Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study establis...Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.展开更多
The performance of gas-drilling(drilling oil and gas wells with air, nitrogen, or natural gas) is very unpredictable in many areas due to lack of proper design of drilling parameters because of limited understanding o...The performance of gas-drilling(drilling oil and gas wells with air, nitrogen, or natural gas) is very unpredictable in many areas due to lack of proper design of drilling parameters because of limited understanding of gas–rock interaction which requires knowledge of heat transfer in the well system. Complete analysis of rock failure requires an accurate mathematical model to predict gas temperature at the bottom hole. The currently available mathematical models are unsuitable for use for the purpose because they do not consider the effects of formation fluid influx, Joule–Thomson cooling, and entrained drill cuttings. A new analytical solution for predicting gas temperature profiles inside the drill string and in the annulus was derived in this study for gas-drilling, considering all these three effects. Results of sensitivity analyses show that formation fluid influx can significantly increase the temperature profiles in both the drill string and the annulus.The Joule–Thomson cooling effect lowers the temperature in the annulus only in a short interval near the bottom hole.The drill cuttings entrained at the bottom hole can slightly increase the temperature profile in the annulus.展开更多
The energy industry faces a significant challenge in extracting natural gas from offshore natural gas hydrate(NGH)reservoirs,primarily due to the low productivity of wells and the high operational costs involved.The p...The energy industry faces a significant challenge in extracting natural gas from offshore natural gas hydrate(NGH)reservoirs,primarily due to the low productivity of wells and the high operational costs involved.The present study offers an assessment of the feasibility of utilizing geothermal energy to augment the production of natural gas from offshore gas hydrate reservoirs through the implementation of the methane-CO_(2)swapping technique.The present study expands the research scope of the authors beyond their previous publication,which exclusively examined the generation of methane from marine gas hydrates.Specifically,the current investigation explores the feasibility of utilizing the void spaces created by the extracted methane in the hydrate reservoir for carbon dioxide storage.Analytical models were employed to forecast the heat transfer from a geothermal zone to an NGH reservoir.A study was conducted utilizing data obtained from a reservoir situated in the Shenhu region of the Northern South China Sea.The findings of the model indicate that the implementation of geothermal heating can lead to a substantial enhancement in the productivity of wells located in heated reservoirs during CO_(2)swapping procedures.The non-linear relationship between the temperature of the heated reservoir and the rate of fold increase has been observed.It is anticipated that the fold of increase will surpass 5 when the gas hydrate reservoir undergoes a temperature rise from 6℃ to 16℃.The mathematical models utilized in this study did not incorporate the impact of heat convection resulting from CO_(2)flow into the gas reservoir.This factor has the potential to enhance well productivity.The mathematical models’deviation assumptions may cause over-prediction of well productivity in geothermal-stimulated reservoirs.Additional research is required to examine the impacts of temperature drawdown,heat convection resulting from depressurization,heat-induced gas pressure increment,and the presence of free gas in the formation containing hydrates.The process of CH4-CO_(2)swapping,which has been investigated,involves the utilization of geothermal stimulation.This method is highly encouraging as it enables the efficient injection of CO_(2)into gas hydrate reservoirs,resulting in the permanent sequestration of CO_(2)in a solid state.Additional research is warranted to examine the rate of mass transfer of CO_(2)within reservoirs of gas hydrates.展开更多
Development of unconventional tight oil and gas reservoirs such as shale pays presents a huge challenge to the petroleum industry due to the naturally low permeability of shale formations and thus low productivity of ...Development of unconventional tight oil and gas reservoirs such as shale pays presents a huge challenge to the petroleum industry due to the naturally low permeability of shale formations and thus low productivity of oil and gas wells.Shale formations are also vulnerable to the contamination of the water in the drilling and completion fluids,which further reduces reservoir permeability.Although gas-drilling(drilling with gas)has been used to address the issue,several problems such as formation water influx,wellbore collapse,excessive gas volume requirement and hole cleaning in horizontal drilling,still hinder its application.A new technique called gas-lift drilling has recently been proposed to solve these problems,but the optimal design of drilling operation requires a thorough investigation of fluid flow field below the asymmetric drill bits for evaluating the fluid power needed to clean the bottom hole.Such an investigation is conducted in this work based on the Finite Element Method(FEM)implemented in an open source computational framework,FEniCS.Pressure and flow velocity fields were computed for three designs of drill bit face characterized by radial bit blades and one eccentric orifice of discharge.One of the designs is found superior over the other two because it generates relatively uniform flow velocities between blades and provides a balanced fluid power needed to clean all the bit teeth on each bit blade.To quantify the capability of borehole cleanup presented by three drill bit designs,the energy per unit volume is calculated in each region of drill bit and compared with the required value suggested by the literature.In addition,the developed FEM model under FEniCS framework provides engineers an accurate tool for optimizing drill bit design for efficiently gas-lift drilling unconventional tight oil and gas reservoirs.展开更多
Development of marine gas hydrate resources presents a huge challenge to the energy industry owing to the well production complications such as wellbore collapse,sand production,and low productivity.Radial lateral wel...Development of marine gas hydrate resources presents a huge challenge to the energy industry owing to the well production complications such as wellbore collapse,sand production,and low productivity.Radial lateral wells(RLW)and horizontal snake wells(HSW)have been proposed separately to mitigate these complications.We compare the productivity potentials of these two types of wells using the recently developed analytical models and field case data from a gas hydrate reservoir in the South China Sea.It is concluded that RLW will yield slightly higher gas productivity than HSW under similar conditions.Sensitivity analysis with the well models indicates that the productivity of RLW is directly proportional to the number of laterals,length of laterals,and radius of laterals,while the productivity of HSW is directly proportional to the length and radius of the horizontal wellbore.The decision of using RLW or HSW can be made based on economic analysis of well completion and production,which should be addressed in future studies.展开更多
This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water.Three types of...This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water.Three types of vertical well completions are considered:frac-packed well with vertical hydraulic fracture;frac-packed well with horizontal hydraulic fracture,and a cased-hole gravel-packed well.Sensitivity analysis was conducted with analytical well inflow models to determine factors that affect the gas well productivity.The results of the analyses indicated that proppant mass pumped during fracture treatment slightly improves well productivity for frac-packed natural gas hydrate wells.Well productivity increases nonlinearly with fracture productivity up to a threshold value of 50,000 md for fracpacked well with horizontal fracture,above which further increase in fracture conductivity would create no benefit.With a proppant mass of 50,000 Ibm and a corresponding proppant volume of 504 ft3,commercial gas production rates of 14.9 MMscf/d,5.621 MMscf/d,and 11.35 MMscf/d are possible for frac-packed well with vertical fracture,frac-packed well with horizontal fracture,and cased-hole gravelpacked well,respectively.Because hydraulic fracture orientation depends on the in-situ formation stress,whether a well should be hydraulic-fractured or not depends on in-situ formation stress.展开更多
文摘Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.
基金supported by the China National Natural Science Foundation Funding No.51134004
文摘The performance of gas-drilling(drilling oil and gas wells with air, nitrogen, or natural gas) is very unpredictable in many areas due to lack of proper design of drilling parameters because of limited understanding of gas–rock interaction which requires knowledge of heat transfer in the well system. Complete analysis of rock failure requires an accurate mathematical model to predict gas temperature at the bottom hole. The currently available mathematical models are unsuitable for use for the purpose because they do not consider the effects of formation fluid influx, Joule–Thomson cooling, and entrained drill cuttings. A new analytical solution for predicting gas temperature profiles inside the drill string and in the annulus was derived in this study for gas-drilling, considering all these three effects. Results of sensitivity analyses show that formation fluid influx can significantly increase the temperature profiles in both the drill string and the annulus.The Joule–Thomson cooling effect lowers the temperature in the annulus only in a short interval near the bottom hole.The drill cuttings entrained at the bottom hole can slightly increase the temperature profile in the annulus.
基金funding the project“Safe,Sustainable,and Resilient Development of Offshore Reservoirs and Natural Gas Upgrading through Innovative Science and Technology:Gulf of Mexico–Mediterranean,”through Contract No.EC-19 Fossil Energy。
文摘The energy industry faces a significant challenge in extracting natural gas from offshore natural gas hydrate(NGH)reservoirs,primarily due to the low productivity of wells and the high operational costs involved.The present study offers an assessment of the feasibility of utilizing geothermal energy to augment the production of natural gas from offshore gas hydrate reservoirs through the implementation of the methane-CO_(2)swapping technique.The present study expands the research scope of the authors beyond their previous publication,which exclusively examined the generation of methane from marine gas hydrates.Specifically,the current investigation explores the feasibility of utilizing the void spaces created by the extracted methane in the hydrate reservoir for carbon dioxide storage.Analytical models were employed to forecast the heat transfer from a geothermal zone to an NGH reservoir.A study was conducted utilizing data obtained from a reservoir situated in the Shenhu region of the Northern South China Sea.The findings of the model indicate that the implementation of geothermal heating can lead to a substantial enhancement in the productivity of wells located in heated reservoirs during CO_(2)swapping procedures.The non-linear relationship between the temperature of the heated reservoir and the rate of fold increase has been observed.It is anticipated that the fold of increase will surpass 5 when the gas hydrate reservoir undergoes a temperature rise from 6℃ to 16℃.The mathematical models utilized in this study did not incorporate the impact of heat convection resulting from CO_(2)flow into the gas reservoir.This factor has the potential to enhance well productivity.The mathematical models’deviation assumptions may cause over-prediction of well productivity in geothermal-stimulated reservoirs.Additional research is required to examine the impacts of temperature drawdown,heat convection resulting from depressurization,heat-induced gas pressure increment,and the presence of free gas in the formation containing hydrates.The process of CH4-CO_(2)swapping,which has been investigated,involves the utilization of geothermal stimulation.This method is highly encouraging as it enables the efficient injection of CO_(2)into gas hydrate reservoirs,resulting in the permanent sequestration of CO_(2)in a solid state.Additional research is warranted to examine the rate of mass transfer of CO_(2)within reservoirs of gas hydrates.
基金This research was supported by the Open Fund(PLN201704)of the China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation at the Southwest Petroleum University and the China National Natural Science Foundation Founding Nos.51874252,51534006 and 51674044.This research was also supported by the China Scholarship Council Founding No.201808510219.
文摘Development of unconventional tight oil and gas reservoirs such as shale pays presents a huge challenge to the petroleum industry due to the naturally low permeability of shale formations and thus low productivity of oil and gas wells.Shale formations are also vulnerable to the contamination of the water in the drilling and completion fluids,which further reduces reservoir permeability.Although gas-drilling(drilling with gas)has been used to address the issue,several problems such as formation water influx,wellbore collapse,excessive gas volume requirement and hole cleaning in horizontal drilling,still hinder its application.A new technique called gas-lift drilling has recently been proposed to solve these problems,but the optimal design of drilling operation requires a thorough investigation of fluid flow field below the asymmetric drill bits for evaluating the fluid power needed to clean the bottom hole.Such an investigation is conducted in this work based on the Finite Element Method(FEM)implemented in an open source computational framework,FEniCS.Pressure and flow velocity fields were computed for three designs of drill bit face characterized by radial bit blades and one eccentric orifice of discharge.One of the designs is found superior over the other two because it generates relatively uniform flow velocities between blades and provides a balanced fluid power needed to clean all the bit teeth on each bit blade.To quantify the capability of borehole cleanup presented by three drill bit designs,the energy per unit volume is calculated in each region of drill bit and compared with the required value suggested by the literature.In addition,the developed FEM model under FEniCS framework provides engineers an accurate tool for optimizing drill bit design for efficiently gas-lift drilling unconventional tight oil and gas reservoirs.
文摘Development of marine gas hydrate resources presents a huge challenge to the energy industry owing to the well production complications such as wellbore collapse,sand production,and low productivity.Radial lateral wells(RLW)and horizontal snake wells(HSW)have been proposed separately to mitigate these complications.We compare the productivity potentials of these two types of wells using the recently developed analytical models and field case data from a gas hydrate reservoir in the South China Sea.It is concluded that RLW will yield slightly higher gas productivity than HSW under similar conditions.Sensitivity analysis with the well models indicates that the productivity of RLW is directly proportional to the number of laterals,length of laterals,and radius of laterals,while the productivity of HSW is directly proportional to the length and radius of the horizontal wellbore.The decision of using RLW or HSW can be made based on economic analysis of well completion and production,which should be addressed in future studies.
文摘This work focuses on the assessment of the effect of well completion types on gas productivity in subsea gas hydrate reservoirs of class 1G type where the gas hydrates have decomposed into gas and water.Three types of vertical well completions are considered:frac-packed well with vertical hydraulic fracture;frac-packed well with horizontal hydraulic fracture,and a cased-hole gravel-packed well.Sensitivity analysis was conducted with analytical well inflow models to determine factors that affect the gas well productivity.The results of the analyses indicated that proppant mass pumped during fracture treatment slightly improves well productivity for frac-packed natural gas hydrate wells.Well productivity increases nonlinearly with fracture productivity up to a threshold value of 50,000 md for fracpacked well with horizontal fracture,above which further increase in fracture conductivity would create no benefit.With a proppant mass of 50,000 Ibm and a corresponding proppant volume of 504 ft3,commercial gas production rates of 14.9 MMscf/d,5.621 MMscf/d,and 11.35 MMscf/d are possible for frac-packed well with vertical fracture,frac-packed well with horizontal fracture,and cased-hole gravelpacked well,respectively.Because hydraulic fracture orientation depends on the in-situ formation stress,whether a well should be hydraulic-fractured or not depends on in-situ formation stress.
