A system dynamic model for natural gas safety supply and demand balance mechanism

The security of natural gas supply and demand has always been an important topic, and as a result, analyzing and predicting the supply and demand of natural gas has received considerable attention from researchers. Numerous studies have extensively researched the supply and demand of natural gas. The main purpose of this study is to explore the supply‐demand balance mechanism for natural gas security. A system dynamics model is constructed to assess the supply and demand of natural gas in Sichuan Province, China. A new system dynamics model based on domestic gas, production gas, ecological environment and natural gas supply is proposed. The study considers four scenarios: natural development, economic priority development, environmental priority development and coordinated development. The results show that the rapid economic development has led to an excessive environmental carrying capacity, a larger gap between natural gas supply and demand, a decline in the quality of life of residents, and even affected the energy security of Sichuan Province and China. The findings also show that people's overprotection of the environment can lead to slow economic development, which prevents it from achieving its desired goals. The coordinated development scenario in this paper not only ensures the production of natural gas and the quality of life of residents, but also is an optimal scheme with low energy consumption and pollution. According to the research conclusions, considering the overall situation of China's energy security and the situation in Sichuan Province, the author proposes reforms from the supply and demand sides of natural gas.

2][3] Natural gas is now widely used in residential, industrial and commercial areas.In growing economies such as China's, the country has pledged to peak carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060. 4 The construction of the natural gas supply and demand system is an important force in building a new domestic and international "dual circulation" pattern, and it is also an essential link.The "China New Era Energy White Paper" clearly pointed out that China should deepen the supply-side structural reform as its main task and build a diversified clean energy supply system.As a clean energy source, natural gas provides a favorable guarantee for the synergies of production-living-ecological (PLE).During the 14th Five-year Plan period, natural gas will play a key role, driven by policies such as air pollution, carbon peaking and carbon neutrality.Sichuan province is one of the earliest areas in the world to exploit natural gas and is a significant natural gas producer in China, leading the development of the domestic natural gas industry. 5,6However, as a major province of resources and energy consumption, there are some problems, such as the contradiction between supply and demand, the phenomenon of "price inversion" of natural gas external transfer and internal delivery, the uncoordinated development of regions, and the severe situation of energy conservation, the stable development of natural gas market is facing great challenges.Under the background of the slowdown of China's economic growth, we need to scientifically and systematically forecast the variation trend of natural gas production and consumption in Sichuan, and the control ability of related factors.This will help optimize the natural gas industry policy and promote the optimal allocation of the natural gas resource market, which is of great strategic significance to the coordinated development of PLE.
However, the variation trend of natural gas production and consumption is dynamic and complex.Using traditional techniques to predict future trends or results may ignore the volatility of complex systems, making these methods unreliable.The system dynamics (SD) approach can make up for these deficiencies.Based on the natural gas supply and demand of SD model, this paper will introduce PLE idea, integrating different elements, such as natural gas supply, demand and production, living and ecological relationship.Based on the SD approach of natural gas supply and demand, it can carry out the Sichuan natural gas utilization of scene simulation, and provide scientific decision-making for the state natural gas in the development of long-term use of reference.The key recommendations can be adopted by other countries around the world.

| Supply and demand of the natural gas industry
Now the research on supply and demand of the natural gas industry mainly focuses on method improvement, system structure and optimal distribution.Xie and coworkers 7 focused on the external environment and supply-demand characteristics of natural gas and identified the main factors.Using the principal component analysis method, this initially affected the security of natural gas supply and demand.Ye et al. 8 also studied natural gas security from the perspective of supply and demand, NGSI was formulated, and provided a reference method for energy security evaluation for countries with different policies.Considering seasonal fluctuations in natural gas demand, Lin et al. 9 constructed a model of China's natural gas distribution system, there were four main factors: the perspectives of supply, demand, transportation system and pricing mechanism.SD approach has been drawn up for review all aspects of the natural gas system.Nair was the first to use the idea of SD in energy planning in 1973, when he developed a model for the U.S. natural gas industry. 10The SD approach was used to model Iran's natural gas supply and demand system to determine whether the current policies meet its long-term natural gas demand. 11,12A new SD approach had been established from the aspects of natural gas investment, reserve exploration and well construction in China to analyze the impact of investment, policy and technology on the natural gas industry. 13Mu and co-workers 14 established the dynamics of natural gas supply and demand system to analyze and predict the consumption of natural gas in China from the two factors of GDP and national population.Besides, different scenarios for natural gas export in Iran, such as export at citygate prices, transfer through electricity markets, direct transfer at forward and hub prices, and conversion into electricity for exporting at a forward price, had been established using SD. 15

| The coordinated development of PLE
According to the report of the 19th National Congress of the Communist Party of China (CPC), the direction of the development of civilization in the new era is to develop production, live a well-off life, and maintain a sound ecological environment, that is, to coordinate the development of life, ecology, and production.At present, the development of urbanization and industrialization has aggravated the deterioration of the ecological environment.To alleviate the contradiction between life, production and ecology, it is a primary national task to make the three develop harmonically.Domestic scholars on the PLE mainly focus on three aspects: the first is the study of land use function.Heng et al. 16 simulated the urban and rural residential areas in Aksu city with high precision, discussed the main tasks of PLE in different areas, and put forward the layout optimization.Someone has taken the GBA in China as an example to comprehensively evaluate the sustainable development level of the space from the perspective of PLE, using a dual environmental assessment system consisting of resource and environmental carrying capacity assessment and territorial spatial development suitability assessment.This method provides a useful reference for any country. 17,18The second is the study of the space carrying capacity of PLE.0][21] Third, researchers constructed the evaluation system from the perspective of PLE optimization, which can provide a better basis for the optimal allocation of regional land resources. 22,23It can be seen that the coordinated development of PLE space is conducive to promoting the sustainable development of economy and environment.
In conclusion, we noticed that there are two gaps in the current research.First, shale gas in China is in the initial stage of development, and there are few studies on the prediction of shale gas output.Especially, Sichuan is rich in shale gas resources, which will play a vital role in the supply of natural gas in the future, and has important strategic significance for the in-depth study of shale gas.Second, the natural gas supply and demand system is a complex and dynamic feedback system, which is closely related to life, production and ecology.Currently, there are limited dynamic studies on the supply and demand of natural gas from the perspective of PLE.In particular, the quality of life of residents is seldom taken into consideration in the natural gas supply and demand system, and its decision-making ability needs to be improved.
This study makes innovative additions and contributions to the current deficiency.This study will deliver a novel SD approach to natural gas supply and demand systems to help predict the supply and demand of natural gas in the future.The differences between this study and previous studies are in its structure and purpose.The approach cleverly incorporates PLE into the system structure, which more comprehensively reflects the supply and demand of natural gas compared with the current research.The other specification of this study is its purpose, and the approach aim is to show that the sustainable development of natural gas industry is a complex and dynamic feedback system, which is closely related to life, production and ecology and affects the life quality of the residents.Therefore, the quality of life of residents can be improved through the approach.

| METHODOLOGY
SD is a powerful modeling approach based on control and nonlinear dynamics theory, which was originally conceived by Jay Forrester in 1961. 24SD revolves around creating computer simulations to understand how different feedback mechanisms influence the behavior of complex systems.In essence, SD provides a means to understand how various factors interact and influence the dynamic evolution of the system as time progresses.The essence of the SD model is a first-order differential equation with delay.Figure 1 and Formula (1) contain exactly the same information and are strictly equivalent. 11,25The SD approach is widely applied to energy problems.Taking the Australian energy sector as the research object, Laimon and coworker 26 adopted a SD method to explore the impact of renewable energy systems on energy sector performance.Aslani et al. 27 also used an SD method to explore the role of renewable energy in Finland's energy dependence.Mu et al. 14 established a natural gas supply and demand model in China based on SD, and simulated the natural gas demand and consumption structure in China.

| System boundaries and basic assumptions
The natural gas supply and demand system not only conforms to the characteristics of integrity, correlation and dynamics, but also conforms to the characteristics of nonlinear, high-order and multi-loop behavior, so it meets the requirements of SD modeling.Based on the classic Energy-economy-environment (3E) system, it follows the principles of representativeness, simplicity and availability, 28 combined with the actual development situation in Sichuan, and comprehensively considering the factors affecting the sustainable development of natural gas, the system is composed of four subsystems: domestic gas, production gas, ecological environment and natural gas supply (Figure 2).To better construct the model and ensure its stable operation, the model mainly considers assumptions as following: (1) The system does not take into account major policy changes and large economic fluctuations; (2) Assume that policies and technologies have no significant fluctuations during conventional natural gas development; (3) The price of natural gas is not considered.

| Data source and model description
The

| System flow diagram and main parameters are determined
To clarify the interaction and feedback mechanism of Sichuan natural gas supply and demand balance system from the perspective of PLE, the dynamic flow diagram of Sichuan natural gas supply and demand system (Figure 3) is established.The model contains 54 variables, among which state variables include total population, GDP and shale gas production, and rate variables include population change, GDP increase, shale gas constant increment, and the rest variables are auxiliary variables.
The large-scale and commercial development time of Sichuan shale gas is 2016, so the shale gas before 2016 is not included in the parameter of shale gas production in this system.The forecast data is based on the actual development situation, and regression and fitting of parameters such as the GDP growth rate, production, per capita consumption, natural gas consumption per unit GDP, natural population growth rate, urban population ratio, transfer volume from the province, R&D personnel and other parameters with the help of MATLAB tools, The prediction model is presented, and the error between the calculation result of the fitting model and the actual data is small.Individual data can be modified by expert evaluation and empirical prediction.For the missing part of the data and methods, such as exponential smoothing, formula derivation, fuzzy comprehensive evaluation, and expert evaluation are mainly used for calculation.Some constant parameters adopt the method of weighted average and arithmetic average to select the data.In the life dimension, the parameter of resident happiness index is selected for analysis.The equation draws on Lingling's 29 formula for calculating the national happiness index, as shown in the following formula: where R is the income growth rate of residents in Sichuan Province; P the environmental pollution index; T inflation; S the unemployment rate; and G the Gini coefficient.

| The main equation setting of the model
Explain the equations involved in the model.
(  had no error, and the model running did not produce ill results, the construction of the model is reasonable.

| Historicity test of model
Another validity test is the historical simulation tests that compares real data with simulation results.this study used a historical time series consisting of 15 years, GDP, natural gas consumption and natural gas supply are selected to test，the absolute error rate of relative parameters is less than or equal to11.3%(Figure 4).The fitting effect of the model is significant, and the simulated values calculated by the model match the actual values, 30 which can predict and simulate the supply and demand security of natural gas in Sichuan in the next few years.

| The sensitivity of the model
Sensitivity analysis plays a critical role in validating the model, as it focuses primarily on examining how sensitive the state or output variables of an analytical system model are to changes in system parameters or surrounding conditions. 31Taking the consumption factor as an example, the adjustment of the proportion of industrial gas is utilized in this demonstration, as shown in Figure 5. Notably, altering a single parameter does not The main system dynamics equation of Sichuan natural gas supply and demand model.

Main variable Equation Unit
Transfer volume from the province IF THEN ELSE(consumption − conventional natural gas production − shale gas production + transfer volume from the province ≥0 , consumption − conventional natural gas production-shale gas production+transfer volume from the province, 0) ×10 9

| Scenario modeling
The situational settings in this article are based on the overall development goals of the "14th Five-Year Plan for Energy Development of Sichuan Province" and the "14th Five-Year Plan for National Economic and Social Development in Sichuan Province".To examine the effects of changes in policies, technology, and natural gas consumption structure on the quality of life, production efficiency, ecological environment and supply effects of residents, four scenarios are designed (Table 2).The first scenario is the continuation of the current policy and the natural development (model Ⅰ), The parameter values in this scenario remain the same as the 2019 values.
The second scenario is the economic priority development (model Ⅱ), It increases the proportion of the workforce, enhances the intensity of investment in science and technology, increases the energy tax reduction ratio, and increases the proportion of industrial gas.At the same time, considering the cost of policies, it lowers the emission requirements for environmental pollutants.Other parameters remain consistent with the first scenario.
The third scenario is the environmental priority development (model Ⅲ), aims to directly stimulate environmental protection investment by reducing the proportion of the environmental pollution index.This reduces the emissions of SO 2 and COD, shifting the system's development towards environmental protection.Meanwhile, other parameters are reduced.
The fourth scenario is the coordinated development of economic development and environmental protection (model Ⅳ).The coordinated development of the system emphasizes the combined effects of different policies.In this article, adjustments are made to all important parameters under the coordinated scenario, but the magnitude of these adjustments is smaller than that of the corresponding specific scenarios, even though the system tends towards coordinated development.

| Natural development scenario
The natural development scenario mainly predicts the supply of natural gas in Sichuan based on the current economic development, the law of population growth and government policy unchanged.As can be seen from Figures 6-8, the average happiness index residents is 7.12 according to the natural development mode.With the maturity of shale gas exploitation technology, the production of shale gas has a trend of rapid rise.By 2030, the production of shale gas will reach 56.89 billion cubic meters, and the supply will reach 92.37 billion cubic meters.However, with the development of economy and the improvement of residents' requirements for quality of life, the demand for natural gas continues to increase, reaching 92.36 billion cubic meters by 2030, and the inflow from other provinces reached 10.22 billion cubic meters in the same year.Carbon dioxide emissions will peak at 4.281 million tons by 2029.

| Economic priority development scenario
The economic priority development scenario is mainly to increase the proportion of industrial gas, increase scientific and technological input, increase the ratio of the workforce, and increase government financial input, but it brings economic benefits and at the same time brings irreversible costs to the environment, and people's quality of life is also constant decline.As seen from Figures 6-8, fiscal and tax policies and economic levers have effectively increased the output of natural gas, especially shale gas.By 2030, the output of shale gas will reach 81.55 billion cubic meters and the supply will reach 146.36 billion cubic meters, far exceeding the output of the other three development modes and 50 billion cubic meters more than that of the coordinated development mode.67.77 billion cubic meters more than the environment-priority model; but the rapid economic development also makes the demand gap for natural gas of residents greater.By 2030, the consumption of natural T A B L E 2 Variation of regulatory parameters in the dynamic model of Sichuan natural gas supply and demand system.

| Environmental priority development scenario
The environment-priority development model is mainly achieved by reducing the government's subsidies for and tax policies, the intensity of investment in science and technology, and the proportion of industrial gas consumption.As can be seen from Figures 6-8, the happiness index of residents is the highest, with an average index of 17.01.By 2030, carbon dioxide emissions will also be low, at 1.958 million tons.Due to strict environmental monitoring, the consumption of natural gas is also the lowest, which will be only 43.67 billion cubic meters in 2030, 102.69 billion cubic meters less than that in the mode of economic priority development.From the perspective of the transfer of natural gas from other provinces, it will be zero from 2018.However, the supply of natural gas will only reach 78.59 billion cubic meters in 2030.According to Sichuan province's "14th Five-Year" Petroleum and Natural Gas Development Plan, the natural gas output will reach about 85 billion cubic meters, which is far from the strategic target.

| Collaborative development scenario
The collaborative development scenario mainly combines source taxes, appropriate financial subsidies for shale gas extraction, increases the intensity of scientific and technological investment, and also considers the improvement of residents' quality of life, taking into account the economic, environmental, and quality of life aspects.Appropriately increase the intensity of the policy, and reduce the levy part to achieve green, clean and efficient use of energy.As seen from Figures 6-8, the production curve of shale gas is close to that of the economic priority development model.By 2030, the production of shale gas will reach 71.71 billion cubic meters, which is only 9.84 billion cubic meters less than that of the economic priority development model; consumption and carbon dioxide emissions are very close to the consumption of modelⅠ, and the carbon dioxide emission curves of model I and modelⅣtend to coincide.However, from the perspective of the inflow from other provinces, the inflow is small, with an average annual inflow of only 2.52 billion cubic meters, and the average annual inflow in 2019, 2024, 2025, 2026 and 2030 is 0. Meanwhile, people's quality of life was relatively high, with an average happiness score of 11.07.

| Overall scenarios comparison
From the economic development perspective, modelⅡ is better than the other three models.The accelerated economic growth rate increases Sichuan province's total GDP rapidly, increasing the demand for natural gas consumption in production and living.But it seriously exceeds the environmental carrying capacity, and the gap between supply and demand of natural gas increases sharply, which seriously affects the energy security of Sichuan province and even China.
From the ecological perspective, modelⅢ is better than the other three models.Because it can effectively control, the amount of carbon dioxide emissions, the quality of life of residents is guaranteed, which is consistent with the direction of improving people's health in China's "Healthy China 2030" plan outline, and also well fulfills the commitment of the UN 2030 Agenda for Sustainable Development.
From the perspective of the coordinated development of the PLE, modelⅣ is more effective.It takes into account all aspects of the economic, environmental, and quality of life.While ensuring the adequate supply of natural gas and the safe use of various consumption areas, it also effectively reduces environmental pollution.In line with the actions of "Healthy China 2030" Planning Outline, and create favorable conditions for the realization of a civilized development path featuring production development, a prosperous life, and a sound ecological environment.ModelⅣ provides an ideal scenario for the sustainable development of natural gas in Sichuan.
The sustainable development of the natural gas industry should consider people's livelihood, national policies and the ecological environment, which is conducive to industry managers and decision-makers making accurate judgments and decisions.The results of our research are well-matched with the study conducted by Man et al. [32][33][34]

| CONCLUSION
The presented model in this paper, the safety supply and demand system of natural gas is designed from the perspective of PLE, including four sub-systems: domestic gas, production gas, ecological environment, and natural gas supply and demand.The SD approach is used to simulate the natural development scenario, economic priority development scenario, environmental priority development scenario and collaborative development scenario are simulated.
This model examines how the different factors the dynamic system, and by simulating the results, the government can potentially make complementary policies from the supply and the demand sides.Furthermore, the results from the study show that the natural gas supply in the later stage is mainly from shale gas, and the investment in science and technology and fiscal and tax policies are the main factors that affect shale gas production.This requires varying measures of increasing investment in science and technology and rationally distributing tax policies.In terms of natural gas consumption, population growth rate, residents' quality of life, economic development and residents' attitude to environmental pollution treatment will all affect the consumption of natural gas.This requires varying measures of accelerating the construction of crossprovincial cooperation and using economic leverage to optimize the gas consumption structure.

| LIMITATION
In this study, Vensim software was used to simulate and analyze the balance mechanism of natural gas supply and demand in Sichuan, which provided a reference for the sustainable development of natural gas in and can also help other cities to solve the problem of natural gas supply and demand.However, there were some limitations in this study, as more data needed to be collected on shale gas production, and all consumption sectors were considered as a whole with the same natural gas price, which was not sufficiently reflected in the peak regulating mechanism and the price mechanism, which needs to be improved in future research.

F I G U R E 3
Natural gas supply and demand model system flow diagram.

4
Real data simulated results.(A) GDP, (B) natural gas consumption, and (C) natural gas supply.F I G U R E 5 Changes in the sensitivity of the model triggered by the proportion of industrial gas indicators.

7 8
Simulation results of natural gas consumption and provincial allocation from 2005 to 2030.(A) Consumption and (B) transfers from other provinces.Simulation results of residents' happiness index and carbon dioxide emissions from 2005 to 2030.(A) Resident happiness index and (B) carbon dioxide emissions.