PREDICTING DIRECT AND INDIRECT USES OF GEOTHERMAL ENERGY IN MAJOR OILFIELDS OF CHINA

Transcription

1 PREDICTING DIRECT AND INDIRECT USES OF GEOTHERMAL ENERGY IN MAJOR OILFIELDS OF CHINA 1 MEET SHAH, 2 JATIN AGARWAL 1,2 Student at Pandit Deendayal Petroleum University Gandhinagar India, Manager at Pandit Deendayal petroleum University Gandhinagar India meet @gmail.com, jatin.agarwal27@gmail.com Abstract- 80% of China s energy needs are addressed through the use of fossil fuels. To overcome this, there is a growing focus on the use of renewable sources of energy mainly wind and solar. As a result, the existing geothermal resources in the dying oilfields of China get ignored. There are numerous oilfields which are no longer economically productive and have entered a stage of more than 95% water cut. The hot water associated with such oilfields can be utilized directly or indirectly as a geothermal resource. The geothermal gradient of various oilfields located on eastern, north eastern and central sedimentary basins of China namely DQ (Heilongjiang province), XN (Sichuan basin), CQ (Ordos basin), HN (Dongpu depressions) and HB,SL,LH (all located in offshore Bohai basin) are reviewed. The graph of reservoir temperature versus depth is utilized in obtaining the geothermal temperature gradient for these fields. Based on the geothermal temperature gradient the Lindal diagram is plotted. Lindal diagram indicates the direct application at low to intermediate temperature ranges ( o C) and indirect application at high temperature ranges ( o C) of geothermal resources.. The direct application of geothermal resource is in agriculture,, and agro-based industries, while, the indirect application is for steam or electricity generation ( o C). In addition, the heat loss of water when reached at surface is calculated based on the assumption of real field case. The heat loss indicates that the surface temperature is different as compared to temperature of the water in the reservoir resource of the dead oil field. Thus, this drop in water temperature will shift both direct application and indirect application of geothermal resources on Lindal diagram. Therefore, Lindal diagram with change in temperatures are also displayed in this paper. In short this paper will provide a basic information of direct and indirect application of geothermal reservoirs associated with above mentioned dead oil fields of China. Index Terms- China Geothermal, Lindal Diagram, Oilfields OBJECTIVE To identify both direct and indirect applications of geothermal energy from dead oil wells of abandoned oil fields of China at both reservoir and surface temperature conditions with the help Lindal diagram. I. INDTRODUCTION China is ranked first in terms of installed capacity of Geothermal plants with 17,870 MW, outranking USA which is second at installed capacity with MW. China is also ranked first in terms of annual energy use (TJ/yr) and direct use capacity with heating pumps(mw) worldwide. [1], [2] Geothermal Power plant establishment started in late 20 th century. The first geothermal power generation plant in China was installed in Dengwo of Fengshun county, Guangdong province. Geothermal water with 92 C temperature generated 86 KW electricity at the beginning which was later upgraded to a 300 kw power plant.[3] II. OILFIELD LOCATIONS AND GEOTHERMAL GRADIENT The oilfields data in Liu et al.(2016) are chosen because the fields have majority oil wells which are dead and they no longer produce oil, or if can produce, it isn't commercially viable. Location of oilfields with geothermal gradient is described below in Table 1: [4] Table 1: Description of locations of dead oil fields along with their geothermal gradients (Liu et al 2016) 1

2 III. TEMPERATURE VS. DEPTH GRAPH FOR OILFIELD This change in temperature conditions will result in changing temperature for utilization of direct and indirect application of the geothermal energy when water is brought at the surface and finally changing the Lindal diagram. In order to acclimatize this change of temperature conditions, heat loss calculations were conducted based on the following assumptions mentioned in Table 2. [5] Table 2 Figure 1: Geothermal Temperature vs. depth based on data from HB oilfields. (Data from: Xiao, 2001; Lin et al., 2005; Zhang e al., 2007; Liu et al., 2016) The figure 1, is taken from Liu et al. (2016), where it shows Temperature vs. Depth graph of oil wells of HB oilfield. Oil wells present in and in close proximity to the geothermal direct use envelope and stratigraphic geothermal reservoirs envelope can be used to provide the heat required in various geothermal applications. The Lindal Diagram in Figure 2 is plotted based on the reservoir temperature conditions of water. It is indicating both direct and indirect application of geothermal energy in an intelligent and economical manner. Different oilfields are colour coded and plotted in a text box at a particular temperature range where heading of the box shows the application of geothermal energy for that particular range.[6] Furthermore sometimes insulations are not used in the production pipeline and there is a heat loss to surrounding environment. Thus, this heat loss will result a different surface temperature conditions in comparison with reservoir temperature conditions. In order to calculate the heat loss and find the changes in surface temperature onditions, the algorithm after Lindal Diagram(figure 2) was utilized to calculate water temperature at the surface. The calculations were conducted by considering both insulated pipe and not insulated pipe. 2

3 LINDAL DIAGRAM: (Figure 2) Lindal Diagram at Reservoir Conditions [6] 3

4 4

5 5

6 ALGORITHM Predicting Direct and Indirect Uses of Geothermal Energy in Major Oilfields of China Figure 3 is showing Lindal Diagram of water at surface condition not taking insulation into account. Lindal Diagram changes drastically as visible in the Figure 3. When k is taken into account the Lindal Diagram obtained is very similar to that of Figure 2 hence not plotted. CONCLUSION Geothermal gradient of various dead oil wells of abandoned oil fields of China (HB, SL, LH, DQ, XN, HN, CQ) was reviewed based on Liu et al. (2016) which showed tremendous scope of direct or indirect application of geothermal energy for economical purposes. With reference to available geothermal gradient, at reservoir temperature conditions, Lindal diagram was built to display the economical and intelligent usage of geothermal energy.. Generally in real fields, reservoir temperatures and surface temperatures are not same due to heat loss in the surrounding environment. Therefore, heat loss calculations were calculated based on the real field assumptions. Heat loss calculation displayed change in surface temperature conditions in comparison with real reservoir temperature conditions. Therefore, based on these changes a new Lindal diagram was prepared and displayed. As the source of geothermal energy is coming from the dead oil fields, there is a possibility of traces of oil can come along with water. These traces may damage the agricultural crops or our equipments, thus, we need to remove the traces for oil by using filtration or any other economical techniques for smooth usage of geothermal energy. NOMENCLATURE Density (ρ, ) ; Mu (µ, cp); Prandtl number (Pr ); Reynolds Number (Re); Nusselt Number (v); Heat Transfer Coefficient (h, ); Resistance(R1, R2, R3); Heat(Q, ) REFRENCES Ω [1] Cheng et al 2005 [2] John W. Lund, Derek H. Freeston, and Tonya L. Boyd: "Direct Utilization of Geothermal Energy 2010 Worldwide Review"; World Geothermal Congress, Bali, Indonesia, April 2010 [3] Wikipedia(September 2012) [4] Geothermal Gradient in the Oilfields in China- Changwei Liu, Kewen Li, Youguang Chen, Jinlong Chen; China university of geosciences (Beijing), China. Stanford University, Stanford, California, February 22-24, 2016 SGP- TR-209 [5] Pipe and pipe flow assumptions from [6] Lindal Diagram overview: Uses of geothermal energy in food and agriculture- FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, Rome, 2015-Minh Van Nguyen, Sigurjón Arason, Margeir Gissurarson & Páll Gunnar Pálsson 6