Development Of Unconventional Resources Research Articles

Pore Structure Characteristics and Their Controlling Factors of Deep Shale: A Case Study of the Lower Silurian Longmaxi Formation in the Luzhou Area, Southern Sichuan Basin.

Recently, deep shale reservoirs are emerging as time requires and commence occupying a significant position in the further development of shale gas. However, the understanding of pore characteristics in deep shale remains poor, prohibiting accurate estimation of the hydrocarbon content and insights into fluid mobility. This study focuses on the Longmaxi Formation from the Luzhou (LZ) region, southern Sichuan. Scanning electron microscopy (SEM), low-temperature N2/CO2 adsorption, X-ray diffraction, and geochemical analysis were performed to investigate the micro–nanopore size distribution, main controlling factors, and unique pore features distinct from other regions. Results showed that the pores can be classified into four categories, organic matter (OM) pores, intergranular pores, intragranular pores, and microfractures, according to SEM images. The total pore volume is overwhelmingly dominated by mesopores and contributed by pores in the range of 0.5–0.6, 2–4, and 10–30 nm. The specific surface area is primarily contributed by micropores and mesopores in the range of 0.5–0.7 and 2–4 nm. By analyzing the influencing factors extensively, it is concluded that the buried depth, geochemical factors, and mineral composition can impact the pore structure in the overmature deep shales. Specifically, the total organic carbon content plays a more effective and positive role in the development of micropores, mesopores, total pores, and the porosity when compared with vitreous reflectance (Ro). The micropores are inferred to be OM-related. On the contrary, clay mineral is detrimental to the development of micropores and mesopores and the petrophysical properties (porosity and permeability), which may be attributed to the occurrence of chlorite and kaolinite instead of illite. The plagioclase conforms to the same law as clay due to their coexistence. Quartz, carbonate minerals, and pyrite can barely contribute to the pores. Eventually, the compared results suggest that the Longmaxi Formation of the LZ region are qualified with a superior pore size distribution, complicated structure, and diverse morphology, implying a potential to generate and store hydrocarbons. Overall, this study improves the understanding of complex pore structures in deep shale and provides significant insights into the development and exploration of unconventional resources in the future.

Surrogate-assisted hydraulic fracture optimization workflow with applications for shale gas reservoir development: a comparative study of machine learning models

Unconventional reservoirs have become the main alternative for increasing oil and gas reserves around the world. Owing to their ultralow permeability properties and special pore structure, hydraulic fracturing technology is necessary to realize the efficient development and economic management of unconventional resources. To maximize the production capacity of wells, several fracture parameters, including fracture number, length, width, conductivity, and spacing, need to be optimized effectively. The optimization of hydraulic fracture parameters in shale gas reservoirs generally demands intensive computations owing to the necessity of numerous physicalmodel simulations. This study proposes a machine learning (ML)–assisted global optimization framework to rapidly obtain optimal fracture parameters. We employed three supervised ML models, including the radialbasis function, K-nearest neighbor, and multilayer perceptron, to emulate the relationship between fracture parameters and shale gas productivity for multistage fractured horizontal wells. Firstly, several forward shale gas simulations with embedded discrete fracture models generate training samples. Then, the samples are divided into training and testing samples to train these ML models and optimize network hyper parameters, respectively. Finally, the trained ML models are combined with an intelligent differential evolution algorithm to optimize the fracture parameters. This novel method has been applied to a naturally fractured reservoir model based on the real-field Barnett shale formation. The obtained results are compared with those of conventional optimizations with high-fidelity models. The results confirm the superiority of the proposed method owing to its very low computational cost. The use of ML modeling technology and an intelligent optimization algorithm could greatly contribute to simulation optimization and design, prompting progress in the intelligent development of unconventional oil and gas reservoirs in China.

Ultrastable N2/Water Foams Stabilized by Dilute Nanoparticles and a Surfactant at High Salinity and High Pressure

The rapid development of unconventional oil and gas resources presents challenges for foam flooding for reservoirs with high salinity and high heterogeneity at elevated temperatures. In this study, hydrophilic anionic sulfonate-modified nanoparticles (NPs) exhibited a synergistic effect with a cationic surfactant in stabilizing N2/water foam in the presence of concentrated divalent ions from ambient temperature up to 70 °C. With low concentrations of both the sulfonated NPs (SNPs) and cationic surfactant, the foams remained stable for 4 days at 50 °C and atmospheric pressure, while the surfactant-stabilized foams collapsed completely in 1 day. This stability mechanism of foams by the SNPs and cationic surfactant is described in terms of phase behavior, bulk shear rheology of the aqueous phase, and the dilational modulus of the gas-brine interface. The high surface elastic dilational modulus E' observed upon addition of the SNP provided stability against coarsening according to the Gibbs criteria. The cryo-SEM images also showed the compact bubble structure of foams provided by the SNPs. Consequently, very minor changes in the foam bubble size were observed at 208 bar (3000 psi) and 50 °C for up to 48 h with only 0.1 wt % or 0.3 wt % SNPs and 0.01 wt % Arquad 12-50, indicating excellent foam stability. The ability of the surfactant and NPs to stabilize foams at low concentrations broadens the application of foams in subsurface reservoirs at high temperatures and salinities.

A simple and effective evaluation method for lacustrine shale oil based on mass balance calculation of Rock-Eval data

Because the profit from the development of unconventional resources can be small, success usually depends on the quick identification of favorable areas. It is therefore very important to identify a rapid and robust resource potential evaluation method. However, it is challenging to evaluate shale oil content, especially the recoverable oil part. We explore a new evaluation index (SE) by using Rock-Eval data and mass balance. When SE ˃ 0, the shale interval has already expelled a certain amount of hydrocarbons, so it has poor shale oil potential. When SE is near 0, almost all the generated hydrocarbons are trapped in the shale itself, and simultaneously, no externally migrated hydrocarbons enter the shale. In the case of an SE near 0, the shale oil potential may depend on whether it is organic-rich; however, this type of shale tends to be compact and does not develop fractures. When SE ˂ 0, externally migrated hydrocarbons entered the shale interval, which usually indicates good shale oil potential. The more negative the SE is, the greater the shale oil potential. One of the advantages of this index is that it takes into account not only the residual oil content but also the conditions of hydrocarbon expulsion and migration. Moreover, this method is economical and convenient and is based on commonly available Rock-Eval data.

Fracture’s Impact on the Recovery of Hydrocarbon from Low-Permeability Rock’s Pores: New Insights from 1H Nuclear Magnetic Resonance Experiment

Summary Successful examples of hydraulic fracturing (HF) have led to a general consensus that fractures enhance hydrocarbon production as it connects isolated pockets filled with oil. However, the fracture’s impact on the hydrocarbon recovery from rock’s pores, which can account for a significant amount, is not well studied but experimentally investigated here. Uniquely, we fill our samples' fractures with a slime made of guar gum and heavy water (D2O). Such slime cannot penetrate into pores, and the heavy water does not generate nuclear magnetic resonance (NMR) signals detectable by our apparatus. Using such slime as a fracture filling material allows us to isolate and eliminate the NMR signals from fractures. Subsequent huff ‘n’ puff (HnP) experiments show that fracture results in a decline of the total HnP recoverable oil. We reasoned that fracture reduces the treatment gas’ sweeping efficiency. This issue can be partially mitigated by injecting N2 instead of CO2; N2 can enter rock’s pores more efficiently as a treatment agent. Nevertheless, N2 HnP still suffers a noticeable reduction in the total recovery for samples with smaller pores. Our experiments provide an important new insight into the development of unconventional hydrocarbon resources. Maximizing fracture intensity in the field HF operation may negatively impact the later HnP oil recovery. At last, this observation is only possible with our unique experiment design; a misleading and opposite finding will be reached if one directly compares the results from before and after fracturing the samples. We reinforce that pore structures are changed during the fracturing process in our experiment (and possibly other researchers’ work); such change needs to be properly accounted for to assess fracture’s impact on pore fluid movement fairly.

Study on Effect of Perforation Orientation on Hydraulic Fracturing of Shale

The core technology to realize the development of unconventional oil and gas resources is the large-scale volume transformation of shale reservoirs, but volume fracturing is a complex physical and mechanical process, and its mechanism remains to be further studied. In this paper, starting from the current research status of shale volumetric fracturing, the perforation orientation of volumetric fracturing is numerically simulated by using the finite element software. The following conclusions are drawn: ① when the ground stress conditions are equal, with the increase of perforation angle, the maximum principal stress at the front of perforation decreases gradually; that is, when the perforation is along the horizontal minimum principal stress, the maximum principal stress at the front of perforation is the largest, which is most conducive to fracturing of shale reservoirs. ② When the perforation is along the direction of the horizontal minimum principal stress and the horizontal stress difference is zero, the smaller the horizontal stress, the greater the maximum principal stress at the front of the perforation. Therefore, the smaller the horizontal stress, the more conducive to the rupture of shale reservoirs. ③ When the perforation is along the horizontal minimum principal stress, the maximum principal stress at the front of the perforation increases with the increase of the horizontal stress difference. Therefore, the larger the horizontal stress difference, the more favorable for the fracture of shale reservoirs.

Application of atom force microscope and nanoindentation to characterize nanoscale mechanical properties of shale before and after supercritical CO2 immersion

Understanding the microscopic effects of supercritical CO2 (SC–CO2) on shale plays an essential role in carbon capture utilization and storage (CCUS). The variation of shale microstructures and micromechanical properties induced by SC-CO2 immersion is obscure, which is crucial in CO2-enhanced shale gas recovery. In this study, the organic matter (OM) and minerals of shale are identified in the microscale by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), atom force microscope (AFM) and nanoindentation. The microstructures and micromechanical properties are measured before and after SC-CO2 exposure. The micromechanical properties variation of shale minerals and OM of shale are analyzed. The results show that the mechanical properties of OM have changed significantly after SC-CO2 exposure. Due to the interaction of CO2, the elastic modulus of OM increased by 124%. With the dissolution of CO2, the porosity of calcite increases from 7.1% to 8.1%, while decreasing by 6% in elastic modulus. By comparing the surface roughness calculated by AFM, the clay and OM swell. Although the mechanical properties are more discrete after CO2 immersion, the correlation between Young's modulus and hardness is better. These findings help understand the SC-CO2 exposure effects on shale and provide insights into the applications of SC-CO2 in unconventional resource development from a microscale perspective.

Geochemical characterization and hydrocarbon potential of Cambay Shale in the south Cambay Basin, India: implications to unconventional resource development

Geochemical characterization and hydrocarbon potential of Cambay Shale in the south Cambay Basin, India: implications to unconventional resource development

Development and performance evaluation of epoxy resin system for repairing agent

AbstractIn the development of unconventional oil and gas resources, such as offshore oil, high pressure oil and sour wells, casing‐casing annulus pressure is a common problem. To prevent casing‐casing annulus pressure, bisphenol F epoxy resin, dicyandiamide hardener SH‐500A and urea accelerator SH‐A100 are added to develop an epoxy resin system. The thickening time and the compressive strength at 90°C are used as the main evaluation indexes. The optimal formulation was found to be as follows: bisphenol F epoxy resin NPEF‐170 with 20 wt% of diluent benzyl glycidyl ether, 9.0 wt% of hardener dicyandiamide and 0.5–0.4 wt% of urea accelerator SH‐A100. The experimental results showed that the initial consistency of the epoxy resin system is less than 30 Bc, the thickening time is 3–4 h, and the compressive strength at 90°C is above 27 MPa, which meet the requirements of on‐site construction.

Anisotropic Elastic Properties of Montmorillonite With Different Layer Charge Densities and Layer Charge Distributions Through Molecular Dynamic Simulation

The knowledge of the anisotropic elastic properties of clay minerals is of crucial importance for the exploration and development of shale oil and gas. Montmorillonite (MMT) is a common natural clay mineral with different layer charge densities and layer charge distributions due to different geological conditions. Therefore, it is important to understand the currently poorly known effect of layer charge density and layer charge distribution on the anisotropic elastic properties of MMTs. This work aims to obtain such knowledge by studying the anisotropic elastic properties of different MMTs under stratigraphic conditions through molecular dynamic simulations. We showed that the in-plane compressional coefficients C11, C22 and C12 decrease with the increasing layer charge density for MMTs with different layer charge distributions, and the MMTs with the layer charges distributed on the two tetrahedral (T) sheets were found to have the smallest C11, C22 and C12. We also showed that the out-of-plane compressional coefficients C33, C13 and C23 of the MMTs with the layer charges distributed in the two T sheets decrease, while those with the layer charges in the octahedral (O) sheet increase and those with layer charges distributed in both the O sheet and the T sheets do not vary much with the increasing layer charge density. The variations of the anisotropic compressional elastic coefficients with different layer charge densities and layer charge distributions were found to be a result of the impact of the density and distribution of layer charges on the molecular interactions within the MMT layer. We further demonstrated that the layer charge density and layer charge distribution do not influence significantly the shear coefficients C44, C55, and C66. The results revealed the mechanisms of how the density and distribution of layer charges affect the anisotropic elastic properties of MMTs and will contribute to the more successful exploration and development of unconventional resources in MMT bearing shale reservoirs.

Unconventional energy resources: a system dynamics evaluation of social, environment and economic aspects

This study substantiates the usefulness of a systemic approach to investigate the multi-dimensional challenges regarding environmental, economic, and social impacts facing the sustainable development of unconventional energy resources, particularly oil sands (OS) in Canada. This research uses the system dynamics (SD) methodology to examine the impact of shocks in oil demand using real and theoretical scenarios. This was done by identifying leading indicators critical to OS resource development to capture sustainable development effects. The study identifies the contribution of OS resources in Canada to global sustainable development and has developed a model structure that captures the critical parameters associated with the economic-dynamics, socio-dynamics, and enviro-dynamics for the next 30 years. It also includes the impact of sudden oil supply and demand shocks and presents various recovery scenarios. The results from these scenarios indicate that it may take up to 25 years for the industry to return to its pre-shock trajectory, even assuming a rapid recovery. As such, the study proposes an adaptive model to assist sustainable energy development policies and decision-making. Accordingly, the approach can be helpful for academicians, policymakers, and practitioners for objective decision-making regarding sustainable development. Meanwhile, it provides cogent and valuable information for natural resource governance.

Statistical Modelling for the Source Rock Parameters of the Montney Formation, NE British Columbia, Canada

Hydrocarbons in self-sourced reservoirs are determined by the concentration and maturation of organic matter in sediments. As a result, lowering risk in unconventional resource research and development requires knowledge of hydrocarbon potentiality factors. The geochemical data for the Montney Formation samples studied suggest that it is a fair to good source rock with type IV kerogen that can generate gas in general. The statistical modelling of the analyzed data reveals a valuable technique for identifying characteristics, clusters, and linkages that affect source rock assessment. The Spearman’s correlation coefficient showed a good positive correlation between the total organic carbon (TOC) and free hydrocarbons (S1), generating potential (S2), and potential yield (GP). There was a weak correlation with the maturity index (Tmax) and hydrogen index (HI) and a highly negative correlation between the TOC and oxygen index (OI). On the other hand, the principal component analysis (PCA) showed the presence of three factors affecting the source rock evaluation. Factor 1 included TOC, S1, and S2, which are related to organic richness and hydrocarbon potentiality; factor 2 contained the production index (PI), and the generated CO2 (S3) was related to the organic matter source. Factor 3 included the Tmax and HI related to the type of organic matter and thermal maturity. In addition, the TwoStep cluster analysis separated the source rock in the study area into two major groups. Cluster 1 is characterized relatively by high HI, TOC, S1, S2, and PI, with Tmax < 455 °C indicating good source rock in the mature level with the capability to generate little oil and condensate gas. Cluster 2 is characterized by relatively low HI, TOC, S1, S2, and PI, with Tmax > 455 °C, indicating an over-mature source rock in the dry gas window.

Groundwater sources for the Mataranka Springs (Northern Territory, Australia)

The Mataranka Springs Complex is the headwater of the iconic Roper River of northern Australia. Using environmental tracers measured in springs and nearby boreholes, the origin of groundwater contributing to the springs was evaluated to help assess the impact of proposed groundwater extraction in the Cambrian Limestone Aquifer (CLA) for irrigation agriculture and for hydraulic fracturing in the Beetaloo Sub-basin (an anticipated world-class unconventional gas reserve). Major ions, Sr, 87Sr/86Sr, δ18O-H2O, δ2H-H2O, 3H, 14C-DIC were consistent with regional groundwater from the Daly and Georgina basins of the CLA as the sources of water sustaining the major springs (Rainbow and Bitter) and one of the minor springs (Warloch Pond). However, 3H = 0.34 TU in another minor spring (Fig Tree) indicated an additional contribution from a young (probably local) source. High concentrations of radiogenic 4He (> 10–7 cm3 STP g–1) at Rainbow Spring, Bitter Spring and in nearby groundwater also indicated an input of deeper, older groundwater. The presence of older groundwater within the CLA demonstrates the need for an appropriate baseline characterisation of the vertical exchange of groundwater in Beetaloo Sub-basin ahead of unconventional gas resource development.

Microbial fuel cells a state-of-the-art technology for wastewater treatment and bioelectricity generation

Wastewater treatment and electricity generation have been the major concerns for the last few years. The scarcity of fossil fuels has led to the development of unconventional energy resources that are pollution-free. Microbial fuel cell (MFC) is an environmental and eco-friendly technology that harvests energy through the oxidation of organic substrates and transform into the electric current with the aid of microorganisms as catalysts. This review presents power output and colour removal values by designing various configurations of MFCs and highlights the importance of materials for the fabrication of anode and cathode electrodes playing vital roles in the formation of biofilm and redox reactions taking place in both chambers. The electron transfer mechanism from microbes towards the electrode surface and the generation of electric current are also highlighted. The effect of various parameters affecting the cell performance such as type and amount of substrate, pH and temperature maintained within the chambers have also been discussed. Although this technology presents many advantages, it still needs to be used in combination with other processes to enhance power output.

Failure evaluations for packers in multistage fracturing technology with immobile strings

With the development of unconventional oil and gas resources, the multi-stage fracturing technology with immovable string has been developed rapidly due to its advantages of large construction capacity and multiple fracturing stages. But the failure of packer has become a bottleneck restricting the development of technology. In this paper, the mechanical properties of corroded ((under the environment of I(North Troyes),II(Jeannajor) and III(Khasib)) ) and uncorroded rubber of the packer were tested by designed experiments at first. The experimental values showed that elastic modulus, shear strength and tensile strength decreased when packers were corroded. Then, according to packers' structure and load characteristics, taking the rubber cylinder, rubber support, center pipe, tubing and string as research object, the dynamic model was established for tubes and packers in fracturing layers. Based on conditions of the shear strength, pressure seal and axial movement for rubber cylinder, the safety evaluation method was proposed for packer sealing system. And the failure evaluation of multistage fracturing packer in Gao182-151 well in Daqing Field was carried out by the method established in this paper. At last, we could get the following results: the sealing safety coefficients of upper and lower packers were all greater than 1.0 during the fracturing process of layer I to IV. The axial displacement of the packer's rubber of the non-corrosive and corrosivewere all 0.00. So the packers were sealed well in each stage of fracturing, and no leakage accidents occurred during the entire fracturing process of Gao 182-151 Well. But in the fracturing layer I, the shear safety factor of the corroded (under corrosive environment of I(North Troyes),II(Jeannajor) and III(Khasib)) rubber were is 1.00, 1.10, 0.99 respectively. The shear strength was less than or equal to 1.10 and it didn't not satisfy the shear strength. Therefore, we could get the conclusion that the corroded rubber did not meet the shear strength and rubber tearing was prone to occur in the fracturing layer I. So it is recommended to replace the rubber with a new one before the construction of Gao 182-151Well.

Technology Focus: Hydraulic Fracturing Modeling (November 2021)

In the past decades, the success of unconventional hydrocarbon resource development can be attributed primarily to the improved understanding of fracture systems, including both hydraulically induced fractures and natural fracture networks. To tackle the fracture characterization problem, several recent papers have provided novel insights into fracture modeling technique. Because of the complex nature and heterogeneity of rock discontinuity, fabric, and texture, the fracture-modeling process typically suffers from limited data availability. Research shows that modeling results reached without interrogation of high-resolution petrophysical and geomechanical data can mislead because the fluid flow is actually controlled by fine-scale rock properties. A more-reliable fracture geometry can be obtained from an enhanced modeling process that preserves the signature from high-frequency data. Advanced techniques to model fracturing processes with proppant transportation and thermodynamics require even more-sophisticated simulation and computation power. When the subsurface is too puzzling to be described by a physical model and existing data, machine learning and artificial intelligence can be adapted as a practical alternative to interpret complex fracture systems. Taking a discrete fracture network (DFN) as an example, a data-driven approach has been introduced to learn from outcrop, borehole imaging, core computed tomography scan, and seismic data to recognize stratigraphic bedding, faults, subseismic fractures, and hydraulic fractures. Input data can be collected by hand, 3D stereophotogrammetry, or drone. When upscaling DFN into a coarse grid for reservoir simulation, deep-learning techniques such as convolutional neuron networks can be used to populate fracture properties into a dual-porosity/dual-permeability model approved to yield high accuracy compared with a fine-grid model. Furthermore, the new techniques greatly extend the application of fracture modeling in the arena of the energy transition, such as in geothermal optimization. Recommended additional reading at OnePetro: www.onepetro.org. SPE 203927 - Numerical Simulation of Proppant Transport in Hydraulically Fractured Reservoirs by Seyhan Emre Gorucu, Computer Modelling Group, et al. SPE 202679 - Deep-Learning Approach To Predict Rheological Behavior of Supercritical CO2 Foam Fracturing Fluid Under Different Operating Conditions by Shehzad Ahmed, Khalifa University of Science and Technology, et al. SPE 203983 - A 3D Coupled Thermal/Hydraulic/Mechanical Model Using EDFM and XFEM for Hydraulic-Fracture-Dominated Geothermal Reservoirs by Xiangyu Yu, Colorado School of Mines, et al.

Geological parameters controlling the bedding-parallel vein distribution in Vaca Muerta Formation core data, Neuquén Basin, Argentina

It is important to understand the occurrence of bedding-parallel veins in the Vaca Muerta Formation because this helps to predict their presence away from well controls so that they can ultimately be incorporated in reservoir simulators and hydraulic fracturing modelers. Given that their occurrence has a significant impact on the propagation of hydraulic fractures, their spatial distribution will help to select sweet spots for unconventional resource development. In this study, we try to identify the key parameters that control bedding-parallel veins. Therefore, detailed sedimentological core descriptions were performed on 10 different wells, including total organic carbon measurements at a spacing of 0.5 cm and several degrees of maturity ranging from 0.7% to 1.8% vitrinite reflectance. Through a comparison between bedding-parallel vein localization and sedimentological descriptions, we built a statistical method to identify key parameters controlling the localization of such veins within the Vaca Muerta Formation. We show that bedding-parallel veins are primarily located at facies boundaries (70%) rather than in homogeneous facies (30%). The major rheological discontinuities, such as ashbeds and calcitic concretion boundaries, as well as organic-rich facies have a significant impact on the localization of both bedding-parallel veins. The total organic carbon seems to influence the generation of bedding-parallel veins by locating these fractures in organic-rich areas with more than 2 wt. % in total organic carbon. We also found a correlation between the degree of maturity of the source rock within a same sequence stratigraphy and the (1) number of bedding-parallel veins and (2) thickness of the bedding-parallel vein, suggesting a strong link between the generation of hydrocarbons during the burial of the rock with the generation and distribution of bedding-parallel veins.

Progress in Catalytic Pyrolysis of Oil Shale.

This paper briefly describes the research status of oil shale pyrolysis technology and the main factors affecting oil shale pyrolysis, with emphasis on four kinds of commonly used catalysts: The effects of natural minerals, metal compounds, molecular sixes, and supported catalysts on the pyrolysis of oil shale were discussed. The changes of the pyrolysis mechanism and product composition of oil shale with the addition of different catalysts were discussed. Finally, the development direction of preparation of new catalysts was discussed, in order to provide a prospect for the development and utilization of unconventional and strategic alternative energy resources around the world.

Research and Application of EUR Prediction Method for Tight Sandstone Gas Wells: Taking Bajiaochang Shaximiao Formation Gas Reservoir as an example

Tight gas is currently an important area for the exploration and development of unconventional oil and gas resources at home and abroad. However, due to the low permeability and high-water saturation characteristics of tight gas reservoirs, gas wells exhibit low productivity, rapid decline in production, and water production in some wells. Such characteristics have reduced the single-well EUR to a certain extent, affecting the recovery rate of the gas reservoir. For new blocks, single-well EUR is the basic condition for long-term high and stable production of oil and gas wells. It is an important indicator for evaluating development effects, analyzing development potential, and formulating development-specific measures. How to quickly and accurately predict and analyze single-well EUR has always been tight Important research work for the development of gas. This paper takes the tight sandstone gas reservoir in the Bajiaochang block as an example. Based on the analysis of the production characteristics of the implemented wells, the production instability analysis method is used to analyze the variation rules and control factors of the single well EUR at different stages, and establish a single well EUR forecast analysis. plate. The analysis results show that the single-well EUR calculation result is more reliable for more than 2 years of continuous production, and can reach more than 80% of the final value. This method provides convenience for the rapid and accurate prediction of single-well EUR, and has a better field application effect.

Characterization of the Pore Structure and Fluid Movability of Coal-Measure Sedimentary Rocks by Nuclear Magnetic Resonance (NMR).

Analyzing and mastering the pore structure and fluid movability characteristics of coal-measure sedimentary rocks is significant for the safe and effective development of unconventional resources. In this work, nuclear magnetic resonance (NMR) experiments were carried out on three common fine sedimentary rocks (i.e., shale, mudstone, and sandstone) from a coal-measure stratum in northern China. NMR transverse (T2) of the water-saturated and centrifuged rock samples are compared and analyzed. Moreover, the pore size distribution (PSD) and the free-fluid volume index (FFI) of the investigated samples are discussed. Results have shown that the shale and mudstone samples are mainly dominated by adsorption pores with a diameter of 0.01–1 μm, while the sandstone samples are dominated by seepage pores with a diameter of 1–100 μm. The FFI results calculated by the cutoff and the area methods are 11.15–77.62 and 7.56–75.96%, respectively. There are good correlations between FFI and porosity, permeability, and reservoir quality index (RQI). Also, the effects on FFI are different on various kinds of clay minerals. The contents of illite and chlorite are negatively correlated with FFI, while kaolinite is positively correlated with FFI.