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Prediction of coalbed methane content based on seismic identification of key geological parameters: a case in a study area, Southern Qinshui Basin

Liu Jing, Chang Suoliang, Zhang Sheng, Li Yanrong, Hao Yaju, He Guoxian, He You, Liu Bo

Acta Geophysica

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2023

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Vol. 71, no. 6

2645--2662

EN

The coalbed methane content (CMC) is an important parameter to evaluate the degree of coalbed methane enrichment, and also an important reservoir parameter to calculate coalbed methane resources, productivity prediction and reservoir simulation. Accurately identifying the distribution of CMC is crucial to the exploration of CBM. In this study, we developed a prediction method for the CMC distribution via seismic techniques identification of key geological parameters such as structure, coal thickness and sedimentation. Firstly, the geological factors that control the generation and preservation of CBM in the study area are quantitatively characterized by using five parameters: surface (X1), residual (X2), dip (X3), coal thickness (X4) and the ratio of sand to mud (X5). Secondly, the geological parameters are extracted by seismic structure interpretation and inversion prediction technology. Thirdly, the key geological parameters of CMC are screened out by grey correlation analysis. Finally, the functional relationship of CMC and the key geological parameters is established to predict the CMC distribution. The method is applied to the CMC distribution prediction of two coal seams of a study area in the southern Qinshui Basin, China. Results show that different coal seams differ in key geological parameters of CMC, resulting in various CMC distribution laws. The CMC prediction method based on the key geological factors can effectively delineate the CBM enrichment area in the study area, providing important reference for the CBM exploration and development.

2

Precise time‑depth conversion of coal measure strata based on velocity splicing: a case application in Qinshui basin

Zhang Qifan, Chang Suoliang, Zhang Sheng, Zhao Lipeng, Shi Xiaohong, Guo Chunsheng, Yu Guangming, Liu Jing, Liu Bo

Acta Geophysica

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2023

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Vol. 71, no. 4

1729--1746

EN

Transforming seismic data from the time domain to the depth domain is a very important step when using 3D seismic exploration to guide the exploration and development of coalbed methane (CBM). However, the conventional time-depth conversion method has difficulty meeting the control accuracy requirements of CBM development based on horizontal well technology when the 3D seismic data in a mining area are old. Therefore, a precise time-depth conversion method was found to improving the accuracy of time-depth conversion, which is based on the splicing of seismic inversion velocity and poststack migration velocity. The first step of this method is obtaining the standard layers in the time domain by precise interpretation of seismic data. Then, the inversion velocity and poststack migration velocity are spliced to obtain the complete interval velocity volume of the study area, and the results are corrected. The next step is the prediction of the coal seam floor elevation based on the spliced velocity, and the predicted coal seam floor elevation is corrected by borehole data. Finally, the mesh is between standard layers in the depth domain to obtain the 3D data volume in the depth domain. The method was applied to the time-depth conversion of 3D seismic data in the Yangquan X study area. The results show that the relative error between the predicted results and the borehole data of No. 3, No. 8 and No. 15 coal seam is only 0.72% through the validation of the reserved boreholes, indicating that the method is effective. This study provides a precise method of time-depth conversion for seismic data when there is only poststack seismic data in the mining area, which can not only improve the interpretation accuracy of standard layers but can also improve the prediction accuracy of other layers between standard layers, which can better guide the well location arrangement of coalfield and CBM.

3

Dynamic load analysis of the connecting bolts in a universal joint

An Yuchen, Liu Jing, Li Zengguang

Eksploatacja i Niezawodność

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2022

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Vol. 24, no. 2

211--225

EN

Dynamic loads of the connecting bolts in a universal joint can greatly affect the bolt fatigue and fracture, as well as the machinery safety and stability. But few researches focused on those. To obtain the dynamic load characteristics of the connecting bolts in a universal joint, this paper established a flexible dynamic model for the connecting bolts. A multibody dynamic model of a universal joint is developed. The dynamic loads on the connecting bolts of the universal joint are analyzed. The influences of the preloads, speeds and loads are studied. The amplitude and frequency properities are obtained. The effect of the preload is small when the preload is in the range of 80%~120% of the standard value. The load and speed have great influence on the time- and frequency-domain dynamic loads of the bolts. The flexible dynamic model of the connecting bolt is closer to the actual situation than the rigid model since it can consider the preload and deformation of the bolts. This study can provide guidance for the fatigue life prediction of the universal shaft and its bolts.

4

Integrated seismic–geological prediction of tectonic coal via main controlling factors

Liu Jing, Chang Suoliang, Zhang Sheng, Li Yanrong, Chen Qiang

Acta Geophysica

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2022

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Vol. 70, no 1

173--190

EN

Tectonic coal in coal seams not only seriously restricts the development of coalbed methane (CBM), but also easily forms coal and gas outburst risk areas. Therefore, it is of great significance to effectively predict the tectonic coal in coal seams under the development scale. Currently, the prediction methods of tectonic coal include geological prediction and geophysical prediction. Due to the large scale of geological analysis and the low identifiability of geophysical response of thin coal seam, these two methods are difficult to meet the prediction requirements of tectonic coal in the development process. Therefore, this paper proposes a new method for predicting tectonic coal based on seismic–geological integrated analysis of main controlling fac tors. Firstly, the control factors of tectonic coal and their quantitative characterization are determined by geological analysis. Then, the characterization parameters of control factors are obtained by various seismic technologies. Finally, the main control factors are screened by grey correlation analysis, and the prediction model of tectonic coal distribution is established by using the main control factors, and applied in the Qinshui Basin. The results show that the structure, surrounding rock lithology and coal thickness are three kinds of geological factors controlling the development of tectonic coal and the control weight of each factor is different. Structure plays the most important role in controlling the development of tectonic coal, followed by coal thickness and surrounding rock lithology. The prediction error of two verification wells is less than 2%, which indicates that the method can provide effective guidance for coal structure evaluation in the process of CBM development and coal mining.

5

Influence of the local defect distribution on vibration characteristics of ball bearings

Liu Jing, Xu Yajun, Wang Linfeng, Xu Zidan, Tang Changke

Eksploatacja i Niezawodność

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2019

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Vol. 21, no. 3

485--492

EN

Local defects in ball bearings may occur at the center line of raceway and its surrounding areas. However, most current studies were concentrated in studying the influence of the local defect located at the centerline of raceway on the bearing vibrations, where the effects of local defects surround the centerline were ignored. To overcome this problem, based on Hertzian point contact theory and multi-body dynamic algorithm, a multi-body dynamic model considering the offset and angular distributions for a ball bearing with a local defect on its outer raceway is established. The influences of offset distance and skew angle between the geometric center of local defect and the centerline of outer raceway on the bearing vibrations are investigated. The relationship between the offset distance and the impulse waveform characteristics is obtained, as well as that between the skew angle and the impulse waveform characteristics. The results show that the offset distance and skew angle of the local defect have a great influence on the time-domain impulse waveform characteristics of the bearing accelerations. This paper can provide a useful guidance for the accurate diagnosis of early local fault in the ball bearings.

PL

Wady lokalne łożysk kulkowych mogą występować na linii środkowej bieżni oraz w otaczających ją obszarach. Jednak większość dotychczasowych badań nad wpływem wad lokalnych na drgania łożyska koncentruje się na wadach linii środkowej bieżni ignorując oddziaływanie wad zlokalizowanych w obszarach otaczających tę linię. Aby rozwiązać ten problem, w przedstawionej pracy wykorzystano teorię kontaktu Hertza oraz algorytm do analizy dynamiki układów wieloczłonowych, co pozwoliło na utworzenie modelu dynamiki układu wieloczłonowego uwzględniającego przesunięcie i rozkłady kątowe łożyska kulkowego z lokalną wadą na bieżni zewnętrznej. Badano wpływ wartości przesunięcia i kąta nachylenia między geometrycznym środkiem wady lokalnej a linią środkową bieżni zewnętrznej na drgania łożyska. Otrzymano zależności pomiędzy wartością przesunięcia a charakterystyką przebiegu impulsu, a także między kątem nachylenia a charakterystyką przebiegu impulsu. Wyniki pokazują, że wartość przesunięcia i kąt nachylenia wady lokalnej mają duży wpływ na przebieg przyspieszeń łożyska w dziedzinie czasu. Praca dostarcza pożytecznych wskazówek na temat trafnego diagnozowania lokalnych uszkodzeń łożysk kulkowych w ich wczesnych stadiach.