Dual rotating stripper rubber drilling head

A drilling head with dual rotating stripper rubbers designed for high pressure drilling operations ensuring sealing under the extreme conditions of high flow or high pressure wells such as horizontal drilling. The dual stripper rubbers seal on the same diameter yet are manufactured of different materials for different sealing functions. The lower stripper rubber is manufactured from a more rigid, abrasive resistant material to divert the flow from the well. The upper stripper rubber is manufactured of a softer sealing material that will closely conform to the outer diameter of the drill string thereby preventing the flow of fluids through the drilling head.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates to drilling heads for oil and gas wells and, in 
particular, to a drilling head which employs dual rotating stripper 
rubbers to seal against the well string preventing the flow of fluids 
upwardly through the drilling head. 
II. Description of the Prior Art 
Early drilling heads employed a single stripper rubber to divert the flow 
of drilling fluid away from the rig floor. The stripper rubber was fixedly 
mounted within the drilling head and the drill string rotated and moved 
longitudinally through the stripper rubber as it is attempted to seal 
against the string. It was determined that the action of the drill string 
caused considerable wear on the stripper rubber requiring frequent 
replacement. To reduce the abrasive wear, the stripper rubber was rotated 
with the drill string to maintain sealing contact. However, a drill string 
typically includes various diameter sections. For example, the drill 
collars joining sections of drill string have a greater diameter than the 
drill pipe itself. Thus, the stripper rubber was sized to maintain sealing 
contact with the drill pipe or the smallest diameter component which 
travelled through the drilling head. Because of the different diameters of 
the drill string, the stripper rubber needed to be rigid enough to 
withstand the pressures of the drilling fluid yet resilient enough to 
maintain a seal on the drill collars as they passed through the drilling 
head and thereafter return to the original configuration to seal against 
the smaller diameter drill pipe. The operating cycle of the drilling head 
was directly proportional to number of drill collars which passed through 
the single stripper rubber since the stripper would not return to its 
original sealing diameter. 
In an attempt to maintain sealing contact with both the smaller drill pipe 
and the drill collars, dual stripper rubber drilling heads included 
stripper rubbers with different inner diameters designed to seal against 
the drill collars and drill pipe. Early versions only rotated one of the 
stripper rubbers since the lower stripper was fixedly mounted within the 
drilling head. More recently, dual rotating stripper rubbers, each with a 
different inner diameter, have been employed in drilling heads by mounting 
the lower stripper rubber to a drive ring extension which is connected to 
the drive bushing at the upper end of the drilling head. Despite the 
advantages of the prior known dual stripper rubber drilling heads, only 
one of the stripper rubbers is typically in sealing contact with the drill 
string. Accordingly, the dual stripper rubbers do not provide additional 
sealing against the flow of drilling fluids. 
SUMMARY OF THE PRESENT INVENTION 
The present invention overcomes the disadvantages of the prior known 
drilling heads by providing dual rotating stripper rubbers which have 
similar inner diameters to provide additional sealing in high pressure 
environments. 
The drilling head of the present invention includes a lower inlet flange 
for mounting to the well, a side outlet flange through which the drilling 
fluids are diverted for disposal/recycling, a main body which houses dual 
rotating stripper rubbers and bearing assemblies, and a drive assembly 
mounted at the upper end of the main housing for engagement with the kelly 
drive of the drill string. Each of the stripper rubbers are rotatively 
connected to the drive assembly at the upper end of the drilling head. As 
a result, as the drive bushing rotates within the drilling head in 
conjunction with the kelly and drill string, the stripper rubbers will 
also rotate thereby maintaining sealing contact with the drill string to 
divert the drilling fluid from the well to the outlet flange. 
The dual rotating stripper rubbers have substantially identical inner 
diameters to simultaneously seal against the drill string, specifically 
the smaller diameter drill pipe. However, the stripper rubbers are each 
manufactured of different materials to perform different functions within 
the drill head. Accordingly, the dual sealing action provides improved 
operation in high flow or pressure wells such as in horizontal drilling or 
geothermal wells. In a preferred embodiment, the lower stripper rubber can 
be manufactured from a material which is abrasive resistant to divert a 
majority of the flow while the upper stripper rubber can be manufactured 
from a more resilient material better suited for sealing pressure than for 
abrasion and erosion. 
Other objects, features, and advantages of the invention will be apparent 
from the following detailed description taken in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
Referring to FIGS. 1 and 2, there is shown a drilling head 10 incorporating 
the present invention for accepting a drill string (not shown) while 
diverting drilling fluid from the rig floor. The drilling head 10 
generally includes a housing 12 with a bottom flange 14 for securing the 
drilling head 10 on top of the well. The housing 12 may be of a multiple 
piece construction to permit access to the interior of the drilling head 
10 for repair/replacement of the bearing assemblies 16, drive assembly 18 
and either of the stripper rubbers 20 as will be subsequently described 
herein. The housing 12 includes an axial passageway 22 through which the 
drill string extends. A kelly drive 24 at the top of the drilling head 10 
cooperates with the kelly of the drill string as is well known. The 
housing 12 preferably includes a side outlet passageway 26 through which 
drilling fluids from the well are diverted for processing. 
Referring more specifically now to FIG. 2, the drilling head 10 is 
dependent upon the bearing assembly 10, the drive assembly 16 and the 
stripper rubbers 20 for proper operation to accept the drill string while 
sealing against the drill string to prevent drilling fluids from flowing 
upwardly through the drilling head 10. The bearing assembly 16 ensures 
smooth rotation of the drill string and drive assembly 18 within the 
drilling head 10. The bearing assembly 16 may include roller bearings 28 
mounted within a lubricant passageway 30 for maintaining lubrication of 
the entire bearing assembly 16. High pressure seals 32 at the ends of the 
passageway 30 prevent debris from fouling the lubricant while maintaining 
a closed system. Lubrication ports 34 may be included to allow addition of 
lubricant. 
The bearing assembly 16 facilitates smooth rotation of the drive assembly 
18 in association with the kelly and drill string. Clamp assemblies 36 
maintain the integrity of the drive assembly 18 but allow simple access 
for repair/replacement. In a preferred embodiment of the present 
invention, the drive assembly 18 includes a drive bushing 38 and a drive 
ring extension 40 and a drive ring 42 associated with the bearing assembly 
16. These components will rotate within the drilling head 10 in 
conjunction with the drill string and, in particular, the stripper rubbers 
20 as will be subsequently described. 
Although dual rotating stripper rubbers 20 for drilling heads 10 are known, 
the prior art drilling heads 10 utilized strippers having different inner 
diameters so that at least one stripper was always in sealing contact with 
the drill string. In the present invention, the dual stripper rubbers 20 
include upper stripper rubber 44 and a lower stripper rubber 46 which have 
substantially identical inner diameters which maintain contact with the 
drill string. The upper stripper rubber 44 is mounted to the drive bushing 
38 while the lower stripper rubber 46 is mounted to the drive ring 
extension 40 to position the second stripper 46 axially below the first 
stripper rubber 44. Both stripper rubbers 44 and 46 rotate with the drill 
string and are sized to maintain sealing contact with the smallest 
diameter of the string, typically the drill pipe. As a result, the 
stripper rubbers 44 and 46 will expand as collars and joints pass 
therethrough and thereafter contract to seal against the drill pipe. 
The upper and lower stripper rubbers 44,46 are preferably manufactured of 
different material to perform different functions within the drilling head 
10 and thereby ensure that drilling fluids and the like from the well are 
diverted to the side outlet port 26 and prevented from flowing up through 
the drilling head 10 to the rig floor. The lower stripper rubber 46 is 
preferably formed of an abrasive resistant material to divert the drilling 
fluid from the axial passageway 22 to the side outlet 26. This material is 
preferably highly resistant to the abrasive and erosive action of the 
drilling fluids and as such has a more rigid form. Examples of such 
stiffer abrasive resistant materials include urethane, nitrile and butyl. 
In contrast, the upper stripper rubber 44 is preferably formed of a 
softer, sealingly resilient material which maintains and retains sealing 
pressure on the drill string as it travels therethrough. Thus, the lower 
stripper rubber 46 will divert a bulk of the fluids from the well 
particularly the heavier drilling fluids while the upper stripper rubber 
44 ensures sealing contact to prevent any remaining fluids, particularly 
gases, from travelling through the drilling head 10. Examples of sealingly 
resilient materials for use in the upper stripper rubber include natural 
rubber, HSN and butyl. In the dual rotating stripper rubber configuration, 
the lower stripper rubber acts as the primary seal preventing flow of 
drilling fluids through the drilling head. The upper stripper rubber 
blocks any bypass flow while acting as a secondary seal as the lower seal 
wears or fails under pressure. The majority of wear from the rig 
operations is directed to the lower stripper rubber while the upper 
stripper rubber acts as a backup. In addition, the dual stripper rubbers 
simplify tripping in and out of the well. While tripping in and out of the 
well, the upper stripper rubber is removed leaving at least the lower 
stripper rubber to protect against fluid flow from the well. Thus, the 
present invention provides dual rotating stripper rubbers which seal on 
the same diameter yet which perform different functions to ensure sealing 
diversion of drilling fluids. 
The foregoing detailed description has been given for clearness of 
understanding only and no unnecessary limitations should be understood 
therefrom as some modifications will be obvious to those skilled in the 
art without departing from the scope and spirit of the appended claims.