Numerical simulation of the in situ stress in a high-rank coal reservoir and its effect on coal-bed methane well productivity

2018 ◽  
Vol 6 (2) ◽  
pp. T271-T281 ◽  
Author(s):  
Shuai Yin ◽  
Airong Li ◽  
Qiang Jia ◽  
Wenlong Ding ◽  
Yanxia Li
Keyword(s):  
Stress Field ◽  
In Situ Stress ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Small Displacement ◽  
Small Scale ◽  
Burial Depth ◽  
Single Well ◽  
Coal Reservoir

In situ stress has an important influence on coal reservoir permeability, fracturing, and production capacity. In this paper, fracturing testing, imaging logging, and 3D finite-element simulation were used to study the current in situ stress field of a coal reservoir with a high coal rank. The results indicated that the horizontal stress field within the coal reservoir is controlled by the burial depth, folding, and faulting. The [Formula: see text] and [Formula: see text] values within the coal reservoir are 1–2.5 MPa higher than those within the clastic rocks of the roof and floor. The [Formula: see text]–[Formula: see text] values of the coal reservoir are generally between 2 and 6 MPa and increase with burial depth. When the [Formula: see text]–[Formula: see text] value is less than 5 MPa, production from a single well is high, but when the [Formula: see text]–[Formula: see text] value is greater than 5 MPa, production from a single well is low. In addition, the accumulated water production is high when the [Formula: see text]–[Formula: see text] value is greater than 5 MPa, demonstrating that a higher [Formula: see text]–[Formula: see text] value allows the hydraulic fractures to more easily penetrate the roof and floor of the coal seam. In coal-bed methane development regions with high [Formula: see text]–[Formula: see text] values, repeated fracturing using the small-scale plug removal method — which is a fracturing method that uses a small volume of liquid, small displacement, and low sand concentration — is suggested.

scholarly journals Study on the Coalbed Methane Development under High In Situ Stress, Large Buried Depth, and Low Permeability Reservoir in the Libi Block, Qinshui Basin, China

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Jinkuang Huang ◽  
Shenggui Liu ◽  
Songlei Tang ◽  
Shixiong Shi ◽  
Chao Wang
Keyword(s):  
Coalbed Methane ◽  
Horizontal Wells ◽  
In Situ Stress ◽  
Low Permeability ◽  
Qinshui Basin ◽  
Hole Pressure ◽  
Bottom Hole ◽  
Single Well ◽  
Coal Reservoir

Coalbed methane (CBM) has been exploited in the deep area of the coal reservoir (>1000 m). The production of CBM vertical wells is low because of the high in situ stress, large buried depth, and low permeability of the coal reservoir. In this paper, efficient and advanced CBM development technology has been applied in the Libi Block of the Qinshui Basin. According to the characteristics of the coal reservoir in the Libi Block, the coiled tubing fracturing technology has been implemented in four cluster horizontal wells. Staged fracturing of horizontal wells can link more natural fracture networks. It could also expand the pressure drop range and control area of the single well. This fracturing technology has achieved good economic results in the Libi Block, with the maximum production of a single horizontal well being 25313 m3/d and the average single well production having increased by more than 60% from 5000 m3/d to 8000 m3/d. Based on the data regarding the bottom hole pressure, water production, and gas production, the production curves of four wells, namely, Z5P-01L, Z5P-02L, Z5P-03L, and Z5P-04L, were investigated. Furthermore, a production system with slow and stable depressurization was obtained. The bottom hole pressure drops too fast, which results in decreasing permeability and productivity. In this work, a special jet pump and an intelligent remote production control system for the CBM wells were developed; hence, a CBM production technology suitable for the Libi Block was established. The maximum release for the CBM well productivity was obtained, thus providing theoretical and technical support for CBM development with geological and engineering challenges.

Reservoir Pressure of Coal-Bed Methane Prediction Research Based on Analysis Method by Neural Net-Work

2013 ◽  
Vol 756-759 ◽  
pp. 4758-4762
Author(s):  
Xing Peng Jing
Keyword(s):  
Neural Network ◽  
In Situ Stress ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Neural Net ◽  
Reservoir Pressure ◽  
Neural Network Prediction ◽  
Quantitative Results ◽  
Network Prediction

In Order to Achieve Accurate Quantitative Results of Parameters for Reservoir Pressure of Coal-Bed Methane, Neural Network Prediction Analytic Method is Adopted to Predict the Reservoir Pressure of Coal-Bed Methane. the Main Controlling Factors such as Conformation Stress, Buried Depth, in-Situ Stress and Permeability are Investigated. Mathematical Models of Neural Network of Reservoir Pressure of Coal-Bed Methane of Mathematical Analysis and System Architecture are Established; Taking the Qinshui Basin Coal Seam as Example to Forecast and use Reservoir Pressure of Coal-Bed Methane. Projections Show that: the use of Neural Network Prediction of Reservoir Pressure of Coal-Bed Methane is Feasible; Neural Network Method Makes up a Mathematical Point of Linear and Regularity in Order to Solve the Non-Linear Complex Relationship between the Input and Output Parameter Variables.

scholarly journals Characteristics of the In Situ Stress Field and Engineering Effect along the Lijiang to Shangri-La Railway on the Southeastern Tibetan Plateau, China

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Chunyang Chai ◽  
Sixiang Ling ◽  
Xiyong Wu ◽  
Ting Hu ◽  
Dai Sun
Keyword(s):  
Tibetan Plateau ◽  
Stress Field ◽  
Principal Stress ◽  
Pressure Coefficient ◽  
In Situ Stress ◽  
Burial Depth ◽  
The Tibetan Plateau ◽  
Rock Masses ◽  
In Situ Stress Field

This work aims to characterize the in situ stress field along the Lijiang to Shangri-La railway and identify possible engineering geological problems when constructing tunnels along this railway on the margin of the Tibetan Plateau. The in situ stress measured at 76 points in 12 boreholes by the hydraulic fracturing method was analysed. A rose diagram of the maximum principal stress direction was plotted based on the measured in situ stress data. The results show that the measured in situ stress is mainly horizontal stress, corresponding to a strike-slip fault-related tectonic stress field with a moderate to high in situ stress value. The main stress values have a good linear relationship with the burial depth, and the maximum horizontal principal stress (σH) increases by 1.1–8.8 MPa per 100 m, with an average gradient value of 3.6 MPa per 100 m. The maximum and minimum horizontal principal stresses and the stress differences increase with depth, and the lateral pressure coefficient (σH/ σ v ) is generally 1–1.5. The ratio of the maximum and minimum effective stresses is less than the threshold at which faulting occurs, resulting in faults that are relatively stable at present. The direction of the maximum horizontal principal stress is oriented at a small angle to the axial direction of the deeply buried tunnel along the railway line; therefore, the tunnel sidewalls could readily deform during the construction process. Rock bursts are expected to occur in strong rock masses with high risk grades, whereas slight to moderate deformation of the rock surrounding the tunnel is expected to occur in weak rock masses. This study has significance for understanding the regional fault activity and issues related to the construction of deeply buried tunnels along the Lijiang to Shangri-La railway.

scholarly journals GAN inversion method of an initial in situ stress field based on the lateral stress coefficient

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Qian ◽  
Tianzhi Yao ◽  
Zuguo Mo ◽  
Jianhai Zhang ◽  
Yonghong Li ◽  
...  
Keyword(s):  
Stress Field ◽  
In Situ Stress ◽  
Inversion Method ◽  
Burial Depth ◽  
Lateral Stress ◽  
Distribution Law ◽  
Underground Engineering ◽  
Generative Adversarial Network ◽  
In Situ Stress Field

AbstractThe initial in situ stress field influences underground engineering design and construction. Since the limited measured data, it is necessary to obtain an optimized stress field. Although the present stress field can be obtained by valley evolution simulation, the accuracy of the ancient stress field has a remarkable influence. This paper proposed a method using the generative adversarial network (GAN) to obtain optimized lateral stress coefficients of the ancient stress field. A numerical model with flat ancient terrain surfaces is established. Utilizing the nonlinear relationship between measured stress components and present burial depth, lateral stress coefficients of ancient times are estimated to obtain the approximate ancient stress field. Uniform designed numerical tests are carried out to simulate the valley evolution by excavation. Coordinates, present burial depth, present lateral stress coefficients and ancient regression factors of lateral stress coefficients are input to GAN as real samples for training, and optimized ancient regression factors can be predicted. The present stress field is obtained by excavating strata layers. Numerical results show the magnitude and distribution law of the present stress field match well with measured points, thus the proposed method for the stress field inversion is effective.

scholarly journals Evaluation Method of Coal-Bed Methane Fracturing in the Qinshui Basin

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Zhengrong Chen ◽  
Tengfei Sun
Keyword(s):  
Support Vector Machine ◽  
In Situ Stress ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Support Vector ◽  
Stress Difference ◽  
Qinshui Basin ◽  
Five Factors ◽  
Net Pressure

In order to evaluate the productivity effects of coal-bed methane well fracturing, the relationship between the five factors of horizontal in situ stress difference is analyzed: fracturing friction, net pressure, fracture morphology, fracturing curve shape, and fracturing effect, taking the coal-bed methane wells in the Qinshui Basin as the research target. The results show that the smaller the horizontal in situ stress difference, the larger the fracture stimulation volume; the smaller the fracturing friction and the net pressure, the higher the productivity of the coal-bed methane well; the greater the proportion of coal-bed methane wells with complex fractures in the form of fracturing fractures, the greater the productivity; the fractures formed by descending and mixed fracture curves are ideal, and the effect after fracturing is better. Based on support vector machine for the above five factors, a fracturing effect classification and evaluation model is established using the fractured wells in the target block as training samples, and the effect prediction of nearby coal-bed methane wells is performed. The results show that the prediction results are in excellent agreement, comparing the prediction classification results of support vector machine with the average daily gas production. This theoretical method realizes the classification of the complex effects of coal-bed methane fracturing and provides a theoretical basis for the design of coal-bed methane well production stimulation and effect prediction.

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