental footprint of the fracturing operations for the production of the required volume of oil.
In conclusion, improving the quality of our environment is a logical goal, worthy of support from every one of us. Replacing oil and gas consumption with more environmentally friendly alternatives is a step in the right direction. Government and political leaders are best positioned to address the relevant issues and recommend/legislate steps for its implementation. The effectiveness of these steps depends on the wisdom and depth of knowledge behind them. A prudent way to address the relevant issues is to seek participation and input from knowledgeable experts in the various aspects of each decision and avoid taking action based on the popular mood of the time.
As long as oil and gas contribute to our overall energy needs (even though playing a smaller part), their more effective production should be part of the overall environmental strategy. Hydraulic fracturing operations improve productivity of our reservoirs, reduce the need for drilling many more wells, and reduce the overall environmental impact of production operations while meeting present and future oil and gas needs. Banning use of fracturing by the industry will be unwise and will actually run contrary to the objective of improving environmental quality. Its main result will be eliminating the production of oil and gas from our land-based reservoirs and replenishing our needs with imported products. If this is the goal, then banning frac’ing is the answer!