SPE 167025 Unconventional Oil Production from ...

SPE 167025 Unconventional Oil Production from Underground Coal Gasification and Gas to Liquids Technologies Greg Perkins, Ernest du Toit, Bert Koning and Andreas Ulbrich, Linc Energy Limited.

Copyright 2013, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Unconventional Resources Conference and Exhibition-Asia Pacific held in Brisbane, Australia, 11–13 November 2013. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Enginee rs is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract The combination of underground coal gasification and gas to liquids technologies offers the potential to produce high quality synthetic oil and associated products from deep coal reserves that are unsuitable or uneconomic to extract using conventional methods. This paper provides a summary of achievements made over the past five years at the world’s only Demonstration Facility where UCG and GTL technologies have been successfully integrated and operated to produce synthetic oil products. The process of UCG is described, along with the key features of the proprietary technology developed and operated by Linc Energy. A number of the experiences gained from operating multiple underground gasifiers over several years are outlined. The GTL facility at the Demonstration facility is described, along with selected results from operations of the gas conditioning unit and the synthesis of liquid hydrocarbons using the Fischer-Tropsch process. The products generated from the facility are summarised. In the second half of the paper an outline is provided of a commercial UCG to GTL facility and some of its characteristic performance parameters. Technology selection and project execution considerations for commercial scale plants are discussed. Finally, the global potential of UCG as a method for producing unconventional gas from deep coal is discussed and some of the challenges and opportunities for producing unconventional oil via integration of UCG and GTL are summarised. Introduction The world currently consumes around 90 million barrels of oil per day and spends in excess of 400 billion dollars per annum on oil exploration and production to maintain that supply. Most of this oil is refined into transportation fuels, such as gasoline, diesel and jet fuel. There is general consensus that demand for transportation fuels will continue to rise over the next few decades, particularly in countries such as India and China, while the ability to produce sufficient oil from conventional sources is becoming increasingly difficult and costly. Figure 1, overleaf, shows graphically the relationship between conventional and unconventional oil and gas resources. Conventional resources of light and medium oils are relatively easy to produce but represent small volumes in comparison to other resources. Unconventional resources are large, though they require the use of advanced technologies to produce them in economically acceptable and environmentally sustainable ways. Figure 2, overleaf, shows the worldwide proved reserves of oil and coal for the important regions of the world (IEA, 2009). It can be seen that apart from the Middle East and South America, all the regions have proved reserves of coal that are many times greater than their proved oil reserves. For many nations with large coal resources, some of these resources are co-located in the same sedimentary basins as the conventional – and now depleted – light oil reservoirs. For example, the Powder River Basin in the USA and the Western Canadian Sedimentary Basin.

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Figure 1: Graphical comparison of conventional and unconventional resources. Unconventional resources require advanced production technologies in order to be recovered in economically and environmentally sustainable ways.

Figure 2: Worldwide proved reserves of coal and oil (data from IEA, 2009).

In general, we may identify four methods by which oil reserves can be increased: 1. Discovering new fields 2. Discovering new reservoirs 3. Extending reservoirs in known fields 4. Redefining reserves because of changes in economics of extraction technology Methods 1, 2 and 3 all require drilling and the definition of new accumulations that can be economically recovered using conventional means. In general this is becoming increasingly difficult to sustain, and thus oil prices have moved materially higher in the last decade. Method 4 involves increasing the reserves by changing technology and/or economic conditions to make the recovery of the known resources economically feasible. A recent example of method 4, has been the application of horizontal drilling and fracking techniques to produce tight gas and tight oil resources, especially in North America. In situ coal gasification, more commonly referred to as Underground Coal Gasification (UCG) is a method which is ready for widespread commercial application. Its competiveness as an extraction technology is underpinned by relatively low cost horizontal drilling technology and the abundance of large, stranded deep coal resources, which are readily available in most locations as shown in Figure 2. By combining UCG with Gas to Liquids (GTL) technologies, high quality synthetic liquid transportation fuels, such as Diesel and Jet fuel, can be produced. Relatively pure carbon dioxide captured as part of the

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integrated UCG to GTL facility can be used for CO2-miscible enhanced oil recovery (EOR) operations in depleted oil reservoirs. This technology combination has the potential to create large new reserves of synthetic and conventional light oil, and enable them to be produced with environmental and economic advantages over alternate conventional and unconventional processes. In this article we summarise how Linc Energy’s UCG technology, which turns deep stranded coal into valuable syngas, can be used to produce synthetic oil and can facilitate the recovery of light oil reserves from depleted conventional reservoirs using CO2-miscible flooding enhanced oil recovery techniques. Underground Coal Gasification In the Underground Gasification process coal, oxygen and steam are reacted at high temperatures in situ to form synthesis gas (syngas) being predominately CO, H2, CH4 and CO2 (Perkins, 2005, Perkins and Sahajwalla, 2008). The composition of the syngas mixture depends on coal seam quality, depth and the injected oxidant composition - air, enriched air or pure oxygen (Perkins and Sahajwalla, 2006). Underground gasification in general enables deep, stranded coal that is unsuitable for any other extraction process to be converted into energy. In some cases UCG is a substitute for surface coal gasification which requires that coal is first mined then subsequently reacted with oxygen and steam at high temperatures and pressures in specially designed gasification reactors. The major challenges and expense associated with surface gasification includes coal mining, solids handling, crushing, transport to the gasifier, pressurised gasification equipment, and ash and slag handling equipment (Rezaiyan and Cheremisinoff, 2005; Higman and van der Burgt, 2008). Due to the need for significant amounts of solids handling equipment and reactor vessels operating at high pressure and temperature, conventional surface gasifiers are relatively expensive to build and maintain. In addition, the reliability of these unit operations is a major consideration for the design of the integrated facility. In some plants, spare gasification reactors have been installed in order to achieve high syngas availability, impacting on the project capital costs (Higman and van der Burgt, 2008). In contrast, modern underground gasification techniques involve using oil and gas drilling technology to create long horizontal wells in deep coal to construct the gasification reactor. Target coal seams are between 200m and 2000m deep, and preferably at least 500m deep. The pressure and containment of the process is provided by the combination of the geological formation and natural reservoir pressure. Figure 3 shows a schematic of Linc Energy’s latest UCG technology, incorporating a horizontally drilled oxidant injection well and a vertically drilled production well (Linc Energy, 2013a). In this technology, the oxidant is brought to the coal deep underground via horizontal well technology. The produced syngas from UCG is piped to the surface and then undergoes primary processing, involving removal of trace amounts of solids and separation of condensed water and oils from the syngas. The production rate of the UCG syngas is controlled via the operating pressure, injection flowrate of the oxidant and the movement of the location of the oxidant injection along the horizontal well over time. As a result, the gas production rate from a single well remains stable, and does not drop off over time like natural gas or shale gas wells due to natural pressure decline in the reservoir. In commercial projects between 5 and 25 gasifiers are expected to operate simultaneously, ensuring that the UCG field produces a consistent quality and production rate of syngas with very high availability.

Figure 3: General layout of an underground coal gasifier. Note: not to scale; coal seam thickness has been expanded for artistic reasons (Linc Energy, 2013a).

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The availability of syngas production from UCG is very high due to the simplicity and reliability of the process which avoids the need for solids handling and containment of a high temperature and pressure chemical process. These inherent features of UCG lead to major advantages when compared to surface gasification, as follows:  for UCG the deep coal resource itself has little market value, and by gasifying it in situ one produces savings in avoided mining costs, transportation, storage, handling, grinding, and metered charging to the reactor. This represents a significant saving in plant operating costs.  many of these avoided steps – especially storage, grinding and charging - introduce reductions in plant reliability and higher maintenance expenses for surface gasification plants.  these un-needed steps in UCG avoid environmental impacts as they require electricity, heavy mining equipment fed by diesel oil, and trucks and trains for transport that are fed by diesel and gasoline. Further, most of these avoided mining and transportation steps are big dust producers and often require the construction of new roads and rail spurs. Demonstration Facility Description Linc Energy has been practicing UCG since 1999 and owns a Demonstration Facility located near Chinchilla, some 350km west of Brisbane, Australia. Linc Energy’s Demonstration Facility consists of UCG facilities and a GTL plant, including a waste water treatment facility, a tank farm, a chemical laboratory and supporting infrastructure. To date, five gasifiers have been developed and operated at the site. Gasifier 5 is Linc Energy’s fifth generation technology and forms the basis of the company’s proprietary commercial offering. Figure 4 shows a schematic of the Chinchilla Demonstration facility plot plan.

Figure 4: Linc Energy’s Chinchilla Demonstration Facility Schematic Plot Plan (Linc Energy, 2013b).

Geology The coal seams targeted for UCG at the Chinchilla Demonstration Facility, are the combined Macalister A and B seams within the Juandah Coal Measures of the Surat Basin. The Macalister A and B seams average 6 and 4 meters in thickness respectively, occurring together to form an approximate 10 meters thick unit between approximately 125 and 136 meters below ground level. The A and B seams are separated by an approximately 1m parting of fine siltstone, the thickness of which increases to the east. The coal seams are known to be unconformably overlain by the Springbok Sandstone. The overburden (Springbok and Westbourne Formations) comprises a sequence of medium grey interbedded carbonate cemented lithicfeldspathic siltstones and fine sandstones with minor carbonaceous mudstone, mudstone and coal stringers. Medium to coarse grained, weakly cemented quartzo-feldspathic sandstone lenses less than 1m in thickness are noted in many drillholes in the region in a zone between 90 and 100m deep.

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Near the contact with the coal, the fine sandstone and siltstone becomes increasingly interbanded/interlaminated with carbonaceous mudstone and rare coal stringers. The uppermost unit in the sequence is Tertiary - Quaternary cover which unconformably overlies the Springbok/Westbourne and averages 30 to 40 meters in thickness. This unit comprises clays, clayey silts and clayey sands deposited on the Condamine River floodplain during regular flooding events. Coal seams within the site have been described as flat with a slight dip ( 46

Aromatic content

< 0.1 wt%

< 11 wt%

Sulphur Content

< 0.1 ppm

< 10 ppm

0.78 kg/l

0.82 to 0.845 kg/l

Density Other

Comply with conventional diesel specifications

Commercial Facility Description At the Chinchilla Demonstration Facility the integration of UCG and GTL has been proven. Design and operational learnings from both UCG and GTL are being used by Linc Energy to optimise the commercial facilities. The characteristics of a commercial facility are outlined in this section, and several key differences between the demonstration plant and a commercial plant are discussed. In a commercial facility, the syngas requirements will be met by operating multiple gasifiers in parallel. Typically a 5,000 bpd GTL facility will require between 20 and 25 UCG gasifiers to be operated at any one time depending on site conditions. This ensures very high availability of the syngas production. Over time, further scale-up of the UCG process capacity is anticipated. Commercial UCG projects will preferably be converting coal resources which are deep enabling the syngas to be produced to surface at between circa 50 and 100 bar. This ensures that the optimum pressure profile through the integrated facility and eliminates the need for syngas compression. Deep coals have the added advantage that their permeability and connection to water aquifers is generally very low, thereby ensuring low water ingress into the gasification process from the formation. This will have the benefit of increasing the efficiency of the UCG process. Linc Energy expects that the oxygen utilisation in deep coals (>500m deep) will be approximately 15 and 25% better than the performance achieved in the shallow coal seams at Chinchilla. Figure 9 shows a simplified block flow diagram of a commercial UCG to GTL project. An ASU will supply high purity oxygen for UCG. The raw syngas will be processed in the raw gas water wash and the syngas sent to an acid gas removal unit. The produced water will be cleaned up in a water treatment facility and recycled for use in the facility, while the coal condensate will be stabilised and sent to storage for sale. In the commercial facility, both CO 2 and H2S will be removed in the AGR unit. The AGR can use chemical solvents such as Amine as demonstrated in the Chinchilla facility or physical solvents such as used in the Selexol® and Rectisol® processes. The CO2 is recovered as a separate stream and can be used as a solvent for CO2-based miscible flooding enhanced oil recovery (EOR).

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Oxygen

UCG

ASU

Wet Syngas Raw Gas Wash

Sulphur

Acid Gas Removal

CO2 Export

Syngas

Coal Condensate

FT

Upgrading

Diesel Naphtha Jet

Figure 9: Simplified block flow diagram of a UCG to GTL commercial facility.

In the commercial facility the syngas is conditioned to achieve CO+H 2 content of >95 mol% and with a H2/CO ratio of circa 2 as required for the optimum operation of the Fischer Tropsch (FT) catalyst. In the product upgrading unit, the FT waxes are hydrocracked and combined with the FT middle distillates and hydrotreated. The hydrotreated products are then fractionated into the primary streams of diesel, naphtha and jet fuel. The product slate can be optimised on a project by project basis to meet market demands. The FT tail gas will be recycled or used for power generation. The ASU and the GTL plant have considerable power demands. The power balance of the commercial facility can be designed to be power import, power neutral or power export. The optimum choice will depend on the local availability and market conditions for power. If cheap power is available, the capital cost of the facility can be reduced and the required power imported. If not, then UCG syngas can be used to ensure that sufficient power is produced to run the entire facility. Linc Energy is focusing on designs which are configured to be power neutral or where power can be imported, as these facilities maximise the yield of liquid products from each unit of UCG syngas produced. Polygen facilities which produce multiple primary products can be considered for commercial projects. Producing a combination of liquid fuels via GTL and chemicals such as Ammonia and Urea or Olefins (Propylene, Ethylene) may be of interest in some locations. Modular Construction Conventional technologies for coal gasification and gas into liquids require very large scale plants to be constructed in order to achieve sufficient economies of scale to make the undertaking commercially attractive. Existing coal to liquid plants in South Africa have plant capacities of over 150,000 bpd of production and have dedicated coal mining facilities to supply the coal. Using UCG, the need for a coal mine is eliminated and the surface impacts are very much reduced. The unwanted ash byproducts in coal are left in the coal seam as a predominately vitrified inert slag. As seen in Figures 5 and 6, UCG surface facilities are by their nature modular. UCG is therefore very amenable to developing in smaller, more manageable project sizes. This approach also fits well with new developments in GTL technology which apply process intensification principles to reduce conventional reactors by an order of magnitude by improving heat and mass transfer rates using micro-channel reactor technology. As such the combination of Linc Energy’s modular UCG technology with modular gas to liquids technology offer the potential to unlock a greater range of resources and achieve acceptable returns on investment at smaller project scales than can be achieved with conventional stick built plants and project execution strategies. Linc Energy is working on modular UCG to GTL plants with single train capacities in the range of 5,000 to 10,000 bpd of synthetic liquid products. Larger scale plants would be constructed with multiple trains and synergies would be achieved via sharing of site development, infrastructure and scale-up of some of the utilities, such as the water treatment and tank farm. Figure 10, overleaf, shows a 3D model of Linc Energy’s GTL plant design with a single train capacity of 5,000 bpd of GTL products.

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Figure 10: 3D model of a modular UCG to GTL plant (Linc Energy, 2013b).

In the modular plant philosophy, the aim is to maximise the amount of fabrication which is done in the controlled environmental of a construction yard and where a dedicated labour force can be employed. This ensures high quality and minimisation of the amount of site labour, which is generally expensive, especially in remote locations. As most of the potential coals suitable for UCG are located inland, the plant module size and weight envelopes must be chosen carefully in order to enable transport to site. At this stage, Linc Energy envisages using modules which are truckable and which have maximum weight of circa 60 tons. For those locations where the coal is close to a large river, an inlet or the sea, larger module sizes would be employed to take advantage of the ability to transport them to site as single units. Due to the scale of the projects being targeted, a small number of the individual equipment items, such as distillation columns, reactors and so forth will be too big for the standard module envelope and would be transported to site separately. Enhanced Oil Recovery Primary and secondary (waterflood) recovery of oil fields generally only produces between 25 to 35% of the original oil in place (OOIP) (Speight, 2006). Application of enhanced oil recovery (EOR) is becoming an important means of adding to existing oil reserves, without the need to discover new fields and reservoirs. The available EOR methods are as varied as the available petroleum reservoirs, and include CO2-miscible floods, polymer floods, hydrocarbon floods, immiscible floods, insitu combustion floods, thermal methods, amongst many others. For many depleted oil reservoirs, CO2-miscible displacement is a preferred candidate for recovering up to 25% more oil from the reservoir (Sheng, 2011). In the process, CO2 is injected into the target reservoir at high pressure above the Minimum Miscibility Pressure (MMP) and mixes with the oil accumulated in the pores of the reservoir, forming a single phase. This new oil phase is pushed to the production well in some cases using alternating slugs of water and CO2 injection. Carbon dioxide is a preferred candidate for miscible flooding due to the fact is has a relatively low MMP, a high density and a low viscosity, all of which aid in the increasing oil production via improving mobility, oil swelling and miscibility (McDaniel Branting and Whitman, 1992; Gao et al., 2010). The technical risks associated with CO2 EOR are relatively low given the knowledge base of the target reservoirs obtained from primary and secondary recovery operations, which generally precede an EOR development. At surface, the produced oil and CO2 are separated with the CO2 being recycled for further use. Figure 11 shows a schematic of the process. On a net basis three to six barrels of oil can typically be produced from each ton of CO2 injected into the oil reservoir (McDaniel Branting and Whitman, 1992). At current oil prices this makes CO2 a valuable commodity for oil production and is recognised as the preferred geo-sequestration method in the short to medium term due to the existing knowledge of the geological and reservoir performance and the fact that there is an economic benefit achieved by performing CO2 EOR. CO2-miscible EOR is practised in several basins around the world and is expected to become more utilised in the future. CO2 based EOR techniques are already widely practised in the Permian basin in southwest Texas, the Powder River Basin in the Rocky Mountain region of the US (McDaniel Branting and Whitman, 1992), the US Gulf Coast and the Western Canadian

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Sedimentary Basin (Shaw and Bachu, 2002). There is growing interest in EOR techniques for recovering oil in the Middle East, Asia and the Americas etc. Enhanced oil recovery is projected to provide one-third of the net increase in OPEC oil production out to 2030 (IEA, 2009). The opportunities for EOR have been reviewed and summarised by Manrique et al. (2010). In the USA alone, assessments indicate that up to 84 billion barrels of oil are technically recoverable using CO2-based EOR (US DOE, 2010). In many of these locations, the depleted oil reservoirs are co-located with large resources of deep, stranded coal suitable for UCG.

Figure 11: Schematic of the CO2-miscible enhanced oil recovery process (US DOE, 2010).

In some locations, the availability of large quantities of CO 2, is the critical element preventing the implementation of EOR projects to recover more oil from depleted reservoirs. As we have seen, in the GTL plant CO2 is removed and available at high quality and pressure. In Linc Energy’s GTL plant design, the CO2 is captured from the AGR unit, and this represents up to 89% of the potential CO2 emissions from the plant, depending upon configuration. The remaining CO2 emissions are from utility and power generation systems which do not have carbon capture facilities. An integrated UCG to GTL and EOR project, with a single train 5,000 bpd GTL section would export approximately 3700 tpd of pressurized CO2 which could potentially produce an additional 7,500 to 22,000 bpd of high quality oil products in the context of an established flooding operation. Environmental Performance Linc Energy has already proven that UCG can extract coal resources too deep and not suitable for conventional mining using oil and gas wells with a minimal operational footprint. In terms of greenhouse gas emissions, when compared with conventional coal utilisation, UCG has many advantages including: elimination of mining activities, elimination of coal transportation, elimination of spontaneous combustion of waste coal and spoil piles and effective utilisation of all the trapped methane in the coal (Hyder et al., 2012). When the UCG process is combined with GTL, the produced oil products are of particularly high quality, with reduced emissions during use. The so-called well to wheel greenhouse gas emissions are indicators of the environmental performance of various pathways of producing oil from hydrocarbons. Table 4 shows the estimated well to wheel GHG emissions for producing oil from conventional and unconventional hydrocarbons. The well to wheel emissions are made up of the well to tank and tank to wheel emission components (see Edwards et al., 2011 for details). It should be noted that the tank to wheel GHG emissions depend on the efficiency of the vehicle fleet and are not affected by the feedstock and production technology. The U.S. average baseline for gasoline and ultra low sulphur diesel are 93 and 92 gCO2e/MJ, respectively (Mui et al., 2010).

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The well to wheel GHG emissions from conventional diesel in the European context is 76 gCO 2e/MJ (Edwards et al., 2011). The U.S. values are higher than the European equivalents due to the presence of imported and domestically produced heavy oil in the refinery feedstock mix and differences in the vehicle fleet and efficiency. Over time, it can be expected that an increase of heavier oil feedstocks in the refining mix could well increase the well to tank component of the GHG emissions, while the trend to more efficient vehicles will reduce the tank to wheel GHG emissions component. From Table 4, the processing of oil sands into transport fuels is found to produce between 15 to 20% more CO2 than the U.S. average baseline. The production of fuels from oil shale without carbon capture and storage (CCS) leads to even higher GHG emissions, being around 36 to 60% higher than the baseline value. The use of natural gas as a feedstock for GTL leads to reduced GHG emissions relative to the conventional pathways. In Linc Energy’s UCG to GTL plant design, up to 89% of the CO2 is captured and available for geosequestration. For this configuration the greenhouse gas emissions are up to 1% lower than the U.S. baseline values, and in a similar range as to the processing of oil sands. If the captured CO2 from the UCG to GTL plant is used in EOR (assuming 4 bbl/t-CO2 net injected), and the produced light crude oil is refined in the conventional manner, the overall GHG emissions from the total liquid fuels produced is further reduced and can be lower than the U.S. baseline value for ultra low sulphur diesel by up to 14%. In Table 5 the estimated well to wheel emissions for the various UCG to GTL plant configurations and EOR performance outcomes are provided in more detail. The power configurations analysed include: 1. power import (where power is imported and the associated GHG emissions are ignored, eg. where power is provided by nuclear or renewable energy) 2. power import using natural gas combined cycle gas turbine (assuming average 469 gCO 2e/KWh for the CCGT) 3. power neutral case (wherein the internal power requirements are met by consuming UCG syngas in a combined cycle power island) Table 4: Estimated well to wheel greenhouse gas emissions in terms of CO2 equivalents for various pathways to producing oil from conventional and unconventional hydrocarbons. Resource and Production Technology

Typical (gCO2e/MJ)

Relative to U.S. 2005 Baseline (+/-%)

(gCO2e/MJ)

Range

Reference

U.S. 2005 Average Baseline (Gasoline)

93

-

-

Mui et al. 2010

U.S. 2005 Average Baseline (Ultra Low Sulphur Diesel)

92

-

-

Mui et al. 2010

European Conventional Diesel

76

-17

72 – 81

Edwards et al., 2011

Oil sands (mining and upgrading)

106

+15

101 - 111

Mui et al. 2010

Oil sands (in situ SAGD and upgrading)

110

+20

101 - 116

Mui et al. 2010

Oil shale (in situ without CCS)

125

+36

113 - 137

Mui et al. 2010

Oil shale (ex situ without CCS)

147

+60

135 - 159

Mui et al. 2010

Natural gas to liquids (without CCS)

59

-36

53 - 65

Edwards et al., 2011

Deep coal (Linc Energy UCG to GTL with 89% CO2 capture and geosequestration)1

91

-1

91 – 146

Linc Energy, 2013c

Deep coal (Linc Energy UCG to GTL with 89% CO2 capture and enhanced oil recovery)2

79

-14

76 – 98

Linc Energy, 2013c

Table 5: Estimated well to wheel greenhouse gas emissions in terms of CO 2 equivalents for UCG to GTL for three different power generation configurations for a range of performance for CO2-miscible enhanced oil recovery. Enhanced Oil Recovery Performance (net bbl-oil/t-CO2-injected)

1

Power Import

Power from NG CCGT

Power Neutral

(CO2e/MJ)

(CO2e/MJ)

(CO2e/MJ)

0 (ie. No EOR)

91

104

146

2

81

86

98

4

79

82

89

6

76

81

85

This case assumes a power-import UCG to GTL facility, importing 0.014 MW/bpd of electricity. The emissions associated with this power generation are ignored in the value presented as typical. The impact of emmissions from the required power generation are included in the upper range case, presented in column 4 and assuming a UCG-IGCC with CCGT efficiency of 52%. 2 This case assumes 4 bbl/t-CO2 are produced via CO2-miscible EOR on a net basis and that the produced oil has a well to wheel GHG emissios profile of 76 gCO2e/MJ which is equivalent to Euroepean conventional diesel. All of the captured CO2 is sequestered in the oil reservoir and emissions from CO2 separation and recycle in the EOR field are ignored. The range covers an EOR performance of 2 to 6 bbl/t-CO2 and the high case includes emissions from power generation as per the above footnote.

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It can be seen that depending on the configuration of the UCG to GTL plant with respect to power generation and the performance of enhanced oil recovery the overall well to wheel GHG emissions can be slightly lower or slightly higher than the U.S. average baseline of 92 gCO2e/MJ. In summary the application of UCG, GTL and EOR is a potentially compelling combination of production technologies which can produce oil products with limited environmental impacts, with GHG emissions similar to the conventional pathways and significantly lower than some of the alternatives. Another benefit of implementing EOR projects is that it produces additional oil from existing fields, thereby avoiding or delaying the need to produce new oil from environmentally sensitive areas. Conclusion Apart from the Middle East and South America, all the major regions of the world have proved reserves of coal that are many times greater than their proved oil reserves. The combination of underground coal gasification and gas to liquids technologies offers the potential to produce high quality synthetic oil and associated products from deep coal reserves that are unsuitable or uneconomic to extract using conventional mining methods. In the UCG process coal, oxygen and steam are reacted at high temperatures exceeding 1000 oC in situ to form synthesis gas (syngas) being predominately CO, H2, CH4 and CO2. Linc Energy’s UCG technology involves using oil and gas directional drilling techniques to create long horizontal wells in deep coal seams to construct the gasification reactor. Target coal seams can be between 200m and 2000m deep, and preferably at least 500m deep. The pressure and containment of the process is provided by the combination of the geological formation and natural reservoir pressure. Linc Energy has developed proprietary designs for downhole ignition and injection of pure oxygen and water via coiled tubing. The utilization of UCG syngas to produce synthetic oil products using GTL technologies has been proven at the Chinchilla Demonstration Facility. Operating experience from this facility is being used to optimize the integration of UCG and GTL in commercial plants with single train capacities of 5,000 to 10,000 bpd. A focus of this integration is to use modular construction philosophies. The combination of Linc Energy’s modular UCG technology with modular gas to liquids technology offer the potential to unlock a greater range of resources and achieve acceptable returns on investment at smaller project scales than can be achieved with conventional gas to liquids projects. The carbon dioxide from the UCG to GTL process can be captured and either geo-sequestrated or used for CO2-miscible enhanced oil recovery. The application of the CO2-miscible flooding has the potential to recover light sweet crude oil from depleted oil fields, thereby increasing proven oil reserves. The environmental performance of UCG has many advantages over conventional coal utilization methods since it avoids many high energy activities, such as mining, coal transport and the exposure of waste coal to spontaneous combustion conditions. The synthetic oil products manufactured from GTL have superior environmental performance during use compared to diesel refined from conventional crude oil. When combined with CO2 geosequestration and/or CO2-miscibile EOR flooding the overall GHG profile of the UCG to GTL manufacturing process is similar to conventional refining. The major technology challenges associated with an integrated UCG-GTL project have been solved. The remaining challenges are associated with identifying the best initial project locations and in engineering, constructing and operating a first-of-kind plant. The technical and economic risks of constructing such plants has been significantly reduced by over thirteen years of UCG demonstrations and over five years gas clean up and GTL conversion operating experience at Linc Energy’s Chinchilla Demonstration Facility. Acknowledgements The authors acknowledge Brian Deurloo, Bill Preston, Muller Retief and Adam Bond (all from Linc Energy) for proof-reading the manuscript and providing helpful suggestions to improve it. Linc Energy Ltd. is acknowledged for allowing publication of this article. References 1.

T. Ahmed, “Reservoir Engineering Handbook”, 3 rd Edition, 2006, Gulf Professional Publishing, Oxford, UK.

2.

D. Bell, B. Towler and M. Fan, “Coal Gasification and its Applications”, 2011, Elsevier, Oxford, UK.

3.

R. Edwards, J-F. Larive, J-C. Beziat, “Well-to-wheels Analysis of Future Automotive Fuels and Powertrains in the European Context, WELL-to-WHEELS Report”, Tehnical Report Version 3c, July 2011, European Commission, Joint Research Centre, Institute for Energy and Transport, Petten, The Netherlands.

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4.

P. Gao, B. Towler and H. Jiang, “Feasibility Investigation of CO 2 Miscible Flooding in South Slattery Minnelusa Reservoir, Wyoming”, SPE 133598, 2010, Society of Petroleum Engineers, Inc.

5.

D. W. Gregg, “Relative merits of alternate linking techniques for underground coal gasification and their system design implications”, In Situ, v4, n3, pp207 - 236, 1980.

6.

C. Higman and M. van der Burgt, “Gasification”, 2nd Edition, 2008, Gulf Professional Publishing, Oxford, UK.

7.

R. W. Hill and M. J. Shannon, “The Controlled Retracting Injection Point (CRIP) System: A Modified Stream Method for In situ Coal Gasification”, Technical Report UCRL-85852, 1981, Lawrence Livermore National Laboratory, University of California, Berkeley, CA, USA.

8.

Z. Hyder, N. Ripepi and M. Karmis, “Underground Coal Gasification and Potential for Greenhouse Gas Emissions Reduction”, Carbon Management Technology Conference, CMTC 151155, 2012, FL, USA.

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