UK: UKOG reports aggregate flow rate of the Horse Hill-1 oil discovery likely the highest of any UK onshore new field discovery well
21 Mar 2016
UK Oil & Gas Investments (UKOG) has announced that Horse Hill Developments Ltd ('HHDL') has informed the Company that the final Horse Hill 1 ('HH-1') Portland test flowed at a stable dry oil rate of 323 barrels of oil per day ('bopd'), double the previously reported rate. The final total aggregate stable dry oil flow rate from two Kimmeridge limestones plus the overlying Portland sandstone stands at 1688 bopd. Over the 30-90 hour flow periods from each of the 3 zones, no clear indication of any reservoir pressure depletion was observed. Further analysis of data is ongoing and will be reported shortly.
Given these exceptional results, the Company has commissioned Nutech to investigate a possible upgrade to the oil in place ('OIP') calculated within all 3 test zones together with engineering studies to examine possible flow rates from a horizontal well. Reservoir engineering analyses by Nutech and Xodus are also underway, and will likely result in an estimation of potential recoverable volumes. Results of these studies will be reported shortly.
Preparation is now underway to obtain regulatory permissions to conduct extended production tests from all 3 zones at the site, followed by a horizontal sidetrack in the Kimmeridge and a possible new Portland development well.
Flow Test Highlights
- The final Portland test of 323 bopd, over an 8.5-hour, period is the highest stable dry oil flow rate from any onshore UK Portland well. On further testing, with a larger pump, the rate doubled from the previously reported stable dry oil rate of 168 bopd. The Portland was produced at maximum pump capacity and showed no clear indication of depletion. It is likely that the rate can be further increased using a higher capacity downhole pump during the next planned test.
- Proof that the Kimmeridge limestones contain significant volumes of moveable light oil that can be flowed to surface at commercial rates
- As previously reported, the stable, natural dry-oil flow rate of 464 bopd from the Lower Kimmeridge Limestone is the first ever flow from this rock unit in the Weald Basin and onshore UK
- Based on the analysis of published reports from all significant UK onshore discovery wells, the Company concludes that the well's 1688 bopd is likely the highest aggregate stable dry-oil flow from any onshore UK new field wildcat discovery well
- Based on the analysis of published reports from all significant UK onshore discovery wells, the Company concludes that the 901 bopd from the Upper Kimmeridge zone is likely the highest stable natural dry oil flow rate from a single reservoir in any UK onshore new field wildcat discovery well
- High quality Brent Crude produced: light, sweet oil (40 degrees API in Kimmeridge, 35-37 degrees API in Portland) 1,940 barrels delivered to the Esso Fawley refinery
- Preliminary analysis confirms that the Lower and Upper Kimmeridge Limestone units are naturally fractured reservoirs with high deliverability
- Strong possibility for further optimisation and increased flow rates from all 3 zones in future development and production wells, particularly through the use of horizontal wells
Summary Table of Test Results
Final Portland Flow Test
As previously reported, the first Portland test period gave a stable dry oil rate of 168 bopd over 9 hours. Further periods of flow using the same pump, re-seated immediately above the perforated zone, resulted in a similar stable dry oil flow over a two-day period. It was apparent that the rate was limited by the 7-ft stroke capacity of the pump. A larger 26-ft stroke pump was installed resulting in a maximum rate in excess of 360 bopd and an average stable rate of 323 bopd over 8.5 hours. This flow rate was still limited by pump capacity. During pumping, annulus fluid levels did not drop appreciably, implying little pressure depletion.
HH-1 Overview and Recap
The HH-1 discovery well, completed in November 2014, was the first modern well since the 1980s to test the entire Jurassic and Triassic section of the Weald Basin, reaching Palaeozoic basement at circa 8500 feet. The well was drilled with oil-based mud to ensure good electric log data collection. A comprehensive suite of modern Schlumberger log data, including magnetic resonance data, was acquired. Geological samples were collected at 10 ft intervals throughout the well specifically for geochemical analysis.
The analysis of thermal maturity data (vitrinite reflectance) from geological samples, by a leading analyst in Switzerland, showed that the Kimmeridge section of the well was within the peak oil generative window. Previous researchers had stated that the Kimmeridge was thermally immature, and whilst recognised to be the time equivalent of the North Sea's main oil source rock, had likely only generated either early stage immoveable bitumen or minor quantities of moveable oil, as seen in the Upper Kimmeridge Limestone in Balcombe-1, 15 km to the south of HH-1.
As previously announced, geochemical analysis of samples throughout the c. 1300 ft thick Kimmeridge shale section of HH-1, showed that the shales comprised a world class oil source rock. Analysis of 277 samples showed 780 ft of drilled section exceeding 2% total organic carbon ("TOC") by weight, with an average of 4.1% TOC. The richest section, and possible sweet-spot, lay between the Upper and Lower Kimmeridge Limestones with an average of 5% TOC and a high of 9.4% TOC. The organic shales demonstrated high oil generative potentials ranging from an average of 35 kg/tonne to a high of 103 kg/tonne and with high Hydrogen Indices ("HI") averaging 754. Further significant potential source rock sections were identified in the Middle Jurassic and Lias sections of the well.
Both Nutech and Schlumberger, leaders in the field of electric log analysis in rocks with low permeabilities, were then engaged to investigate the presence of oil in the HH-1 well. The Company reported the results during 2015, which indicated that a mean estimated total of between 9.97 and 10.99 billion barrels of OIP, or oil in the ground, existed under the HH-1 licence area, contained in shales and limestones of the Kimmeridge, Oxford Clay and Lias.
As previously stated by the Company, it is emphasised that the above estimated OIP volumes should not be construed as recoverable resources, contingent or prospective resources.
The Kimmeridge flow test programme was designed to test the concept that significant moveable oil had been generated within the Kimmeridge shales and had migrated directly into the more permeable and porous, naturally fractured limestones. Some degree of oil generation from thin interbedded organic rich layers within the limestones was also predicted. The limestones were also targeted for their suitability for conventional well stimulation methods to help improve flow. The use of massive fracking in the Kimmeridge is currently prohibited by UK law as the formation in HH-1 is shallower than the UK government's 1000 metre (~3300 ft) massive-fracking ceiling.
Both Nutech's and in-house petrophysical analyses demonstrated that a conventional oil accumulation lay within the Upper Portland sandstone of the HH-1 well. Xodus calculated an estimated P50 OIP of 21 million barrels for the accumulation. Electric log analysis showed that the well had circa 100 feet of gross pay with water saturations often exceeding 50%. The flow test results of 100% dry oil thus require the log evaluation to be revisited and to review a possible upgrade to the OIP. Xodus will integrate this with the available flow test analyses to derive recoverable Portland resources. This will be reported in due course.
Stephen Sanderson, UKOG's Executive Chairman, commented:
'The flow test results are outstanding, demonstrating North Sea-like oil rates from an onshore well. This simple vertical well has achieved an impressive aggregate oil rate equivalent to 8.5% of total UK onshore daily oil production. The Portland also has greater flow potential as rates were limited by the test pump's maximum capacity. Further significant flow rate improvements may be achieved from all zones using horizontal sidetracks during future planned operations.
These results also cause us to rethink and recalibrate many prior geological assumptions. Nutech will now reinvestigate the presence of significant natural fracturing and oil in place figures for both the Portland and Kimmeridge units given that all flow periods produced 100% dry oil.
Most importantly, this well has proven that the new Kimmeridge oil play is a reality within our Licence interests. Whilst there is still much work to be done, this test has moved the project into a potential commercial reality. The Horse Hill licence owners remain committed to ensuring that any resultant future commercial operations will respect the rural beauty of the Weald basin and the way of life of local residents.
In a wider sense, whilst it is absolutely correct for us all to press for low cost, renewable sources of electrical energy, we must be mindful that oil fills a very different strategic role. Oil is not used for electrical power generation but fuels all transport and the manufacture of essential everyday products, such as plastics and pharmaceuticals. Oil provides the vital feedstock for components that are essential for all industrial sectors. We are delighted, therefore, that this discovery has the serious prospect of being a meaningful addition to the UK's own supply of oil in a period where North Sea production is declining more rapidly than expected.'
Horse Hill-1 Discovery Well Location and Licence
The well is located within onshore exploration Licence PEDL137, on the northern side of the Weald Basin near Gatwick Airport. UKOG owns a 19.968% interest in PEDL137.