To prevent the deposition of natural gas hydrate in deepwater gas well,the hydrate formation area in wellbore must be predicted.Herein,by comparing four prediction methods of temperature in pipe with field data and co...To prevent the deposition of natural gas hydrate in deepwater gas well,the hydrate formation area in wellbore must be predicted.Herein,by comparing four prediction methods of temperature in pipe with field data and comparing five prediction methods of hydrate formation with experiment data,a method based on OLGA&PVTsim for predicting the hydrate formation area in wellbore was proposed.Meanwhile,The hydrate formation under the conditions of steady production,throttling and shut-in was predicted by using this method based on a well data in the South China Sea.The results indicate that the hydrate formation area decreases with the increase of gas production,inhibitor concentrations and the thickness of insulation materials and increases with the increase of thermal conductivity of insulation materials and shutdown time.Throttling effect causes a plunge in temperature and pressure in wellbore,thus leading to an increase of hydrate formation area.展开更多
Distribution laws of casing external pressure,which are obtained by different scholars in different conditions,are not the same.Thus,a model to calculate the external pressure of casing is established with finite elem...Distribution laws of casing external pressure,which are obtained by different scholars in different conditions,are not the same.Thus,a model to calculate the external pressure of casing is established with finite element method.In the model a contact is built between the outer wall of the casing and the inner wall of the cement sheath.The casing external pressure can be got through extracting contact force of results.The numerical results and analysis show that:The largest casing external pressure exists in the direction of minimum horizontal stress of formation rather than in the direction of the maximum horizontal stress.There exists such matching between the cement sheath elastic modulus and formation elastic modulus:When the elastic modulus of the cement sheath is small,reducing its value is conducive to reduce the casing external pressure and to prolong casing service life.When the elastic modulus of the cement sheath is large,increasing its value is conducive to reduce the casing external pressure and to prolong casing service life.The casing external pressure will become large with the increase of Poisson's ratio of cement sheath.With the increase of the degree of the formation stress unevenness,the maximum casing external pressure increases and the smallest external decreases.The increasing of the non-uniformity degree of formation stress makes the non-uniformity degree of casing external pressure and the risk of casing failure increase.The study can provide certain reference for drilling workers to take measures to prolong service life of casing.展开更多
文摘To prevent the deposition of natural gas hydrate in deepwater gas well,the hydrate formation area in wellbore must be predicted.Herein,by comparing four prediction methods of temperature in pipe with field data and comparing five prediction methods of hydrate formation with experiment data,a method based on OLGA&PVTsim for predicting the hydrate formation area in wellbore was proposed.Meanwhile,The hydrate formation under the conditions of steady production,throttling and shut-in was predicted by using this method based on a well data in the South China Sea.The results indicate that the hydrate formation area decreases with the increase of gas production,inhibitor concentrations and the thickness of insulation materials and increases with the increase of thermal conductivity of insulation materials and shutdown time.Throttling effect causes a plunge in temperature and pressure in wellbore,thus leading to an increase of hydrate formation area.
基金The authors would like to thank the National“863”Plan Project of China(No.2013AA09A215)CNPC's Science and Technology Research Project(No.2014B-4315)for providing financial support to this research work.
文摘Distribution laws of casing external pressure,which are obtained by different scholars in different conditions,are not the same.Thus,a model to calculate the external pressure of casing is established with finite element method.In the model a contact is built between the outer wall of the casing and the inner wall of the cement sheath.The casing external pressure can be got through extracting contact force of results.The numerical results and analysis show that:The largest casing external pressure exists in the direction of minimum horizontal stress of formation rather than in the direction of the maximum horizontal stress.There exists such matching between the cement sheath elastic modulus and formation elastic modulus:When the elastic modulus of the cement sheath is small,reducing its value is conducive to reduce the casing external pressure and to prolong casing service life.When the elastic modulus of the cement sheath is large,increasing its value is conducive to reduce the casing external pressure and to prolong casing service life.The casing external pressure will become large with the increase of Poisson's ratio of cement sheath.With the increase of the degree of the formation stress unevenness,the maximum casing external pressure increases and the smallest external decreases.The increasing of the non-uniformity degree of formation stress makes the non-uniformity degree of casing external pressure and the risk of casing failure increase.The study can provide certain reference for drilling workers to take measures to prolong service life of casing.
