BACKGROUND TO THE INVENTION

Specialised downhole pumps are used in the hydrocarbon exploration and production industry in various applications, and in particular for the production of hydrocarbons to surface from significant wellbore depths. There are several types of downhole pump in use, including Electrical Submersible Pumps (ESPs) and Sucker Rod Pumps (SRPs ). An ESP is typically located at the bottom of the production tubing, and comprises a downhole electric motor powered and controlled from surface by a power cable which connects to the wellhead. ESPs are highly efficient pumps capable of high production rates, and are particularly well-suited to the production of lighter crude oils, and are less capable with heavy crudes.

An SRP system is powered by a rod extending from surface to the downhole pump, and the stroking action, can be achieved by a "nodding donkey" reciprocating machine, or long stroke hydraulically powered machines. The SRP is also referred to as a reciprocating pump. The downhole pump typically comprises a standing valve and a traveling valve. The standing valve is attached to the tubing. The traveling valve reciprocates with the rod string. Both valves typically comprise a ball check arrangement.

Downhole pumps are sensitive to sands and other abrasive solids being present in the production fluid. The amount of sand which is produced from a well depends on characteristics of the formation, and various methods are used to control sand production. However, it is common for some amount of sand or abrasive solids to be present in the production fluid. ESPs are particularly sensitive to sand presence due to the nature of their internal components.

With many production systems which use a downhole pump, problems can arise when the pump is shut down after a period of pumping fluid up the production tubing to surface.

With an ESP, gravity acting on the sand particles present in the column of fluid above the pump (which could be several thousand metres) causes the sand and any other solids to fall back towards the pump with the fluid column inside the tubing. On pump shutdown, flow ceases very quickly as the fluid levels in the production bore and the annuluses equalise. Due to the complex configuration of the interior features of the pump, there is no direct path for the sand to pass through the pump. And therefore it tends to settle on top of the pump or in the top portion of the pump. This can cause the pump to become plugged - or can cause internal components to erode.

When production operations are resumed, a higher load is required to start the pump and push the plug of sand up from the pump. In some cases this can cause motor burn out in an ESP, a broken shaft, or component erosion over time. Such failure of the downhole pump requires a work-over involving pull-out and reinstallation of the completion. This is an expensive and time-consuming operation.

When production ceases with an SRP the fluid column is sustained in the tubing by the stationary valve. The entrained solids will fall with gravity in the static fluid column inside the tubing. The falling sand can accumulate several feet on top of the traveling and stationary valve. It is amongst the aims and objects of the invention to provide a downhole apparatus and method which addresses the above-described deficiencies of downhole pump systems.

Further aims and objects will become apparent from reading the following description.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a downhole apparatus to collect solids fallback. It consists of at least one section of the flow path having an unobstructed flow and the remaining flow path having a container or several containers to collect the solids fall back. The surfaces of the container may be made of filter material, contain slits or V grooves which seat rods. The rods may be scored with fine grooves allowing the rod to act as a filter.

With all configurations the device will allow fluid to pass during normal pump operation whether the container or containers are full of sand or empty of sand. Chemical treatment inside the tubing from the surface will be allowed to pass through the device whether the container or containers are empty or full of sand. Under normal conditions the containers will be cleaned of sand upon restart of the downhole pump operation. Before restarting the pump the device will store the caught sand until the downhole pump is restarted. According to a further aspect of the invention it comprises a body configured to be coupled to a production tubular and comprising an upper opening and a lower opening;

Inside the tubular body are baskets occupying a portion of the flow area, so fluid can move freely around the basket, in the event of solids fall back, the basket will collect any solids falling directly above it.

If more than one basket, the baskets can be arranged to collect fall back solids from different sectors of the tube, the baskets may overlap each other in terms of coverage.

The base of the basket can be a filter, or a non return valve (NRV). With an ESP the NRV will unseat and be open during normal pumping operation, and seat and be closed when the system ceases operation and the fluid inside the production tubing falls back with gravity. The NRV may be a flapper, ball check, poppet or other type of NRV.

The downhole apparatus may form a part of a hydrocarbon production system, and may be used during production of hydrocarbons. The apparatus may therefore collect solid particles from a production fluid.

The arrangement could be part of an SRP system and incorporated into the pump plunger body. The baskets could also be arranged to fit onto a joint of a rod lift shaft, and arranged to collect sand or solids fallback

The SRP version shall attach to the reciprocating shaft of the rod lift string and reside above the downhole pump. The device shall comprise a housing and end adapters to attach to the rod string shaft. A concentric housing resides inside the housing allowing fluid to pass uninterrupted in the annular space. A funnel above the basket may direct the solids to the basket inlet. Several chambers reside inside the inner housing. The chambers consist of a base, storage tube, cap and connector rod. Sand is captured in the annular space between the storage tube and the inner housing. Narrow slits in the storage tube, the base outer diameter surface, and the base inner diameter surface allow fluid to pass during normal operation while capturing falling sand when pumping ceases. The base and storage tube may in some cases not contain slits. The cap resides on top of the storage tube. A gap between the storage tube top and the cap allows collected sand to fall down to the lower container when the upper container is full. The cap also directs falling sand to the annular space between the storage tube and inner housing.

There is no flow restriction or check valve in the downward direction at the device entrance or exit, this enable the pump to be back flushed if required

Preferably, the hydrocarbon production system is an artificial lift production system, which may comprise one or more downhole pumps located below the downhole apparatus.

The apparatus may contain one or several individual storage chambers. The ESP, PCP or SRP system may have one apparatus or several. The apparatus may also be through tubing deployable and retrievable, eliminating the need for a rig to workover the well

The pumps may be Electrical Submersible Pumps (ESPs) or rod lift (nodding donkey). Therefore, the apparatus may prevent passage of the solids downward through the apparatus and towards a downhole pump. The solids are prevented from passing through or settling on the downhole pump by being collected in the apparatus.

It will be appreciated that the downhole apparatus may be connected to production tubing at the lower opening, or may be installed on or in a downhole pump with no intermediate tubing or via a specialised connecting sub-assembly.

The apparatus maybe installed before the pump inlet, and inverted to collect solids before they enter the pump

A solids fallback device located between the downhole sub-terranean SRP pump and the surface. The device captures sand and solids falling entrained in a static fluid column within the tubing before they reach the downhole pump. The device stores these sands and solids while the fluid column is static. The device cleans the captured sand and solids when the downhole pump produces fluid.

One or more pockets or chambers within the device capture the solids.

The device is attached to the rod shafting.

The device is attached to the tubing with the rod shaft cycling inside. The base of the pockets or chambers may have slits on the outer and inner diameter which allow sand to bridge, thus blocking the falling sand to pass; when producing fluid from the wellbore the slits allow fluid to pass assisting the cleanout of captured sand and solids.

The storage tube in each of the pockets or chambers may have longitudinal or other directional slits which allow sand to bridge blocking the falling sand to pass; when producing fluid from the wellbore the slits allow fluid to pass assisting the cleanout of captured sand and solids.

Each pocket or chamber may have a cap to diverts the falling sand or solids to the annular space between the device housing and storage tube.

The cap is situated to allow a gap between the storage tube top and cap bottom to allow accumulated sand in a chamber to enter the storage tube inner diameter and fall into the chamber beneath.

A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a check valve

A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a ball non return valve

A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a flapper non return valve A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a poppet non return valve

A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a expanding rubber slit

A device to capture sand or solids situated between the ESP and surface may have several pockets or chambers with base incorporating a deforming plastic shelf

BRIEF DESCRIPTION OF THE DRAWINGS

There will now be described, by way of example only, embodiments of the invention with respect to the following drawings,

Figure 1 is a section side view of a well bore production configuration with a typical ESP system.

Figure 2 is a similar view to Figure 1 but with the solids fallback protection device.

Figure 3 is a section side view of a well bore production configuration with a typical SRP system.

Figure 4 is a similar view to Figure 3 but with the solids fallback protection device.

Figure 5 is a cross sectional and two longitudinal sectional views of the ESP solids capture invention with several storage chambers

Figure 6 shows deposits of captured sand or solids in the ESP invention.

Figure 7 is a section view of the SRP solids capture invention with two storage chambers.

Figure 8 shows the deposits of captured sand or solids in the SRP invention. Figure 9 is section view of one chamber from the ESP device with a flapper valve in the base.

Figure 10 is section view of one chamber from the ESP device with a ball check in the base. Figure 11 is section view of one chamber from the ESP device with a poppet style valve in the base

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to figures 1 and 2, there is shown a typical ESP system. The downhole ESP system 120 consists of an electric motor, seal section, and multistage centrifugal pump. Power cable 112 conveys power provided by the variable speed drive 110. The power cable connects to the motor 121. The motor rotates the seal section 122 and multistage centrifugal pump 123. The pump pushes the fluid up the production tubing 150. Figure 2 shows the addition of a solids fallback device 130 located between the downhole ESP system and surface apparatus.

Referring to Figures 3 and 4, there is shown a typical SRP system. The main components of the downhole SRP system 220 are a traveling valve 122 and a stationary valve 221. A beam pump 210 on the surface provides an oscillating linear motion to the rod shaft string which lifts and lowers the traveling valve. Figure 4 shows the addition of a solids fallback device 250 located inside the tubing between the downhole pump and the surface apparatus.

Referring to Figure 5, there is shown a section view of the ESP solids capture device with four chambers, whereas the device may have one or numerous chambers. The apparatus is attached to tubing string members above and below. The main components are a shelf or base 301 (shown in the lefthand longitudinal sectional view), each shelf or base supporting a mesh screen or filter mechanism 302, and a communication window 303 (shown in the righthand longitudinal sectional view, this sectional view being perpendicular to the lefthand longitudinal sectional view).

Referring to Figure 6, there is shown sand 350 captured in the ESP device. Referring to Figure 7, there is shown a section view of the SRP solids capture device with two chambers, whereas the device may have one or several chambers. The device resides inside the tubing 455 and is connected to the rod shafting 450. The storage chambers base 401, storage tube 402, and storage cap 403 are retained inside a housing 404. The storage tube is shown with slits.

Referring to Figure 8, there is shown sand 460 captured in the SRP device.

Referring to Figure 9, there is shown an ESP solids capture device with an alternate base configuration using a flapper style valve 500. When the production system is producing fluid to the surface the flapper valve 510 will open.

Referring to Figure 10, there is shown an ESP solids capture device with an alternate base configuration using a ball check style valve 520. When the production system is producing fluid to the surface the ball 530 will unseat.

Referring to Figure 11, there is shown an ESP solids capture device with an alternate base configuration using a poppet style valve 540. When the production system is producing fluid to the surface the poppet 550 will unseat.