Techno-economic performance of multi-generation energy system driven by associated mixture of oil and geothermal water for oilfield in high water cut

Highlights

• Poly-generation energy system is presented.

• Associated geothermal water is the heat source.

• Thermodynamic and economic analyses are conducted.

• The economic performance is excellent.

Abstract

Geothermal energy is an important renewable energy. Oilfields in high water cut stage are also geothermal fields. We propose a geothermal cascade utilization system, including organic Rankine cycle (ORC) power generation, Li-Br absorption refrigeration, oil gathering and transportation heat tracing (OGTHT) and heat. Associated geothermal water from abandoned oil wells is used as a renewable heat source. The thermodynamic and economic analysis of the cascade utilization system is carried out by establishing a mathematical model. In ORC system, we use two-stage series evaporation to reduce irreversible losses. The results show that there is an optimum evaporation temperature to maximize the net output power, thermal efficiency and exergy efficiency. It is found that the mass flow of the working fluid has a great impact on the system performance. In economic analysis, we find that both cost and benefit increase with the increase of geothermal water temperature (T_{gw in}) and driving heat source temperature. We use the payback period (PBP) as a comprehensive evaluation index of economy. The results show that there is an optimal temperature combination to minimize PBP. The smallest payback period occurs at the T_{gw in} is 383 K and the driving heat source temperature is 363 K, which is 3.07 years.

Introduction

People are facing an energy transition, which means that high-carbon energy dominated by traditional fossil energy is gradually replaced by low-carbon new energy and renewable energy (He, 2015). By 2040, renewable energy will account for 2/3 of global investment in power plants, because they become the lowest cost of electricity generation in many countries (Aie, 2017). In different renewable energy sources, geothermal energy has attracted more and more attention. Because geothermal energy has the advantage of large reserves and continuity (Zhu et al., 2015), Røksland et al. (2017) believe that the rational use of geothermal resources will contribute significantly to the global energy crisis. Mature oil and gas fields produce a large amount of wastewater with a temperature of 65−150 °C, and the water output gradually increases over the life of the field, so geothermal energy from existing oil and gas fields can be used to balance water management expenditures (Liu et al., 2018). In addition, the geothermal energy stored in hydrocarbon reservoirs has great potential, not only because but also compared with traditional geothermal fields, oilfields can exploit geothermal energy in a low-cost and low-risk way through existing wells and facilities (Wang et al., 2018a, 2018b).

In recent years, some field tests and preliminary studies have been carried out successfully to extract heat from oil fields. Due to increased operating costs and declining oil production, DOE used NPR-3 as a demonstration site for low-temperature geothermal energy recovery and installed a 250 kW organic Rankine Cycle (ORC) power plant to utilize the low enthalpy energy produced by hot co-produced water in the field (Bronicki, 2008; Sullivan et al., 2013). In 2011, CNPC installed a 400 kW binary generator in the Huabei oilfield, which was the first installation in China to generate electricity using the low enthalpy energy of a hydrocarbon field (Jin et al., 2016). Both mature and some unconventional fields are reported to produce large amounts of geothermal water (Xin et al., 2012; Kondash et al., 2017), and the heat energy needs to be extracted before the geothermal energy of these high water cut oil fields is used. Geothermal water with temperature is produced to the surface along with hydrocarbons, and the geothermal energy is then separated and used in a separator. Geothermal water at the outlet of producing wells should be classified according to temperature and flow rate. Geothermal water with low temperature can be used directly for building heating, greenhouse planting, crop drying and some industrial processes. In addition, it can be used for special oilfield applications, including oil gathering heat tracing, crude oil transportation and geothermal water flooding (Sullivan et al., 2013).

In the case that geothermal water temperature is slightly higher, geothermal energy is mainly considered to generate electricity. Limpasurat et al. (2011) pointed out that the accumulated electrical energy generated by the recovered geothermal energy of the reservoir by using the most advanced technology is about 246 MW. McKenna et al. (2005) found that fields along the Gulf Coast could generate more than 1000 MW of power. Kujawa et al. (2006) evaluated the possibility and usefulness of obtaining geothermal energy from an existing producing well, Jachowka K-2. Cheng et al. (2016) proposed a new method to improve the geothermal utilization efficiency by developing oil Wells, and the results showed that the geothermal well with thermal reservoirs could produce about 4 times the heat and electric power output as that without thermal reservoirs. Caulk and Tomac (2017) investigated the applicability of abandoned Wells in California for enhanced geothermal system (EGS) and low temperature deep borehole heat exchanger (BHE) applications. Scholars have done a lot of research on the ground power generation devices for the utilization of geothermal energy in oil fields with high water cut.

Since the geothermal water at the outlet of the hydrocarbon well is mostly medium and low temperature, the organic Rankine cycle (ORC) is an important technology for medium and low temperature thermoelectric conversion (Zhang et al., 2018a, 2018b, Zare and Palideh, 2018; Wang et al., 2017a, 2017b; Prananto et al., 2018; Zhang et al., 2018a, 2018b; Bina et al., 2017). The improvement of the basic ORC circular structure mainly includes the following aspects: Some scholars, such as Rong (2013); Desai and Bandyopadhyay (2009); Yari (2009); Mago et al. (2008a), (2008b) proposed a new ORC system with internal heat exchanger (IHE) to improve the performance. Zhou et al. (2016) showed that the novel partial evaporating organic Rankine cycle (PEORC) with R245fa/R227ea is able to generate about 24.7% more power than the traditional subcritical Organic Rankine cycle (SCORC) with R227ea as working fluid. Li et al. (2015, 2016) used two-stage evaporation technology to divide the heat source fluid into two temperature sections. The results show that two-stage evaporation can effectively reduce the irreversible loss caused by temperature difference heat transfer. Wang et al. (2012); Zhang et al. (2013); Shu et al. (2014) proposed a dual-loop Organic Rankine cycle (DORC), which consists of a high-temperature cycle and a low-temperature cycle.

Since only 10% of the energy of geothermal fluids can be converted into electricity in the geothermal power plant, waste water with a certain temperature after power generation should be reused (Zarrouk and Moon, 2014). Based on the geothermal energy generated by oil wells in the high water-cut period, LI et al. (2014) proposed a novel co-production system, including ORC, absorption refrigeration, gathering heat tracing, direct and indirect heating, and oil recovery. The results showed that R601a has the best system performance and the auxiliary cold source will increase the power output. Meng et al. (2020a) (2020b) compared four combined heating and power (CHP) systems and pointed out that the double flash organic Rankine cycle based CHP system had the highest generation efficiency under the coupling of geothermal fluid temperature and dryness. Mago et al. (2010) combined ORC with heating system, proposed CHP-ORC system and applied it to small commercial buildings. Sun et al. (2017) combined ORC with heating and refrigeration systems to make more cascade use of energy, and proposed CCHP-ORC system. Wang et al. (2018a) (2018b) put forward one kind of a novel combined cooling, heating and power (CCHP) system combined with compressed air energy storage (CAES) and use organic Rankine cycle (ORC) to recover the heat carried by air turbine exhaust. Mosaffa and Farshi (2018) compare the Regenerative CCHP (RCCHP) system with the Basic (BCCHP) system. The results show that RCCHP system has the smaller total cost rate while their thermodynamic performances are approximately the same. Lian (2014) have proposed a set of complementary renewable energy systems, including solar biogas fermentation, micro-gas turbine biogas power generation and ORC waste heat power generation. Meng et al. (2020a) (2020b) proposed a new distributed building energy supply system, and the results showed that the ORC as the power source of the vapor compression cycle (VCC) eliminated the conversion of mechanical work and electrical energy between ORC and VCC process.

In this paper, in order to improve energy efficiency and economy, a cascade utilization system, including power generation, refrigeration, the oil gathering and transportation heat tracing (OGTHT) and heating, is established on the basis of high water cut oilfields. Thermodynamics and economy of the system are also analyzed.