Unconventional Resources最新文献

The Shaanbei Chang 7 shale oil reservoir in the Ordos Basin develops vertically with multiple lithologic superimpositions. The interlayer stress of sand-mud-shale thin interbeds is different, and the stress within the small layer is variable, resulting in high hydraulic pressure fractures and short extension distances. The effective retrofit volume did not meet expectations. Based on the in-situ stress of key layers tested by the Kaiser in-situ stress test, the in-situ stress distribution law of vertical multi-interbedded layers with different lithologies was obtained by finely interpreting the single-well in-situ stress logging results, combined with the geological, structural and sedimentary characteristics of the block, established a three-dimensional in-situ stress regional model of complex lithologic reservoirs based on fine geological bodies, simulated the regional in-situ stress distribution law of sand-mud-shale multi-thin interbedded lithology, and mastered the geological The spatial lateral and vertical differences of the stress field. The calculation results show that the overall three-dimensional stress of the block is ${\sigma }_V>{\sigma }_H>{\sigma }_h$, the maximum principal stress range of the longitudinal upper interlayer is 35∼58 MPa, the minimum principal stress range is 28∼55 MPa, and the horizontal stress difference range is 6∼8 MPa, the stress value of sandstone in the lateral upper layer is greater than that of shale and that of mudstone, and the difference of horizontal stress in the vertical direction increases with the increase of depth. By analyzing the in-situ stress distribution of different interlayer depths and bedding lithologies, it provides parameter guidance for the fracturing design of complex lithologic reservoirs in the Chang 7 Member in northern Shaanxi, Ordos Basin.

In response to the global climate change and the need for green and low-carbon development, hydrogen energy has been recognized as a clean energy source that can achieve carbon neutrality unlike fossil fuels. As a country with a shortage of energy resources, the development of hydrogen energy is of significant importance for China to adjust its energy structure and accelerate the new era of energy transformation. Based on the development of China's hydrogen energy industry, this paper elaborates on the current status and development trends of key technologies in the entire industrial chain of hydrogen energy in various stages including production, storage, transportation, and application, and identifies the problems and challenges of hydrogen energy development. The paper focuses on the analysis of hydrogen storage and transportation application scenarios and clarifies the selection of hydrogen storage and transportation technologies in different scenarios. To achieve healthy development of China's hydrogen energy industry, it is necessary to strengthen top-level design, make strategic planning, encourage large-scale state-owned energy enterprises to play a leading role, promote the development of the entire industry chain, increase technological research and development efforts, prevent the risk of core technology constraints, and vigorously promote the application of hydrogen energy to realize the construction of a hydrogen energy society.

Natural fractures are quite important for the high and stable production of tight sandstone gas reservoirs. However, it is commonly difficult to accurately characterize their distribution in tight sandstone gas reservoirs due to the strong heterogeneity. A comprehensive characterization of natural fractures in tight sandstone gas reservoirs of the Xujiahe Formation in the Yuanba area, Sichuan Basin, was carried out by multimethod of core description, log interpretation and seismic prediction. The results show that (1) the natural fractures in the Xujiahe Formation are mainly low-angle fractures, with a few medium- and high-angle fractures. The degree of fracture development is mainly controlled by the distance from the fault, the flexural degree of the strata and the thickness of the rock mechanical layer. (2) The fracture-sensitive seismic attributes such as the preferred maximum likelihood, structure entropy, illuminant-based symmetry and high-precision curvature are taken as the input, and the unsupervised cluster analysis algorithm based on Bayesian probability model is applied to predict the distribution of large-scale fractures at different dip angles; on the basis of narrow azimuthal pre-stack CMP gather optimization, the anisotropy detection technique of Hampson-Russell's ProAZ full CMP gather is used to characterize the distribution of small- and medium-scale fractures, and the predicted fracture development intensity matches the fracture interpretation results of the imaging logs by more than 85%. Moreover, the predicted fracture orientation is basically consistent with that of the imaging loggings. (3) The fault-genesis fractures of the Xujiahe Formation are mainly distributed near the fault on the southeast flank of the Jiulongshan anticline, and are distributed in a narrow strip in NE direction. The fold-genesis fractures are mainly developed in the Xu 3rd Member, and are located in the axis of the Jiulongshan anticline and its southeast flank where the strata are strongly flexed. This study provides a solid foundation for the development of tight sandstone gas reservoirs and extends the approaches for the accurate characterization of fractures.

The sedimentary environment of the marine-continental transitional facies leads to complex reservoir lithologies characterized by rapid changes in lithology, the presence of thin interbeds, and strong heterogeneity in both vertical and horizontal directions. The resultant difficulties with lithology identification pose challenges to the evaluation of reservoir parameters and the prediction of sweet spots. This study investigated the reservoirs of marine-continental transitional facies in the Permian Longtan Formation in area A, southwestern Sichuan. Based on core descriptions, mineral composition analysis, and log responses, this study divided the reservoir lithologies into eight types, i.e., coals, carbonaceous shales, mudstones, argillaceous siltstones, siltstones, fine sandstones, calcareous mudstones, and bauxitic mudstones. Then, this study determined the log response characteristics of different lithologies, established the charts for identifying typical lithologies from log data, and formed a set of methods and processes for identifying complex reservoir lithologies from log data. Furthermore, this study established lithology identification models using methods of multi-resolution graph-based clustering (MRGC), cross plot - decision tree, and random forest. These models had an accuracy rate of 84.3%, 85.6%, and 91%, respectively, indicating high identification precision overall. In addition, this study compared and analyzed the application conditions, advantages, and disadvantages of different lithology identification methods, providing guidance for subsequent identification of complex reservoir lithologies from log data.

Expectations from unconventional reservoirs are often overly optimistic when estimation criteria are transferred from one location to another but some of the many important elements of petroleum systems remain unaccounted for. Feature engineering used in model construction to improve the quality of the machine learning process can improve the performance of unconventional reservoir estimates.

The compositions of petroleum fluids are represented by spectra obtained from various analyses, which vary greatly in shape and dimensions, contain large amounts of data, and cannot be processed as single numbers. Selection of relevant features in the spectra can simplify interpretation, reduce dimensionality, and improve data compatibility.

The features have been selected in GC-MS, NMR and MALDI-TOF spectra of bitumen from the Bayan-Erkhet tar sand deposit in Mongolia for comparison with bitumens from other regions of the world. The GC-MS spectra have a similar baseline shape, either a triangle or two humps with peaks eluted to varying degrees. The comparison made it possible to isolate poorly eluted peaks of carbon number groups in the studied bitumen. Since NMR spectra of petroleum fluids are most often published without NMR parameters, simple indices are developed to compare the shapes of the spectra. The values of these indices are consistent with the characteristics of the samples. The sequences of hydrocarbon compounds determined in the MALDI-TOF spectrum are very similar to those of the Banik black shale, Iraq, which allowed to clarify the sequences. Some peaks are also found in the spectra of two other crude oil samples. The feature selection in spectral analyses enables revealing the hidden information.

In recent years, with the in-depth development of oil and gas exploration in the eastern slope of the western Sichuan Depression, breakthroughs have been made in the research on high-quality gas reservoirs in the Da'anzhai Member of the Ziliujing Formation in this area. Fine logging identification of lithology in the Da'anzhai Member in the eastern slope of the western Sichuan Depression is the core subject of reservoir sweet spot prediction. In this paper, taking the Da'anzhai Member in the western Sichuan Basin as an example, the work flow and comparisons of multi-lithology logging models have been systematically conducted, using a large number of cores, geological data and logging interpretation models. The research shows that there are four main lithologies developed in the Da'anzhai Member, namely shale, marl-bearing limestone, shell limestone and sandstone. Intersection and spider diagram methods can effectively screen out the logging parameters that are sensitive to lithology, including natural gamma (GR), neutron (CNL), deep lateral resistivity (RD), and acoustic wave time difference (AC). The lithology of the Da'anzhai Member in the study area can be identified with high precision via the "lithology probability factor", "BP neural network" and cluster analysis methods. Among them, the "lithologic probability factor" and "BP neural network" methods have a prediction accuracy of lithology exceeds 80%. Therefore, these two methods are optimized as the most effective methods for logging identification of lithology in the Da'anzhai Member. This study has certain reference value for the lithology identification of similar gas reservoirs worldwide.

Fetkovich or Blasingame type rate decline analysis is a common and practical method to obtain reservoir parameters and evaluate well productivity. Pseudo-steady-state constant is an indispensable parameter for establishing these new type rate decline curves and works as a bridge linking conventional productivity and new type productivity. Refracturing is widely used to enhance tight oil wells’ productivity and improve their economic benefits, the pseudo-steady-state constant of refracturing horizontal wells has been presented in our previous research, but an in-depth discussion on the definition, accuracy, sensitivity, and application of this constant has not been conducted. It results in the insufficient understanding of the physical meaning, characteristics, and functions of pseudo-steady-state constant at present. In this study, taking the derived pseudo-steady-state constant for refracturing horizontal wells with fracture reorientation as an example, its accuracy was verified by an equivalent model presented in the literature, and the sensitivity of relevant key parameters on this constant was investigated. For the refracturing horizontal well defined in this study, pseudo-steady-state constant is independent of time, and related to fracture conductivity, fracture face damage, reorientation fracture number and permeability anisotropy. Results show that this constant decreases with the increase of fracture conductivity, but tends to remain unchanged when fracture conductivity increases to a certain extent. Meanwhile, this constant shows a positive correlation with fracture face damage and permeability anisotropy, but an inverse correlation with reorientation fracture number. Blasingame type rate decline curves of refracturing horizontal wells with fracture reorientation were also established, regarding as a practical application of this pseudo-steady-state constant and a concrete manifestation of its bridge-linking function. These type curves are directly conducive to the inversion of reservoir properties and fracturing parameters and the prediction of future productivity for refracturing horizontal wells. More importantly, this study is helpful to understand and strengthen the role and importance of pseudo-steady-state constant, and also beneficial to the establishment of new type rate decline curves of other similar models.

Experiments on the dynamic and static elastic parameters under distinct loading conditions help clarify the effects of loading rate and strain amplitude on dynamic and static elastic moduli, and gain further insight into the moduli. Significant scientific guidance are provided for fracturing transformation of oil shale reservoirs. AutoLab 1500, servo-controlled triaxial equipment with ultrasonic transducers, is used in an elastic parameter test on shale oil samples. The test concludes that the loading rate moves the dynamic elastic modulus little, with a maximum change rate of 0.8%, while it significantly affects the static elastic modulus by 31.7% at most. In the loading or unloading phase, the larger the initial differential stress (or strain), the higher the dynamic Young's modulus. The static elastic modulus, on the other hand, presents a significant negative correlation with the stress amplitude. To be specific, the smaller the strain amplitude, the higher the measured modulus; the larger the strain amplitude, the smaller the modulus. Given the loading rate, the smaller the differential stress, the smaller the difference between the dynamic and static elastic moduli. This study can provide a reference base for fracturing construction in oil shale.

The presence of water, competing with methane for the space, weakens the ability of methane adsorption and diffusion in coal dramatically. The study on the occurrence of water in coal has direct effects on coalbed methane exploitation. In this study, NMR technology was used to obtain water vapor adsorption curves, moreover, the surface adsorption, water cluster formation and pore filling of water in coal pores of coal samples were characterized. Meanwhile, the method based on NMR was first used to quantify the water in different occurrence state in coal pores. The results show that modified BET model can not fit the data in all the pressure history of high rank coal with well-developed micropores and mesopores. Moreover, for pores in high-rank anthracite coal, adsorption water is mainly the indirect adsorption water, and for pores of low-rank bituminous coal, the proportion of direct adsorption water is 50%.

Time-frequency analysis is an important tool for seismic signal analysis and time-frequency resolution is the key to high-precision reservoir prediction. The time-frequency method of conventional S-transform is difficult to meet the requirements of high precision reservoir prediction at present. In this paper, an improved window-parameter optimization S-transform (IWPOST) method is proposed. In the IWPOST method, the scale parameters of the window function can be adaptively obtained according to the amplitude spectrum of the actual signal, and a new optimization adjustment parameter is introduced to further improve the window parameters. The comparison analysis of the synthetic signals shows that the IWPOST method has better time-frequency aggregation and can maintain high resolution at both high-frequency and low-frequency. Finally, the proposed method is used to extract the reservoir fluid mobility attribute from the real seismic data and the results indicate that the fluid mobility has a higher time resolution and exhibits better performance for reservoir delineation. The proposed method is conducive to delineate the reservoir range and provides reference for the exploration and development of the oil and gas reservoirs in this area.