Directional drilling has been established in the coal industry as a viable means of gas drainage, exploration and water management. But the environment in and around coal seams is not always conducive to stable condit...Directional drilling has been established in the coal industry as a viable means of gas drainage, exploration and water management. But the environment in and around coal seams is not always conducive to stable conditions while drilling and borehole stability after the drilling has been completed. This paper identifies the conditions which cause unstable drilling conditions and the various means which are used to attempt to manage or bypass those conditions. Ultimately, equipment does become bogged in these adverse environments and requires recovery by over-coring.展开更多
To solve the problem of borehole trajectory uncertainty, some methods such as error ellipsoid posture characterization, sectional error ellipse solution and error elliptic cylinder construction were proposed and an ap...To solve the problem of borehole trajectory uncertainty, some methods such as error ellipsoid posture characterization, sectional error ellipse solution and error elliptic cylinder construction were proposed and an application example was given. According to the definition of inclination, azimuth and tool-face angle, a characterization method of error ellipsoid posture of borehole trajectory was presented. By intercepting the error ellipsoid with an arbitrary plane in space, the general concept and algorithm of sectional error ellipse were established to analyze the borehole trajectory errors in horizontal plane, plumb plane, normal plane, etc. Based on the theory of surface tangency and curve projection, a construction method of error elliptic cylinder of borehole trajectory was put forward to evaluate the axial enveloping error of borehole trajectory and its variation along well depth. The research shows that the deeper the well, the greater the borehole trajectory error will be. In deep and ultra-deep wells measured using conventional measurement while drilling(MWD),the borehole trajectory position error reaches tens of meters. The research results provide a complete set of analysis methods for borehole trajectory error, which can evaluate the accuracy and reliability of borehole trajectory monitoring.展开更多
In order to accurately calculate drilled trajectories,the method of quantitatively recognizing borehole trajectory models was provided,and a case analysis was conducted.Because the measurement-while-drilling data prov...In order to accurately calculate drilled trajectories,the method of quantitatively recognizing borehole trajectory models was provided,and a case analysis was conducted.Because the measurement-while-drilling data provide with measured values of tool-face angle besides inclination angle and azimuth angle,this paper presents the technological approach of recognizing borehole trajectory models based on tool-face angle.A universal tool-face angle equation was established based on the directional deflection mechanism of steerable drilling tools,and it can calculate the tool-face angles with characteristic parameters of various borehole trajectory models.Then,by evaluating the error between the theoretical values and the measured values of tool-face angle,the trajectory model most consistent with the actual well trajectory can be selected.The model recognition of borehole trajectory provides with the quantitative evaluation index and selection basis of survey calculation methods,which can avoid subjectively and randomly selecting the survey calculation method,and consequently improve the monitoring accuracy and reliability of borehole trajectory.展开更多
The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi MS= 6.8 earthquake occurred on February 24, 2003. Its features are as follows. j Anomaly types are complete. The trend anomaly, short-...The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi MS= 6.8 earthquake occurred on February 24, 2003. Its features are as follows. j Anomaly types are complete. The trend anomaly, short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month before the event, respectively; k Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10?5, which is rare in the past 20-year observation records at Wushi station; l Strain rate fluctuates sharply with obvious alternation of tension and compression. According to the magnitude of strain anomaly, time of expo- nential anomaly appearance and regional features of recorded anomaly, we could predict the magnitude, occur- rence time and potential region to a certain degree.展开更多
Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a pot...Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a potential solution for enhancing borehole stability while considering gas production.In this work,we improved and implemented a dual-porosity,fully coupled geomechanical-hydraulic numerical model into COMSOL Multiphysics to investigate into this factor.The sophisticated numerical model incorporates various critical factors,including desorption-induced matrix shrinkage,stress-dependent anisotropic fracture permeability,and the interactions of gas flow and reservoir deformation in matrices and fractures.A suite of simulation scenarios(e.g.,varying coal strength)was carried out to quantify the impact of drilling azimuth on coal permeability evolution,cumulative gas production,and the borehole break-out width for Goonyella Middle Seam of Bowen Basin,Australia.The model was calibrated against both theoretical permeability values and field gas production data.Due to the lack of directly measured matrix permeability data,the actual gas production was used to back calculate the best-matched matrix permeability,which is 0.65μD for this particular work.Moreover,based on the breakout shape and induced volumetric strains around the borehole,drilling along the maximum horizontal stress does not necessarily lead to the best stability of the borehole,as generally believed.A drilling azimuth between 0and 60results in similar breakout width,whereas a drilling azimuth between 60and 90achieves the most efficient gas production.By considering both gas production efficiency and borehole stability,for this particular reservoir condition,the optimum drilling azimuth is determined to be between 45and 60.This study presents a practical approach for determining the optimum drilling azimuth in coal seam gas extraction through in seam boreholes.展开更多
文摘Directional drilling has been established in the coal industry as a viable means of gas drainage, exploration and water management. But the environment in and around coal seams is not always conducive to stable conditions while drilling and borehole stability after the drilling has been completed. This paper identifies the conditions which cause unstable drilling conditions and the various means which are used to attempt to manage or bypass those conditions. Ultimately, equipment does become bogged in these adverse environments and requires recovery by over-coring.
基金Supported by the China National Science and Technology Major Project(2017ZX05005-005)
文摘To solve the problem of borehole trajectory uncertainty, some methods such as error ellipsoid posture characterization, sectional error ellipse solution and error elliptic cylinder construction were proposed and an application example was given. According to the definition of inclination, azimuth and tool-face angle, a characterization method of error ellipsoid posture of borehole trajectory was presented. By intercepting the error ellipsoid with an arbitrary plane in space, the general concept and algorithm of sectional error ellipse were established to analyze the borehole trajectory errors in horizontal plane, plumb plane, normal plane, etc. Based on the theory of surface tangency and curve projection, a construction method of error elliptic cylinder of borehole trajectory was put forward to evaluate the axial enveloping error of borehole trajectory and its variation along well depth. The research shows that the deeper the well, the greater the borehole trajectory error will be. In deep and ultra-deep wells measured using conventional measurement while drilling(MWD),the borehole trajectory position error reaches tens of meters. The research results provide a complete set of analysis methods for borehole trajectory error, which can evaluate the accuracy and reliability of borehole trajectory monitoring.
基金Supported by the China National Science and Technology Major Project(2017ZX05005-005)
文摘In order to accurately calculate drilled trajectories,the method of quantitatively recognizing borehole trajectory models was provided,and a case analysis was conducted.Because the measurement-while-drilling data provide with measured values of tool-face angle besides inclination angle and azimuth angle,this paper presents the technological approach of recognizing borehole trajectory models based on tool-face angle.A universal tool-face angle equation was established based on the directional deflection mechanism of steerable drilling tools,and it can calculate the tool-face angles with characteristic parameters of various borehole trajectory models.Then,by evaluating the error between the theoretical values and the measured values of tool-face angle,the trajectory model most consistent with the actual well trajectory can be selected.The model recognition of borehole trajectory provides with the quantitative evaluation index and selection basis of survey calculation methods,which can avoid subjectively and randomly selecting the survey calculation method,and consequently improve the monitoring accuracy and reliability of borehole trajectory.
文摘The borehole strain meter at Wushi station recorded obvious anomaly before Jiashi MS= 6.8 earthquake occurred on February 24, 2003. Its features are as follows. j Anomaly types are complete. The trend anomaly, short-term anomaly, short-imminent anomaly and exponential anomaly appeared 19 months, 56 days, 4 days, and more than 1 month before the event, respectively; k Anomaly is large in magnitude. The maximal magnitude of strain anomaly is 1.7×10?5, which is rare in the past 20-year observation records at Wushi station; l Strain rate fluctuates sharply with obvious alternation of tension and compression. According to the magnitude of strain anomaly, time of expo- nential anomaly appearance and regional features of recorded anomaly, we could predict the magnitude, occur- rence time and potential region to a certain degree.
文摘Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a potential solution for enhancing borehole stability while considering gas production.In this work,we improved and implemented a dual-porosity,fully coupled geomechanical-hydraulic numerical model into COMSOL Multiphysics to investigate into this factor.The sophisticated numerical model incorporates various critical factors,including desorption-induced matrix shrinkage,stress-dependent anisotropic fracture permeability,and the interactions of gas flow and reservoir deformation in matrices and fractures.A suite of simulation scenarios(e.g.,varying coal strength)was carried out to quantify the impact of drilling azimuth on coal permeability evolution,cumulative gas production,and the borehole break-out width for Goonyella Middle Seam of Bowen Basin,Australia.The model was calibrated against both theoretical permeability values and field gas production data.Due to the lack of directly measured matrix permeability data,the actual gas production was used to back calculate the best-matched matrix permeability,which is 0.65μD for this particular work.Moreover,based on the breakout shape and induced volumetric strains around the borehole,drilling along the maximum horizontal stress does not necessarily lead to the best stability of the borehole,as generally believed.A drilling azimuth between 0and 60results in similar breakout width,whereas a drilling azimuth between 60and 90achieves the most efficient gas production.By considering both gas production efficiency and borehole stability,for this particular reservoir condition,the optimum drilling azimuth is determined to be between 45and 60.This study presents a practical approach for determining the optimum drilling azimuth in coal seam gas extraction through in seam boreholes.
