Note: the first Horse Hill-1 flow test, located within an 83 ft perforated section of the Lower Kimmeridge Limestone, recorded stable and sustained natural flow rates in excess of 450 barrels per day over a three-day test period. The light, sweet, 40 degree API gravity oil that was recovered flowed to surface naturally without any artificial lift or pumping.
Flow testing is a key and normal part of evaluating the commercial development potential of a hydrocarbon discovery. Without it, the flow capacity of a reservoir can only be inferred from static well data. So, to more thoroughly evaluate any discovery well, it is necessary to equip the well to allow reservoir fluids to enter the wellbore and be safely conveyed to surface where they are metered, analysed and sampled.
The data recorded during flow testing of the Horse Hill-1 (“HH-1”) well will be used to help estimate the recoverable reserves potential of the Portland sandstone reservoir and to determine if oil can be flowed to surface from the Kimmeridge limestone tight oil play, from an unstimulated vertical well. The information will also be used to assess the most appropriate potential development scenarios for both the Portland sandstone and Kimmeridge limestones, particularly with respect to whether horizontal wells or stimulation may be required to achieve commercial flow rates.
In Horse Hill-1, the zones of interest lie behind a cemented casing. The objectives of the series of flow tests are to establish the flow capacity of the single Upper Portland sandstone layer and of two limestone layers (the Kimmeridge Micrites), and to recover oil samples. Each zone will be perforated to allow flow into the wellbore. Flow will pass up the well through a valve arrangement, known as a “Christmas tree”, then on into the flow testing equipment at the surface.
An extended flow test is planned and will consist of three separate flow tests: in the lower and upper Kimmeridge Micrites (limestones) and in the Upper Portland sandstone at depths of 900m, 840m and 615m below ground surface level respectively. The flow tests are designed to test oil lying within conventional limestone and sandstone rocks, not shale oil. Importantly, our objectives contain oil and do not have any free gas component in the subsurface.
Please note that the three Horse Hill-1 flow tests are all taking place above the current UK-wide ceiling of 1000m (3,300ft) below ground level, above which massive hydraulic fracturing (“fracking“) is not permitted by law. Therefore, the flow test zones cannot be fracked.
Note: hydraulic fracturing is currently defined by UK law (the Infrastructure Act 2015) as involving the total aggregate injection of more than 10,000 cubic metres (approximately 2.2 million Imperial gallons) of water into a rock formation at a pressure above the fracture gradient of that rock formation. This limit corresponds to the minimum injected fluid volume typically required to enable hydrocarbons to flow commercially from shale rocks.
A generic flow test configuration from a recent UK flow test is shown in Figures 1 and 2. It should be noted that this was not a UKOG flow test and the equipment used in UKOG’s HH-1 flow test may be different. Note also that the physical footprint and activity level of the testing period are both significantly less than during the drilling phase. Figure 3 shows a schematic of a typical flow testing equipment arrangement.
Oil and water will be transported from site via road tankers, to a trans-shipment point and to a licensed disposal site respectively. During each flow test a stable flow rate will be metered, sample reservoir fluids will be taken and then the well will be shut in to record pressure. The number of road tanker loads will be minimised during the flow test programme.
The amount of time to execute the entire flow testing programme is estimated at 30 days. This includes mobilisation, setting-up and removal of all related equipment from the well site. Heavy goods vehicle movements will be arranged to minimise road traffic.
Effective 31st December, 2015, the flow test has full regulatory consents from the Oil and Gas Authority, Health and Safety Executive and Environment Agency together with the existing planning permission from Surrey County Council. The flow testing will be conducted in strict accordance with the terms and conditions of the permits.
Figure 1: Layout in Recent UK Onshore Flow Test, View from Front
Figure 2: Layout in Recent UK Onshore Flow Test, View from Rear
Figure 3: Schematic of Typical Oil & Gas Flow Test
Flow Testing Update, February 2016
As announced on 16 February 2016, the first HH-1 interval to be flow tested, the Lower Kimmeridge limestone, flowed a steady rate of over 463 barrels of oil per day through a 32/64 in choke. The tested oil was sweet and light at 40 degrees API, and contained very little water.
As further announced on 17 February 2016, flow continued for a second day at a steady rate of over 456 barrels of oil per day, through a 28/64 in choke. No water was produced on the second day of flow testing the Lower Kimmeridge limestone. Further HH-1 flow tests will follow shortly.
The following photographs show activities at the HH-1 site during the flow testing programme.
Photos of the Flow Test operations can be found here.