Is It Going To Be Fracking?

Naturally Fractured…

Despite the unconventional geology currently targeted by Angus Energy, the company describes itself as a ‘conventional’ oil & gas company at every opportunity, and re-iterates that there will be no hydraulic fracturing because the Kimmeridge is naturally fractured.

However, in his expert commentary on Brockham, David Smythe – Emeritus Professor of Geophysics in the University of Glasgow – points out that the natural fractures (which are visible in the outcrop at the Kimmeridge Bay) are vertical, so it is difficult to see how lateral drainage (from a near vertical well) of the reservoir can be achieved. Elsewhere, Prof Smythe notes that, prior to the Horse Hill discovery in 2016, some 55 or so wells had been already drilled through the Kimmeridge in the wider Wealden area, and that none of them had free-flowing oil anywhere in the Kimmerigian layers.

From another expert source, we understand that it is not possible to conclude that a naturally fractured reservoir will flow oil based only on borehole imaging. The fractures might be closed due to overburden pressure, or they might not be connected enough to enable flow of oil. No tests have been done yet on the Kimmeridge at Brockham. Angus continues to tout the Horse Hill (nick-named the Gatwick Gusher) reportedly successful test flow rates, but forgets to mention the disappointing results at Broadford Bridge in Q4 2017/Q1 2018, where UKOG concluded that the Kimmeridge “appears to be unproductive due to low reservoir permeability” and that new completion and other reservoir stimulation techniques will need to be considered on future wells. In any case, even if an unconventional reservoir is naturally fractured, it will still require the drilling of back-to-back wells in order to drain the fractures efficiently, and it will likely require acid stimulation.

The original interviews are here and here

Acid Stimulation

Acid stimulation* can be described as a type of fracking performed on limestone or sandstone-rich shale that dissolves the rock enlarging or creating new fractures. We believe that this is the process Angus Energy’s MD, Paul Vonk, describes in this podcast talking about the plans at Brockham (from c.4 to 5 min).

Acid stimulation, which the industry sometimes refers to as an “acid squeeze”, includes matrix acidising (fluid pumped below formation fracture pressure) and acid fracking (fluid pumped above formation fracture pressure). It uses less water than high volume hydraulic fracturing, but because it’s an acid-based method, the concentrations of acid and other chemicals are higher. In addition to high strength hydrochloric or hydrofluoric acids (used on limestone and sandstone respectively), other chemicals are added, similar to those used in the hydraulic fracturing process.

Unlike hydraulic fracturing, acid stimulation has not been researched widely, but the available studies, as well as common sense, suggest that the expected risks of this process are the same as of hydraulic fracturing: risk of pollution to groundwater, surface water and air, stress on water supplies, toxic and potentially radioactive wastewater, and industrialisation from drilling multiple wells in close intervals, both in space and time. (1,2)

* Acid stimulation should not be confused with acid wash – decades-old and widely used method of cleaning of the wellbore by circulating small volumes of acid in the wellbore (but not pumping it under pressure into the formation).

Legislative & Regulatory Framework

Unfortunately, acid stimulation, like hydraulic fracturing that doesn’t meet the arbitrary thresholds of injected fluid volume set out in the Infrastructure Act 2015, is exempt from the Government definition of associated hydraulic fracturing, and from the regulations introduced by the IA2015.

The Environment Agency (EA) clarified how they view acid stimulation only in January 2018. It is a welcome step; however, there is no meaningful regulation behind it, the de minimis exclusion criteria are unclear. No guidance has been provided so we don’t know whether there any common rules on de minimis that the EA is applying, or whether each local permitting team is using its own criteria. The operators are not required to provide detailed acid injection plans or notice either to regulators or the local community about when these procedures are taking place.  The EA’s monitoring is limited to site visits (frequency varies greatly from site to site) and on-site document check. We believe that this is not adequate to effectively monitor acid injections and ensure that only operations that are permitted within the scope of permit are actually performed.

Specifically at Brockham and other sites in Surrey, Surrey County Council (the relevant Minerals Planning Authority) operate according to an outdated Minerals Local Plan that doesn’t include any specific policies for unconventional hydrocarbons. SCC has never seen hydrocarbon extraction as a serious issue and so it operates well behind the curve.  The MLP concentrates on minerals extraction (i.e. the sand, gravel, chalk and bentonite industries).

Regulation Elsewhere

For comparison, in California all acid-based stimulation is regulated within the state’s fracking regulations (in the same way as hydraulic fracturing) that follow the framework set out in Senate Bill No. 4 of 2013. Regulations require both a notice to the regulator and to people living in the vicinity of the oil/gas well so they can arrange pre and post testing of water quality in their water wells.

In Florida, a bill seeking to ban all types of fracking, “including hydraulic fracking, acid fracking and matrix-acidizing” is currently going through the state legislature.



(1) Abdullah, K. (2016). Acidizing Oil Wells, a Sister-Technology to Hydraulic Fracturing: Risks, Chemicals, and Regulations. UCLA.
(2) Toxicity of acidization fluids used in California oil exploration, Khadeeja Abdullah, Toxicological & Environmental Chemistry Vol. 99, Iss. 1, 2017


Weekend Long Read: Campaigners call for tougher rules on acid use at Weald oil sites
In-depth post on acidising by Kathryn McWhirter on Drill or Drop
Conservancy of South-West Florida: ADDRESSING OUTDATED OIL AND GAS LAWS
Weald Action Group Leaflet
Could fracking creep under the radar? David Smythe & Stuart Haszeldine, Nature, Aug 2017
What’s in a name: The risks from re-defining fracking, Stuart Gilfillan and Stuart Haszeldine, Energy & Carbon Blog, April 2016
New York Times: Unlikely Battle Over Fracking Intensifies in Florida