The Experts below are selected from a list of 2559 Experts worldwide ranked by ideXlab platform
Wang Zijian - One of the best experts on this subject based on the ideXlab platform.
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Time delay effect due to pore pressure changes and existence of cleats on Borehole Stability in coal seam
International Journal of Coal Geology, 2011Co-Authors: Ruichen Shen, Wang ZijianAbstract:Abstract When horizontal wells are drilled underbalanced in coal seam, it was found that Borehole which kept stable at the beginning would probably collapse in some time. The phenomenon was called as time delay effect. In order to clarify the concept of time delay effect, the influence of pore pressure on stresses of cleats was analyzed based on the characteristic that cleats are abundant in coal seam, indicating that pore pressure influences the normal stresses of cleat surface while it has no impact on the tangential stresses. Using the data from field production in a CBM well, the influence of pore pressure changes on Stability of coal rock was analyzed, indicating that contents of coal fines in drained water increases as pore pressure decreases. Pore pressure changes due to seepage in underbalanced drilling or overbalanced drilling were analyzed. This study above demonstrates that the time delay effect exists absolutely in Borehole Stability in coal seams during underbalanced drilling. The pore pressure changes are the main factor on the time delay effect, while cleats are the internal cause. In order to analyze further time delay effect quantitatively, the fluid–solid coupling during underbalanced drilling was numerically simulated, and the relationship between pore pressure and time was fitted, and the equation for computing the delaying time was posed by means of Borehole Stability theory in fracture mechanics. The analysis of the time delay effect can guide the field drilling operation and avoid the inStability caused by pore pressure changes. The delaying time can be altered through adjusting bottom hole pressure in order to supply sufficient time for drilling operation.
Tongqiang Xia - One of the best experts on this subject based on the ideXlab platform.
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Application of a non-linear viscoelastic-plastic rheological model of soft coal on Borehole Stability
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Chun Liu, Fubao Zhou, Jianhong Kang, Tongqiang XiaAbstract:Abstract Time dependent deformation of coal has a significant effect on the Stability of underground structures. In this study, taking the visco-elastic–plastic characteristics and the damage effect into account, a non-linear model was proposed to describe the creep behavior of soft coal. Meanwhile, the creep equations of the proposed non-linear model were derived and the three-dimensional creep equations were constructed by generalizing the one-dimensional creep equations. At the same time, the uniaxial creep tests on soft coal specimens under different axial stress conditions were carried out to validate the proposed model. It is found that the present model can not only reproduce the transient creep under low axial stress level, but also can accurately predict the steady and accelerating creep stages under high axial stress level. Finally, Borehole Stability in soft coal seam was investigated based on the proposed model. The results show that the vertical displacement and plastic zone range around Borehole gradually increase while the increasing rate decreases and tends to be stable after 20 days. It can also be obtained that the creep duration tends to be stable when it is about 20 days after drilling excavation under the simulation conditions. The analysis results should be useful for the long-term Stability of Boreholes in soft coal seam for gas extraction.
Ruichen Shen - One of the best experts on this subject based on the ideXlab platform.
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Time delay effect due to pore pressure changes and existence of cleats on Borehole Stability in coal seam
International Journal of Coal Geology, 2011Co-Authors: Ruichen Shen, Wang ZijianAbstract:Abstract When horizontal wells are drilled underbalanced in coal seam, it was found that Borehole which kept stable at the beginning would probably collapse in some time. The phenomenon was called as time delay effect. In order to clarify the concept of time delay effect, the influence of pore pressure on stresses of cleats was analyzed based on the characteristic that cleats are abundant in coal seam, indicating that pore pressure influences the normal stresses of cleat surface while it has no impact on the tangential stresses. Using the data from field production in a CBM well, the influence of pore pressure changes on Stability of coal rock was analyzed, indicating that contents of coal fines in drained water increases as pore pressure decreases. Pore pressure changes due to seepage in underbalanced drilling or overbalanced drilling were analyzed. This study above demonstrates that the time delay effect exists absolutely in Borehole Stability in coal seams during underbalanced drilling. The pore pressure changes are the main factor on the time delay effect, while cleats are the internal cause. In order to analyze further time delay effect quantitatively, the fluid–solid coupling during underbalanced drilling was numerically simulated, and the relationship between pore pressure and time was fitted, and the equation for computing the delaying time was posed by means of Borehole Stability theory in fracture mechanics. The analysis of the time delay effect can guide the field drilling operation and avoid the inStability caused by pore pressure changes. The delaying time can be altered through adjusting bottom hole pressure in order to supply sufficient time for drilling operation.
Mian Chen - One of the best experts on this subject based on the ideXlab platform.
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A chemo-mechanical coupling model of deviated Borehole Stability in hard brittle shale
Petroleum Exploration and Development, 2014Co-Authors: Hang Wen, Mian Chen, Yan Jin, Kai Wang, Yang Xia, Jingnan Dong, Chengcheng NiuAbstract:Abstract A chemo-mechanical coupling model of Borehole Stability in hard brittle shale considering structure characteristics and targeted hydration was established, the influencing factors of the distribution of collapse pressure were analyzed based on the model, and a field case analysis was conducted. Based on the physicochemical properties of hard brittle shale, a drilling fluid activity window was proposed for calculating collapse pressure by establishing the relationships of drilling fluid activity vs. swelling ratio of rock and rock activity vs. moisture content to determine critical swelling ratio of rock and reasonable moisture content. The results show that, when fixing the dip angle of weak plane, the collapse pressure appears a quarter symmetric distribution with the change in tendency, there is no azimuth angle who has a monotonic increasing or decreasing collapse pressure, and dangerous sections and safe sections exist alternately; compared with cohesion of weak plane, collapse pressure is more sensitive to internal friction angle. Field case shows that, accurate prediction of collapse pressure distribution can be obtained by the chemo-mechanical coupling model, in which Borehole Stability can be ensured and the density of drilling fluid can be decreased as long as the drilling fluid activity is controlled in the window.
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Analysis of the vertical Borehole Stability in anisotropic rock formations
Journal of Petroleum Exploration and Production Technology, 2012Co-Authors: Yan Jin, Mian Chen, Jianbo Yuan, Bin Hou, Zhipeng ZouAbstract:The objectively existing in situ stress field and the physical mechanical properties of rock are closely related to the Borehole Stability in petroleum engineering. However, in present engineering design, rock mass is simply treated as isotropic material. This method may be acceptable for shallow rock engineering, but for deep rock engineering, with the increase of drilling depth, the anisotropic properties of rock mass become stronger and should be considered. In the past, accurate methods to predict critical fracturing or collapse pressures were unavailable. Simple isotropic stress equations have been used to some extent, but these have failed to take into account real rock properties that are clearly anisotropic. On the basis of some rock testing experiments, the vertical Borehole Stability in transversely isotropic media was the main focus of this study. By solving the stress distribution on the Borehole wall, a new vertical Borehole Stability model was established. The results obtained in this study showed that the anisotropy of the rock and the horizontal stress ratio greatly affect the stress distribution and the failure plane of vertical wellbores. Neglecting this effect can lead to errors in Stability predictions. Therefore, it was seen that the effect of the rock anisotropy is of practical importance in the life of a well since it can avoid Borehole inStability issues.
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A Mechanical Model of Borehole Stability for Weak Plane Formation Under Porous Flow
Petroleum Science and Technology, 2012Co-Authors: Mian Chen, Y. Jin, Guangqing ZhangAbstract:Abstract Based on influence of porous flow on weak plane model, the authors established a mechanical model of Borehole Stability for weak plane formation under porous flow and analyzed effect of weak plane on Borehole Stability under porous flow. The results indicated that porous flow decreased strength of weak plane, enlarged the affecting domains of weak plane for rock mass strength, and worsened Borehole inStability in weak plane formations. With porous flow increasing, water content of weak plane increases. For the weak plane with DIP 30°, it is opposite to the situation of 10° < DIP < 30°. While weak plane formation is next to be saturated, the minimum drilling fluid density for Borehole Stability does not change with weak plane azimuth and Borehole Stability is the worst. The mechanical model ...
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Borehole Stability in naturally fractured reservoirs during production tests
Petroleum Science, 2008Co-Authors: Fuxiang Zhang, Shaoli Zhang, Xuehai Jiang, Mian ChenAbstract:Based on the plane of weakness theory, a model for predicting Borehole Stability in fractured reservoirs under different stress states was estiblisted and the equations for solving Borehole Stability were developed. The minimum downhole pressures required to maintain Borehole Stability under different natural fracture occurrences were calculated by using the data from a well in the Tazhong (central Tarim) area, Tarim Basin, west China. Several conclusions were drawn for naturally fractured reservoirs with a dip angle from less than 10 ° to greater than 30 °. Application in three wells in the Tazhong area indicates that this model is practically useful.
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Real-time prediction method of Borehole Stability
Petroleum Exploration and Development, 2008Co-Authors: Mian Chen, Yan JinAbstract:Abstract Based on the close relationship between seismic and logging information, a real-time prediction model of Borehole Stability is established using seismic, logging, and geological data to control Borehole wall sloughing inStability. First, seismic attributes are extracted from Borehole-side seismic traces of target wells and drilled offset wells. The mapping models of relationships between seismic attributes and logging data of various formation intervals in drilled wells are then constructed using wavelet neural network. Using the seismic attributes of formation under bit and the corresponding mapping model, the acoustic and density logging data of the current undrilled formation can be predicted. On the basis of the prediction results, the mechanical model of Borehole Stability is employed to calculate pore pressure, collapse pressure, and fracture pressure, thus predicting the safe drilling fluid density range. Practical application in Tarim Oilfield shows that real-time operation performance of the model is excellent and the prediction accuracy of parameters is satisfactory.
Chun Liu - One of the best experts on this subject based on the ideXlab platform.
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Application of a non-linear viscoelastic-plastic rheological model of soft coal on Borehole Stability
Journal of Natural Gas Science and Engineering, 2016Co-Authors: Chun Liu, Fubao Zhou, Jianhong Kang, Tongqiang XiaAbstract:Abstract Time dependent deformation of coal has a significant effect on the Stability of underground structures. In this study, taking the visco-elastic–plastic characteristics and the damage effect into account, a non-linear model was proposed to describe the creep behavior of soft coal. Meanwhile, the creep equations of the proposed non-linear model were derived and the three-dimensional creep equations were constructed by generalizing the one-dimensional creep equations. At the same time, the uniaxial creep tests on soft coal specimens under different axial stress conditions were carried out to validate the proposed model. It is found that the present model can not only reproduce the transient creep under low axial stress level, but also can accurately predict the steady and accelerating creep stages under high axial stress level. Finally, Borehole Stability in soft coal seam was investigated based on the proposed model. The results show that the vertical displacement and plastic zone range around Borehole gradually increase while the increasing rate decreases and tends to be stable after 20 days. It can also be obtained that the creep duration tends to be stable when it is about 20 days after drilling excavation under the simulation conditions. The analysis results should be useful for the long-term Stability of Boreholes in soft coal seam for gas extraction.