Unconventional Resources最新文献

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.

Ordos Basin is rich in shale oil resources. Fuxian area in the southern Ordos Basin is an important area where Sinopec is expected to make a breakthrough in the exploration and development of lacustrine shale oil. To further identify the exploration target of shale oil in Chang 7 Member of Fuxian area, Ordos Basin, this study systematically analyzed the sedimentary characteristics, source rock characteristics, reservoir characteristics, oil-bearing characteristics, fracability and preservation conditions of Chang 7 Member in this area. The results show that: (1) the organic matter abundance of shale in the Chang 7 Member is high, and its type is dominated by type I-II1; the maturity is also relatively high, with Ro generally greater than 0.8% in the central and western parts, which is favorable for the generation and accumulation of shale oil. The development of fractures is pretty low, and thus the structure preservation conditions are relatively favorable. Delta front deposits are mainly developed in the northeastern part, while deep lake - semi-deep lake mudstone and gravity-flow deposits are developed in the western part, and the shale oil types are mainly type II and III. (2) Comparing with the western Ordos Basin, the reservoir in Fuxian area has rapid lateral variation and relatively thin cumulative thickness; the thickness of high-quality shale and maturity are low, resulting in low intensity of hydrocarbon generation and low mobility of oil-bearing saturation. Therefore, there is still a need for further improvement and refinement in the exploration evaluation, effective development and engineering techniques. (3) Integrating sedimentary characteristics with shale oil types, source conditions, oil-bearing properties, mobility, fracability and preservation conditions, it is clarified that the Type II shale oil of Chang 72 sub-,Member in Fuxian area is the current realistic exploration type of shale oil, and its favorable target is located in the development area of delta front in the central part and gravity flow in the western part.

Using a combination of field observations, textural analysis, scanning electron microscopy (SEM), mineralogical X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and thin-section analysis, the hydrocarbon and paleoenvironmental characteristics of the Cretaceous sandstones of the southern Bida Basin, Nigeria, were evaluated. SEM data were used to display the mineral morphology, degree of cementation and presence of clay minerals on the grain surfaces and their pores on both sandstones of the Patti and Lokoja formations. The lithofacies analyses revealed three distinct facies associations. The XRD data showed that for the Lokoja and Patti sandstone reservoirs contained quartz from 49 to 67% and 43–68%, respectively. The XRF data also showed that both formations' sandstone reservoirs have a high percentage of silicon and low aluminum content. The grain size study showed that the Lokoja sandstone reservoirs include medium-coarse sandstone (−0.63 to 1.30 _ф) that are poorly-moderately sorted (0.72–1.82 _ф). In contrast, the Patti Formation is primarily made up of fine-medium sandstones at investigated outcrops, which typically display reasonably good to poor sorting (0.70–2.53 _ф). The skewness of the sandstone reservoirs ranged from fine to coarse, and their kurtosis ranged from very platykurtic to leptokurtic. The research area's predominant depositional environments include shoreface/foreshore, estuary mudflat, and estuarine delta with fluvial interference, according to an analysis that combined sedimentary facies and textural data. This demonstrates that the sandstones from the two units have moderate quality prospective hydrocarbon reservoirs based on their physical and chemical characteristics.

The Chang 7 oil-bearing layer of Yanchang Formation is rich in shale oil resources. However, the reservoir indicates strong reservoir heterogeneity and has obvious differences in productivity among wells. The brittleness acts as an important factor causing the above phenomenon. Studies on rock mechanical properties and brittleness evaluation can provide technical support for drilling and fracturing design, but current methods have many disadvantages such as difficulty in obtaining parameters. In this study, the neural network method is used to construct the relationship between elastic modulus, Poisson's ratio and logging curve on the basis of measured rock mechanical parameters, construct rock mechanics parameter profile in the whole well section of Chang 7 oil-bearing layer, and finally quantitative evaluate shale oil reservoir brittleness. The results indicate that, (1) the neural network method is an effective method for rock mechanical parameter prediction and brittleness evaluation. The error between the predicted and measured values of elastic modulus and Poisson's ratio is low, generally within 10%; (2) according to the brittleness evaluation results, on the whole, the brittleness index of the Chang 7₂ reservoir is high, and the brittleness index of the Chang 7₃ reservoir is low. The results can provide scientific guidance for benefit development of Chang 7 shale oil in the Ordos Basin.

The shale oil reservoirs in the Jimsar Sag are strongly heterogeneous. Therefore, it is of practical significance to relate the dynamic elastic stiffness to the static elastic stiffness under the assumption of transverse isotropy. The acquisition of stiffness parameters depends on lab measurements or Sonic Scanner logging. Aiming at the problem that the lab measurements results are limited and discontinuous, the acquisition of special logging data is difficult in the well site, a method using only the conventional well-log data to predict the dynamic elastic stiffnesses of shale is proposed. Inspired by ultrasonic experimental test method, the study simplified the types of tested waves and complemented missing datas. According to the experimental proof, we concluded that: (1) Under the assumption of transverse isotropy, using simplified Thmosen model and velocity conversion relationship can accurately calculate the P-wave and S-wave velocities in the 45° angle direction. (2) Compared with the conventional isotropic algorithm, specify this algorithm can better reflect real mechanical conditions of the formation, and better characterize the variation of mechanical parameters with depth. (3) Effective conversion models between dynamic elastic modulus and static elastic modulus in vertical and horizontal directions were obtained in some areas of Jimsar.

The shale oil exploration, in the Middle Jurassic Lianggaoshan Formation in the Fuxing area of Sichuan Basin, is in preliminary stage, requiring further in-depth study on shale oil and gas enrichment conditions. The lithological, organic geochemical, and reservoir characteristics of the Lianggaoshan Formation shale were analyzed using a suite of tests, including common thin section observation, organic carbon determination, pyrolysis experiment, combined N₂-high pressure mercury test and argon ion polishing-scanning electron microscope, to elucidate source rock and reservoir qualities and their variation in vertical. Results suggest that the medium-carbon argillaceous shale, medium-carbon shell calcareous-argillaceous shale, and low-carbon argillaceous shale facies were mainly developed in Member 1 and Member 2 of the Lianggaoshan Formation. The medium-carbon argillaceous shale facies in the sub-layer ④ was rich in organic matter, with abundant sapropel, chitinous and secondary organic components, which were considered as a set of medium-quality source rocks. The medium-carbon shell calcareous-argillaceous shale and low-carbon argillaceous shale in the sub-layers ② and ③ have relatively low organic matter abundance, with vitrinite and inertinite as major organic microscopic components, revealing poor hydrocarbon generation potential. The porosity of shale reservoirs in sub-layers ②‒④ was higher than 3.0%, with predominant mesopores, followed by macropores, consisting of mainly clay mineral pores, organic pores, and microfractures related to organic matter. The medium-carbon argillaceous shale facies at the Lianggaoshan Formation is high-quality source rocks and reservoirs and is thus a potential target for lacustrine shale oil exploration in the Fuxing area of the Sichuan Basin.

Water distribution can affect the storage and transport of methane in coal. There are many reports involving the distribution of water and methane in coal, but the microscopic mechanism of water-methane interaction is still unclear. In this study, realistic molecular structure models of bituminous and anthracite coals were constructed based on the chemical structures of two coal samples. And the chemical structures were analyzed by solid-state nuclear magnetic resonance, Fourier-transform infrared, and X-photoelectron spectroscopy. Then slit-pore models with different pore sizes were constructed based on the molecular structures to simulate the methane-water interaction in bituminous and anthracite coals. Results show that water molecules tend to form water bridges and water films in the pores of bituminous and anthracite coals, respectively. The significant displacement of pre-adsorbed water by methane was observed through simulation. It is found that the water molecules on the pore surface and the interfaces of small-size water bridges are more easily displaced by methane. In the larger pores, methane molecules mainly drive water molecules to agglomerate larger water bridges in bituminous coal. While methane molecules mainly drive water molecules to cover the pore surface and form a thicker water film in anthracite coal. This study provides new insights into the microscopic distribution and interaction mechanism of fluids in coal.