Application Research On The Water-base Antisloughing Drilling Fluid In CCSD-SK1

The instability of sidewall is one of the main technical difficult problems in drilling engineering.And,drilling fluid is one of the key factors for sidewall stability.The instability of sidewall is caused by the integrated effects as:original ground stress status of stratum,liquid column of well casing,rock mechanics characteristics of stratum,drilling fluid performance and engineering construction.According to the genesic mechanics,the reasons of sidewall instability are induced in two aspects as below:firstly,after the stratum being broken by drilling,the pressure of drilling fluid in the bore replaces the supporting pressure of bore from stratum,and the original stress balance of stratum is broken.Secondly,after drilling fluid entering the stratum, the pore pressure of stratum is changed.This brings the stratum hydrated,causes the rock strength reduced and aggravates the instability of sidewall.Therefore,the instability of sidewall is not only relating to mechanical issues,but also relate to chemical issues;it's a combination of mechanics and chemistry.We have to combine the two aspects while searching for a effective method to solve the problem of sidewall instability.Considering physical-chemical action and viscoelastic mechanics,the author has established a relation model between time and sidewall reducing stress.Combined with the technical research,design and application in CCSD-SK1,base on a great deal of investigation,the author has selected drilling fluid material optimally,and then combined with indoor test,field test and field application,the author has researched the drilling fluid recipe and techniques,developed the water-base drilling fluid system which prevent collapse and has no damage.At last,the drilling fluid system is used at field engineering.The main research findings are list as followings:1.By establishing the sidewall stability model,the model of calculating the sidewall reducing stress;at the same time,the author has analyzed the influence of moisture content that aspect the elastic ratio strength of mud shale.These had provided parameters for the subsequent research on the calculating of sidewall reducing stress.2.The mechanics of restraining sidewall rock formation(antisloughing drilling fluid)was conclude as following:(1)principle of ionization,(2)peridium action,(3)capping action,(4) principle of activity balance,(5)principle of positive potential barrier.And,aim at the application situation of reagent in CCSD-SK1,the author has analyzed the mechanism of LG, Na-CMC,DFD,FIA—368,NH4HPAN and SAKH.3.The author has developed testing instruments which can test the performance of boring mud suspension and bore protection.While testing the capability of suspending boring mud with boring mud suspension performance testing instrument,we can obtain intuitionistic perceptual knowledge by observing the liquid column.And,we can test the quantitative data by leading in data from the sensor at the bottom of instrument.Bore protection performance testing instrument are both intuitionistic and convenient,it can distinguish supporting capability of drilling fluid by observing the different pressure value from sensor.With the two test mentioned above,shearing & dilution test and expanding test,the evaluation system of maintaining the sidewall stability was composed.Of course,the new style instruments used in testing system have to be improved and standardized from its principle and operation.4.The author has analyzed the mechanism of the selected representative drilling fluid material and done preliminary experiment,then select optimum drilling fluid recipe which combine with the concrete site condition of CCSD-SK1.The drilling fluid system used at job location successfully,and it has a good effect of protecting sidewall.The fluid systems of PAM,LG and DFD—NH₄HPAN—SAKH has separately used in primary project and second project.The PAM fluid system has been in the role of rejecting expansion in mud shale and agglutinating protecting sandrock collapsing.But there is a disadvantage of PAM system which is it has bad incompatibility with other additives.So it is hard to adjust and compound PAM system with other systems to settle the questions may appear in further drilling.The fluid system of LG and DFD—NH₄HPAN—SAKH has be using in the second project.The successful application of drilling fluid system made the field work running safely and without any trouble. Also,the application of the drilling fluid system also can economize project cost and reduce the erection time.The innovation of this paper is list as following:1.By establishing the sidewall stability model,the model of calculating the sidewall reducing stress.2.The author has designed bran-new testing experiment system and developed new style instrument.Then a new performance evaluating indicator of drilling fluid was ascertained by testing and observing the performance of drilling fluid from different aspects.The evaluating indicator contains:boring mud suspension performance test,sidewall protecting performance test, expanding test and shearing & dilution test.These tests can evaluate the antisloughing performance of drilling fluid together,and have exploited new method to testing the performance of drilling fluid.3.The author has obtained series of high cost performance ratio drilling fluid system according to the mechanism action of kinds of drilling fluid addition agent,performance evaluating methods,and combined with the work field of CCSD-SK1.The drilling fluid system has applied in work field and obtained all-right effect.At the same time,the application of the drilling fluid system also can avoid accident,reduce the erection time and economize project cost.