Study On Changing With Hydrophilic Channel Of Wellbore Rock And Mud Cake Drilling Fluid

In recent years,there are encountered frequently major problem in wellbore instability,which is happened frequently in the bad ground of deep well drilling in our country.This has seriously affected safe,high quality,fast drilling and reduced the economic efficiency.The precondition for protecting wellbore stability is to prevent or stop the drilling fluid in the water into the shale formation.At present,protecting wellhole sloughing technique have physical plugging and chemical inhibition,The application of the anti-sloughing drilling fluid technology has good effect,but failed to completely solve the mud shale instability problems,The analysis holds that that there are some difficult problems:? shale pore is very small,it is difficult to effectively seal water entering;?formation of dense mud cake is a process of time,water has entered;?No considering capillary attraction of changing the hydrophilic channel.Focus on these problems need to be solved and based on the partial studies of major cultivation technologic project of Sichuan province,This paper put forward a new water base drilling fluid technology for preventing the collapse,that is hydrophilic channel change method.This means that hydrophobic substance of drilling fluid is involved in the formation of mud cake,which change the mud cake passage from hydrophilic capillary channel into weakly hydrophilic and hydrophilic capillary channel.Capillary entry pressure changes into capillary resistance,stop drilling fluid filtrate to enter water sensitivity mud shale layer,which solve the problem of water absorption wellbore instability.This paper focused on hydrophilic channel change method,the main achievements and recognition include:(1)Starch was modified into hydrophobe with esterification to synthesize SDG.The structure were characterized with infrared spectrum,the results showed esterification occurred;We optimized carbon chain length and degree of substitution in esterifiable matter,the results showed that loss was low when the degree of substitution of SDG is 0.005-0.04,succinic acid anhydride is esterification agent;The performance of SDG in the drilling fluid were evaluated.Anti temperature of SDG is over 150?.SDG is not basically viscosifying action.Anti salt of SDG is not well.(2)Calcium carbonate was modified into hydrophobe with different modifying agents.We analysed the influence factors during modifying.The effect of modifier dosage and type were big.We characterized hydrophobic degree with the activation degree,sedimentation volume and oil absorption value.The structure of modified calcium carbonate was characterized by infrared spectrometer,the results showed that modified calcium carbonate is introduced into hydrophobe group.The modified calcium carbonate particle size variation was analyzed by laser particle size analyzer,the results showed the average particle size of hydrophobic modified calcium carbonate is smaller than unmodified calcium carbonate.The zeta potential of modified calcium carbonate were analyzed with different values of pH,the results showed the Zeta potential of hydropjobic modified calcium carbonate is sharply influenced by pH,the dispersion stability of oleic acid modified calcium carbonate is superior to other modifiers modified calcium carbonate.We analyzed anti temperature capacity and compatibility of unmodified and modified calcium carbonate.The results showed that hydrophobically modified calcium carbonate STG has good anti temperature capacity and good compatibility with other polymer additives.We also analyzed the morphology of unmodified and modified calcium carbonate by scanning electron microscopy.The morphology of unmodified and modified calcium carbonate changes little,cube basic.(3)We select other additive and form drilling fluid system which anti temperature is 150°C based on hydrophobically modified agents SDG and STG.Anti salt and calcium capacity is poor in this drilling fluid system.They may contain 5%drill cuttings.The rejection capability is good.The subsidence stability in 24h of drilling fluid is also good.The average particle size of aged drilling fluid is much smaller than before.Mud cake microstructure can also be seen that the mud cake is compact.Compared to basal drilling fluid,the absolute value of zeta potential reduces a lot.It may be the introduction of the hydrophobic groups.The performance of drilling fluid is compared when system added hydrophobic calcium carbonate or hydrophilic calcium carbonate.The research found that the effect of reducing loss when system added hydrophobic calcium carbonate is superior to hydrophilic calcium carbonate.(4)Based on vertically imbibition experiment,the permeability of oil wet shale are similar,absorbs less water,more oil;the permeability of water wet sandstone are similar,no pressure,no circulation,compared with hydrophobic treating agent is not added into the drilling fluid,before the formation of weak hydrophilic or hydrophobic channel,the imbbiyion amount are similar,but after the formation of weak hydrophilic or hydrophobic channel,the imbbiyion amount of including hydrophobic treating agent is smaller than excluding hydrophobic treating agent.Based on core flow experiments,the absorption length and weight of including hydrophobic treating agent are less than excluding hydrophobic treating agent,and the reservoir damage degree is less than excluding hydrophobic treating agent.These shows the action mechanism of drilling fluid system,that is,hydrophobic substance is added into drilling fluid,positive differential pressure,they will form weakly hydrophilic or hydrophobic channels in the wellbore and mud cake,during drilling,Capillary entry pressure changes into capillary resistance,stop or reduce drilling fluid filtrate to enter water sensitivity mud shale layer,which solve the problem of water absorption wellbore instability.Through the theoretical and experimental study,confirmed the feasibility of changing with channel of wellbore rock and mud cake drilling fluid technology.The result is of profound theoretical and practical significance for enriching the anti-collapsing drilling fluid technology.