Air-Drilling(空气钻井)ppt课件

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Air Drilling(,空气钻井）,1Hole Cleaning,2Equipment,3Drilling Practices,4Problems,5Gas Type,6Mist Drilling,Section 2 Page 1,“,Dry air is labeled as such here to recognize its use as one of the most common types of UB fluids.However,most of the info here applies to any gas used as the UB fluid as well as to air.”,Air Drilling(空气钻井）1Hole Clean,Gas Behavior,Where T is expressed in degrees R.,P,1,x V,1,T,1,=,P,2,x V,2,T,2,1 ft,3,of gas,10,000 ft TVD,BHP=5200 psi,2 ft,3,when,circulated to 5000 ft,Unload condition!,Length of,Fluid Column,=Length of Gas,Gas Rising in,An Open Wellbore,If the injection rate of N2 is 900 scf/minute at 70,0,F and an injection pressure of 600 psi.What is the volume flowrate of this gas downhole at conditions of 5200 psi and a temperature of 250,0,F.,V,2,=(14.7 x 900 x 710)/(5200 x 520)=3.47 ft,3,/m,A standard cubic foot has a pressure of 14.7 psi at a temperature of 60,0,F,To convert Fahrenheit to Rankin add 460,Section 2-Page 2,Gas Law,Gas BehaviorWhere T is express,Hole Cleaning,Hole cleaning with air is a complicated subject.In simple terms,the upward air flow exerts a drag force on the cutting.If the drag force is greater than the gravitational force,the cutting will move upward and out of the hole.,Cuttings removed on most air drilling operations tend to be very fine.The term“dusting”is often used to describe the removal process.The bit generates cuttings comparable in size to overbalance drilling;however,they tend to remain in the hole until ground down to a small enough size for the air flow to lift from the well.,The pressure of the air increases with depth,causing the density of air to increase as well.The increased pressure reduces the air velocity;however,the increase in density assists with the cuttings transport.,Increased Air,Velocity at Less,Air Pressure,Less Effective,Hole Cleaning,As Depth Increases,Drag Force,Due to Air Velocity,Gravitational,Settling Force,Cutting,Resulting,Cutting Velocity,Section 2-Page 3,Hole CleaningHole cleaning wit,Air/Gas Injection Requirements,Air injection required for adequate hole cleaning is very difficult to calculate.Angel(1957)suggested that effective cuttings transport is related to the kinetic energy of the air(gas)striking the cutting.,KE=,D,v,2,D,density of air(gas),v,annular velocity of air(ft/sec),Through testing and experiments on shallow blast drilling it was determined that 3000 ft/min proved to be an effective minimum air velocity for cuttings transport.,Section 2-Page 4,Air/Gas Injection Requirements,Cutting Carrying Capacity of a Fluid,Larger cuttings are more easily transported in a viscous fluid.,In Air Drilling cuttings are ground down before transporting.,Hole angle has the same effect unselective of fluid type.,In a gaseous fluid the liquid phase is the main transporting medium.Annular velocity is too low for gas.,Dependent upon:,Fluid“Viscosity”,Fluid Velocity,Cutting Size,Hole Angle,There is an indirect relationship between the viscosity and the velocity.Without dealing with Rheology:,the greater the viscosity the less the velocity,.,Air Drilling requires 3000 ft/min.,Some Drilling Muds require 100 ft/min.,Section 2-Page 5,Cutting Carrying Capacity of a,Factors Effecting Hole Cleaning,Annular Geometry,Hole,Angle,Gas Inflows,Annular Geometry,BHA members cause an increase in air annular velocity due to the reduced flow area.The resulting loss of velocity at BHA tops make it a likely area for larger sized cuttings to gather and settle.Annular velocity is proportional to the square of the annular diameter.,Hole Angle,In normal mud drilling,high angle holes are much more difficult to clean than vertical holes.The same is true with air drilling.Tests have shown that the critical air velocity increases with increasing hole angle.,Gas Inflows,Inflowing gas into the annulus creates a restriction or back pressure on the air stream below the influx.This reduces the air velocity and thusly reducing hole cleaning effectiveness.,Section 2-Page 6,Factors Effecting Hole Cleanin,Choking Velocity,Annulus Pressure Loss,Annular Air Velocity,Critical Air Velocity,Minimum,Pressure Loss,Choking,Velocity,At high air flow rates the cuttings move along nearly at the same velocity as the air column and a“steady-state”condition exists with a constant ROP.By varying air injection rate,one can determine the minimum annulus pressure loss associated with the steady state condition.The velocity associated with this minimum loss is called the critical air velocity.,If the air injection rate was decreased,cuttings would accumulate in the annulus resulting in an increasing annulus pressure loss and increasing BHP.Continuing to decrease the air rate will eventually cause the cuttings to build-up and“pack-off”the annulus.This is known as the choking effect and the minimum air velocity causing this is known as the,choking velocity,.,Section 2-Pa