Advanced Drill Pipe With Streamline Connections Enhances Slim-hole Drilling Performance. Introduction

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Therefore, the tube body and tool joint internal diameters are crucial and should be as large as possible provided that increases in equivalent circulating densities (ECD’s) do not create well control issues.  Consequently, the effect of increased drill pipe size on ECD’s must be evaluated for each potential application. In these applications, increasing the drill pipe size from 3-½ in. to 4 in. did not create adverse ECD related issues.

Fishing Considerations

The need to be able to retrieve the pipe in the event of a failure of the pin connection is the driving factor to the selection of the tool joint outside diameter. The ideal situation is to be able to use a full strength overshot to catch the fish.  Having the necessary clearance in a 6 in. or 6-1/8 in. hole, commonly requires that the tool joints OD be 5 in. or less.

After compiling and evaluating the information discussed above for the subject well projects, the drilling engineers involved selected the drill pipe design described below:

Nominal size 

4 in.


14.0 lb/ft 

Type of upset



to match environment


XT 39


4 7/8 in. or 5 in.

TJ ID                   2 9/16 in.

Under certain conditions, the 4 in. drill pipe can be used to drill both the lower, smaller hole sections and the upper larger hole intervals eliminating the requirement for 5 in. drill pipe.

The relatively small difference between the tube and the tool joint outside diameters led to a limited elevator surface area for lifting the string of pipe. Figure 4 shows the 4 in. 14.0 lb/ft XT39 drill pipe elevator capacity curve. Although the elevator capacity is somewhat reduced compared to the 3 ½ in. drill pipe configuration, it was more than adequate for the target applications.  Note, also if a higher lifting force is required that provide by the elevator shoulder area a sub can be made-up into the top of the string to provide additional lifting capacity.

Saudi Aramco QTF Field Case Histories

The Saudi Aramco well designs mandated that the hole size in the producing zone be 6-1/8 in. and that 7 in. casing be run from surface to the top of the producing zone. In wells without this design constraint the 7 in. is normally run as a liner thereby allowing a combination of 5 in. x 3 1/2 in. drill pipe to be used. The QTF well design precluded the use of 5 in. drill pipe in the drill string for the 6-1/8 in. hole section. 

The torque and drag simulation required a high performance slim hole drill string capable of transmitting a torque up to 20,000 ft-lb and withstanding high tension. Another requirement was to give drillers the ability to fish the pipe both in the 7 in. casing and the 6-1/8 in. open hole with a high strength slim-hole overshot. 

Extended Reach Drilling (ERD) was required for this oilfield due to two main considerations:

•  The proximity of surface infrastructures required that the drill sites be moved away from these facilities. Therefore, to reach the reservoirs underneath these facilities ERD technology was required.

•  Since the field also extends offshore, it was determined that ERD drilling was more cost effective than building offshore platforms.

In the typical well design, the kick off depths are usually in the 17 in. hole section below the 18-5/8 in. casing shoe at 700 ft. Long radius build rates are used for both the initial build then the final build into the producing zone following a long tangent section. Intermediate casings strings of 13-3/8 in. and 9-5/8 in. are run prior to the long 7 in. production casing set at the target entry and top of the producing zone. The wells are completed with approximately 5,000 ft of 6 1/8 in. open hole. See figure 5 for a graphic illustration of the well designs.

Torque simulations were performed based on three friction factors levels (maximum, expected and target). The anticipated drilling torque was then compared to the drill pipe capacity. The retained option was the 4 in. drill pipe with XT39 connection.

Drilling performance was improved with the high torque 4 in. XT39 connection. In particular, the following performance improvements were realized:

•  Higher rotary speeds (and the corresponding higher ROP) could

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