What does fracking bring to oil and gas development?

China's complex and diversified oil reservoirs provide the soil for the progress of fracturing technology. PetroChina's oil and gas production and engineering service enterprises, based on the oilfields, have carried out fruitful research on fracturing technology, and formed distinctive fracturing technologies, which have provided technical guarantee for the increase of oil and gas reserves and production.

In Daqing Oilfield, the fracturing technology of dense and thin interlayer horizontal wells has pushed forward the sustained and stable production of 40 million tons of oil in Daqing Oilfield; in Changqing Oilfield, the large-scale application of the technologies of multi-stage fracturing of straight wells and segmental fracturing of horizontal wells has made it possible to eliminate the “three-low” oil and gas reservoirs, which are “oiled in wells and not flowing from the mouths”. “In Jilin Oilfield, the casing packer slip sleeve fracturing technology can be used to shoot open multiple layers at once, and more than 400 wells have been applied on-site. In Jilin Oilfield, the casing-in-sealer slip-jacket fracturing technology, which can shoot open multiple layers at one time, has been applied in more than 400 wells, and the partial pressure of HeiHping2 well has reached 15 segments, providing important technical support for the effective development and utilization of the Fuyang oil formation in Jilin Oilfield; in Tarim Oilfield, the industrialized fracturing technology of high-pressure dense sandstone gas in the ultra-deep layer of the Kuqa Depression of more than 7.000 meters has been born; and in the southwestern oil and gas field, the fracturing technology has promoted the effective development of the “three-high” reservoirs. In the southwest oil and gas fields, fracturing technology has promoted the effective development of “three high” oil and gas reservoirs.

From the first single-well fracturing construction in Yumen Oilfield in 1955 to the current large-scale horizontal well segmentation and volume fracturing construction; from conventional small-scale sand fracturing to today's platform-type multi-well factory fracturing; and from the single-well construction scale of “one hundred cubic meters of sand and one thousand cubic meters of liquid” to “one thousand cubic meters of sand and ten thousand cubic meters of liquid”, fracturing technology has been developed over a period of more than 50 years. “In more than 50 years, PetroChina's fracturing technology has realized great progress and revolutionary breakthroughs, and its growth path has been steady and fast.

Schematic diagram of segmental fracturing with packer slipcovers

Catching up: the test of technology research and development

Although China has made great progress in the key technologies such as direct well fracturing, horizontal well fracturing and other key technologies, there is still a certain gap compared with the international advanced level. This makes China's reservoir modification technology research and development and application a long way to go.

At present, the ultra-deep well fracturing of low-permeability dense sandstone reservoirs in China has exceeded 7.000 meters, and acid fracturing and hydraulic fracturing of carbonate reservoirs has exceeded 5.000 meters, with the construction pressure reaching 130 MPa, and the stratum temperature rising to 200 degrees Celsius, and the lower limit of the effectively utilized reserves extending, with the permeability of the reservoirs decreasing. The object of reservoir reforming is getting more and more complicated, which puts higher requirements on fracturing equipment, downhole tools, fracturing acidizing materials and so on. All these imply that reservoir remodeling technology needs to constantly challenge the limits.

Meanwhile, China's tight sandstone oil and gas has obvious characteristics of multiple thin layers, and the research idea and transformation mode of reservoir transformation technology needs to move from low permeability to tightness. This poses a new challenge to how to implement fracturing in small subdivided layers. Continuous tubing hydraulic injection fracturing technology has not yet become a mainstream technology in China, and segmental fracturing of multi-branch wells and multi-branch horizontal wells has just started.

Since waterless fracturing technology is still in the experimental stage in the world, most of the fracturing construction is large-scale hydraulic fracturing. According to the production practice in the U.S., shale gas fracturing requires more than 10.000 cubic meters of water for a single well, especially with the increase in the length of horizontal section and the number of fracturing stages, the water consumption increases dramatically in a short period of time. The high consumption of water resources and the impact on local aquatic life, fishing industry, and municipal and industrial water use make fracking a double-edged sword.

Because of this, some environmental organizations and government agencies have protested against the use of large-scale hydraulic fracturing to develop shale gas, and some European countries represented by France have even enacted laws prohibiting the use of large-scale fracturing to extract shale gas and canceled several shale gas projects.

In addition, compared with foreign countries, there is still much room for development in China in terms of low-cost and high-efficiency fracturing fluids and unrestricted selective fracturing tools. The number of fracturing stages in China is relatively small, while foreign countries have more than 50 stages.

Number of fracturing wells with more than 10 segments in PetroChina

Future: technology development is not on the conventional path

Where is the development direction of fracking technology? What kind of reservoir is more suitable for volumetric reforming technology? What level of reservoir modification should be achieved? What fluids and tools are more effective for fracturing? How to realize the win-win situation of fracturing effect and environmental protection? ...... The solution of each question will promote the progress of reservoir modification technology and the effective development of hard-to-use reservoirs and unconventional oil and gas resources.

The experience is worth learning from, and the concept needs to be innovated. Zou Talent believes that “there are many types of oil and gas reservoirs in China, with different lithology, thickness and water content, the fracturing technology is different. The development of fracking technology can't be completely copied from foreign models, but should be supported by its own unconventional ideas, unconventional technology and unconventional management.”

The innovation of theory and technology as well as the improvement of comprehensive system research and development capability are the primary problems that China's fracturing technology needs to be solved urgently at present. While drawing on advanced foreign technologies, we should systematically summarize the characteristics of domestic reservoir reforming technologies and research a fracturing technology system that is truly suitable for China's actual situation. “This requires major oil and gas production enterprises to further strengthen the combination with engineering and technology research units to realize joint planning, joint research and joint design. The enterprises should strengthen exchanges and cooperation among themselves to realize resource sharing, result sharing and benefit sharing.” Zhao Yerong, deputy general manager of the engineering technology branch, pointed out.

High-efficiency, low-cost and environment-friendly fracturing technology is an important development direction in the future. For example, high-speed channel fracturing, volumetric modification, waterless fracturing, platform-type multi-well factory fracturing and other technologies that have begun to be tested. Meanwhile, existing fracturing technologies such as continuous tubing fracturing and small borehole fracturing need to be developed and integrated, and fracturing fluid systems and supporting technologies for different rock characteristics should also be developed. Fracturing equipment should be developed in the direction of high power, modularization and miniaturization, which can not only reduce the number of equipment used, thus greatly reducing the land occupation area, but also facilitate the fracturing construction under complicated ground conditions. Fracturing tools should be developed in the direction of ultra-long horizontal segment fracturing tools and selective segment fracturing tools. Fracturing fluids should be developed in the direction of low cost, harmlessness and recyclability, so as to maximize the effect of fracturing while minimizing the impact on the environment.