Editorial: advances in accumulation conditions of unconventional oil and gas resources in complicated structure areas

Assessment of global unconventional oil and gas resources

The demand for energy is increasing along with the rise in population. Indonesian people rely on conventional resources such as coal, oil, and natural gas to meet their energy needs. It is estimated that coal can only be exploited for up to 61 years, natural gas for 34 years, and oil for 19 years. Meanwhile, Indonesia possesses unconventional oil and gas resources (e.g., coal bed methane (CBM), tight gas, shale gas and oil, and methane hydrate), estimated to reach 1,800 trillion cubic feet (TCF). These resources are in the exploration stage and have yet to be fully exploited due to technological limitations. Nevertheless, the Indonesian government continues to emphasize the development of this type of energy resource. Therefore, this study conducts a review of the potential of unconventional oil and gas resources in Indonesia, covering characteristics, potential occurrences in Indonesia, exploitation methods, utilization as a source of energy, and opportunities and challenges in their application. The method used is a narrative review based on secondary data by examining papers published in reputable national and international journals in the last ten years. Results show that unconventional oil and gas resources have different characteristics, including permeability, porosity, and depth. CBM can be found at the shallowest depth, followed by tight gas, methane hydrate, and the deepest is shale gas. Potential occurrences of these resources in Indonesia include gas hydrate (858.2 TCF), then shale gas (574.07 TCF), coal-bed methane (453.3 TCF), and shale oil 11.24 million tons. Exploitation can be done in various ways, such as dewatering for CBM, hydraulic fracking for tight and shale, and depressurization for methane hydrate. Once exploited, methane gas can be used for power plants, vehicle fuel, and industrial and household needs. Opportunities and challenges from various aspects, as well as applicable laws in Indonesia, are also discussed. In this light, the contribution of our study is to provide a comprehensive review of the characteristics, location, exploitation methods, opportunities, and challenges of utilizing unconventional oil and gas resources in Indonesia.

As conventional gas resources are depleted, unconventional gas (UG) resources (gas from tight sands, coal beds, and shale) are becoming increasingly important to U.S. and world energy supply. The volume of UG resources is generally unknown in most basins outside North America. However, in 25 mature North American basins, UG resources have been produced for decades, and resources and reserves are well characterized. The objective of this work was to evaluate recoverable UG resources and determine the quantitative relations between known conventional and unconventional hydrocarbon resources in mature North American basins, with the goal of using these relations to estimate unconventional hydrocarbon resources in basin outside North America, which we call frontier basins.We used data from the U.S. Geological Survey, Potential Gas Committee, Energy Information Administration, National Petroleum Council, and Gas Technology Institute to evaluate relations among hydrocarbon resource types in the Appalachian, Black Warrior, Greater Green River, Illinois, San Juan, Uinta-Piceance, and Wind River basins. We chose these seven basins for preliminary analysis of relations between conventional and unconventional gas resources because they are mature basins for both conventional and unconventional oil and gas production. To conduct this analysis, we wrote a computer program that we call PRISE (Petroleum Resources Investigation Summary and Evaluation). Input data for PRISE, obtained from the published data sources, were the values of technically recoverable resources, which were the sum of the following resource categories: cumulative production, proved reserves, growth, and undiscovered recoverable resources. We then compared technically recoverable conventional and unconventional resources for each basin to evaluate relationship between conventional and unconventional resource volumes in these seven basins.For the seven basins studied, we found that 10% of the total recoverable hydrocarbon resources are conventional oil and gas, whereas 90% of the recoverable hydrocarbons are unconventional resources. We propose that the results of this study may be used to estimate recoverable resources from unconventional gas reservoirs in target (frontier) basins, where conventional oil and gas resources are known but unconventional resources have not been evaluated.

Global oil and gas resources include both conventional and unconventional oil and gas resources. There are four parameters for evaluating conventional oil and gas resources, namely, cumulative production, remaining recoverable reserves, reserve growth from discovered oil and gas fields, and undiscovered recoverable resources. Seven main types of unconventional oil and gas resources, including shale oil/tight oil, heavy oil, oil sands, oil shale, shale gas, tight gas, and CBM have been evaluated. During this evaluation, the conventional and unconventional oil and gas resources have been considered as a whole, and a system of processes and methods have been established to evaluate all types of conventional and unconventional oil and gas resources by oil and gas accumulation play considering each basin as a whole and each petroleum system as a core.

The Ordos Basin is the largest oil and gas producing basin in China, where tight oil, shale gas, oil shale, and other unconventional oil and gas resources have been found in the Chang7 subsection of the Triassic Yanchang Formation. However, the mechanism of formation and the distribution of unconventional oil and gas resources in the shale layers have not been systematically investigated until now. According to the type of unconventional oil and gas resources, main controlling factors, and the maturity, depth and abundance of organic matters, the shale oil and gas resources from Chang7 region are divided into five zones that include an outcrop-shallow oil shale zone, a middle-matured and medium-burial shale oil zone, a medium-matured and medium-burial in situ conversion process (ICP) shale oil zone, a high-maturity and deep-burial shale gas zone, and an adjacent-interbedded tight sandstone oil zone. By the distribution of resources, orderly evolution of oil and gas resources and coexistences in lacustrine shale formations have been put forward, and also a strategy of integrated exploration and development of resources in the shale formations is proposed. Overall, the outcome of this study may guide on the effective utilization of unconventional oil and gas resources in other shale formations.

Historically, renewable energy technologies have been seen as a source of competition by the oil and gas industry. However, the oil and gas industry is now one of the primary sources of investments in renewable energy technologies. The oil and gas industry in California, in particular, has been making significant investments in renewables and leveraging the latest renewable energy technologies to reduce the carbon footprint of oilfield applications. This study analyzes the latest advances in renewable energy solutions, their impact on energy transition efforts in the state, and the potential of further developing conventional and unconventional oil and gas resources in California. This paper has focused on conducting a thorough review of literature related to the latest advances in renewable energy technologies and energy transition efforts in California and the applications of these technologies in reducing the carbon footprint of oilfield activities, along with examples of renewables as a complementary resource to oil and gas. Furthermore, the availability of conventional and unconventional oil and gas resources in the state has been summarized. The potential of developing these resources in the future is analyzed in detail. The literature includes a comprehensive set of references ranging from peer-reviewed journal publications and proceedings to data from market studies and other non-technical publications and market predictions by renowned experts. The position of renewable energy resources either as a competing or complementary source to oil and natural gas in California and the impact of these resources in energy transition efforts in the state are discussed. Examples of the use of renewable energy technologies to improve various processes within oil and gas production operations are provided, and the prospect of further developing conventional and unconventional oil and gas resources in the state has been investigated to conclude the impact of both these energy sources to the regional energy supply and demand dynamics. In addition, the benefits, drawbacks and challenges in scaling up the use of these energy sources are discussed in detail. This study provides a comprehensive overview of the current status of renewable energy resources, energy transition efforts, and the future of conventional and unconventional oil and gas resources in California. It serves as a single source of reference to the oil and gas industry in laying out relevant data and information related to renewable energy resources from the point of view of oil and gas market dynamics and closes the gap in highlighting the latest advances and the future of the energy industry in California.

Joint exploration and development: A self-salvation road to sustainable development of unconventional oil and gas resources

Distribution and potential of global oil and gas resources

To meet future global oil and gas demands, the energy industry will need creative thinking that leads to the discovery and development of new fields. Unconventional gas resources, especially those in frontier (exploratory) basins, will play an important role in fulfilling future energy needs. To develop unconventional gas resources, we must first identify their occurrences and quantify their potential. Basin analog systems investigation (BASIN) is a computer software that can rapidly and inexpensively evaluate the unconventional gas resource potential of frontier basins. BASIN is linked to a database that includes petroleum systems and reservoir properties data from 25 intensely studied North American “reference” basins that have both conventional and unconventional oil and gas resources. To use BASIN, limited data from a frontier or “target” basin are used to query the database of North American reference basins and rank these reference basins as potential analogs to the frontier basin. Based on analog comparisons, we can predict unconventional gas resources and make preliminary engineering decisions concerning resource development and the best drilling, completion, stimulation, and production practices to use in the frontier basin. Initial software validation shows consistent results. If a basin is selected as the target basin while the same basin is also in the reference basin list, the results show that the basin is a 100% analog to itself. Other basins in the reference basin list are less than 100% analogs. Also, BASIN performed favorably when it was tested against analog basin decisions made by of a team of industry experts. BASIN rapidly and inexpensively identifies and ranks reference basins as analogs to a frontier basin, providing insights to potential gas resources and indicating the preliminary best engineering practice for resource development. It is an effective tool that provides guidance to inexperienced professionals and new perceptions for seasoned experts.

In order to increase the potential and trend prediction accuracy of unconventional oil and gas resources, a potential and trend prediction method of unconventional oil and gas resources based on combination forecasting model of variable weight for multi-factor is proposed. First of all, the present situation and trend of oil and gas resources development are analyzed and introduced. It is pointed out that it is influenced and restricted by many factors and external environment, which shows the characteristics of its complexity and non-linear historical evolution trend. Secondly, the optimal variable weights are determined by using the variable weight combination forecasting model and then the potential and trend prediction accuracy of unconventional oil and gas resources is realized to be increased. Finally, the validity of the proposed method is verified by the simulation experiment.

ABSTRACT: Shale oil in northeast China is about to enter the stage of large-scale hydraulic fracturing. Cement sheath integrity must be ensured for horizontal shale oil wells. In this paper, the mechanical parameters of cement sheath are measured. A numerical model of casing - cement sheath - formation assembly is established to analyze the stress law of cement sheath. The integrity of the cement sheath is analyzed. The results show that the elastic modulus of cement is 6 GPa and the Poisson’s ratio is 0.17. The compressive strength and tensile strength of cement after cyclic loading are 90MPa and 7.5mpa ~ 11.25mpa respectively. The maximum radial stress of cement sheath increases with the increase of fracturing pressure, the decrease of displacement, and the increase of elastic modulus. The maximum tangential stress of cement sheath increases with the increase of fracturing pressure and elastic modulus of cement. The tensile strength of cement sheath cannot meet hydraulic fracturing requirements. The elastic modulus of cement should be reduced to 4 GPa or the tensile strength should be increased to be higher than 15 MPa. This study would guide the shale oil wells in northeast China. 1. INTRODUCTION As hydraulic fracturing technology matures and international oil prices recover, more and more unconventional oil and gas resources are being developed, such as shale gas, conglomerate reservoirs, and shale oil. In particular, shale oil resources are becoming a new direction of exploration and development of unconventional oil and gas resources in China. Shale oil has been developed scaled in Jimsar block, in Inner Mongolia, and Tianjin district. At the same time, shale oil resources have been successfully explored in northeast China and will soon enter the stage of large-scale development. Based on the development experience of shale gas and other unconventional oil and gas resources over the past few years, casing deformation and sustained casing pressure are the most common problems in horizontal wells during multistage fracturing (Adams, 2017; Atkinson, 2020; Chaojie Zhao, 2020; Xi Yan, 2021.). Well integrity issues have a significant impact on the safety and production of horizontal wells. Fig. 1 shows the casing deformation logging results of Wel-Wei204H39-6 in the Weiyuan block and Well-JHW033 in Jimsar Block, Xinjiang respectively. Logging results showed casing deformation in both wells. One of the wells is a shale gas horizontal well and the other is a shale oil horizontal well. Thus, shale oil wells face the same well integrity issues as shale gas wells.

With the continuous in-depth development of oil and gas resources, unconventional oil and gas resources show great potential. In recent years, 70% of the proven oil and gas resources in China are unconventional oil and gas resources. Therefore, the development of unconventional oil and gas resources has a huge impact on the increase in the production capacity of the oil and gas resources in China. Staged fracturing of horizontal wells is the main technical measure to improve unconventional oil and gas production stimulation. In the fracturing process, the soluble bridge plug technology can not only effectively solve the problems of large investment in drilling and grinding of composite bridge plugs, high risks, self-locking of oil, casing deformation, etc., causing the bridge plug to be unable to be drilled and remove and affect subsequent production but also can successfully make up for the problems of subsequent production. The large-diameter bridge plug cannot achieve the full diameter of the wellbore and cannot carry out operations such as postproduction logging and refracturing, which can ensure the integrity of the wellbore to the greatest extent. In this paper, HNBR was used to modify MPU to prepare HNBR/MPU soluble rubber, and the effect of blending ratio on the vulcanization characteristics, mechanical properties, compatibility, thermal stability, and degradation behavior of composites was studied. The results showed that with the increase in the amount of HNBR, the degree of cross-linking of the composite material decreased gradually, and the mechanical properties decreased slightly. With the increase in the amount of HNBR, the thermal stability of the material decreases. The use of HNBR greatly reduced the degradation rate of MPU. When the amount of HNBR was changed from 20 phr to 40 phr, the tensile strength retention rate of the composite after soaking increased from 14.73% to 39.72%.

ABSTRACT: Hydraulic fracturing is one of the main technologies for developing unconventional oil and gas resources. Effective placement of proppant in the fracture has an important impact on the formation of channels with high conductivity. In order to study the migration and settlement law of proppant in complex fracture, computational fluid dynamics (CFD) is used to simulate the migration process of proppant in fracture, and drag and lift models are added in the simulation process. The proppant migration and settlement law under different impact factors is analyzed from three dimensions: sand dune length ratio, maximum height ratio of sand dune and sand dune area ratio. The simulation results show that the proppant tends to enter and settle in the branch fracture close to the entrance of the main fracture. When the main-branch fracture angle is smaller, the proppant is more likely to be carried into the branch fracture for settlement. When the fracture is inclined downward, the sand dune pattern in the main fracture moves to the depth of the fracture as a whole, which is not conducive to the effective filling of proppant near the wellbore. Increasing the viscosity and injection rate of fracturing fluid, the proppant migration trends in the main fracture and branch fracture are different. The numerical simulation results and conclusions will provide reference for the optimization of fracturing construction in the field. 1. INTRODUCTION Unconventional oil and gas resources have gradually become the focus of development (Liao et al., 2022). The unconventional oil and gas resources are mainly shale oil and gas, tight sandstone oil and super heavy oil (Meng et al., 2023; Ardakani et al., 2022). The rock properties of shale and sandstone make sand fracturing technology as the preferred measure for reservoir stimulation (Hou et al. 2014; Zhao et al., 2012). Successful sand fracturing requires effective fluid flow channels in the fracture (Yao et al., 2022). At the same time, a large amount of proppant is injected into the fracture to support the fracture and prevent it from closing.The migration and settlement trend of proppant directly affects the hydrofracture morphology and conductivity after fracturing. Therefore, it is necessary to study the impact of different factors on proppant placement during fracturing.

Conventional petroleum exploration targets have become increasingly complex recently. Although geological research of unconventional oil and gas resources has received much attention in recent years, such resources also face many complex geological and scientific problems. In this context, the 8th International Symposium on Hydrocarbon Accumulation Mechanisms and Petroleum Resources Evaluation was held in Beijing from 21 to 23 October, 2022. Experts presented and discussed their latest research findings on this topic relating to both conventional and unconventional oil and gas resources. They also discussed various development strategies for the petroleum industry taking into account the global objectives of “carbon peaking and carbon neutrality” to mitigate the impacts of climate change. Six significant theoretical advances and some new technologies were introduced at this conference. These advances related to the “Whole Petroleum System” theory, shale oil and gas exploration, deep and ultra-deep petroleum exploitation, clean energy issues, and alternative types of unconventional oil and gas resources. In response to these technological advances, four major current challenges were identified. These challenges related to the petroleum industry’s ongoing growth and development in the context of carbon-neutrality goals, the evolution of hydrocarbon laws relating to petroleum accumulations and their exploitation, organic and inorganic effects on petroleum generation and accumulation mechanisms, and artificial intelligence applications related to hydrocarbon prediction. Cited as: Jin, Z. Hydrocarbon accumulation and resources evaluation: Recent advances and current challenges. Advances in Geo-Energy Research, 2023, 8(1): 1-4. https://doi.org/10.46690/ager.2023.04.01

China's conventional and unconventional natural gas resources: Potential and exploration targets