Optimising stimulation of U.K. shales with Geo Tool-Inject

4D Active Seismic of Fracture Network (5m barrels injected)
4D Active Seismic of Fracture Network (5m barrels injected)

The UK is looking enviously at the success of the U.S. shale industry (energy self-sufficiency, job creation, inward investment), but there are a number of important differences between the two countries. The UK has stricter rules on environmental permits, surface footprint, health and safety, well integrity, and induced seismicity. Ultimately these stricter rules will drive a safer and more environmentally sustainable industry, but they present significant challenges as the UK industry seeks to get off the ground.

The European Shale Gas and Oil Summit 2015 (Manchester 15-16, October) spoke to Dr Frederic Santarelli, Chief Technology Officer at Geomec Engineering AS, about their experience of fracturing shale formations using GeoTool-Inject, and about the Geomec project, sponsored by Innovate UK, under their ‘Developing technologies for safe and responsible exploitation of shale gas’ competition.

“Rocks do not follow corporate policy!” says Frederic. “Neither do they follow governmental policy. They react to what we do to them, and that reaction depends on a number of factors, including the composition of the rocks, their organic content, depth, temperature and the nature of the stresses that they are under.

“For example”, he continues, “it is very likely that if you inject at high rate and high pressure into a formation that is highly faulted, you will trigger microseismic events, as was seen at Preese Hall 1 and in many U.S. wells.”

Dr. Santarelli and his colleagues have used GeoTool-Inject to analyse and optimise several thousand injection cycles into shale in the North Sea, and their work for Innovate UK is allowing them to demonstrate that the traditional U.S. techniques for fracturing shales, simply won’t work in this country. Moreimportantly, the project is giving Geomec the platform to show that there are better alternatives – ones that will help operators to address the public’s concerns and achieve significantly better operating results in the UK’s thick shale formations.

U.S. methods rely on 20-40 pumping trucks lining up to achieve the high injection rates (100 – 200 barrels per minute) that allow formations containing natural fractures to be opened up. Unfortunately the rock formations that are targeted under the U.S. model (stiff rocks, with naturally occurring fractures) are precisely the kinds of formations that will experience micro-seismicity. In addition, traditional fracking techniques don’t really give operators visibility or control of the nature of the fracture network that is created.

Bear in mind also that in the U.S., the economy of a shale province is typically demonstrated only after drilling and testing about 500 wells. It doesn’t seem feasible that the UK will be able to sustain that kind of investment in the face of the public’s concerns about fracking.

Dr Santarelli believes that these kinds of challenges are in no way insurmountable:. “At Geomec,” he says, “we believe firmly in two things: firstly, that technical challenges can be solved and secondly, that if you pay careful attention to how the rocks are behaving then you can work with them rather than against them.”

Similar regulatory concerns about waste injection in the Norwegian Continental Shelf led to the creation of GeoTool-Inject, which allows operators to monitor and analyse their injection operations in real time. Geomec’s technology allows operators to demonstrate that their fractures are contained, and also to maximise the amount of waste that they can safely inject into each well.

GeoTool-Inject is now considered the best available technique for monitoring and analysing injection operations in the Norwegian Continental Shelf. Crucially, the key economic driver for success in waste injection (maximising volume of waste injected per volume of formation) is very similar to the key economic driver for success in shale stimulation (maximise the volume of connected fractures per volume of formation to unlock the hydrocarbons).

By using Geo Tool-Inject to monitor and analyse their operations on one of the largest NCS fields, ConocoPhillips have been able to create large, dense fracture networks (containing up to 5m barrels of injectate per well), while being able to demonstrate the complete confinement of the injection within the intended zone. 5m barrels is roughly 40x the amount of water that is injected in a typical U.S. well (5m gallons) – and all the fractures were created a-seismically, meaning that they were not picked up at all by the field’s permanent seismic monitoring system (Paper SPE 170851-MS).

Dr. Santarelli explains how a different technique was used for developing the fracture network. ”We injected just a couple of pumps at a high pressure but a low rate, over a larger number of injection cycles. By analysing the shale’s response, and by adjusting injection cycles to the reaction of the rock to previous cycles, we were able to work with the shale rather than against it. The shale swelling stress inhibits the growth of the primary fracture whilst thermal effects favour the creation of orthogonal secondary fractures in the wall of the primary fracture.”

This technique is significantly more reliable in creating fracture networks than classic U.S. approach, where 80% of the hydrocarbons come from 20% of the fracked intervals. It also allows fractures to be successfully developed in the high-clay-content shales which appear in many of the UK formations, which are, under the high-rate model, considered ‘un-frackable’. The low rates involved in Geomec’s methodology are much less likely to trigger microseismic events than high rate fracking. Finally, the use of two pumps instead of 20 to 40 is very appealing from a surface footprint perspective.

Geomec is now in discussions with operators and service companies in the U.S. to develop ‘pilot well’ scenarios and are using the Innovate UK project as an opportunity to build more IP into their core technology. For example, they’ve recently developed (patent pending) methods to measure the extent of a fracture network in real time – which is very exciting from a safety and environmental perspective. Dialogue has also begun with one of the U.S. regulators about how to establish whether or not injection is causally linked to some of the earthquakes that they have been experiencing, and how appropriate alarms could be designed for the operators.

“We’re excited about presenting some of our findings at the ESGOS event on 15th & 16th October in Manchester, and getting to know some of the UK operators!” says Dr. Santarelli, with eyes on the future.

This is a guest post from our partners at Charles Maxwell Events. Authors: Geomec and Josh Potts

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