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Content archived on 2022-12-27

METAL/METAL SEALING SYSTEMS FOR BOTTOM HOLE EQUIPMENT FOR DRILLING AND COMPLETION

Objective

Increasing the lifetime of bottomhole equipment used for drilling or completion of wells constitutes a very important objective within the oil industry, as it may imply a significant cost reduction, regarding both the drilling phase and the completion phase during the life of the wells.
The lifetime of this equipment is presently limited by their sealing systems, based on elastomers whose failure may not only lead to very costly work-over operations, but also have an impact on the safety of wells.
ASTEC PART
Sliding bearing testing :
The purpose of the initial sliding bearing test programme had been to establish the best materials combination form which to design a new bearing.
The repeat Sliding Bearing Test Eb conducted on the 101 Zyalon and VDD Shaft had confirmed the good results of the previous Test E showing excellent wear characteristics together with low friction co-efficient. The cumulative testing of over 260 hours had thus identified these materials as the ideal combination from which to design the combined radial and thrust bearing.
However, practical constraints such as the time required to finesse the new VDD material dictated that the well-proven PCD would be used together with Zyalon 101 for the bearing application on the new test rig.
MOTI PART
Hydraulically controlled safety valve (VSF)
As explained in our previous report, we had to orientate our work programme to use less ambitious jack or rod pistons systems of a simpler design but which a greater chanceof success.
But in order to have a more innovative product we decide to use previous studies results to be able to design a tubing retrievable to be installed in smaller casing internal diameter than the normal diameter requested :
- nominal diameter valve 2-3/8" to be installed into a 4" nominal size casing
- 5000 psi working pressure :
* OD will become 3.1" (78,74 m/m) instead of 3.625"
while ID will be at 1.812 instead of 1.87.
- nominal diameter valve 3-1/2" to be installed into a 5-1/2" nominal size
casing - 5000 psi working pressure :
* OD will become 3.85" (97,95 m/m) instead of 5.875"
while ID will remain at 2.812".
- nominal diameter valve 4-1/2" to be installed into a 7" nominal size casing - 5000 psi working pressure :
* OD will become 5.74" (146 m/m) instead of 7.300"
while ID will remain at 3.812".
DOUBLE SEALING STATIC CONNECTION
- very encouraging results were obtained, which are used for the liaison between elements of the tubing retrievable.
DYNAMIC SEALING
- sealings with rigid waves gave satisfactory results.
The object of the project is to develop metal/metal sealing systems, without elastomers in order to solve the so-called "dynamic" sealing problems on bottomhole equipment, such as :
- subsurface safety valve, sliding circulating valve, expansion joint, for wells completion;
- downhole motors and jars for wells drilling.
The proposed technological development is based on the utilization of ceramic materials, offering the following characteristics :
- very low dry friction coefficient in order to eliminate the seizing and wear risks;
- indifference to well bottomhole conditions : high temperature, corrosion, erosion, pressure...;
- high accuracy machining and grinding in order to optimize the clearance and the contact pressures.
Tribological tests on models of different metal/metal sealing systems will allow to select the best ceramic couples.
Metal/Metal sealing systems will be adapted to two types of bottomhole equipment :
ASTEC PART
In the volumetric downhole motor, the main partto be studied is the bearing project.
The main object is to research suitable materials for bearing elements which will operate in harsh environments and to test these materials in various combinations and configurations. On another hand, ASTEC developed an innovative new motor concept which does not rely on elastomere seals in the power section, this motor will have a useful life in excess of 200 hours and no current bearings are presently able to perform consistenly for 200 hours. It is why ASTEC is developing these mud lubricated bearings.
Three discrete bearing types are to be investigated :
a) sliding bearing
b) radial bearing
c) thrust bearing
MOTI PART
Hydraulically controlled safety valve (VSF), whose "dynamic" sealing between the valve body and the sliding tube inside the valve must be perfect, whether in opened or closed position.
Sliding circulating valve (VCC), activated from the surface by a specific tool, whose "dynamic" sealing between the outside and the inside ofthe production tube must be perfect in closed position.
After the tests under simulated conditions, prototypes of these equipments will be tested under real operating conditions in an experimental well (in France in ELF Aquitaine Test Center at le Fourc and in Scotland at Montrose).

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Coordinator

MACHINERY & OIL TOOLS INTERNATIONAL
EU contribution
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Address
ZA DE MONTARDON
64121 SERRES CASTET
France

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