There is a close theoretical similarity between water pressure gradients in aquifers and applied voltage gradients in aqueous solutions. A series of electric field analogue experiments has been conducted by focusing ...There is a close theoretical similarity between water pressure gradients in aquifers and applied voltage gradients in aqueous solutions. A series of electric field analogue experiments has been conducted by focusing on symmetrical multi-lateral wells and dual-lateral wells of arbitrary angles between laterals. This research not only evaluates the productivity equations of a symmetrical multi-lateral well showing the effect of angles on productivity, but also proposes the concept of the multi-lateral productivity coefficient. Moreover, the multi-lateral productivity coefficient equation is designed to calculate the productivity of dual-lateral wells of variable angles, which is in turn supported by experiment. It also helps provide the experimental basis for optimizing the configuration, and building the semi-analytic productivity model, of multi-lateral wells.展开更多
Raising the in situ decomposition rate of natural gas hydrate and increasing the decomposition contact area are two main ways to raise the productivity of hydrate. An exploitation technique based on large borehole wit...Raising the in situ decomposition rate of natural gas hydrate and increasing the decomposition contact area are two main ways to raise the productivity of hydrate. An exploitation technique based on large borehole with multi-lateral branches (LB & MB) was proposed in this paper. This technique is mainly intended for the clayey silt hydrate reservoir in the South China Sea, and its main purpose is to alleviate the sand output from formation for maintaining the stability of the reservoir and to greatly increase the gas productivity of the reservoir. In this paper, the following aspects were mainly expounded: definition of the basic geometric parameters for layout of multi-lateral branches in clayey silt hydrate reservoir, simulation of the stimulation effect of a typical well profile with two branches, and prediction and simulation of the reservoir failure risk in a well profile with eight branches. The results show that the LB & MB effectively improves the flow field in the formation, raises the productivity of the reservoir and may also help to decrease the produced water-gas ratio (WGR). When the lateral branches spacing is too small, the failure zones around adjacent lateral branches overlap each other, possibly causing reservoir failure in a larger range. Therefore, the geometric parameters of multi-lateral branches depend on the dual control of the productivity and geotechnical risk factor of reservoir. Further study is being carried out, so as to obtain the optimal combination of parameters of multi-lateral branches.展开更多
The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitiv...The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitive. The complex relationships between water and gas production, the contribution from multiple coal seams as well as from organic rich shales, and the impact of well interference combined with anisotropic fracture permeability are investigated through a series of numerical simulations of four well-pads (on the corners of a square mile of land with decreasing well spacing from 1, 3, to 4 laterals per pad). After 25 years of production, the two pads with optimally-oriented laterals with respect to the fracture permeability anisotropy produce 61% of the recovered gas for the 1 lateral/pad model, 52% for the 3 laterals/pad model, and 50% for the 4 laterals/pad model. Downspacing has a greater impact on increasing the gas production from pads with the poorly-oriented main laterals than from the pads with the optimally-oriented main laterals. The cumulative gas production at the end of the 25 year history is 4.2% higher for an optimally-oriented pad (pad1) and 1.1× higher for a poorly-oriented pad (pad3) for a model with 4 laterals/pad than 3 laterals/pad and an optimally-oriented pad is 1.1% higher for an optimally-oriented pad and 1.5× higher for a poorly-oriented pad for a model with 3 laterals/pad than 1 lateral/pad. Although downspacing from 3 to 4 laterals/pad has a greater impact on increasing the cumulative gas production from optimally-oriented pads than downspacing from 1 to 3 laterals/pad, the lower impact on poorly-oriented pads results in a lower total increase the cumulative gas production from the four pads. At the end of the 25-year production history, 9.0% more gas is recovered for the 4 lateral/pad model than the 3 lateral/pad model, which predicts 1.2× more gas than the 1 lateral/pad model. The recovered shale gas exceeds the recovered coal gas after ~7 years of production. The higher contribution of produced coal gas predicted due to downspacing results from a higher contribution of recovered gas from the main coal seam, while the contribution from the minor coal seams is lower. Downspacing has a minimal impact on the cumulative water production;after 25 years of production a difference of 1.0% is predicted between models with 4 and 3 laterals/pad and 1.7% between models with 1 and 3 laterals/pad. While downspacing increases the cumulative water production for the poorly-oriented pads (1.1× for 3 to 4 laterals/pad and 1.3× for 3 to 1 lateral/pad after 25 years), the cumulative water production for the optimally-oriented pads is lower over the majority of the production history (after ~4 years and 3.2% lower after 25 years for 3 to 4 laterals/pad and after ~6 months and 1.1× lower after 25 years for 1 to 3 laterals/pad).展开更多
Enhanced geothermal development system is an effective means to develop hot dry rock geothermal resources,and its reasonable structural design is crucial to the efficient exploitation of hot dry rocks.In this paper,a ...Enhanced geothermal development system is an effective means to develop hot dry rock geothermal resources,and its reasonable structural design is crucial to the efficient exploitation of hot dry rocks.In this paper,a multi-lateral well enhanced geothermal development system,which is composed of one low-permeability thermal reservoir,three multi-lateral injection wells,three multi-lateral production wells and three artificial fractures,was designed based on the traditional dual-well development model.Then,a 3D hydrothermal coupling numerical evaluation model was established by using the local heat balance method,and its accuracy and reliability were verified according to Lauwerier analytical theory of fractured flow and heat transfer.Finally,the influence of reservoir parameters,well layout parameters,and injection-production parameters on the heat production performance of this enhanced geothermal development system were explored based on the water-rock coupling mechanism inside the reservoir in the process of thermal production.And the following research results were obtained.First,the“rock invasion effect”of the cold front in the fractures of the multi-lateral well development system is stronger than that in the matrix.Increasing the reservoir permeability can improve the internal heat transfer effect,but also enhances the“invasion performance”of cold front.Second,the annual thermal energy extraction of the system gradually decreases over time and it also decreases with the increase of the injection temperature.It increases with the increase of the reservoir permeability in the early stage of the operation,but decreases greatly after the completion of the thermal breakthrough.Third,the system's thermal energy extraction rate and production mass flow rate are less influenced by reservoir porosity and injection temperature,but they decrease with the increase of the vertical spacing of injection-production wells.Fourth,the production temperature decreases greatly with the increase of the reservoir permeability,increases with the increase of the reservoir porosity,and decreases with the decrease of the vertical spacing of injection-production wells.Fifth,the heat production performance of the system in the early stage can be improved by increasing the length of the production well,and the heat production capacity of the system can be enhanced to a certain degree by increasing the injection-production pressure difference,but excessive pressure difference will impact the service life of the reservoir seriously.展开更多
Due to the nature of coal bed,slack coal production is inevitable in gas recovery sby water drainage.When coalbed methane(CBM)wells are reentered after low energy exploitation and shut-in,the negative effect of slack ...Due to the nature of coal bed,slack coal production is inevitable in gas recovery sby water drainage.When coalbed methane(CBM)wells are reentered after low energy exploitation and shut-in,the negative effect of slack coal production on productivity of CBM is irreversible.In this paper,the CBM occurrence characteristics and multi-lateral horizontal well trajectory in the Qinshui Basin,Shanxi Province,were analyzed.In the multi-lateral horizontal wells,the expected gas production rate could not be reached and the production rate after shut-in maintenance could not restore to the level before shut-in.The reason for these issues is that migration pathways in the reservoirs are blocked by slack coal deposits,while formation water and slack coal deposit accumulated at the troughs of horizontal sections enlarge the resistance for gas to flow into the bottom hole.Furthermore,three key technologies to deal with slack coal blockage were proposed.Firstly,CBM horizontal well trajectory should follow the principle of keeping the wellbores smooth and updip instead of being“wavy”,on the premise of guaranteeing CBM drilling rate.Secondly,the cavities of production wells,as an important part of multi-lateral horizontal wells,are capable of settling sand,and can be used for gaseliquidesolid separation.And thirdly,a tree-like horizontal well with its main hole set on stable seam top or floor,provides a stable well flushing passage for coal powder.This research provides a useful attempt in solving the problem of slack coal production in gas recovery by water drainage.展开更多
Multi-lateral multi-issue negotiations are the most complex realistic negotiation problems. Automated ap- proaches have proven particularly promising for complex ne- gotiations and previous research indicates evolutio...Multi-lateral multi-issue negotiations are the most complex realistic negotiation problems. Automated ap- proaches have proven particularly promising for complex ne- gotiations and previous research indicates evolutionary com- putation could be useful for such complex systems. To im- prove the efficiency of realistic multi-lateral multi-issue ne- gotiations and avoid the requirement of complete informa- tion about negotiators, a novel negotiation model based on art improved evolutionary algorithm p-ADE is proposed. The new model includes a new multi-agent negotiation protocol and strategy which utilize p-ADE to improve the negotia- tion efficiency by generating more acceptable solutions with stronger suitability for all the participants. Where p-ADE is improved based on the well-known differential evolution （DE）, in which a new classification-based mutation strategy DE/rand-to-best/pbest as well as a dynamic self-adaptive pa- rameter setting strategy are proposed. Experimental results confirm the superiority of p-ADE over several state-of-the-art evolutionary optimizers. In addition, the p-ADE based multi- agent negotiation model shows good performance in solving realistic multi-lateral multi-issue negotiations.展开更多
China has been involving itself in the international efforts to solve the Sudanese Darfur problem since 2004.In this process,China has adopted three approaches to finding ways out of the crisis:multilateral cooperatio...China has been involving itself in the international efforts to solve the Sudanese Darfur problem since 2004.In this process,China has adopted three approaches to finding ways out of the crisis:multilateral cooperation,bilateral coordination,and the involvement of Chinese enterprises in Sudan.These approaches are interactive and mutually promoted in a consistent and effective frame.Multilateral activities in the UN provide more opportunities for China to assist in shaping the contents of the resolutions related to Darfur.China also pays attention to conducting cooperation with relevant regional organizations in this process.On the basis of its multilateral approach,the bilateral coordination on key issues between China and the US and,China and Sudan exert a significant impact on solving the problem.Chinese enterprises in Sudan also play a mixed role in the whole process through their economic influences there.展开更多
文摘There is a close theoretical similarity between water pressure gradients in aquifers and applied voltage gradients in aqueous solutions. A series of electric field analogue experiments has been conducted by focusing on symmetrical multi-lateral wells and dual-lateral wells of arbitrary angles between laterals. This research not only evaluates the productivity equations of a symmetrical multi-lateral well showing the effect of angles on productivity, but also proposes the concept of the multi-lateral productivity coefficient. Moreover, the multi-lateral productivity coefficient equation is designed to calculate the productivity of dual-lateral wells of variable angles, which is in turn supported by experiment. It also helps provide the experimental basis for optimizing the configuration, and building the semi-analytic productivity model, of multi-lateral wells.
基金This research was supported by Project of Distinguished Experts of Taishan Scholars (ts201712079)Youth Foundation of National Natural Science Foundation of China (41606078)+1 种基金Open Foundation of Pilot National Laboratory for Marine Science and Technology (QNLM2016ORP0207)Marine Geological Survey Program (DD20190231). Anonymous reviewers and Dr. Hao Zi-guo and Dr. Yang Yan were grateful for their constructive suggestions on the manuscript.
文摘Raising the in situ decomposition rate of natural gas hydrate and increasing the decomposition contact area are two main ways to raise the productivity of hydrate. An exploitation technique based on large borehole with multi-lateral branches (LB & MB) was proposed in this paper. This technique is mainly intended for the clayey silt hydrate reservoir in the South China Sea, and its main purpose is to alleviate the sand output from formation for maintaining the stability of the reservoir and to greatly increase the gas productivity of the reservoir. In this paper, the following aspects were mainly expounded: definition of the basic geometric parameters for layout of multi-lateral branches in clayey silt hydrate reservoir, simulation of the stimulation effect of a typical well profile with two branches, and prediction and simulation of the reservoir failure risk in a well profile with eight branches. The results show that the LB & MB effectively improves the flow field in the formation, raises the productivity of the reservoir and may also help to decrease the produced water-gas ratio (WGR). When the lateral branches spacing is too small, the failure zones around adjacent lateral branches overlap each other, possibly causing reservoir failure in a larger range. Therefore, the geometric parameters of multi-lateral branches depend on the dual control of the productivity and geotechnical risk factor of reservoir. Further study is being carried out, so as to obtain the optimal combination of parameters of multi-lateral branches.
文摘The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitive. The complex relationships between water and gas production, the contribution from multiple coal seams as well as from organic rich shales, and the impact of well interference combined with anisotropic fracture permeability are investigated through a series of numerical simulations of four well-pads (on the corners of a square mile of land with decreasing well spacing from 1, 3, to 4 laterals per pad). After 25 years of production, the two pads with optimally-oriented laterals with respect to the fracture permeability anisotropy produce 61% of the recovered gas for the 1 lateral/pad model, 52% for the 3 laterals/pad model, and 50% for the 4 laterals/pad model. Downspacing has a greater impact on increasing the gas production from pads with the poorly-oriented main laterals than from the pads with the optimally-oriented main laterals. The cumulative gas production at the end of the 25 year history is 4.2% higher for an optimally-oriented pad (pad1) and 1.1× higher for a poorly-oriented pad (pad3) for a model with 4 laterals/pad than 3 laterals/pad and an optimally-oriented pad is 1.1% higher for an optimally-oriented pad and 1.5× higher for a poorly-oriented pad for a model with 3 laterals/pad than 1 lateral/pad. Although downspacing from 3 to 4 laterals/pad has a greater impact on increasing the cumulative gas production from optimally-oriented pads than downspacing from 1 to 3 laterals/pad, the lower impact on poorly-oriented pads results in a lower total increase the cumulative gas production from the four pads. At the end of the 25-year production history, 9.0% more gas is recovered for the 4 lateral/pad model than the 3 lateral/pad model, which predicts 1.2× more gas than the 1 lateral/pad model. The recovered shale gas exceeds the recovered coal gas after ~7 years of production. The higher contribution of produced coal gas predicted due to downspacing results from a higher contribution of recovered gas from the main coal seam, while the contribution from the minor coal seams is lower. Downspacing has a minimal impact on the cumulative water production;after 25 years of production a difference of 1.0% is predicted between models with 4 and 3 laterals/pad and 1.7% between models with 1 and 3 laterals/pad. While downspacing increases the cumulative water production for the poorly-oriented pads (1.1× for 3 to 4 laterals/pad and 1.3× for 3 to 1 lateral/pad after 25 years), the cumulative water production for the optimally-oriented pads is lower over the majority of the production history (after ~4 years and 3.2% lower after 25 years for 3 to 4 laterals/pad and after ~6 months and 1.1× lower after 25 years for 1 to 3 laterals/pad).
基金Project supported by the Science and Technology Planning Project of Sichuan Province“Design of Hot Dry Rock Geothermal Resources Development Scheme and Research on Thermo-Hydro-Mechanical Coupling Mechanism”(No.:2020JDRC0088)the Youth Team Project for Scientific and Technological Innovation on Process Equipment Mechanics and Safety Evaluation of Southwest Petroleum University(No.:2018CXTD12).
文摘Enhanced geothermal development system is an effective means to develop hot dry rock geothermal resources,and its reasonable structural design is crucial to the efficient exploitation of hot dry rocks.In this paper,a multi-lateral well enhanced geothermal development system,which is composed of one low-permeability thermal reservoir,three multi-lateral injection wells,three multi-lateral production wells and three artificial fractures,was designed based on the traditional dual-well development model.Then,a 3D hydrothermal coupling numerical evaluation model was established by using the local heat balance method,and its accuracy and reliability were verified according to Lauwerier analytical theory of fractured flow and heat transfer.Finally,the influence of reservoir parameters,well layout parameters,and injection-production parameters on the heat production performance of this enhanced geothermal development system were explored based on the water-rock coupling mechanism inside the reservoir in the process of thermal production.And the following research results were obtained.First,the“rock invasion effect”of the cold front in the fractures of the multi-lateral well development system is stronger than that in the matrix.Increasing the reservoir permeability can improve the internal heat transfer effect,but also enhances the“invasion performance”of cold front.Second,the annual thermal energy extraction of the system gradually decreases over time and it also decreases with the increase of the injection temperature.It increases with the increase of the reservoir permeability in the early stage of the operation,but decreases greatly after the completion of the thermal breakthrough.Third,the system's thermal energy extraction rate and production mass flow rate are less influenced by reservoir porosity and injection temperature,but they decrease with the increase of the vertical spacing of injection-production wells.Fourth,the production temperature decreases greatly with the increase of the reservoir permeability,increases with the increase of the reservoir porosity,and decreases with the decrease of the vertical spacing of injection-production wells.Fifth,the heat production performance of the system in the early stage can be improved by increasing the length of the production well,and the heat production capacity of the system can be enhanced to a certain degree by increasing the injection-production pressure difference,but excessive pressure difference will impact the service life of the reservoir seriously.
文摘Due to the nature of coal bed,slack coal production is inevitable in gas recovery sby water drainage.When coalbed methane(CBM)wells are reentered after low energy exploitation and shut-in,the negative effect of slack coal production on productivity of CBM is irreversible.In this paper,the CBM occurrence characteristics and multi-lateral horizontal well trajectory in the Qinshui Basin,Shanxi Province,were analyzed.In the multi-lateral horizontal wells,the expected gas production rate could not be reached and the production rate after shut-in maintenance could not restore to the level before shut-in.The reason for these issues is that migration pathways in the reservoirs are blocked by slack coal deposits,while formation water and slack coal deposit accumulated at the troughs of horizontal sections enlarge the resistance for gas to flow into the bottom hole.Furthermore,three key technologies to deal with slack coal blockage were proposed.Firstly,CBM horizontal well trajectory should follow the principle of keeping the wellbores smooth and updip instead of being“wavy”,on the premise of guaranteeing CBM drilling rate.Secondly,the cavities of production wells,as an important part of multi-lateral horizontal wells,are capable of settling sand,and can be used for gaseliquidesolid separation.And thirdly,a tree-like horizontal well with its main hole set on stable seam top or floor,provides a stable well flushing passage for coal powder.This research provides a useful attempt in solving the problem of slack coal production in gas recovery by water drainage.
文摘Multi-lateral multi-issue negotiations are the most complex realistic negotiation problems. Automated ap- proaches have proven particularly promising for complex ne- gotiations and previous research indicates evolutionary com- putation could be useful for such complex systems. To im- prove the efficiency of realistic multi-lateral multi-issue ne- gotiations and avoid the requirement of complete informa- tion about negotiators, a novel negotiation model based on art improved evolutionary algorithm p-ADE is proposed. The new model includes a new multi-agent negotiation protocol and strategy which utilize p-ADE to improve the negotia- tion efficiency by generating more acceptable solutions with stronger suitability for all the participants. Where p-ADE is improved based on the well-known differential evolution （DE）, in which a new classification-based mutation strategy DE/rand-to-best/pbest as well as a dynamic self-adaptive pa- rameter setting strategy are proposed. Experimental results confirm the superiority of p-ADE over several state-of-the-art evolutionary optimizers. In addition, the p-ADE based multi- agent negotiation model shows good performance in solving realistic multi-lateral multi-issue negotiations.
文摘China has been involving itself in the international efforts to solve the Sudanese Darfur problem since 2004.In this process,China has adopted three approaches to finding ways out of the crisis:multilateral cooperation,bilateral coordination,and the involvement of Chinese enterprises in Sudan.These approaches are interactive and mutually promoted in a consistent and effective frame.Multilateral activities in the UN provide more opportunities for China to assist in shaping the contents of the resolutions related to Darfur.China also pays attention to conducting cooperation with relevant regional organizations in this process.On the basis of its multilateral approach,the bilateral coordination on key issues between China and the US and,China and Sudan exert a significant impact on solving the problem.Chinese enterprises in Sudan also play a mixed role in the whole process through their economic influences there.
