Continued advances in horizontal drilling and hydraulic fracturing techniques have propelled the industry to longer lateral lengths and greater depths in unconventional reservoirs. But alongside the hydrocarbon bonanza these new technologies deliver, innovative services that ensure hydraulic fracturing operations are sustainable from an environmental standpoint are being prioritized by the industry as mission-critical.

The material and energy requirements that go along with developing unconventional carbonate, sandstone, and shale reservoirs have prompted companies to address the environmental impact of their operations. Heightened public concern and stringent restrictions and regulations also are impacting the ability of companies to develop these resources globally, with scrutiny increasing as activity expands closer to heavily populated centers.

In response to those challenges, service companies have developed technologies that reduce environmental impact and leave a smaller footprint. These include:

  • More efficient ways of managing resources and reducing the materials needed to fracture wells without compromising well performance;
  • New cementing technologies such as self-healing and expanding cements and cement evaluation methods for ensuring wellbore integrity;
  • Transparency regarding the chemicals being pumped; and
  • Cleaner alternatives to power operations and reduce emissions.

Safer, more sustainable

In a move toward providing more efficient, safe, responsible, and sustainable methods of hydraulically fracturing wells, Schlumberger in 2010 commercialized the HiWAY flow-channel hydraulic fracturing service. The service, engineered specifically for complex fracture networks, efficiently manages the use of proppants and water required for stimulation.

The safety, environmental, and operational benefits of this technique have been achieved in more than 15,000 stages and more than 1,300 wellbores, helping operators worldwide eliminate significant amounts of proppant, water, COemissions, and energy consumption. The service represents a step-change in the way hydraulic fracturing treatments have been performed over the last 67 years, where proppant is pumped continuously to fill fractures created in the reservoir. Oil and gas are then forced to flow through the narrow gaps left between the prop-pant grains after the well goes online – an approach that can still leave the well under-stimulated.

The new method, by contrast, uses a pumping method where proppant is added in short pulses, alternating with proppant-free pulses, to place stable, high-conductivity channels that are conduits for the flow of oil and gas. Specialized fibers maintain the integrity of the proppant pulses as they travel from surface to formation, promoting placement of the proppant in the fracture in the form of clusters, a process that requires less solids and water and enables better production. The reduction in materials means fewer trucks and minimizing transportation to and from the well site, thus reducing emissions.

Compared with conventional methods, the HiWAY technique has resulted in production increases of up to 80% and has delivered reductions in water, solids, and horsepower consumption by as much as 60%, 50%, and 33%, respectively. The service has been used for single-stage and multistage vertical and horizontal oil and gas wells, with formation temperatures ranging from 49°C to 174°C (120°F to 345°F).

Beyond its widespread and growing use internationally, the service has been particularly effective in prolific US shale plays such as the Eagle Ford, a region characterized by formations that require hydraulic fracturing at depths of 3,600 m to 3,700 m (11,800 ft to 12,200 ft). Fracture gradients and bottomhole static temperatures are high across this area. Well stimulation typically involves using a multistage horizontal completion method with high-rate slickwater treatments that require millions of gallons of water and millions of pounds of proppant per well. The boom in hydraulic fracturing in the play has reduced the availability of water and proppant, forcing companies to look for ways to increase operational efficiency.

A major operator looking to boost production in the Eagle Ford used the service to stimulate two wells while stimulating two other wells conventionally. During the first 60 days after stimulation, the wells treated with the HiWAY method produced an average of 31,850 boe, while the conventionally treated wells produced an average of 21,850 boe.

The average wellhead flowing pressure for the HiWAYtreated wells was 2,156 psi vs. 1,916 psi for the conventional wells. The channel fracturing process reduced water and proppant usage per well by 58% and 35%, respectively, resulting in a savings of 10 MMgal of water and 2.6 MMlbm of proppant.

Enhancing integrity, transparency

Ensuring wellbore integrity using cement technologies that reduce incidents of surface casing pressure (SCP) is another important way companies are reducing environmental impact. For example, the FUTUR self-healing cement system works from the time the cement is placed until the end of a well’s life, including abandonment. The technology, which has had long-term success in operations globally, repairs cracks and restores the cement sheath within hours, eliminating the need for a well intervention.

Flexible expanding cement, which expands after setting to improve bonding and block hydrocarbon migration, reduces the risk of annular pressure buildup. Cement evaluation services use new-generation sonic logging tools to evaluate any type of cement, providing accurate, real-time evaluation of the cement job and a wide range of casing conditions.

Alongside such innovations are continued efforts to enhance the safety of chemicals being used in fracturing operations with the objective of making wells perform better in an environmentally responsible manner. Schlumberger’s portfolio of environmentally safe additives can be used in slick water, gel, and crosslinking. By making transparency a priority operators receive a level of disclosure on par with that used in the food industry. The use of new, safer additives delivers a triple benefit to customers by ensuring efficacy of the products, a reduced environmental footprint, and improved cost-effectiveness by giving operators cleaner alternatives.

Gas-blending technology substitutes the diesel typically used in traditional combustion engines with natural gas in the form of compressed natural gas or LNG, reducing diesel consumption by 50% to 60%. In addition to fuel cost savings, there has been a significant reduction in regulated emissions when compared to a Tier-2 diesel engine. Continuing development of the natural gas delivery infrastructure will ensure the future viability of this technology.

The oil and gas industry’s ability to continue developing unconventional resources to meet ever-increasing global demand requires an ongoing, proactive commitment to environmental stewardship. By reducing water and prop-pant, using alternative fuels to power operations, ensuring the long-term viability of cement, and continually adjusting the chemical additives used in hydraulic fracturing operations, innovative technologies can help the industry do more with less by improving production while reducing the environmental impact.

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