Bottom discharge seal section

Disclosed is an electric submersible pumping system for use in wellbore. The electric submersible pumping system includes a motor assembly, a pump assembly and a seal section disposed in the wellbore. The pump assembly is below the motor and is driven by the motor. The seal section is between the motor assembly and the pump assembly, and protects the motor assembly from thrust generated in the pump assembly. The seal section includes a shaft that transmits torque from the motor assembly to the pump assembly. A labyrinth chamber in the seal section restricts the flow of wellbore fluids. The seal section can also include a mechanical seal, a thrust bearing, a bag type chamber, an abrasion resistant bearing, and a motor electrical termination.

FIELD OF THE INVENTION

This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a seal section for use with a submersible pumping system.

BACKGROUND

Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.

Components commonly referred to as “seal sections” or “motor protectors” protect the electric motors and are typically positioned above the motor. These components provide several functions, such as transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant.

By way of illustration,FIG. 1shows a prior art submersible pumping system200disposed in a wellbore202, and includes an electric motor204, a pump206, and a seal section208. The submersible pumping system200is attached to production tubing210, which provides a conduit for producing fluids to the surface.

Torque is generated in the motor204and transmitted to the pump206by a shaft in the seal section208. Since the shaft is a potential leak path by which corrosive wellbore fluids can reach the motor204, the seal section208is designed to limit the flow of wellbore fluids along the shaft.

The seal section208also protects the motor204from axial thrust and shock created by the pump206. The pump206pulls in wellbore fluids and propels the fluids up the production tubing210, creating axial thrust that can damage the motor204. The seal section208absorbs some of this thrust, providing a barrier between the motor204and the pump206.

Heat in the wellbore and heat generated by the motor204during operation cause the lubricating oil to expand in the oil filled motor204. Excessive expansion of the lubricating oil can cause damage to the motor if the lubricating oil is not allowed to escape. As a safeguard, the seal section208provides a means by which the oil can escape, preventing the accumulation of excessive pressure inside the motor204.

Similarly, the seal section208also provides a means for accommodating contraction of the lubricating oil during cooling. As the lubricating oil contracts, wellbore fluid is drawn into the seal section208to maintain the appropriate pressure gradient between the motor204, the seal section208and the wellbore. The seal section208is also designed to segregate the lubricating oil and the wellbore fluid to avoid contamination of lubricating oil in the motor204.

Alternate configurations of the pump and motor may also be desirable in a wellbore tool string. For example, in some wellbore operations, fluids are forced down the well from one zone to another. In these operations, it is often desirable to place the pump below the motor at the bottom of the tool string. This configuration increases the risk that wellbore fluids will migrate upward from the pump into the motor. The motor may also be subjected to increased axial thrust from the pump located at the bottom of the tool string. There is therefore a need for protecting the motor from axial thrust and wellbore fluid contamination in configurations where the pump is located below the motor. It is to these and other deficiencies in the prior art that the present invention is directed.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide an electric submersible pumping system for use in wellbore fluids. The electric submersible pumping system includes a motor assembly, an upper seal section, a pump assembly and a lower seal section. The upper seal section is above the motor assembly and accommodates oil expansion in the motor assembly. The pump assembly is below and driven by the motor assembly. The lower seal section is between the motor assembly and the pump assembly. The lower seal section includes a shaft that transmits torque from the motor assembly to the pump assembly and a labyrinth chamber that restricts the flow of the wellbore fluids that migrate from the pump assembly to the motor assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with a preferred embodiment of the present invention,FIG. 2shows an elevational view of a pumping system100attached to production tubing102. The pumping system100and production tubing102are disposed in a wellbore104, which is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas. The production tubing102connects the pumping system100to a wellhead106located on the surface.

The pumping system100preferably includes an upper seal section108, a motor assembly110, a pump assembly112, and a lower seal section114. The seal section108shields the motor assembly110from axial thrust loading produced by the pump assembly112and ingress of fluids produced by the well. The seal section108also affords protection to the motor assembly110from expansion and contraction of motor lubricant. The motor assembly110is provided with power from the surface by a power cable116.

Although only one pump assembly112and only one motor assembly110are shown, it will be understood that more than one of each can be connected when appropriate. The pump assembly112is preferably fitted with an intake section118to allow wellbore fluids from the wellbore104to enter the pump assembly112, where the wellbore fluid is forced to a lower zone through tail pipe120. An optional packer122can be used to separate wellbore fluids between adjacent well zones.

Referring now toFIG. 3, shown therein is an elevational cross-sectional view of a preferred embodiment of lower seal section114. Filled with lubricating oil or other protective lubricant, the lower seal section114is substantially sealed from wellbore fluids and transmits torque from the motor assembly110to the pump assembly112via shaft124. The lower seal section114is connected to the motor assembly110and the pump assembly112with motor coupling126and pump coupling128, respectively. The lower seal section114is designed to protect the motor assembly110from axial shock created by the pump assembly112. The lower seal section114also limits the ingress of wellbore fluids from the pump assembly112to the motor assembly110.

In a preferred embodiment, mechanical seals130,132are placed at strategic locations along the shaft124to prevent the migration of wellbore fluids through the seal section114. The single and double mechanical seals130,132restrict the flow of wellbore fluids along the shaft124. If wellbore fluid migrates around the single and double mechanical seals130,132, the wellbore fluid is collected in chambers134and136, respectively. Although the seal section114can adequately hinder the flow of wellbore fluids without the use of mechanical seals, a preferred embodiment employing the mechanical seals130,132enhances the capability of the seal section114.

To provide extra protection against the migration of wellbore fluid toward the motor assembly110, a preferred embodiment of the present invention also employs labyrinth chambers138,140, which include labyrinth tubes142,144, respectively. Differences in the specific gravities of the wellbore fluid and the lubricant retard the movement of the wellbore fluid through the labyrinth chambers138,140, and ultimately toward the motor assembly110.

In another preferred embodiment, a protective expansion bag146can be used to provide a positive barrier between lubricant and wellbore fluid. Expansion and contraction of fluids in the seal section114due to pressure and heat variations can be accommodated by the expansion bag146as lubricant and wellbore fluids migrate through the seal section114. The expansion bag146is more clearly shown inFIG. 4without the expanded view lines ofFIG. 3.

Axial thrust created by the pump assembly112(or alternatively by a separation device, not shown) is potentially damaging to the motor assembly110. The seal section114absorbs much of the shock created by the axial thrust so that the motor assembly110is subjected to less thrust. Referring again toFIG. 3, in another preferred embodiment, a thrust bearing148absorbs axial thrust and protects internal surfaces of the seal section114that come in contact with the thrust bearing148.

Abrasive substances present in wellbore fluids are harmful to the seal section114, as well as the motor assembly110. Spinning parts are especially susceptible to damage due the repetitive wear realized by adjacent moving parts. In another preferred embodiment, an abrasion resistant bearing150is utilized at the base of the seal section114. Constructing the abrasion resistant bearing150with a hard, durable substance such as tungsten carbide slows the wear associated with abrasive substances in the wellbore fluid.

Typical submersible motors (such as110) employ three-phase power using one of several wiring configurations known in the art, such as a wye or delta configuration. Termination of the wiring connection can be accomplished at the motor assembly110, or alternatively in the seal section114. In another preferred embodiment, a wye point connection152resides in the seal section114near the interface with the motor assembly110. The wye point connection152completes the electric circuit for driving the motor assembly110when the seal section114is attached to the motor assembly110, thereby providing the desired termination. The wye point connection152can be adapted to provide a termination for any desired wiring configuration used for powering the motor assembly110.