Development of shale gas has changed the dynamics of gas markets in the US, and shales may also become a major source of gas in other parts of the world.
Only a few years ago various forecasts said the US would need to import considerable amounts of gas as LNG, but with the development of shale gas, the US now is becoming self-sufficient in gas and may even become a gas exporter.
Enabling technologies
Several technologies have accounted for the explosive growth in shale gas in the last few years although production of gas from shales has occurred for many years with the first production in the 1820s, according to George E. King, Apache Corp. in the paper "Thirty Years of Gas Shale Fracturing What Have We Learned" presented on Sept. 20 at the Society of Petroleum Engineers Annual Technical Conference and Exhibition in Florence, Italy.
King attributed this production growth to such technologies as slickwater fracturing with few additives, horizontal wells that have largely replaced vertical wells, 10-20 or more fracturing stages that have increased fracture contact with the formation, and simultaneous or sequential fracturing that uses real-time stress changes created by fracs in an offset well to divert fractures in an adjacent well into nonstimulated zones.
These technologies have allowed recovery of gas from shale to increase in some cases to about 50% of the gas in place from the 2% believed recoverable a decade ago, although current typical ultimate recovers are in the 15-35% range, according to King.
Development of these technologies such as horizontal wells, multistage fracturing, and slickwater fracturing dates back to work in the 1970s through the 1990s by a loose alliance of the US Department of Energy, the Gas Research Institute, and numerous operators in the Devonian shales of eastern US, King said. But he added that the technologies did not catch on with shale gas operators until the technologies were refined, enlarged in scope, and applied in the Barnett shale of north-central Texas.
King notes that operators usually drill the new horizontals transverse to the fracture direction with toe lengths of about 2,500 ft to more than 5,000 ft. These horizontals are then either cased and cemented or isolated with packers to enable multistage fracturing.
In addition to these technologies, King lists six other technologies that are beginning to improve or if further developed may improve gas recovery from shales and make the operations more environmentally friendly.
First is the use of a host of technologies that allow operators to obtain more critical information. These technologies include 3D seismic, geologic mapping, cores, petrophysical studies, openhole logs, diagnostic fracture injection tests, fluid efficiency tests, microseismic, tracers, stimulation behavior analysis, flowback information, and production response analysis.
Second is the use of more than 20 fracture stages to increase fracture-to-shale contact area.
Third is to enhance and stabilize production by improving the development, placement, and longevity of small fractures such as fissures, microcracks, or opened laminations.
Fourth is the use of a hybrid fluid in cases where slickwater does not provide sufficient flow capacity. The hybrid fluid job entails opening the fissures with slickwater and then placing a more viscous fluid with proppants in the fissures.
Fifth are the evolving shale gas production techniques for keeping wells from loading up with produced or condensed water.
Last on his list are methods for treating and reusing flowback water as well as using higher salinity water for fracturing. This would reduce freshwater use and water disposal costs.
Transferring the technology
The technology developed for producing gas from shales in the US has started to be transferred to various parts of the world that have potential for shale gas production such as China, India, Poland, Sweden, Germany, France, North Africa, and many others. Canada already has sizable shale gas production.
Although these technologies may allow gas from shales to be produced, there remain issues such as government policies, land access, and environmental considerations that need to be addressed before many of these countries will realize substantial gas production from shales.
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