Mechanical Engineering Meeting the Energy Needs of Tomorrow - Well Drilling and Shale Gas Fracturing (‘Fracking’).4th February 2013 Keith Shotbolt B.Sc. 1962
UK Energy Demand Percentage of Total Year 1970 2010 Future Coal and coke (exc. Electricity gen.) 29.0 1.3 Further decline Coal gas 7.5 0.0 Imports zero in 2000 - now Natural gas 2.5 34.0 around 50% Electricity 11.3 19.0 Increasing Biomass and Waste 0.0 2.0 Increasing Oil (Transport, Industry and Heating) 47.0 42.0 Gradually decreasing Source: http://www.decc.gov.uk/en/content/cms/statistics/publications/ecuk/ecuk.aspx Table 1.5.Note: Total demand is approximately 220 million tonnes of oil equivalent per year.Oil provides 42% and gas provides 34% + 9% (share of electricity generation), giving atotal of 85% for oil and gas. On 24 Jan 2013, Ed Davey, Secretary of State for Energy,said: “Oil and gas will form an integral part of the UK energy mix for decades to come.Over 70 percent of the UKs primary energy demand may still be filled by oil and gasinto the 2040s.”1 tonne of oil equivalent = 11,630 kWh. The energy demand of the average house isaround 20,000kWh per annum. Approximately 25% of that is for electricity. UK houseshave mainly gas fired heating.
Natural gas (methane - CH4) is formed by rotting vegetation, animal digestion, and instagnant ponds and swamps.Deep oil and gas deposits were formed from dead animals and plants being coveredby layers of sedimentary rock. The sediments consist of small particles which werecarried down by rivers from exposed areas of land into the sea. The thickness ofsedimentary rock over North Sea oil and gas fields is around 2 to 3 km.Most oil and gas produced to date has been from relatively permeable, large-grainedsandstone or limestone, where the hydrocarbons can flow readily into the wellbores.When the reservoir pressure drops in old wells, production has been increased byacidizing and/or hydraulic fracturing the sandstone to ease release of hydrocarbons.Fracturing or ‘fracking’ was first used in 1947. There will be more detail on that later.
Electricity Generation Percentage of Total Year 2010 Future Natural Gas 47.0 Steady In decline. Drax converting to Coal 28.0 50% biomass-fired. Nuclear 16.0 Accidents - USA, Russia, Japan Renewables (wind, biomass, hydro) 7.0 Target is 20% by 2020 Oil 1.0 Imports (mainly from France) 1.0Installed wind power capacity at end of 2012 was 7,800 MW (~14% of 56,000 MWpeak demand). There are over 4,200 wind turbines, and the average size is of thelatest machines is around 3MW. By 2020, installed wind power capacity could bearound 50% of electricity demand, needing approximately 7,000 more turbines.Nuclear Plant Accidents: 1979 – Three Mile Island, USA. 1986 – Chernobyl, Russia. 2011 – Fukushima, Japan.
INFRASTRUCTURE. The UK has a vast pipeline network, mainly for thedistribution of natural gas (red). The National Grid company is responsible foroperation, maintenance and investment of both gas and electricity grids.
History of Natural Gas supplies into Europe1959 - Discovery of large Groningen gas field in Netherlands1965 - Discovery of first UK offshore gas field, West Sole1970-90 - Installation of ten 56-inch gas pipelines from Siberia1990-2010 - Large gas pipelines installed from Norway and Algeria.Also, Liquefied Natural Gas (LNG) supplies begin from Qatar and others.Advantages of using methane as a fuel are that a) it is clean to handleby pipeline, and b) generates around half the CO2 than an equivalentamount of energy produced from burning coal.
Western Europe sources most of its natural gas from Russia. Possible routes offuture gas lines are shown in blue. A 2005 Study described the importance ofRussian gas, see: http://www.centrex.at/en/files/study_stern_e.pdf
Modern gas-fired power stations use the Combined Cycle Gas Turbine (CCGT), which hasan associated steam turbine to extract energy from the hot exhaust gases. One CCGT cangenerate up to 500 MW with 70/30 split of gas/steam power.General Electric (USA), Mitsubishi (Japan), Siemens (Germany) and Alsthom (France) arecompeting in this market, and claim up to 60% efficiency on their largest machines.
This new 2400 MW power station at Willington, Derbyshire is proposed byRWE npower.There will be four 500 MW CCGT units and four 100 MW open cycle units.The latter can go from start-up to full power in 10 minutes for rapid response tochange in demand.Rolls Royce supplies the open cycle type, which are based on aircraft engines.
Costs. Extract from: http://en.wikipedia.org/wiki/Wind_power_in_the_United_KingdomA 2004 study by the Royal Academy of Engineering found that wind power cost 5.4pence per kW·h for onshore installations and 7.2 pence per kW·h for offshore,compared to 2.2p/kW·h for gas and 2.3p/kW·h for nuclear.By 2011 onshore wind costs at 8.3/kW·h had fallen below new nuclear at9.6p/kW·h,However, offshore wind costs at 16.9p/kW·h were significantly higher than earlyestimates mainly due to higher build and finance costs,.
Wind-generated power is a variable resource. The amount of electricity produced atany time and location depends on wind speeds, air density, and turbinecharacteristics.In June 2011 several energy companies told the government that 17 gas-fired plantscosting £10 billion would be needed by 2020 to act as back-up generation for wind.The companies said they would require "capacity payments" to make the investmenteconomic, on top of the subsidies already paid for wind.
From 1970 to 1998, the price of gas in the USA averaged between 2.0 and 2.5 dollarsper 1000 cu.ft.. The country then started to import more LNG, and the price averaged inexcess of 5 dollars per 1000 cu.ft. from 2003 to 2009.Between 2006 and 2010, shale (fine-grained, laminated and fissile mudstone) gasproduction increased from 0.7 trillion to 4.6 trillion cu.ft. per annum. This trend hascontinued and both domestic and industrial consumers are benefiting from the reducedprice of gas.Shale gas developments have been made economic by adapting directional drillingand fracturing technologies – mainly used offshore until 2005.
Well Drilling.Access to liquid and gas hydrocarbon fuels is done by drilling a well intothe producing rock stratum.This process is obviously much easier than sinking a mine shaft to allowmen to mine coal, and then providing transport to market. When I startedat University in 1959, Britain was a coal-based economy for house heating,electricity generation and railway locomotives.The first significant gas field in the UK North Sea was not discovered until1965, and an oil discovery followed in 1969. I was employed in the oil andgas industry from 1974 to retirement in 2006.In most cases, the oil and/or gas have sufficient pressure to flow out of thewell and into a gathering pipeline system.Well Drilling is the foundation of present-day standards of living. Thisvideo 01 shows the basic requirements for drilling a vertical onshore well.
Drilling Safety for Personnel and the Environment depends on:1. Good Mud Density Control2. Good Cementing of Casing, and3. An Effective Blowout Preventer (BOP).1. Mud is circulated down the drill pipe, through the bit and back up the annulus.This keeps the bit cool, carries the cuttings back to surface pits, and balancesthe pressure of fluids in any stratum or formation.2. Each casing must be cemented in place to form an effective seal to preventone stratum ‘leaking’ into an adjacent stratum. For example, it is not acceptablefor methane to leak into a fresh water aquifer that is, or may be used fordomestic consumption. The casing should be centralised in the hole to easecement flow around its circumference.3. If the drill bit hits a stratum containing high pressure fluids, and the drillerscannot adjust the mud density to balance the high pressure, the fluids may startto rise up the well bore. It is essential that fluids are contained in the well andthis is done by closing one or more annular or ram type blowout preventers.Simplified Video 02 : Basic steps for drilling any hydrocarbon well.
Casing centralisers have bow springs to hold the casing central in the hole ascement is displaced up the annulus.Poor centralising can lead to leaks from one stratum to another.
Details at Bottom of Macondo Blowout wellBP’s report (Figure 1) states that the primary reservoir sands extended from 18,051 ft to18,223 ft. This diagram shows that the hole diameter reduced from 9.875” to 8.5” at18,126 ft depth – approximately half way through the pay zone.The annular gap around the 7” casing in the 8.5” hole was only 0.75”, instead of the 1.5”to 2” recommended by Halliburton, the cementing Contractor. This tight annulus caused arestriction to mud flow, and a pressure of 3,142 psi was needed to establish circulation.
Rig DeckCasing String in Basic Calculations using Macondo DataMud-filled Riserand Well. 2 2 Derived Units N kg. m. sec bar 100000N. m . tonne 1000. kgf 1 3 3 Density of mud at Macondo well mud 14.17lbf. gal . mud = 1.698 10 kgf. m 3 3 Density of Steel 7850. kgf. m Lengthof Pipe L . 18300ft L = 5.578 10 m 4 Pressure at 18,300ft depth P mud. L P = 1.347 10 psi P = 928.772 bar Extension of long piece of steel rod or pipe under own weight Ext=WL/2AE=density.A.L^2/2.A.E 2 Pipe Youngs Modulus E . steelinmud 200000N. mm Relative density of pipe in mud mud 2 3 3 steelinmud. L steelinmud = 6.152 10 Extension of pipe in m ud kgf. m Ext Ext = 4.693 m 2. E Outside diameter D 7. in Inside diameterd 6. in Wall thickness t 0.5. in 2 2 Casing String Weight W steelinmud. . D d . L W = 226.041 tonne 4 . S 3 Casing Yield Stress S 125000psi Pressure to Yield Py 2. t. Py = 1.436 10 bar d
This float collar is designed to allow mud to enter as the casing string is lowered downhole. Flowin the upwards direction will raise the Auto-Fill Ball to its position as shown. After landing thecasing in its wellhead hanger, mud is pumped down the string and the ball settles in its seat atthe bottom of the Tube.Initially, flow is limited by having to pass through the small circulation port(s). The pump flowmust be increased to above 7 bpm, to induce a pressure drop of around 500 psi, and the entireAuto-Fill Tube is ejected when its retaining pins shear. After Tube ejection, the two Check Valvesare spring-closed - as required to prevent back flow of cement.
US Gulf of Mexico Deepwater Horizon rig – 21st April 2010 11 Men Died What went Wrong?At Macondo, mud circulation down the casing began at the ninth attempt after raising the pump pressure to3,142 psi. The flow rate of mud did not exceed 4 bpm, which was not sufficient to eject the Auto-Fill Tube. BP’sprocedure stated that 8 bpm was required.Cementing proceeded a) without flushing the annulus around the shoe track at sufficiently high rate andduration to ensure full circumferential removal of compressed sediment and good distribution of cement, and b)without converting the float collar to activate its two check valves to prevent cement backflow.There was no cementing evaluation log at Macondo, which may have shown it to be inadequate.Drill pipe was run to 8,367ft ready for mud displacement. During the ‘negative pressure test’, for which therewas no detailed procedure, no flow from the kill line was accepted and 1,400 psi on the drill pipe was ignored.While displacing the mud with seawater, reservoir fluids rising up the casing should have been detected bywater inflow and mud outflow monitoring before arrival of hydrocarbons at the rig floor, but no reasonablyaccurate outflow versus inflow observations were made.After uncontrolled arrival of oil and gas at the rig floor, the blind-shear rams in the BOP stack failed to close dueto the presence of off-centre drill pipe.
Macondo Blind-shear RamsThis diagram shows off-centre drill pipe between the two blind-shear rams (BSRs)as contact is first made. The upper BSR has blades with a Vee having sides set at80 degrees to the axis of motion, and providing very little centralising effect. Thelower BSR has its straight blade perpendicular to the motion axis, with nocentralising effect. Neither ram has side extensions to prevent an outer fold ofmaterial being squeezed between the outer ram faces, thus preventing closure.
Directional or Deviated Drilling.In the mid-1970s at BP’s Forties field in the North Sea, a single platformcould drill multiple wells typically tp 3000m below seabed and out to2000m radius. The hole through the reservoir rock was returned closer tovertical to aid wireline operations, which depend on gravity.
Mud Motor.Hydraulic pumps and motors can be manufactured as helical screws, with one lesslobe on the rotor than in the stator.When drilling the ‘build’ or bend section of the well, the drill string does not rotate,and the drill bit is turned by a mud motor at the bottom, as shown in this shortvideo 03. A typical build rate is 6 degrees per 30 m – giving a radius of ~300m.
Perforating the Casing and Improving Flow into the Wellbore.After cementing the casing through the producing formation (pay zone) aperforating gun with multiple explosive charges punches holes through the casingwall.If the formation has low permeability, flow into the well can be improved byacidizing or fracturing. This artist’s impression shows fractures expected in a tightsandstone formation. Run video 04.
Extract from: http://www.netl.doe.gov/technologies/oil-gas/publications/brochures/Shale_Gas_March_2011.pdfIn the 1990s, long sidetrack horizontal wells were drilled into the 25m thick oilreservoir under the Troll gas field offshore Norway.This well configuration, with long horizontal portions in the producing formation,is used for onshore shale gas developments in the USA.
Experience in the USA has shown that mutiple small stages of fracturing overa longer length cause less damage and are more effective producers than theearlier wells, which had a shorter horizontal section and fewer perforations.There follows a video 05 showing shale gas development in Quebec, Canada.
UK Beneficiary of Shale Gas Developments.KCA DEUTAG is one of the largest international drilling contractors. The companyemploys 8,000 staff in more than 22 countries and it had revenue in 2010 ofUS$1.34 billion.KCA DEUTAG is currently the drilling operations contractor on 33 offshoreplatforms worldwide and owns and operates a fleet of mobile offshore drilling unitsconsisting of 3 jack-ups and 3 self erecting tender barges. The company also ownsand operates a fleet of more than 60 land drilling rigs.The headquarters are in Aberdeen, Scotland. There is an office in Bad Bentheim,Germany, where the central technical support function is located, and regionaloffices in key operational areas - Russia, the Middle East, the Caspian region andNorway.
UK Beneficiary of Shale Gas Developments.Hunting PLC is an international energyservices provider that manufactures anddistributes products that enable theextraction of oil and gas for the world’sleading companies.The global "Upstream" activity is co-ordinated through Hunting Energy Serviceswith a large presence in North America,Europe, the Middle East and Asia. Thecompany owns and develops proprietarypatented products including premiumcasing connections, burst discs, make upprocesses, coating of threads and mud-motors.In strategic locations around the worldHunting owns and operates plants,properties and equipment employing peopleto serve its global customers with localservices and products.
UK Beneficiary of Shale Gas Developments.Weir PLC is a leading global engineering solutions provider. It designs,manufactures and supplies innovative products and expert engineering services forthe minerals, oil & gas and power & industrial markets.Weir operates on a global scale, with around 50 manufacturing facilities and over120 service facilities around the world. The business operations are structuredacross three sector-focused divisions:The Oil & Gas division supplies pumps like the one shown above for fracturingshale gas in the USA. Pressures can reach 1000 bar (100,000 kPa).
Major Concerns about Onshore Drilling and Fracturing:1. Contamination of Ground and Drinking Water2. Earthquakes1. Fluids associated with shale gas developments can be contained provided thewell casing is correctly cemented, and waste water disposal is controlled. Somecontractors have been known to ‘cut corners’ and problems often result. Workersdo not like their activities being watched, but crucial stages must be performed tostandard procedures and specifications. The Macondo blowout is an example ofbadly performed and inadequately regulated activities. My own experience ofoilfield Projects often involved four organisations. The Main Contractor, a ProjectManagement Contractor, a Certifying Authority, and the Owner/Operator.2. Since 2002, there have been 3 earthquakes in the UK >4.0 on the Richterscale. The largest was in Dudley measuring 4.7. There have been 19 quakes>3.0, and each year there are 10 quakes >2.5. Quakes near Blackpool in Springof 2011 were 2.3 and 1.5. They were attributed to fracking, which was stoppedpending a thorough investigation. A Study for the Dept of Energy and ClimateChange Study resulted in approval on Dec 13th, 2012 for drilling and fracking bythe company Cuadrilla to continue. Future quakes greater than 0.5 will be notedand the fracturing will be stopped, pending an investigation of the procedure.
Cuadrilla’s exploratory fracking site near Blackpool . Photo Phil Heywood The GuardianConclusion. Hydraulic fracturing needs water and sand injected at pressures up to 1000 bar.The resulting cracks are held open by larger sand grains which increase formation permeability.Shale gas production has been very successful onshore in the USA, and may be found to beeconomically viable in the UK. Geologists have said it is probable that the UK has five timesgreater reserves of shale gas offshore than onshore. Other countries, e.g. China, Ukraine andPoland, have vast onshore shale gas reserves and are proceeding with their development. References: 1. http://www.eia.gov/analysis/studies/worldshalegas/ 2. http://www.netl.doe.gov/technologies/oil-gas/publications/brochures/Shale_Gas_March_2011.pdf 3. http://og.decc.gov.uk/en/olgs/cms/explorationpro/onshore/cuadrilla_decc/cuadrilla_decc.aspx 4. http://og.decc.gov.uk/assets/og/bo/onshore-paper/uk-onshore-shalegas.pdf