**Preface to "Development of Unconventional Reservoirs 2020"**

After the successful publication of the Development of Unconventional Reservoirs book a subsequent special issue with the same theme "Development of Unconventional Reservoirs 2020" was commenced and a total of 41 papers were published in this edited book.

The topics covered by this special issue are very diverse but they can be grouped into several categories based on the type of unconventional plays covered by each paper.

The first set of the papers covers some aspects of **shale gas plays** that include the following works:

Review of Formation and Gas Characteristics in Shale Gas Reservoirs; by Boning Zhang, Baochao Shan, Yulong Zhao, Liehui Zhang

Effect of Particle Size on Pore Characteristics of Organic-Rich Shales: Investigations from Small-Angle Neutron Scattering (SANS) and Fluid Intrusion Techniques; by Yi Shu, Yanran Xu, Shu Jiang, Linhao Zhang, Xiang Zhao, Zhejun Pan, Tomasz P. Blach, Liangwei Sun, Liangfei Bai, Qinhong Hu, Mengdi Sun

Porosity and Water Saturation Estimation for Shale Reservoirs: An Example from Goldwyer Formation Shale, Canning Basin, Western Australia; by Atif Iqbal, Reza Rezaee

Factors Affecting Shale Gas Chemistry and Stable Isotope and Noble Gas Isotope Composition and Distribution: A Case Study of Lower Silurian Longmaxi Shale Gas, Sichuan Basin; by Chunhui Cao, Liwu Li, Yuhu Liu, Li Du, Zhongping Li, Jian He

Quantitative Analysis of Amorphous Silica and Its Influence on Reservoir Properties: A Case Study on the Shale Strata of the Lucaogou Formation in the Jimsar Depression, Junggar Basin, China; by Ke Sun, Qinghua Chen, Guohui Chen, Yin Liu, Changchao Chen

Molecular-Scale Considerations of Enhanced Oil Recovery in Shale; by Mohamed Mehana, Qinjun Kang, Hari Viswanathan

Dynamic Pore-Scale Network Modeling of Spontaneous Water Imbibition in Shale and Tight Reservoirs; by Xiukun Wang, James J. Sheng

Patent Analysis on the Development of the Shale Petroleum Industry Based on a Network of Technological Indices; by Jong-Hyun Kim, Yong-Gil Lee

An Analytical Model for Production Analysis of Hydraulically Fractured Shale Gas Reservoirs Considering Irregular Stimulated Regions; by Kaixuan Qiu, Heng Li

Development and Calibration of a Semianalytic Model for Shale Wells with Nonuniform Distribution of Induced Fractures Based on ES-MDA Method; by Qi Zhang, Shu Jiang, Xinyue Wu, Yan Wang, Qingbang Meng

Experimental Investigation of the Impacts of Fracturing Fluid on the Evolution of Fluid Composition and Shale Characteristics: A Case Study of the Niutitang Shale in Hunan Province, South China; by Jingqiang Tan, Guolai Li, Ruining Hu, Lei Li, Qiao Lyu, Jeffrey Dick

Reservoir Characteristics of the Lower Jurassic Lacustrine Shale in the Eastern Sichuan Basin and Its Effect on Gas Properties: An Integrated Approach; by Jianhua He, Hucheng Deng, Ruolong Ma, Ruyue Wang, Yuanyuan Wang, Ang Li

The second set of articles are about **tight gas sands** that include the following works:

Controls on Pore Structures and Permeability of Tight Gas Reservoirs in the Xujiaweizi Rift, Northern Songliao Basin; by Luchuan Zhang, Shu Jiang, Dianshi Xiao, Shuangfang Lu, Ren Zhang, Guohui Chen, Yinglun Qin, Yonghe Sun

Investigation of the Pore Structure of Tight Sandstone Based on Multifractal Analysis from NMR Measurement: A Case from the Lower Permian Taiyuan Formation in the Southern North China Basin; by Kaixuan Qu, Shaobin Guo

Finite Element Simulation of Multi-Scale Bedding Fractures in Tight Sandstone Oil Reservoir; by Qianyou Wang, Yaohua Li, Wei Yang, Zhenxue Jiang, Yan Song, Shu Jiang, Qun Luo, Dan Liu Occurrence, Classification and Formation Mechanisms of the Organic-Rich Clasts in the Upper Paleozoic Coal-Bearing Tight Sandstone, Northeastern Margin of the Ordos Basin, China; by Guanqun Yang, Wenhui Huang, Jianhua Zhong, Ningliang Sun

An Analytical Solution for Transient Productivity Prediction of Multi-Fractured Horizontal Wells in Tight Gas Reservoirs Considering Nonlinear Porous Flow Mechanisms; by Qiang Wang, Jifang Wan, Langfeng Mu, Ruichen Shen, Maria Jose Jurado, Yufeng Ye

The third group of papers deals with some aspects of **tight carbonate reservoirs** that include the following works:

Pore-Structural Characteristics of Tight Fractured-Vuggy Carbonates and Its Effects on the P- and S-Wave Velocity: A Micro-CT Study on Full-Diameter Cores; by Wei Li, Xiangjun Liu, Lixi Liang, Yinan Zhang, Xiansheng Li, Jian Xiong

Reservoir Properties of Low-Permeable Carbonate Rocks: Experimental Features; by Aliya Mukhametdinova, Andrey Kazak, Tagir Karamov, Natalia Bogdanovich, Maksim Serkin, Sergey Melekhin, Alexey Cheremisin

Natural Fractures in Carbonate Basement Reservoirs of the Jizhong Sub-Basin, Bohai Bay Basin, China: Key Aspects Favoring Oil Production; by Guoping Liu, Lianbo Zeng, Chunyuan Han, Mehdi Ostadhassan, Wenya Lyu, Qiqi Wang, Jiangwei Zhu, Fengxiang Hou

The fourth group of papers focuses on **coalbeds** that include the following works:

Multi-Phase Tectonic Movements and Their Controls on Coalbed Methane: A Case Study of No. 9 Coal Seam from Eastern Yunnan, SW China; by Ming Li, Bo Jiang, Qi Miao, Geoff Wang, Zhenjiang You, Fengjuan Lan

A Novel Data-Driven Method to Estimate Methane Adsorption Isotherm on Coals Using the Gradient Boosting Decision Tree: A Case Study in the Qinshui Basin, China; by Jiyuan Zhang, Qihong Feng, Xianmin Zhang, Qiujia Hu, Jiaosheng Yang, Ning Wang

Development and Performance Evaluation of Solid-Free Drilling Fluid for CBM Reservoir Drilling in Central Hunan; by Pinghe Sun, Meng Han, Han Cao, Weisheng Liu, Shaohe Zhang, Junyi Zhu

Two papers investigate **gas hydrates** that include the following works:

Research on the Estimate of Gas Hydrate Saturation Based on LSTM Recurrent Neural Network; by Chuanhui Li, Xuewei Liu

Fractional Time Derivative Seismic Wave Equation Modeling for Natural Gas Hydrate; by Yanfei Wang, Yaxin Ning, Yibo Wang

The last group of papers is classified as **miscellaneous subjects** that cover a variety of works dealing with some technical aspects of different unconventional plays:

Reservoir Formation Model and Main Controlling Factors of the Carboniferous Volcanic Reservoir in the Hong-Che Fault Zone, Junggar Basin; by Danping Zhu, Xuewei Liu, Shaobin Guo

Productivity-Index Behavior for a Horizontal Well Intercepted by Multiple Finite-Conductivity Fractures Considering Nonlinear Flow Mechanisms under Steady-State Condition; by Maojun Cao, Hong Xiao, Caizhi Wang

Numerical Investigation of Injection-Induced Fracture Propagation in Brittle Rocks with Two Injection Wells by a Modified Fluid-Mechanical Coupling Model; by Song Wang, Jian Zhou, Luqing Zhang, Zhenhua Han

Proppant Transportation in Cross Fractures: Some Findings and Suggestions for Field Engineering; by Yan Zhang, Xiaobing Lu, Xuhui Zhang, Peng Li

A Novel Equivalent Continuum Approach for Modelling Hydraulic Fractures; by Eziz Atdayev, Ron C. K. Wong, David W. Eaton

Numerical Investigation on Proppant–Water Mixture Transport in Slot under High Reynolds Number Conditions; by Tao Zhang, Ruoyu Yang, Jianchun Guo, Jie Zeng

A Critical Review of Osmosis-Associated Imbibition in Unconventional Formations; by Zhou Zhou, Xiaopeng Li, Tadesse Weldu Teklu

Experimental Investigation and Mechanism Analysis on Rock Damage by High Voltage Spark Discharge in Water: Effect of Electrical Conductivity; by Zhixiang Cai, Hui Zhang, Kerou Liu, Yufei Chen, Qing Yu

Pore-Scale Lattice Boltzmann Simulation of Gas Diffusion–Adsorption Kinetics Considering Adsorption-Induced Diffusivity Change; by Zhigao Peng, Shenggui Liu, Yingjun Li, Zongwei Deng, Haoxiong Feng

Seismic Identification of Unconventional Heterogenous Reservoirs Based on Depositional History—A Case Study of the Polish Carpathian Foredeep; by Anna Łaba-Biel, Anna Kwietniak, Andrzej Urbaniec

Application of Waveform Stacking Methods for Seismic Location at Multiple Scales; by Lei Li, Yujiang Xie, Jingqiang Tan

Theoretical Comparison of Test Performance of Different Pulse Decay Methods for Unconventional Cores; by Guofeng Han, Xiaoli Liu, Jin Huang

Multidisciplinary Characterization of Unconventional Reservoirs Based on Correlation of Well and Seismic Data; by Weronika Kaczmarczyk, Małgorzata Słota-Valim

Adaptive Processing for EM Telemetry Signal Recovery: Field Data from Sichuan Province; by Olalekan Fayemi, Qingyun Di, Qihui Zhen, Yu L. Wang

Prediction of Permeability Using Group Method of Data Handling (GMDH) Neural Network from Well Log Data, by Baraka Mathew Nkurlu, Chuanbo Shen, Solomon Asante-Okyere, Alvin K. Mulashani, Jacqueline Chungu, Liang Wang

Machine Learning-Based Probabilistic Lithofacies Prediction from Conventional Well Logs: A Case from the Umiat Oil Field of Alaska; by Nilesh Dixit, Paul McColgan, Kimberly Kusler

**Keywords:** Unconventional reservoirs; shale gas; shale oil; tight gas sand; coalbed methane; tight carbonates, gas hydrate, hydraulic fracturing, machine learning

> **Reza Rezaee** *Editor*
