Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath i...Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.展开更多
The bonding quality of the cement sheath interface decreases during well completion because of the change in the casing pressure.To explore the root cause of such phenomena,experiments on the mechanical properties and...The bonding quality of the cement sheath interface decreases during well completion because of the change in the casing pressure.To explore the root cause of such phenomena,experiments on the mechanical properties and interface bonding strength of a cement sheath have been carried out taking the LS25-1 high-temperature and high-pressure(HTHP)gas field as an example.Moreover,a constitutive model of the cement sheath has been defined and verified both by means of a full-scale HTHP cement sheath sealing integrity evaluation experiment and three-dimensional finite element simulations.The results show that the low initial cementing surface strength is the root cause of cement sheath interface bonding failure.When the pressure in the casing exceeds a certain limit,the stress caused by the change in the internal pressure in the casing is transmitted to the cement sheath,resulting in the degradation of the interface stiffness of the cement sheath.However,with an increase in the casing wall thickness,the stress transmission capacity decreases.Therefore,it is concluded that improving the interfacial cementing strength,appropriately increasing the casing wall thickness and increasing the initial stress of the cement sheath are the keys to ensuring the sealing integrity of the cement sheath in high-temperature and high-pressure gas wells.展开更多
Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experim...Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experimental results showed that the toughness of the set cement containing XL was improved remarkably. The engineering properties of the slurry containing XL, drag reducer USZ （0.2% BWOC）, filtrate loss additive F 17B （1.2% BWOC） and crystalloid expanding agent F17A （3% BWOC） could meet technical requirements of cementing operation. After perforation, good quality cement sheath enhanced with XL was observed by CBL/VDL logs in a deep well.展开更多
The mechanical properties of Portland cement differ from the weakly consolidated shallow formation in deep water.This results in undesired abrupt changes in the compressive strength and elastic modulus at the cement–...The mechanical properties of Portland cement differ from the weakly consolidated shallow formation in deep water.This results in undesired abrupt changes in the compressive strength and elastic modulus at the cement–formation interface.In this study,a water-borne epoxy resin was applied as a strengthening material to reinforce the weakly consolidated shallow formation and protect the cement sheath from potential failure.The mechanical properties of the unconsolidated clay were tested,including their changes with increases in the temperature and curing time.In addition,the effects of the seawater,cement slurry alkaline filtrate,and saltwater drilling fluid were evaluated.As confirmed by the results,the strengthening fluid was excellent at reinforcing the unconsolidated clay,with a compressive strength of 2.49 MPa(after curing for 7 days),even at a dosage of 5%.A cement slurry filtrate with a high pH was suitable to produce the required strengthening of the formation,especially its early age strength.It should also be pointed out that the used fluid exhibited good compatibility with the saltwater drilling fluid and seawater behaved well as a diluent for the strengthening fluid.展开更多
基金Supported by Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(2020CX040000)Sichuan Science and Technology Program(2020JDTD0019)+1 种基金National Natural Science Foundation of China(52004231)Research Project of Dagang Oilfield(NO.DGYT-2018-JS-244).
文摘Based on the elastoplastic model of cement sheath considering the influence of three-dimensional principal stress and the stress field model of interface crack,a mechanical performance design method of cement sheath is established to meet the wellbore sealing requirements during fracturing.This method takes the failure types of the cement sheath,such as tensile failure,plastic yield,interface crack propagation along interface and zigzag propagation into account.Meanwhile,the elasticity modulus and Poisson's ratio quantitative design charts of cement sheath are constructed based on this method,and the safety and risk areas of wellbores are defined,which quantify the yield strength and tensile strength indexes of cement sheath.The results show that decreasing elasticity modulus,increasing yield strength and Poisson's ratio of cement sheath can avoid plastic deformation of cement sheath;increasing the tensile strength of cement sheath can prevent its tensile failure;increasing elasticity modulus and Poisson's ratio of cement sheath is good for shortening the length of the interface crack,but will increase the risk of interface cracks zigzagging into cement sheath.The model calculation and case verification has proved that the method in this paper can give accurate calculation results and is convenient for field application.
基金The authors gratefully acknowledge the CNOOC scientific research project“Study of risk assessment and countermeasures of well drilling and completion under ultrahigh temperature and high pressure”and“Research on development feasibility of LS25-1 gas field”(Grant Nos.YXKY-ZX-09-2021,2020FS-08).
文摘The bonding quality of the cement sheath interface decreases during well completion because of the change in the casing pressure.To explore the root cause of such phenomena,experiments on the mechanical properties and interface bonding strength of a cement sheath have been carried out taking the LS25-1 high-temperature and high-pressure(HTHP)gas field as an example.Moreover,a constitutive model of the cement sheath has been defined and verified both by means of a full-scale HTHP cement sheath sealing integrity evaluation experiment and three-dimensional finite element simulations.The results show that the low initial cementing surface strength is the root cause of cement sheath interface bonding failure.When the pressure in the casing exceeds a certain limit,the stress caused by the change in the internal pressure in the casing is transmitted to the cement sheath,resulting in the degradation of the interface stiffness of the cement sheath.However,with an increase in the casing wall thickness,the stress transmission capacity decreases.Therefore,it is concluded that improving the interfacial cementing strength,appropriately increasing the casing wall thickness and increasing the initial stress of the cement sheath are the keys to ensuring the sealing integrity of the cement sheath in high-temperature and high-pressure gas wells.
文摘Brittle fracture of cement sheath, induced by perforation and stimulation treatments, can cause cross flow of formation fluid and increase casing damage. A novel agent XL was developed for solving the problem. Experimental results showed that the toughness of the set cement containing XL was improved remarkably. The engineering properties of the slurry containing XL, drag reducer USZ （0.2% BWOC）, filtrate loss additive F 17B （1.2% BWOC） and crystalloid expanding agent F17A （3% BWOC） could meet technical requirements of cementing operation. After perforation, good quality cement sheath enhanced with XL was observed by CBL/VDL logs in a deep well.
基金supported by the Natural Science Foundation of China(51804332,51974355)Major Scientific and Technological Projects of CNPC(ZD2019-184-003)+1 种基金Provincial Geological Exploration Fund of Guizhou Province(208-9912-JBN-UTS0)Shandong Provincial Natural Science Foundation(ZR2017LEE005).
文摘The mechanical properties of Portland cement differ from the weakly consolidated shallow formation in deep water.This results in undesired abrupt changes in the compressive strength and elastic modulus at the cement–formation interface.In this study,a water-borne epoxy resin was applied as a strengthening material to reinforce the weakly consolidated shallow formation and protect the cement sheath from potential failure.The mechanical properties of the unconsolidated clay were tested,including their changes with increases in the temperature and curing time.In addition,the effects of the seawater,cement slurry alkaline filtrate,and saltwater drilling fluid were evaluated.As confirmed by the results,the strengthening fluid was excellent at reinforcing the unconsolidated clay,with a compressive strength of 2.49 MPa(after curing for 7 days),even at a dosage of 5%.A cement slurry filtrate with a high pH was suitable to produce the required strengthening of the formation,especially its early age strength.It should also be pointed out that the used fluid exhibited good compatibility with the saltwater drilling fluid and seawater behaved well as a diluent for the strengthening fluid.
