Gas Development Process Research Articles

An efficient data-driven global sensitivity analysis method of shale gas production through convolutional neural network

The shale gas development process is complex in terms of its flow mechanisms and the accuracy of the production forecasting is influenced by geological parameters and engineering parameters. Therefore, to quantitatively evaluate the relative importance of model parameters on the production forecasting performance, sensitivity analysis of parameters is required. The parameters are ranked according to the sensitivity coefficients for the subsequent optimization scheme design. A data-driven global sensitivity analysis (GSA) method using convolutional neural networks (CNN) is proposed to identify the influencing parameters in shale gas production. The CNN is trained on a large dataset, validated against numerical simulations, and utilized as a surrogate model for efficient sensitivity analysis. Our approach integrates CNN with the Sobol' global sensitivity analysis method, presenting three key scenarios for sensitivity analysis: analysis of the production stage as a whole, analysis by fixed time intervals, and analysis by declining rate. The findings underscore the predominant influence of reservoir thickness and well length on shale gas production. Furthermore, the temporal sensitivity analysis reveals the dynamic shifts in parameter importance across the distinct production stages.

Prediction of formation pressure based on numerical simulation of in-situ stress field: a case study of the Longmaxi formation shale in the Nanchuan area, eastern Chongqing, China

The in-situ stress and formation pressure are important parameters in shale gas development. They directly affect the well wall stability, the direction of horizontal well drilling, and the fracturing effect during the shale gas development process. There are abundant shale gas resources in the southeastern Chongqing-Sichuan area, but the structure in the area is complex, and it is difficult to predict the in-situ stress and formation pressure. Therefore, in this paper, a finite element simulation model was established based on a large number of seismic, logging, and experimental rock mechanics data and the prediction accuracy of the stress field simulation was effectively improved. The construction of the stress field was based on the combined spring model, as well as the data related to the measured in-situ stress and the formation pressure obtained during drilling. The coupling relationship between the in-situ stress, the formation strain, and the formation pressure were derived to carry out the prediction of the distributions of the formation pressure and the formation pressure coefficient. The prediction results showed that the present-day maximum principal stress direction in the study area was about NE65°–110°, and the present-day maximum principal stress was 56.12–93.79 MPa. The present-day minimum principal stress direction was about NE335°–20°, and the present-day minimum principal stress was 48.06–71.67 MPa. The formation pressure was 2.8–88.25 MPa, and the formation pressure coefficient was 0.74–1.55. The formation pressure distribution was greatly affected by fault, tectonic location, in-situ stress and rock petrophysical properties, and the overpressure areas of the formation were distributed in the synclines and the deeply buried areas. This study shows that the finite element based formation pressure prediction method is effective.

Pore Structure and Permeability Variations during Gas Displacement in Unconsolidated Sandstone Reservoirs through CT Reconstruction Analysis

The continuous gas displacement in unconsolidated sandstone gas reservoirs will necessarily result in the pore structure and rock permeability variations, which cannot be neglected in the gas development process. However, the variations have not been comprehensively addressed yet, especially for the rock structure in pore scale. This work presented the quantitative results of pore structure in microscale and permeability variations during gas displacement in unconsolidated sandstone reservoirs through computed tomography (CT) reconstruction analysis. The results indicated that a more than 3% increase in porosity after gas displacement resulted from the enlargement of the pore and throat with a diameter of more than 20 μm and 3 μm, respectively, owing to the release and migration of clay and fine particles, in spite of the distribution frequency decline of both pore and throat with a small diameter. The pore connectivity would be enhanced by the increase of the connected pores as well as the enlargement of the pore and throat sizes. However, the pore-throat coordination number could only change with slight improvement. In terms of permeability and relative permeability changes with pore structure, the improvement of permeability after gas displacement was higher than that of porosity, and the continuous gas displacement would broaden gas-water flow region and lower irreducible water saturation and residual gas saturation, and then, the equal phase relative permeability point would shift to the right. These investigations will contribute to more accurate reserve evaluation and productivity prediction.

Structural Strength Analysis of Tubing Load Measurement System for High Pressure and High Temperature Wells

The tubing load measurement system is used to monitor the force and vibration of the tubing string in the process of perforation, fracturing and extraction and judge the safety of the tubing string during use based on the monitoring values, which is a key equipment for obtaining downhole information of the gas oil and gas development process. In this study, a load measurement system is designed for high-temperature and high-pressure tubular strings in wells, and the full-scale mesh modeling and finite element force calculation are performed to obtain stress distributions and safety factors. The results show that under the condition of axial force of 1000kN, internal pressure of 100MPa and composite loading state, the safety factors of the instrument are 2.0, 2.01 and 1.97 respectively, all of which meet the requirements of safe use.

Coated proppants with self-suspension and tracer slow-release functions

Proppants play an important role to increase oil and gas output in shale oil and gas development process. Tracers are used to study the degree of heterogeneity and dynamic equivalence between injection and production wells to judge the state of oil reservoir. However, it is difficult to integrate both slow-release tracing and shale supporting functions in one material. The development of functional coated proppants with tracer slow-release function is of great significance. Here a simple method is developed to introduce a carbon quantum dots (CQDs) into polyvinyl alcohol (PVA) coated proppants and fabricate novel self-suspension proppants with tracer slow-release function. The PVA coating layer on ceramic proppants achieves the self-suspension ability. In the well, the PVA film melted in fracturing fluid and the CQDs were released as a tracer for downhole monitoring. The surface adhesion force of PVA-CQDs coated proppants is 2 times larger than that of ordinary ceramic proppants, and the liquid conductivity of the self-suspension slow-release tracer proppants (SSTP) can reach 51 D cm, which is 22.45% higher than original ceramic proppants at the closure pressure of 40 MPa. This work combined the coated proppants with the quantum dot tracer and obtained a new type of coated proppants with tracer slow-release function, which has a promising significance to improve oil and gas production and conducting cross-well monitoring.

Experimental Study on a Target Direction Finding Algorithm for Gas Leakage Detection in Underwater Structures

Aiming at the application scenarios of underwater structure gas leakage detection in marine oil and gas development process, the power spectrum characteristics of underwater structure gas leakage radiation noise are analyzed. An new target direction finding algorithm is proposed, and the gas leakage detection-finding software is designed. Then, the test platform is built to complete the experimental study of underwater structure gas leak detection. The test results show that the new target direction finding algorithm used in this paper is compared with the conventional beam forming algorithm. The difference between the maximum beam energy value and the sub-maximum value is bigger, indicates that the target’s resolving power is strong, which effectively improves the detection capability of gas leakage targets in underwater structures.

A slip-flow model for multi-component shale gas transport in organic nanopores

With the rapid development of shale gas resources, the accurate simulation of shale gas development process is becoming more and more important. Shale gas transport through nanopores of shale formation is the basic of shale gas development simulation. At present, the effect of impurities on methane transport through nanopores is neglected. In this paper, a novel model is presented for simulating multi-component shale gas transport through nanopores of shale formation. The effects of multi-component, slippage flow, and Knudsen diffusion are considered in the model. Results show that when the shale gas in nanopores is very thin, the Knudsen diffusion plays the dominant role over wide range of nanopore radius. While the effect of multi-component on Knudsen number and contribution degree can be neglected, both of the slippage flow rate and the Knudsen diffusion rate increase with increasing of CO2 content. Under medium pressure condition, there exists two turning points where the slippage flow and Knudsen diffusion take turns in charge of the shale gas transmission. Under high pressure condition, the slippage flow is the dominant factor over wide range of nanopore sizes. While the conductivities increase with decreasing methane content, the effect of multi-component on contribution degrees of slippage and Knudsen diffusion can be neglected.

Progress and prospects of natural gas development technologies in China

Under the present situation of low global oil prices and vigorous development of green energy resources, China has turned to focus on natural gas in oil and gas sector, both production and consumption of which are soaring high these days and the role of which is gradually prominent in energy sources. With the aims to help promote the further rapid development of natural gas business in China, this paper analyzed natural gas development process and summarized the new advances in natural gas development technologies in the recent years. On this basis, this paper analyzed the prospects of natural gas development in China in the four aspects of production rates, demand potential, import volume, future position of natural gas. The following results were obtained. (1) Since the 12th Five-Year Plan, natural gas business has been doing well with a rapid increase of consumption, diversified supply sources, steadily increasing of reserves and production rates, obviously satisfactory benefits from exploitation. (2) Breakthroughs have been made in technical bottlenecking problems with an improved innovation capacity in the respects of deep-strata gas development, large-scale gas field development adjustment, tight-gas recovery enhancement, development of shale and CBM gas, engineering techniques, and development strategies support system. (3) With the deepening of development, influenced by policies, environment concerns and geological conditions, continuous efficient natural gas development will face up with such challenges as lower ratio of quality reserves, higher gas field development expenses, more difficult benefit development of unconventional gas reservoirs, further compressed upstream benefits, less stable production capacity of those major gas fields, increasingly fierce competition in the energy market, etc. In conclusion, it is demonstrated that natural gas development in China will enter into a new stage of attaching equal importance to both unconventional and conventional gas; natural gas demand potential will be great and its consumption structure will become more diversified; gas imports will rise year by year, resulting in the vigorously increasing external dependency; and natural gas will become the main growth engine in the process of energy mix adjustment.

Public perceptions of shale gas in the UK: framing effects and decision heuristics

Using two equivalent descriptions of the shale gas development process, we asked individuals to indicate their levels of support as well as their perceptions of the risks and costs involved. In version 1, shale gas development was framed as ‘fracking’, whereas under version 2 it was framed as ‘using hydraulic pressure to extract natural gas from the ground’. We find that individuals’ support for shale gas development is much lower when using the term ‘fracking’ as opposed to the synonymous descriptive term, and moreover, these differences were substantive. Our analysis suggests that these differences appear to be largely the result of different assessments of the risks associated with ‘fracking’ as opposed to ‘using hydraulic pressure to extract natural gas from the ground’. Our proposed explanation for these differences rests on the idea that shale gas development is a technical and complex process and many individuals will be bounded by the rationality of scientific knowledge when it comes to understanding this process. In turn, individuals may be relying on simple decision heuristics shaped by the way this issue is framed by the media and other interested parties which may constrain meaningful discourse on this topic with the public. Our findings also highlight some of the potential pitfalls when it comes to relying on survey research for assessing the public’s views towards complex environmental issues.

Trends in the natural gas pricing mechanism reform in China: a perspective of dependency between China and the US natural gas markets

Establishing a natural gas market pricing mechanism is crucial to Chinese market reforms. This paper explores the achievements of pricing mechanism reform since 2013 and examines the current market trends. We used copula function to analyse the relationship between liquid natural gas arrival price in Guangzhou and the Henry Hub natural gas spot price in the USA from 2013-2017. The correlations between the natural gas market prices increased from 2013-2015, with rank correlation coefficient reaching a maximum of 0.73 in 2015; Although the correlations were negative from 2016-2017, the decreasing negativity indicates China's market price converged to that of the USA from 2013-2015 and had a temporary separation in 2016 and 2017. It was concluded that while China's natural gas pricing mechanism is becoming more dependent on market mechanisms, it needs to be strengthened by learning from the US natural gas development process.

Trends in the natural gas pricing mechanism reform in China: a perspective of dependency between China and the US natural gas markets

Establishing a natural gas market pricing mechanism is crucial to Chinese market reforms. This paper explores the achievements of pricing mechanism reform since 2013 and examines the current market trends. We used copula function to analyse the relationship between liquid natural gas arrival price in Guangzhou and the Henry Hub natural gas spot price in the USA from 2013-2017. The correlations between the natural gas market prices increased from 2013-2015, with rank correlation coefficient reaching a maximum of 0.73 in 2015; Although the correlations were negative from 2016-2017, the decreasing negativity indicates China's market price converged to that of the USA from 2013-2015 and had a temporary separation in 2016 and 2017. It was concluded that while China's natural gas pricing mechanism is becoming more dependent on market mechanisms, it needs to be strengthened by learning from the US natural gas development process.

Achieving the 1.5\xa0\xb0C objective: just implementation through a right to (sustainable) development approach

Achieving the 1.5 °C objective of the Paris Agreement on Climate Change in a just manner requires equitably sharing the responsibilities and rights that relate to this objective. This paper examines how international law concerning the Right to Promote (Sustainable) Development can contribute to determining what would be a “just” approach to achieving the 1.5 °C objective. This entails building on both the Right to Development (RtD) and the Right to Promote Sustainable Development (RtPSD). The RtD is a central notion within international human rights law and the RtPSD has been adopted under the UN Framework Convention on Climate Change (UNFCCC). Based on a literature review and legal analysis, we argue that, although the two Rights are prima facie different, in the context of the unanimously adopted Agenda 2030, including the SDGs, they partly complement and partly merge with each other. Together they provide a framework for assessing how a just transition towards a low greenhouse gas development process could be achieved and what this means for phasing out fossil fuels especially in the context of prospective oil producing countries.

Application of three different water treatment technologies to shale gas produced water

Shale gas produced water is a hypersaline wastewater that is generated during the shale gas development process called as a hydraulic fracturing. The produced water contains many substances including inorganic salts, organic compounds, and particulates. The treatment process of the produced water is mainly composed of four parts: oil and water separation, removal of suspended solids, removal of organics, and salts removal. This study focuses on the total dissolved salts removal through applying three different desalination techniques – membrane distillation (MD), reverse osmosis (RO), and evaporative crystallization (EC). The experiments were conducted using synthetic shale gas produced water to understand the changes of chemical properties in permeate and concentrate. In the permeate solution, MD and EC showed more than 99% of salts removal efficiency for all ions, but RO showed relatively low efficiency. In the concentrate solution, the concentrations of all ions varied according to the type of ions and applied treatment methods.

Study on Borehole Stability of Unconsolidated Sandstone in Depleted Reservior

Reservoir pressure will decline generally along with production in the oil and gas development process. There are some problems such as borehole collapse or reduced diameter and lost circulation in drilling of initial production stage in unconsolidated sandstone. As the formation pressure declines the stress around borehole changes, and then collapse pressure and fracture pressure are affected. Especially in directional wells, variation of wellbore stability is more complex with different borehole deviation and azimuth. The calculation models of collapse and fracture pressure in depleted reservoirs were established, and relevant data in unconsolidated sand reservoir of an oilfield in Bohai Sea was used to calculate collapse pressure and fracture pressure of directional wells in the condition of pressure depletion before and after. The results showed that collapse and fracture pressure decreased as formation pressure depletion, and safe drilling fluid density window was wider when drilled to the direction of minimum horizontal principle stress. The calculation results can be reference to drilling design of adjustment wells in unconsolidated sandstones.

Regulation of Shale Gas Development, Including Hydraulic Fracturing

This paper provides one of the first detailed surveys of current oil and gas and hydraulic fracturing (also called fracing, fracking, or hydrofracking) regulation. It identifies and compares the environmental laws and regulations that apply to most stages of the oil or gas development process in shales and tight sands, from conducting seismic testing to constructing a well pad, drilling, withdrawing water, completing a hydraulic fracture treatment, and storing and disposing of waste. It briefly describes municipal ordinances and federal regulations, including recently-announced EPA regulatory efforts, but focuses primarily on the states, comparing regulations in sixteen states. The paper's comparison tables show that state regulations in some areas vary substantially, and the paper attempts to connect the potential risks of oil and gas development from shales and tight sands -- which are addressed in another Energy Institute paper by Professor Ian Duncan -- to the regulation. The paper concludes that states should modify certain regulations to address these risks. Some states do not require specific types of blowout prevention, for example, offering only a narrative standard, yet well blowouts are an important concern at the drilling and fracturing stage. States also should update their casing and cementing regulations to protect well integrity during drilling and fracturing and ensure long-term well integrity, and they should require the testing of water around proposed wells before site construction begins. Ideally, states also would consider implementing a presumption of oil and gas operator liability for water well contamination, as Pennsylvania and West Virginia have done. For risks at the well surface, states should update spill prevention requirements at well sites and consider whether federal Department of Transportation regulations addressing the movement of fracturing chemicals adequately protect against spills. States also must explore better options for disposing of large quantities of new wastes and regulating the withdrawal of large volumes of water for fracturing to prevent adverse impacts to streams and overuse of underground sources of water. Further, states and the federal government must enhance air quality monitoring around sites and consider additional controls. Finally, the collection of more and better data, including information from baseline and post-production water testing, is essential. With states at the regulatory helm, comparison of public law strategies to address development risks can produce fruitful cross-jurisdictional lessons. The Energy Institute at the University of Texas funded the research for this paper.