Simulation And Experimental Study On Down-the-Hole Drilling Fluid Field Of The Hollow DTH Hammer Reverse Circulation Coring And Sampling Technology

At the nineties of elementary,air drive hollow down-the-hole hammer reverse circulation continuous coring and shaping drilling technology owing to at rough stratum display in superiority,it has been applied at solid mineral exploration and hydrology water well drilling received best effect whereas obtain drilling republic ratify and been generalized.However when drilling in complicated stratum its adaptive faculty is less.It is Considered that because of the frame of the bit is not in reason,sometimes hard to form stable reverse circulation,create core extractor plug up enough.It is mainly because of in a great measure of gas easy to leak from among crevice and suction pressure insufficient large and can't get the core or shape to the central passage,even if have no adequate acceleration gotten to arrive terrene.Aim at these problems,the scholars have already make some researchs in the past .It has been reposed by experimental qualitative discuss,have not get one quantitative conclusion and universal fit equation to supervise driller and design bit parameters,furthermore bygone research take the time and money.Author girdled these issues established problem and do research round.ⅠThe subject study content ascertain At the present ,the bit has been multinomial development and betterment through deeply theoretical investigation and laboratory reverse circulation experiment and drilling in well practices to develop successful multijnjector type down-the-hole hammer reverse circulation bit.The reverse circulation is actualized use the basic structure and operation principle of the injector and design the bit air draft holes in the bottom as injector muzzles. Bit bottom structure is designed in reason to have the best mixing chamber and diffusion chamber.Owing to air draft hole of the bit bottom quantity commonly is multi-,so it forms multiinjector structure.Gas from down the hole hammer entrance the injector will produce high velocity to suck the fluid around ,pump the outside crevice .Muti injectors rotary continusly with the bit build up the annularity negative pressure down the hole.Gas pressure resume in the center passage.It is benefit to bring the coring and shaping to the surface of the earth from the center passage and form the reverse circulation .The problem of the bit is quite a few gas has been leaked from crevice or solution cavity crave when drilling in the complex stratum with crash or solution cavity and will failure to make reverse circulaton.Or even if reverse circulation has been done, however because of gas leakage the upward force is less for the core and shape,block up is often made. Advanced method is add a new injector instrument on the bit structure.About the injector instrument,in fact they are some injector holes in the side wall of the bit.The gas has been jetted into the bit center passage with high velocity can pump the gas around and make negative pressure .The pressure difference on some distance will let core accelerate again and get enough velocity to be draft out of the hole.The reverse circulation effect be improved and the block up is less.Even that ,the developed bit has problems also,Such as ,core block up,bit broken ,the poor quanlity of the bit reverse circulation or unstablity in drilling The reasons result these problems have two: One is imprecise maching possible. The other is unreasonable structure of the new injector holes and mutiinjector jet structrue paremeters are not in reason enough.As far as the problem about the new bit added the injector holes shows that the coring technology problem is reverse circulation form principle and process down the hole.So two requirements are advanced,one is to choice the suitable cutting material with good drilling technology,the other is to betterment and design the bit parameters .The best way is to find rational paremeters for a certain size bit.The article aimed at the bit construction parameters made the study extension that is new injector holes and bottom jet hole parameters betterment and to do good for the reverse circulation.Ⅱstudy methods and main conclusions Therical analysis , numerical value computer and experimental researchare three main methods of the science.They are independent and supplement each other.Therical analysis has universality.The factors effection are clear and obvious.Many engineers questions often can't get their precise answers should depend on the numerical value method to get the approximate answer,but the numerical value simulation has a lot of questiones either, Disperse can bring the rational and qualitative errors .So the laboratory experiments are also need to validate the numerical conclusion.Author of the article adopt the researches instrument to study the questions as follows.1.Use the fluid mechanics and aerodynamics knowledge to establish control equation relation the injectot hole diameters( d 1) , obliquity( z1 ), numbers(θ1) and bottom jet hole diameters( z 2), obliquity(θ2), numbers( z 2). Disperse the equation with numerical value method.Setup boundary condition to solve it .2.Do emulator compute for the injector hole and bottom jet hole of the bit parameters about affect bit reverse circulation formation use CFD comutational fluid dynamics technology.3.Experiment for the Study of the reverse circulation emulator plat for injector hole and bottom jet hole parameters.Contrast the outcome with the amulator's find that the two are anastomose basically.So amulator analysis conclusion is right and the instrument can be trusted .4.Establish the regression analysis equation based the SAS.The reverse circulation parameters optimization system use Visual Basic language provides the exploring workman for a parameters optimization tool.Thereby more useful conclusion can be gotten from the amulators technology with less time ,manpower and money as follows:ⅰWhen the center passage diameter( D3 ) is certain,with the injector obliquity(θ1),diameter( d 1),numbers ( z1 )and distributing fashion changed ,the negative pressure and upwards air velocity are all different.So the pump force for the annular airstream and reverse circulation effection are all different too.When the bit diameter( D1 )is certain, with the bottom jet hole obliquity(θ2)and diameter( d 2)change,The negative pressure and upward air velocity are all different and it will make different reverse circulation effection too.ⅱInjector hole parameters optimization design:at first ,make the center passage diameter( D3 )as 30mm for example to analysis ,the conclusion is that when the injector hole diameter ( d 1)is 7mm,the obliquity(θ1)is 15 degree,6 holes distributing equality or the total cross section is 250 mm square will do the best for reverse circulation;With the same analysis method like above, injector hole parameters has been studied in muti center passage diameters.Then regression analysis has been done with statistic way. Conclusions has been gotten:For a certain diameter bit, its center passage diameter( D3 )do a lot of influence for the injector hole parameters. Constrast with it the effection from bit diameter( D1 )can be ingnored.So we can only consider the center passage diameters ( D3 )effect about injector hole parameters such as it's obiquity (θ1),diameter( d 1)and number( z1 )and distributing fashion.From a lot of amulator and experiment studies,the rule equation was gotten between injector hole diameter ( d 2) and bit center passage diameter( D3 )through regression analysis the data gotten : d 1= 3.98987 +0.09523 D3 P<0.01ⅲBottom jet hole parameters optimization design:Make the bit diamete(r D1 ) as 320mm and center passage diamete(r D3 )as 30mm for example ,combined amulator and experiment together to get the conclusion:When the bottom jet hole diameter( d 2)is 13mm,obiquity is 7 degree ,the reverse conclusion effect is best.Later,use the same method to analysis the other kinds of situations such as different bit diameters( D1 ) and center passage diameters( D3 ). Conclusion has been gotten:The center passage diameter( D3 )can be ignored dueing to it do few influence for the bottom jet hole parameters optimize choice.Considering the influence of the bit diamete(r D1 ) to the bottom jet holes parameters ,such as obliquity(θ2) and diameter( d 2),The hole number ( z1 ) common is 3 according the bit structure to design.Regression analysis to the data get the rule as following: The regression equtation between the bottom jet hole diameter( d 2) and bit diameter( D1 )is: d 2= 7.88830 +0.01199 D1 P<0.01The regression equtation between the bottom jet hole liquity(θ2)and bit diameter( D1 )is:θ2= 7.88830 +0.01199 D1 P<0.01ⅳCompromise injection hole and bottom jet hole, get a rules:1) When the ratio of total cross section about the injector hole and bottom jet hole equal to 1.5,bit will make better reverse circulation.2) In addition.the best design distance (h )between injector and bottom jet hole:The conclusion is :h do little influence for the reverse circulation,if h =110mm is appropriate.Or h can be decided by the convenience of the bit structure when be designed.3)The best distance (a ) from center axes of the bottom jet hole to the bit center passage axes :a is mostly related with the bit diameter ( D1 ),the regression eqution is : a = 37.65381+0.11154 D1 P<0.01ⅴThe BRPO (Bit Revers circulation Parameter Optimization)system has been compiled about the reverse circulation bit injector hole and bottom jet hole parameters use the Visual Basic 6.0 sofeware.The system has gathered the experts experiments and summarize with the article's study conclusion successfully provide the reference for bit parameters optimization.ⅵAnatomy has been done aim at the reason about large diameter bit form the reverse circulation difficult and the redesign project has been advanced. As the diameter is 450mm for example.At the first time,the idea combined the double bottom jet hole structure with bottom concave face together to redesign the large diameter.By the amulator analysis to the improved bit based CFD,the result showed the reverse circulation all right and the bit can be cooling in time.So the solution about the large diameter bit reverse circulation formation diffifculty has been gotten theoretically.Ⅲthe main innovation points of the articleⅰ)For the first time,the atmospherical fluid control eqution and flux distribution equation group about the injector holes and bottom jet holes parameters has been established.It provides the therical guide for the bit parameters optimized. ⅱ)The best effect reverse circulation parameters of the injector and bottom jet holes has been gotten by a lot of analysis study,such as, the therical analysis ,amulator simulation and experiment study.Then the eqution relate the bit diameter ,bit center passage diameter and the parameters of the injector holes,bottom jet holes has been done.It provide reference thereunder for find best parameters.The parameters optimized system based the Visual Basic gather the experts'experiment and the article's conclusion commendably make the utilize rate of the knowledge increase.To evaluate the result of the study conclusion,Apllied the develope bits in the enginerring and good effect has been achieved.ⅲ)Redesign the large diameter reverse circulation bit bottom structure,that is,use the idea of combined the double bottom jet hole with the concave bottom face to the bit structure. It has satisfied result from theory,amulator and experiment ,and good design the bit bottom construction use the result get the design scheme of large diameter reverse circulation bit.ⅳ)Has established the reverse circulation drilling and formate principle study amulator drilling flat use AutoCAD and Solidworks etc geometric model establish softwares.The article do a general analysis for the bit injector and bottom jet holes construction .Through a lot of numerical value and experiment study,it has gotten some determine the nature and ration conclusion.They make the hollow down the hole hammer reverse circulation core and shape drilling technology and formation principle study deeper.The conclusion provide the bit structure parameters design optimization with the choice gist. The bits developmented has been tesed and do big reverse circulation.The efficiency of drilling is developed and the core rate hyper to 98 percent.It has proved that the construction of the bit is more reasonable and the function is more credibility. Furthermor,at the theory, a problem solution scheme about large diameter bit has been done by new design the bit bottom structure.