31/5-7
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General information
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Wellbore history
GeneralWell 31/5-7 was drilled to test the Northern Light Carbon Capture and Storage (CCS) prospect between the Troll and Brage fields on the Horda Platform in the North Sea. The well is the first CCS well on the Norwegian Continental Shelf. The overall objective of the well was to investigate whether reservoir rocks in the Early Jurassic are suitable for storage of carbon dioxide (CO2). Specific aims were:· Confirm the ability to inject a minimum of 0.8 Mt/yr CO2.· Confirm Johansen and Cook Formations sandstones presence and with a sufficient reservoir quality for large scale injection purpose· Confirm Drake Formation sealing potential.· Additional well objectives were to collect data to meet requirements on overburden management and implementation of data into geomechanical models and leakage risk assessment.Operations and resultsWildcat well 31/5-7 was spudded with the semi-submersible installation West Hercules on 2 December 2019 and drilled to TD at 2915 m in the Early Jurassic (Hettangian age) Statfjord Group. Drilling operations proceeded without significant problems, but during drill stem testing issues with the Electrical Submersible pump (ESP) and further difficulties with landing the DST string caused 19 days of NPT. The well was drilled with seawater and hi-vis pills down to 931 m and with Glydril water-based mud 931 m to TD.The lower Drake Formation shale thickness is 75 m, and an extended leak-off test (XLOT) confirmed the sealing potential for the future CO2 injection. The underlying injection and storage units, Johansen, and Cook Formations, consist of high-quality sandstones with a total thickness of 173 m. Formation pressure data acquired on wire line show that the rocks over and under the Drake shale cap rock are not in communication and the pressure gradients indicate water in all Viking and Brent Group sands.No hydrocarbon indications were seen on the logs and no shows were seen on the cuttings and the gas levels were very low, below 1 % with gas peaks up to 2.3 %, throughout the upper part of the well. The gas levels were very low throughout the 8 1/2" section as well, between 0.2 and 1 %, without any significant gas peaks. No HC odour or stain was observed in the cores, very weak spotted dull yellow residual fluorescence was seen in core chips between 2907 m and 2765 m, most likely mineral fluorescence.Four cores were cut in the well. Core 1 was cut from 2592 to 2596 m (79.5% recovery) in the Drake Formation cap rock. Core 2 was cut from 2643 to 2697 m (98.9% recovery) in the Cook Formation sandstones. Cores 3 and 4 were cut from 2709 to 2783 m (95.4 and 94.2 % recovery, respectively) in the Johansen Formation sandstones. MDT fluid samples were taken at 2686.3 m in the Cook Formation and at 2743.5 m in the Johansen Formation. Analyses of water samples from both MDT and DST are available on DISKOS.Due to the planned later drilling of a side-track and further plans for CO2 injection, a template was pre-installed at location. The well was suspended on 6 March 2020 as a dry well.TestingOne drill stem test was performed from the interval 2697.5 to 2805 m in the Johansen Formation. A clean-up period of 12 hours was performed to clean the well and to find optimum surface setting for the following main flow. Both choke and ESP were increased in steps. The main flow period was 36 hours on a fixed 44/64” choke size. A corrected water flow rate of approximately 1000 m³/day was achieved. The corrected gas flow rate was around 600 m3/day. No barriers were observed during the test and the observation radius is calculated to between 2200 m to 3200 m. The temperature measured at the gauge depth at the end of the main flow has been extrapolated using Olga flow simulation software down to the top of the probably best producing interval assessed on logs. This gives a temperature of 110 °C at 2770 m. An extensive program for sampling of formation water was carried out. -
Cuttings at the Norwegian Offshore Directorate
Cuttings at the Norwegian Offshore Directorate Cuttings available for sampling?YESCuttings at the Norwegian Offshore Directorate Cutting sample, top depth [m]Cutting samples, bottom depth [m]940.002878.00 -
Cores at the Norwegian Offshore Directorate
Cores at the Norwegian Offshore Directorate Core sample numberCore sample - top depthCore sample - bottom depthCore sample depth - uom22643.02696.4[m ]32709.02744.3[m ]42747.02780.9[m ]Cores at the Norwegian Offshore Directorate Total core sample length [m]122.6Cores at the Norwegian Offshore Directorate Cores available for sampling?YES -
Lithostratigraphy
Lithostratigraphy Top depth [mMD RKB]Lithostrat. unit3383387727721144144214421530158016981698174117781778183818611892189219461957210421402278238224242424243524872510251026382695270228182832 -
Logs
Logs Log typeLog top depth [m]Log bottom depth [m]HRLA PEX18972585MWD - ARC TS411931MWD - ARC TS9311906MWD - GVR ARC TS25842915MWD - PD ARC TS9311906MWD - PD ECS TS SS411944MWD - PD OB ARC TS19062584MWD - TELE338411PEX MSIP931959XPT MSIP FMI9252585 -
Casing and leak–off tests
Casing and leak–off tests Casing typeCasing diam.
[inch]Casing depth
[m]Hole diam.
[inch]Hole depth
[m]LOT/FIT mud eqv.
[g/cm3]Formation test typeCONDUCTOR30407.036411.00.00SURF.COND.20925.026931.01.54LOTINTERM.13 5/81897.017 1/21906.01.57LOTLINER9 5/82583.012 1/42584.01.54LOTOPEN HOLE2915.08 1/22915.00.00