UK’s First Attempts in Unlocking Natural Gas from Unconventional Shales
By: Dr. Sau-Wai Wong
Tags: Energy, Climate Change, Induced Seismicity, Fracking, Natural Gas

UK’s First Attempts in Unlocking Natural Gas from Unconventional Shales

On last flight from UK (selfie)

We are about to cross the finish line of 2020. What a crazy year, to put it mildly. I evacuated from the UK on the last flight from Manchester at the end of March, just before America banned all travel from Europe/UK. The packers came just a day before and cleared my apartment though the shipment didn’t arrive in Houston till some 6 months later. COVID immobilized many things including container shipping across the Atlantic. Just 2 weeks prior, UK was grappling with the new pandemic. Prime Minister Boris Johnson was jovially urging the country to wash their hands while singing ‘happy birthday’ twice, which would apparently amount to the recommended 20 seconds of cleaning with soap and water to rid of the coronavirus. Mask wearing seemed foreign and a difficult concept for the western world to grasp or accept. I boarded the plane, comfortably seated donning a surgical mask and thought it was selfie-worthy.

Fracking at Preston New Road was coming to an end anyhow even before COVID was putting a brake on oil and gas activity.

Cuadrilla’s Preston New Road Frack Site (photo credit: C. Furlong/Getty Images)

A Groundbreaking Technology

Fracking is the unflattering nickname for hydraulic fracturing. The technology has been around for decades to stimulate and increase oil well productivity, but the hugely successful and more recent development relies on the coupling of hydraulic fracturing and horizontal well drilling. It involves injecting fluid at a high rate to fracture the rock formation more than 1.5 miles deep in the earth. Natural gas and even light oil can now flow from the ultra-tight shale rock to the wellbore via these fractures. The same injection process could also take place in other applications such as geothermal energy recovery and geological storage of carbon dioxide.

Literally and figuratively, it is groundbreaking technology. In 2019, USA became the world’s number 1 producer and net exporter of crude oil and petroleum products — a first in a long time. Excessive supply flooded the market and sunk the oil price to a destructively low level. The fracking success in USA drew disdain from the oil sheikhs and environmentalists alike, but for different reasons. While it hadn’t been a controversial technology until its recent success in shale gas/oil production, now everyone has an opinion about Fracking. It became a convenient target and scapegoat for the anti-Big Oil movement. Thousands of wells have been drilled and fracked in USA. As one who knows the technology well, it’d be remiss of me not to point out that, when designed, applied, and regulated properly, it is not a threat to the climate or environment. But of course, it has to do with the argument that all hydrocarbon has to be kept in the ground to cope with Climate Emergency and Fracking has enabled the extraction of more oil and gas which the world can’t afford to burn. Could that be simplistic and short-sighted? Natural gas is the cleanest hydrocarbon, the obvious affordable transitional fuel from coal while renewables are getting up to speed, and a potential feedstock for creating a hydrogen/ammonia economy with geological carbon storage.

The Prize

I flew across the pond and took up the challenge to lead the technical team for Cuadrilla Resources Limited at the beginning of 2019. Cuadrilla is a privately-owned exploration company with a focus on onshore hydrocarbon resources and at the forefront of unlocking the shale gas potential in the UK. In 2011, the first flow of shale gas was demonstrated at Preese Hall near Blackpool, in the Bowland Basin which is known to hold significant unconventional resources in north England. The appraisal operation was halted for several years due to a larger than expected seismicity during fracking injection. In 2018, at the Preston New Road (PNR) site, Cuadrilla continued the exploration and appraisal operation. Two horizontal wells were drilled. PNR-1z was the first to be fracked. It was the first-ever horizontal well stimulated with multiple fractures for unconventional shale gas production in western Europe. Unfortunately, seismicity issues and downhole hardware problems put the operation on hold and a decision was made to move the fracking operation to the second well, PNR-2, with the option of coming back to complete PNR-1z at a later time.

According to the British Geological Survey (BGS), gas-in-place in the Carboniferous Bowland-Hodder rock formation holds roughly 1000 to 2000 trillion cubic feet (tcf). To put in perspective, the total gas consumption in 2018 in the UK was less than 3 tcf. The UK is blessed with not just the Bowland, but also other potentially viable unconventional shales — the Carboniferous Midland Valley in Scotland, the Jurassic shales in the Wessex area and the Weald Basin in southern England. Of course, not all gas-in-place can be technically and commercially produced to surface, perhaps only less than 10% of that is technically feasible with fracking technology.

The thought of leading the technical team to deliver the shale gas production from horizontal wells successfully and safely was exciting. My mind was made up after meeting Cuadrilla’s leadership team and board members. These were dedicated professionals whom I could work with and I was not disappointed. The technical team was a group of highly skilled and committed engineers and geoscientists. To my delight, it’s one of the best teams I have ever managed. We had high hopes and were determined to see the success of PNR-2. The company believes natural gas from shale formation would contribute to Net Zero and the country’s economy.

Seismicity

The operation at PNR site went to great lengths to protect the environment and ensure safety. Wellbore integrity is regularly checked. All emissions into the atmosphere were monitored, measured and reported. The pumping equipment were walled off with noise-reducing acoustic panels. Groundwater boreholes were installed and monitored for contamination. The entire well site surface was protected with impermeable geomembrane and gravel. Any discharge, spill and even rainfall onto the site would be collected and taken off site for proper disposal. Not a trivial task at all considering the rainy locale of Lancashire.

As with any injection process, the resultant microscopic rock movement can be picked up with sensitive downhole geophones, surface seismometers and vibration accelerometers. They were installed to provide real-time information to guide the operation. The observed micro-seismic events provided an indication of the spatial extent of fracture growth, and if fluid migration were to be interpreted outside of a permitted boundary, injection would be terminated. It is well known that if the injected fluid intersects a sizeable natural fault, it can lubricate and promote fault slippage, and may create a larger than expected rock movement or induced seismicity. The installed instrumentation helped to manage and regulate these phenomena. The regulating system used is called the Traffic Light System (TLS) in the UK or Traffic Light Protocol (TLP) in some countries. It specifies a threshold value above which actions must be taken, such as reducing the injection rate/volume or modifying the injection profile; and the injection is stopped altogether if the predefined red-light threshold is exceeded.

Different countries impose different TLS thresholds. UK’s TLS of 0.5 magnitude for red-light is the most stringent of any jurisdiction. The Richter scale for measuring seismicity is logarithmic. TLS of 2.9 magnitude for red-light threshold in Switzerland is about 250 times greater than 0.5 magnitude in terms of amplitudes and 4000 times larger in terms of energy release. In any case, the country experiences more than 200 tremors of 0.5 magnitude or larger every year, according to BGS’ database.

Comparing TLS red-light threshold for different countries

The headline news was unfortunately a felt seismicity of 2.9 magnitude which occurred late August 2019 while no fluid injection was taking place. The formal Hydraulic Fracture Plan estimated a worst-case and unlikely upper bound seismicity of 3.1. But 2.9 was nevertheless a surprise and PNR-2 fracking operation was discontinued. Soon after, a moratorium on fracking was imposed. No correlation has yet been identified between pumping operations, micro-seismicity during pumping and post-pumping events.

Prediction of earthquakes or seismic events, whether naturally occurring or induced is not an exact science and a subject of on-going research. The Traffic Light System assumes that large induced seismicity of a critical strength can be revealed and forecasted by preceding events of smaller strength and that the large critical seismic event can be prevented by modifying or stopping the injection. Evidently, the relatively large seismicity of 2.9 magnitude at PNR-2 occurred when injection has stopped and without sufficient precursors.

Energy Transition

PNR operations persisted despite technical/operational challenges and protests from environmental activists. We succeeded in flowing PNR-2 to produce high-quality natural gas, albeit at a low rate because of incomplete fracture stimulation operation. The experience of PNR wells cast a significant question mark over the design basis of the Traffic Light System. Research papers on the subject are being published and no doubt, there’ll be many more to come. The UK Oil and Gas Authority still expects hydrocarbon to remain an important part of the Energy Mix in the transition to Net Zero carbon. Imported liquefied natural gas to the UK would have a carbon footprint of more than twice that of home-produced gas. As I eagerly await 2021 and my turn at receiving the COVID vaccine, I wonder if there’ll be a future for the country’s abundant onshore natural gas in Energy Transition.