Insights

Insights

Yanchang CO2 EOR: Unique Geology, Unique Challenges

16th January 2016

Topic(s): Carbon capture, Engineering and project delivery, use and storage (CCUS)

The Global CCS Institute has commissioned four knowledge-sharing reports on key aspects of Yanchang Petroleum Group (Yanchang) Integrated CCS Demonstration Project in China. The second report in this series is now available, covering the application of CCS to enhanced oil recovery (EOR). In this Insight Chris Consoli, Senior Adviser for Storage, Asia–Pacific, provides an overview of the project and introduces the report.

Carbon capture, utilisation and storage (CCUS), primarily through enhanced oil recovery using carbon dioxide, or CO2-EOR, has historically been the largest driver for the development of CCUS technologies. CO2-EOR is driven by the need to extract greater volumes of oil from producing reservoirs. As a consequence CO2-EOR operations have enabled the development and commercialisation of more sophisticated methods for the capture, transportation, injection and monitoring of CO2. Chinese governments and industries have a clear mandate to support CO2-EOR technologies leading to the construction of several projects. Also in China, maturing oil fields have been the catalyst for second and third generation of oil production techniques, including CO2-EOR. In the Shaanxi Province of China, Yanchang Petroleum have committed to undertake CCUS pilot and demonstration projects through the integration of their coal-to-chemicals industry with their CO2-EOR operations.

CO2-EOR

Carbon dioxide flooding for enhanced oil recovery (CO2-EOR) has been undertaken in West Texas in the United States for over four decades. The technique and technologies of CO2 EOR have been critical to the development of the CCS industry for two reasons.

Firstly, the technology and experience behind the transportation, injection and monitoring of CO2 was developed through CO2-EOR operations. For example, in Canada over 25 Mt of anthropogenic CO2 has been injected into the Weyburn and Midale oilfields in Saskatchewan, which have served as a 'field laboratory' for the IEAGHG Weyburn-Midale CO2 Monitoring and Storage Project.

Secondly, CO2-EOR has been an important commercial driver for the development of first-of-a-kind large scale CCS projects, including from power stations such as the Boundary Dam Carbon Capture and Storage Project​ and Kemper County Energy Facility, as well as from industrial processes such as the Emirates Steel Industries' Abu Dhabi CCS Project.

CO2-EOR is also an important commercial driver for the Yanchang Integrated CCS Demonstration Project. This project will demonstrate the cost-effective capture of CO2 from coal-to-chemicals processes and its injection into low permeability geological formations. Both of these developments will enable a wider application of CCS and greater potential emissions reductions.

The Yanchang project

Yanchang Petroleum Group (Shaanxi Province) owns large reserves of oil, gas and coal. To optimise the utilisation of its resources, Yanchang has developed technologies to convert coal, natural gas, and residual heavy oil to chemical products at its Jingbian Industry Park. In 2012 the Yanchang Petroleum Group built a 50,000 tons per year (Tpa) CO2 capture plant at its Yulin Coal Chemical Coal Company coal-to-chemical plant. The captured CO2 has been used for the pilot CO2-EOR project. An additional 360,000 Tpa of CO2 will be taken from a separate coal-to-chemicals plant in Jingbian and will enable the expansion of the CO2-EOR activities. The captured CO2 from the Jingbian plant will be transported to the CO2-EOR site by 20 ton truck over a distance of about 140 km. See CCS: A China Perspective Yanchang Petroleum Report 1: Capturing CO2 from Coal to Chemicals, 2015 report for more information relating to the CO2 capture and transport processes.

Yanchang's CO2-EOR operations are located in the Triassic Yanchang Formation on the eastern slope of Ordos Basin, a vast basin in the west of North China hosting abundant energy and mineral resources including coal, gas and oil. The Yanchang Formation is an important oil-bearing rock unit, with about 60% of proven total reserves in the region. Using CO2 from the Yulin Plant, a pilot CO2-EOR operation has been operating since 2012, injecting around 41,000 tonnes of CO2 to date into the Qiaojiawa oil field in the Yanchang Formation.

Using CO2 for EOR is the a preferred option for the Yanchang Project because the northern Shaanxi Province is arid and semi-arid. Access to water for water flooding is difficult, and CO2 is alternate material for EOR. Furthermore, Yanchang can capitilise on CO2-EOR because it will produce a near pure stream of CO2 from its coal-to-chemicals plants, which are positioned close to fields - thereby reducing the costs and emissions associated with transportation.

Key Findings

Yanchang evaluated 176 different oil reservoirs in the Yanchang Formation to produce a set of geological criteria which can be used to help identify oil fields that are suitable for CO2 flooding operations. In this analysis they also identified which reservoir properties had an impact on oil production during CO2-EOR operations. For example, the reservoir temperature has little effect on oil production during CO2 flooding but reservoir depth, pressure and thickness are all very sensitive variables. Based on this analyses, the report's authors found 153 oil fields which could be suitable for CO2 flooding, which was around 80% of total oil reservoirs. The site of the pilot CO2 injection project in the Qiaojiawa oil field was found to be the best match for potential CO2-EOR operations during this evaluation and was chosen for expansion of the CO2-EOR operations.

The pilot project is located in the 203 well block of the Qiaojiawa oil field. The operation has initially injected CO2 from 20 injection wells (grouped with 68 oil production wells). The operation will switch to water alternating with CO2 (known as WAG) in the future. In the meantime a measurement, monitoring and verification (MMV) process is underway and will continue beyond the CO2-EOR operation. Despite the low permeability, Yanchang is expected to achieve an injection rate of up to 10 ton per day from each injection well, achieving a total injection capacity of up to 200,000 tpa.

The Yanchang Formation has low to ultra-low permeability of less than 1 millidarcy (Darcy is a measurement unit of permeability, which is how easily fluids can pass through rocks). A low permeability rock means the pore space between the grains of sand and silt which holds the oil, and eventually the CO2, are not well-connected or those connections are narrow. For example, the CO2-EOR Weyburn-Midale project, which is typically referred to as a low permeability operation has measured permeability ranges from 1 to greater than 50 mD in one of its reservoirs. The reservoir properties from the Yanchang Formation are detailed in Table 1 below.

Table 1. Yanchang Formation reservoir characteristics.

Reservoir Characterisation
Thickness 105-150 m with an average thickness of 127 m
Temperature 40 deg C
Pressure 8.2 MPa
Porosity 8-13.0%, and average porosity is 10.5%
Permeability 0.05-2 mD, and average permeability is 1.02 mD
Total salinity of formation water 50.52g/L~95.11g/L
pH 5.5
Oil reserves 4,354,100 ton

The report outlines the results of laboratory experiments completed on the oil, CO2 and reservoir of the Yanchang Formation and mostly focuses on determining the solubility of the oil when it comes into contact with CO2. Above a certain pressure in the reservoir the oil and CO2 will become soluble, or what is known as miscible and mix increasing the recovery of both. This is called the minimum miscibility pressure (MMP) and for the Yanchang CO2-EOR reservoir the MMP was 22 megapascals. The MMP is very dependent on oil composition and reservoir conditions. MMP experiments are standard but critical experiments to complete for any CO2-EOR operation because it can influence your injection style, or even if the CO2-EOR flooding will increase oil production.

The report also outlines the computational modelling results. According to injection modelling simulations, the WAG will increase production of oil by around 18% and almost 20% if CO2 alone is injected. Around 40% (WAG) to up to 60% (CO2 only) of the CO2 will be stored permanently and under maximum potential this could rise to 80%. If the 200,000 tpa is reached it could mean that a minimum of around 120,000 tpa is stored permanently in the Yanchang Formation.

Figure 1. Simulation results of the primary CO2-EOR reservoir of the Yanchang Formation showing the saturation of oil in the reservoir after CO2 injection. Notice around the CO2 injection well, oil has been pushed out and low values in blue and green are shown when compared to the surrounding reservoir. The bar chart ranges from 20% (blue) to 60% (red) oil saturation.

Finally, the report details the storage resource of the primary CO2-EOR reservoir using the volumetric calculation method of the US Department of Energy. The theoretical storage resources (the entire pore volume of the reservoir) is 4.3 million tonnes (Mt). However, the practical storage capacity in the primary reservoir which takes into account the pore space that can actually host CO2 including well injection scenarios and economic constraints is estimated to be around 2 Mt; a substantial capacity given this calculation is based on one low permeability reservoir in a single field. Interestingly, the CO2 storage efficiency factor is 23%, which is very high compared to the 1-4% efficiency factor that is typically used for more generalised CO2 storage projects worldwide. According to several basin-wide studies the effective storage resource of the entire Ordos Basin could be up to 60-100 Gt.

The report also outlines the economic evaluation of the CO2-EOR operations and found that injection costs is approximately 200 Yuan/ton (~US$30/ton CO2). The report also outlines the baseline and future measurement, monitoring and verification strategy (Table 2).

Table 2.  Baseline surveys

Technology
Reason
Groundwater well monitoring
Understand the groundwater system in the area
Surface and near-surface monitoring
Catalogue surface water sources
Catalogue vegetation growth/change
Catalogue soil type and distribution
Soil gas composition
Atmospheric CO2 concentration and isotopic composition
Dynamic monitoring of injection and production wells
Produced fluid analysis including oil component
Production rate
Pressure and temperature
Interwell tracer injection
Corrosion monitoring

Conclusion

The Yanchang Integrated CCS Demonstration Project will be China's first full-chain, fully-integrated project using coal-to-chemicals for CO2 to be used for enhanced oil recovery in a low permeability reservoir. Typically, low permeability reservoirs are avoided because injection rates of the captured CO2 cannot be matched, but in this case Yanchang, through using multiple wells and variable injection scenarios, can achieve sufficient injection rates. For the EOR operation, using CO2 is clearly seen as a beneficial method to increase oil production rates whilst reducing water use and reducing the emissions of the coal-to-chemical operations though the permanent storage of up to 80% of the total injected CO2. The capture of carbon dioxide from coal-to-chemicals processes and the use of low-permeability reservoirs opens up greater potential for CCS to contribute to global emissions reductions.

 

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