Hydrocarbon Exploration and Production in the Wessex Basin Open University Field Trip To Wytch Farm and Kimmeridge 7th October 2016 Itinerary • 10.00 Godlingstone Look-out • 10.45 Pick up bus at Norden Park and Ride • 11.00 Gathering Station • 11.30 X-Site • 12.00 M/F-Site • 12.45 Norden Park and Ride • 13.30 Kimmeridge car park for lunch • 14.30 Kimmeridge Oil Field • 15.30 Oil Shale Extraction • 16.00 Finish 2 Safety Risks and Controls Insurance information - Each person attending a field meeting does so on the understanding that he/she attends at his/her own risk. The OUGS has Public Liability Insurance cover for field and indoor meetings but Personal Accident and Personal Liability cover remain the responsibility and personal choice of the participant. Field/Safety Equipment Needed: Sturdy and waterproof footwear, waterproof clothing. A hand lens. A geologist’s hammer is not required. Collecting bags can be useful too. Water in case it is hot. Transport and Driving Hazard: Cars and other vehicles, accidents Control: This is the highest risk. Keep aware at all times, Wear seatbelts No mobiles while driving Weather Hazard: cold, wind, sunshine, visibility Control: waterproofs, warm clothing, hat, suntan lotion, sunglasses, food/water Do not stray from the group Sea Hazard: falling in water, ’freak’ waves, cut-off by tides Control: Do not enter sea, care close to water, check tide timetables Rough Terrain, Cliffs Hazard: Steep ground, unstable and uneven surfaces, slippery rock, falling rocks Control Sturdy boots, trekking pole Take extra care near cliff edges (top and bottom) Industrial Sites Hazard: Machines, inflammable liquids, energy potential Control: Follow leaders instructions, stay with the group, no smoking, seatbelts Follow leader for emergency procedures if required Wildlife Hazard: Wasps, Adders, Ticks Control: Be aware. Alert the leader and do not touch, Wear long sleeves, care around bracken 3 7 2 8 3 1 4 5 6 1=Ladram Bay 2=Lyme Regis 3=West Bay 4=Langton Herring 5=Whiteways Hill 6=Kimmeridge 7=Wytch Farm 8=Godlingstone 4 Generalised stratigraphy of the Wessex Basin Alpine Orogeny R The Wessex Basin is a complex of fault bounded sub-basins initiated in the Cimmerian Unconformity Permian that underwent rift related subsidence throughout the Mesozoic. That is from around 260my S 6. Kimmeridge Clay S Kimmeridge to 70my. Basin subsidence R 4. Frome Clay Lst and sedimentation was R Langton Herring interrupted by the Alpine R 3. Bridport Sands orogeny at the end of the S Reservoir West Bay Cretaceous which caused 2. Lias source rocks basin inversion, reversing Lyme Regis the movement on pre- R 1. Sherwood Sst Reservoir existing intrabasinal faults. Ladram Bay After the Alpine Orogeny R more localised subsidence continued within the Tertiary Hampshire Basin. Variscan Orogeny Godlingstone look-out point – Locality 8 Arne Furzey Goathorn Brownsea Sandbanks Peninsular Island Peninsular Island and Studland Wytch Farm is set in a very environmentally sensitive area, and surface operations have been hidden in coniferous forests on Wytch Heath. In 1995,the field won The Queen's Award for Environmental Achievement and the field remains largely unnoticed by the general public. 6 Wytch Farm Reservoirs 7 Wytch Farm Production 120000 T47 rig Long Reach finishes Drilling 100000 80000 Discovery Sherwood of Sherwood Production 60000 Reservoir 1992 water cut 35% Perenco 40000 takes over Bridport BP operatorship Wytch Farm Production Production Operates ~16,825bbl/day 20000 in Oct 2016 Average Oil Production (bbl/day) 2009 water cut 93% 0 1975 1980 1985 1990 1995 2000 2005 2010 2015 Year • Discovered by British Gas 1973 & began Bridport production in 1979, Sherwood in 1989 • BG privatised & Wytch Farm sold to BP & bidding group in 1984. BP sold to Perenco in 2011 • Production peaked in 1997 at ~110,000 bopd. Reserves of 43 Mmbo remained in 2011 • By June 2012, 102 wells drilled from 13 wellsites with a combination of producers and injectors Structure of Wytch Farm Chalk Bridport Bridport Sherwood Sherwood 9 Wytch Farm 1998 3D Seismic Survey Example “Dip-Line” S 98/06-7 N Base Chalk Apto-Albian Unc. Corallian Cornbrash Inf. Oolite Rhaetic - Penarh Sherwood Locality 6 Kimmeridge Bay (SY 909 790) The Kimmeridge Clay which is upper Jurassic in age was deposited around 150 million years ago in a deep water environment. The sea bed was probably anoxic, that means without oxygen, so that there was very little life on the seafloor. The lack of oxygen reduced predation and helped to preserve organic matter in the fine grained muddy sediments. Marine plankton living in the sea included phytoplankton with organic walls and plankton with carbonate tests. The hard bands that stand out on the foreshore and in the cliff are limestones which include more carbonate plankton microfossils. Fossils found here include thin shelled bivalves and ammonites. The ammonites include Aulacostephanos and the smaller Amoeboceras. The bivalves include a small oyster called Liostrea; Lucina which is small, and Protocardia which is rounded with a faint rib pattern. Lucina Protocardia Aulacostephanos Amoeboceras serratum 11 DORset Integrated Seabed Map (DORIS) with Onshore Topography (Courtesy of Infrastrata) Wytch Farm Purbeck Monocline Purbeck Dorset Seabed Map with Basic Interpretation Purbeck Anticline Lulworth Banks Anticline Purbeck Anticline Regional Seismic Line Portland to Dorchester Base Gault Top Inferior Oolite Top Junction Bed Penarth Group Top Sherwood Base BSPB Base Aylesbeare Mudstone 1km 14 Licenses. Kimmeridge Oil Field Petroleum Production Act 1934 covering 2227 square miles2 in S.England. Mining licence ML5 in 1964. Now under a conventional oil and gas license from 2014. D’Arcy Exploration in 1935 who targeted the Jurassic in large anticlines (Porstdown, Henfield and Kimmerige) Summary. Small oilfield drilled in 1959, Today on production since 1961 and is currently still producing around 80 bopd (12,720 litres). First “English gusher” and in 1968 1st well to produce over 100k tons of crude oil. Over 3 million barrels produced in 57 years ! The only producing field in the hanging wall of the main Purbeck disturbance. Many myths about the location and longevity of the field. Reservoir. The oil is produced from extensive fractures in Cornbrash limestone 20m thick, 1% f and 0 k Structure. Cornbrash reservoir in an 1959 anticline close to the main inversion axis and the structure is very small. Source. Lower (Blue) Lias but lighter (API 45) than Wytch Farm (API 35) so from more mature source or fractionation during migration. Not Kimmeridge Clay. Seal and Trap. Overlying Oxford Clay. Trap is simple faulted anticline. Structure poorly imaged on seismic data. 15 History of Kimmeridge Oilfield Reservoir Production history (barrels of oil per day) Production. ~800bbl/day.in. 2016 2005 2010 2015 2020 Broadbench-1 (1936-37) West Kimm Bay. Found light oil in the Sandsfoot Grit at 252m. Bencliff grit target drill string broke in the hole. The well was abandoned at 287m in Osmington Oolite. Then war. Broadbench-2 (Kimmeridge-1, 1959). Beside army area. Oil found in Cornbrash at 512mSS. Production test 30bbl/day up to 4300bbl/day after 2 acid treatments. Completed as a production well. Kimmeridge-2. (1960). Drilled in 1960 670m to East of Kimmeridge-1. Cornbrash at 583m subsea. Mud losses in Corralian. Tests in Oxford clay produced 4bbl/day an worse after acidising. In pressure communication. Kept as observation well. Kimmeridge-3. (1959-1960) 762m SW of K-1. Test Great Oolite and Upper Lias. Losses in Forest Marble/Cornbrash. 26.5 bopd & 4.5mwpd after 3 acid stims. OWC 533mSS. Observation well until 1992 when produced for a while. Kimmeridge-4. (1960) appraisal well 412m NW of K-1. Plugged and abandoned at 262mSS with mechanical failure. Kimmeridge-5. (1980) near K-1 to test deep reservoir after successful deep appraisal of Wytch Farm in 1978. Drilled to Aylesbeare. Weak gas shows in Jurassic. Sherwood had oil shows but was deep (2273mSS) and poor reservoir quality. 16 Contours to top Cornbrash (mSS) using seismic, wells & surface outcrops. History of Kimmeridge Oilfield (Ian West, redrawn from Evans, Jenkins and Gluyas 1998). 17 Kimmeridge Enigmas • Why was oil found in only 1 well ? • How can it have produced so much oil from such a small reservoir • Is oil seeping up a fault and replenishing from a deeper reservoir ? • Why is this the only field in the hanging wall of the Purbeck monocline ? Observations • Fractured reservoir. Fractures probably extend into Kellaways, Forest Marble and Oxford Clay so much larger than it seems • Low reservoir pressures and little water production indicate sealed system so migration from deeper reservoir is very unlikely. • Reservoir decline is relatively normal for fractured reservoir. GOR increases leading to solution gas drive which increases production. Likely to be gas cap in the Oxford clay supporting oil production. Recovery factor will be about 15-30%. STOOIP approximately 10-25mmbbl. Prediction • At some point the well will “gas out”. The relative permeability to oil means that oil will be backed out and production will be 100% gas. There will be a short period of “blow down” which could be lengthened with compression followed by abandonment of the field. Could happen very soon. Probably predictable from the GOR readings. 18 History of Shale Oil Industry Blackstone armlets (John Parkins) Iron Age • Local ’Blackstone’ polished with beeswax • Used as substitute for jet (lignite) • Share working on bay made bracelets using primitive lathes. Romano- British Table • Discarded cores known as Kimmeridge coal money. leg from Blackstone armlets Blackstone Romans • Industry continued with two factories. Romano-British • Two sizes of bracelets from the same core Shale Factories • Used flint tools and later iron. • Also made gold studded mace heads, spindles, tesserae and table legs • Examples found as far away as Switzerland 17th Century – James Clavell • Locals burned the shale but it gave off fumes • First venture producing Alum e.g.