Hydraulic Fracturing Production technology for difficult and complex reservoirs
Hydraulic fracturing is the key technology for producing natural gas from difficult and complex reservoirs. Wintershall has been using this process for 30 years on conventional tight gas reservoirs, working according to the highest environmental and safety standards. In Germany, we are planning to tap a tight gas reservoir (Düste Z10) in Lower Saxony using the hydraulic fracturing technology. In Argentina we started our first shale gas production on the Aguada Federal block in 2015.
Developing conventional tight gas reservoirs with experience and knowledge.
Natural gas from relatively impermeable reservoirs
Most of the natural gas produced to date is located in conventional reservoirs in suitably porous rocks. The gas flows to the well without requiring any further technological intervention. In tight gas reservoirs the natural gas is located in the pore spaces of relatively impermeable sandstone strata, where it has to be 'mobilized' before it can be extracted. This is where hydraulic fracturing is used: millimetre-thin flow paths, known as fractures, are created in the reservoir using water pressure.
Above ground on the well site Hydraulic fracturing equipment
The hydraulic fracturing process typically lasts just a few days, in addition to the preparatory and follow-up measures. The well site changes completely in appearance during this time. In our 3-D tour you can find out more about the equipment modules used and the role they play.
Underground in the reservoir Hydraulic fracturing creates new flow paths
In hydraulic fracturing, millimetre-thin flow paths known as fractures (fracs) are created in the reservoir with pinpoint accuracy using water pressure. To ensure that the artificially created flow paths remain permanently open, filling materials (proppants) are used, such as ceramic beads or sand.
The filling materials are distributed in the flow paths so that the natural gas can flow more easily to the well over an enlarged contact surface. Usually several fracs are applied one after the other, both in vertical and horizontal wells. In Wintershall's Düste Z10 tight gas project, for example, seven fracs are planned in a vertical well.
The hydraulic fracturing technique is not new, but has been constantly developed further: during the past six decades, this method has been carried out in more than one million wells worldwide.
Hydraulic fracturing process
With the so-called multi-frac method, multiple fractures are created one after the other. In principle, multiple fractures can be carried out in both a vertical and a horizontal well along the length of the well running into the reservoir. In Wintershall's Düste Z10 well it is planned to apply seven fracs vertically from the bottom upwards.
Filling materials and their function
Filling materials (proppants) ensure that the created flow paths remain open. Sand or small ceramic spheres are examples of filling materials that are added to the water. Chemical additives are required to enable the proppants to be carried into the fractures. They thicken the fluid and enable it to transport the filling material evenly through the flow paths. Without a carrying fluid, the filling material would immediately sink to the deepest point of the well and block the wellbore. In the Düste Z10 project, the proportion of filling material amounts to around 20 percent.
Chemical additives and their function Overview of the most important additives (based on the example of the planned Düste Z10 tight gas project):
- Gels (polysaccharides): Gels make the water more viscous and ensure that filling material such as small ceramic spheres stay suspended instead of just sinking to the bottom.
- Gel breakers (oxidation agents, enzymes): return the water to a more liquid state so that the fracturing fluid can be pumped back more easily from a certain point.
- Biocides: prevent harmful bacteria from forming and breaking down the gels, as this would otherwise impair the carrying ability of the fracturing fluid.
- Friction reducers: reduce friction between the fracturing fluid and the steel of the production string.
- Surfactants (tensides): change the surface tension and prepare the rock for the fracturing process. (Example: water without soap has a high surface tension, water with soap has a low surface tension).
- Salt (potassium chloride): turns the carrier fluid into a brine that prevents the clays in the reservoir from swelling.
The planned fracturing fluid is classified with water hazard classification level 1 (= slightly hazardous to water) and is not subject to specific labelling requirements according to the legislation on chemicals.
None of the individual substances are environmentally hazardous or toxic. Wintershall is also strongly committed to the further development of environmentally friendly substances.
Composition of Hydraulic fracturing fluid Using the example of Düste Z10
Safety from the Christmas tree to the reservoir The wellbore: Safely protecting the groundwater at all depths
Wintershall uses a range of safety measures to protect the useable groundwater in the proximity of the well. For example, a reliable safety barrier around the wellbore protects the groundwater-bearing rocks against any gas or fluid which may escape. The multiple concentric steel casings in the wellbore are filled with special cement, providing a total steel thickness of around 35 centimetres in the area of the groundwater. All pipes in the wellbore have to successfully pass a pressure test. Pressure sensors are installed in and around the well to continually check the pressure in the production tubing and the annular spaces. The pressure in the annular spaces of the pipes is therefore continuously monitored during the fracking process via a monitoring system.
THE CHRISTMAS TREE
A “Christmas tree” safely seals off the wellbore at the surface. It is firmly connected to the well casing strings using a wellhead. It is fitted with numerous valves and pressure gauges to monitor the production of natural gas and feed it into the pipeline.
Before drilling begins, a conductor casing is driven into the ground until it has passed the last layer of freshwater-bearing rock. During drilling the well is sealed with steel pipes that are cemented into place section by section. Around 900 tons of steel and 300 m3 of cement are used for a natural gas well measuring 4,500 metres in depth.
IMPERMEABLE SAFETY BARRIER
The casing process is carried out in stages by interconnecting a series of pipes. The gaps between the pipes are filled with special cement, creating an impermeable barrier between the well and the rock.
THE SAFETY VALVE
A self-sealing safety valve is installed underground at a depth of around 50 metres. During normal operation the valve is kept open by a hydraulic pressure valve. If the pressure drops, it will close automatically.
PROTECTING THE GROUNDWATER
The outer casing reaches approx. 10 metres deeper than the last layer of freshwater-bearing rock. In this area, a total of 5 concentric steel pipes are cemented in place. The usable groundwater is therefore safely protected against natural gas and fracturing fluids.
The cap rock Natural geological barriers
Situated between the reservoir from where the gas is extracted and the groundwater is the cap rock. In tight gas reservoirs it is usually several thousands of metres in depth and in the case of Wintershall's Düste Z10 project it extends to almost 4,000 metres in depth. This thick, impermeable cap rock, which consists of shale, rock salt or other dense rock formations, serves as a natural seal, ensuring that neither gas nor fracturing fluids can rise up to the usable groundwater.
Natural gas reservoirs cannot exist without impermeable cap rock
Oil and gas reservoirs have been able to form only if an impenetrable geological barrier exists above the reservoir. Over the course of millions of years, natural gas continually migrates upwards from the mother rock in which it is formed. However, if it encounters impermeable rock formations, such as dense salt, it cannot rise upwards any further. It therefore accumulates in the rock pores beneath the dense formation - a reservoir for hydrocarbons is therefore created.
Conventional versus unconventional reservoirs The difference
|Property||Ideal reservoir (conventional)||Tight gas (conventional)||Shale gas (unconventional)|
|Gas:||In the pore space (reservoir rock)||In the pore space (reservoir rock)||In the source rock|
|Permeability:||Good – very good||Moderate||Poor (like concrete)|
|Cap rock:||Necessary||Necessary||NOT necessary|
|Production:||Free flowing||Uneconomic without hydraulic fracturing||No production without hydraulic fracturing|
|Experience:||> 60 years||> 30 years||Still none in Germany|
“Düste Z10” tight gas project Tight gas from 4,000 metres below ground
Wintershall is investigating a new natural gas reservoir near Barnstorf in Lower Saxony (Germany) with the Düste Z10 project. The 'Düste Carboniferous' tight gas reservoir is located at a depth of 4,000 metres. An estimated ten billion cubic metres of recoverable natural gas are situated there in the particularly dense sandstone. As part of the Z10 project, Wintershall has already drilled an initial well into the conventional reservoir. The next step will include a production test that will contain hydraulic fracturing measures. This presupposes, however, that there is a legally effective statutory framework for hydraulic fracturing in Germany.
Ask the expert Tight gas expert Steffen Liermann in interview:
Tight gas production has long been part of our energy supply. The technology for producing tight gas, called hydraulic fracturing, has been in use worldwide for 50 years. In Germany, the extraction of tight gas from sandstone layers has also been tried and tested with great success, for example in Lower Saxony. Wintershall itself has been producing natural gas from tight gas reservoirs for many years - in the Netherlands, Russia, Argentina and Germany.
The topic of hydraulic fracturing is a very emotionally charged issue among the general public. This is mainly due to – admittedly false – images of burning water taps from the USA. Hydraulic fracturing must be viewed and treated very differently according to each reservoir. For example, the difference between shale gas and tight gas should not be confused. Although hydraulic fracturing is used for both types of reservoir, but it is used in very different ways. Hydraulic fracturing used in tight gas reservoirs has been a proven method for decades. Thanks to the geological and well site conditions it is absolutely safe.
The exploration of the Düste Carboniferous reservoir is currently one of Wintershall's most important projects relating to tight gas in Germany. For Wintershall as a company, it is also an important ticket to major international projects. This is because producing natural gas in Germany is becoming more difficult as well as technologically more demanding. It requires considerable technological expertise and caution. Domestic production brings a competitive advantage: in contrast to projects abroad, production in Germany involves working with the highest level of environmental standards on a daily basis, which sets a very high benchmark. Wintershall therefore sees great potential for the expertise it is gaining in Lower Saxony, particularly for developing new tight gas reservoirs. It is securing us access to energy sources worldwide.
The natural gas resources that exist in Germany are valuable and important for ensuring Germany's energy supply. From a social and political point of view, it would be very short sighted not to exploit all the possibilities for exploring and developing new natural gas reservoirs in Germany. Furthermore, every euro invested in Germany strengthens Germany as a centre for technology and also secure jobs. As Germany's largest producer of crude oil and natural gas with over 60 years of experience in domestic gas production, Wintershall therefore sees its responsibility in continuing to invest in Germany in future.
Do you have any more questions on hydraulic fracturing or tight gas? Contact us: deutschland[at]wintershall.com