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Cracking technical challenges
Technologies are helping to open up tight and shale gas, resources of natural gas trapped in rock 1,000 times less permeable than conventional gas reservoirs.
In many conventional gas reservoirs just a few vertical wells every 2.5 square kilometres (around one square mile) are enough to produce the natural gas resource available.
But tight and shale gas does not flow easily and is often spread over a much larger area than conventional gas so it is harder to access the gas.
Shell drills wells in different directions from a central location that penetrate the reservoir vertically, often in an S-shape. or horizontally. This limits the number of drilling locations – known as wells pads – on the surface.
Today, well pads can be spaced up to five kilometres (three miles) apart and can accommodate up to 50 wells or more each.
In Changbei we have drilled an extensive network of wells, stretching underground for lengths of up to two kilometres (1.2 miles). “Drilling in this way opens up a much greater area below the surface for gas extraction,” explains George Ling, Changbei General Manager. “We have increased potential production to ten times more than achieved through conventional techniques.”
We use mobile drilling units that we move between well pads. This avoids dismantling and reassembling drilling equipment for each pad, making the process quicker and saving resources.
Watch the animation to see how hydraulic fracturing technology safely unlocks tightly trapped gas and oil.
Opening up rock
When we have completed a well we need to coax the gas from the very tight rock. “We have massive quantities of gas here,” says Craig Schenk, Shell China Senior In-Field Well Engineer for Jinqiu and Fushun Projects. “But if you just drill through the rock it won’t flow naturally or extract enough gas to make the well economical.”
We pump fluids into the well to make fractures in the rock that allow the gas to flow. This takes place kilometres underground and at pressures high enough to create the fractures. The fluids consist mainly of water with a small percentage of chemical additives. These chemicals help to keep the pipes cool and prevent scale build-up.
Sand or ceramic particles are also pumped in with the fracturing fluid to keep the fractures open. Gas can still flow through the large pores of these solids. Ceramic particles are stronger than sand and are better suited to rock at greater depths and pressure. At our Pinedale site we reduced the average cost of fracturing by some 60% using a number of approaches that included replacing man-made ceramic particles with sand where appropriate.
During this process, we sometimes place a string of sensors in a nearby well to pick up the popping and creaking of the controlled opening of the rock deep underground. The sounds help us to map out the contours of the cracked rock.
We also lower temperature-sensitive fibre-optic strands to monitor the wells. Cooler zones show us where gas is flowing freely into the wells. This information allows us to adjust our operations and improve efficiency.
We line the wells with steel pipes and cement them in place from the surface to below the level of drinking water supplies. These barriers help to contain the fracturing fluid and, along with the depth at which we fracture, prevent the fluid from mingling with drinking water close to the surface.
Electricians working at Groundbirch, Canada.
During our operations we monitor the wells with pressure sensors to check that they are firmly sealed. We also monitor the fractures and the fluids, which helps us to make production as efficient as possible and protects the environment.
Hydraulic fracturing technology was developed in the 1940s and has been continuously improved. Shell has made the process more efficient by using advanced sensors to record what happens when we fracture the rock.
We use the latest software to map out fields below the surface and better target our fracturing. We have also improved efficiency by fracturing in stages, locating the spots where tight gas will flow.
In the USA nearly one million wells have been hydraulically fractured since the process was first introduced. However, as the oil and gas industry enters new areas, local communities are becoming concerned over production activities and fracturing in particular.
Studies by the US Environmental Protection Agency (EPA) and the Ground Water Protection Council have shown that the process is safe. A new study into fracturing has also been launched by the EPA
At Shell we have decades of experience with this technology and we continue to follow strict measures to protect drinking water supplies.