Patent Application
20090173501
Embodiments of the invention relate to systems for borehole cleaning that allow removal of materials in a borehole preventing flow. In particular, embodiments of the invention relate to system for use in wells such as oil and gas wells.
As oil and gas are extracted from producing wells, sand and heavy oils that have flowed through the perforations accumulate. These are too heavy to flow to the surface along with the usual fluids produced by the well at normal production rates, and tend to accumulate in low-lying areas as shown in
In most well cleanout applications, the reservoir pressure is high enough, and the rock permeability low enough, to allow increase of pressure in the well while performing cleanout operations. In others, foam can be used to sweep the fill up. However there are still many wells that either cannot hold a foam column, or where foam use is restricted due to logistics reasons (e.g. procurement and disposal of N2 foam). In these situations, the only existing cleanout solution is a concentric coiled tubing (CCT) service to power a downhole jet pump. Using CCT implies a high use of power liquid to move the fill out and is limited in length by the weight of the coil-in-coil assembly.
Examples of CCT techniques can be found in U.S. Pat. No. 2,548,616, U.S. Pat. No. 5,033,545, U.S. Pat. No. 5,269,384, U.S. Pat. No. 5,375,669, U.S. Pat. No. 6,263,984, U.S. Pat. No. 6,015,015, U.S. Pat. No. 6,497,290, U.S. Pat. No. 6,640,897, U.S. Pat. No. 6,712,150, U.S. Pat. No. 5,503,014, and WO 2005085580 A.
Embodiments of the invention aim to provide an alternative to CCT techniques while also extending the depths at which clean-out operations can be performed. An embodiment of the invention is based on the use of a downhole pump that is powered by a cable running inside the tubing conveyance.
One aspect of the invention provides apparatus for borehole cleaning, comprising:
A second motor and pump can be located in the tubular conveyance above the pump so as to provide extra lift to the material to be removed from the well. Additional ‘booster’ pumps can be added in this way up to the power limit of the wireline cable.
A gas supply line can extend at least part way along the inside of the tubular conveyance and be arranged to introduce gas into the material-laden flow in the tubular conveyance above the pump.
The apparatus can further comprise a filter between the nozzle and the pump to prevent large particulate material passing into the pump from the borehole. Preferably, the filter removes material of greater than 1 mm from the flow.
It is particularly preferred that the apparatus comprises means to move the nozzle when the pump is operated downhole. Movement of the nozzle can be used to further mobilize the fill and suspend it in the fluids in the well. The means can rotate and/or reciprocate the nozzle. A separate motor can be provided to enable this mobilizing movement. Alternatively, a mechanical connection to a rotor in the pump can be provided for this purpose.
Features can be provided on the outside and/or inside of the nozzle to accelerate the flow of material when operated downhole to aid in movement of solids.
The tubular conveyance is preferably coiled tubing.
Another aspect of the invention provides a method of cleaning a well using an apparatus as defined above, comprising:
The method can further comprise injecting gas into the materials in the tubular conveyance to create foam of reduced density to assist pumping of the materials to the surface.
Preferably, the solid materials are agitated downhole to improve removal by the pump.
The nozzle can be rotated or reciprocated while operating the pump.
Alternately advancing and withdrawing the tubular conveyance over a limited distance can be used to reciprocate the downhole end of the conveyance in the region to be cleaned.
In one embodiment, the tubular conveyance is extended until the pump is located at the bottom of a region to be cleaned and progressively withdrawing the conveyance to move the pump upwards through the region as the pump is operated. In another, the tubular conveyance is extended until the pump is positioned at the top of a region to be cleaned and progressively advancing the conveyance to move the pump downwards through the region as the pump is operated.
The power required to overcome the vertical height (TVD) hydrostatic pressure can be relatively large compared to the power usually available for downhole tools powered via an electric cable (e.g. wireline tools). Since 3-9 kW of electrical power is typically available to power the pump with current wireline technology, for a flow rate of 10 gpm (considered as suitable for this type of application), flow can only be assured for the first few kilometres (depending on CT size and fluid/fill density and viscosity). Therefore, an additional boost may be required to move the fluid mixture to the surface where it can be disposed of or separated.
One method of boosting the hydraulic power is to add a second pump/motor combination 34 in series with the first pump of an embodiment of this invention; either right next to it, or further up along the CT 22. Another method of using dual pumps to carry cuttings during drilling has been disclosed in GB2416550A.
Another preferred method of assisting the fluid to reach the surface is to run a pilot line 38 partway along the CT (to point 36) to inject N2 gas via a nozzle 40. The length of this pilot line 38 can be determined a priori by knowing the geometry of the well, as it is preferable to inject the gas into the CT above the horizontal section. This will decrease the hydrostatic weight of the fluid above the injection point as the gas moves up, and will also avoid the risk of creating a gas ‘plug’ if the gas were injected lower (if the gas is injected in the horizontal section 42, then the pump 30 will need to push the fluid and the gas up the CT 22, thus increasing the system losses and causing a ‘slug’ flow condition where gas and fluid ‘slugs’ alternatively flow to the surface; leading to a less efficient carrying capacity system).
In the case of the sand plug where it is not possible to force the end of the CT 22 through merely by pushing the CT from the surface, pump operation can start from the top of the plug and the CT 22 slowly be run-in-hole to pump a mixture of well fluid and sand.
A mechanical sand mobilization means may be beneficial under this situation so as to fluidize the sand and make it easier to flow through the pump and up the CT. These are described below in more detail in relation to
In the case of leftover drilling muds or heavy oils, then the apparatus can be run to the bottom of the well and pulled out of hole while the pump is operated. This will use the heavy fluids behind (i.e. above) the apparatus to act as a temporary dynamic seal and the removal of fluid from the lower part of the well can create a localized drawdown at that level. If the upper fluid is not viscous enough, then the drawdown will not materialize locally, but rather from a reduction of the well fluid level; in turn lowering the hydrostatic pressure over the entire well. If this is not desired, water or other appropriate fluid can be injected at the well head to compensate for the fluid removal through the CT.
During a clean-out operation, the apparatus may encounter pebbles and larger particles that have gravitated to the low side of the well and are mixed with the fill. One particular embodiment of the invention for use in such circumstances is shown in
The effectiveness of the mobilization of the fill can be greatly enhanced if a mechanical mixing of some sort takes place. There are various techniques that can be used for creating mechanical mobilization of fine particles and sand.
The surface injector can be used to stroke the CT backwards and forwards over a predetermined length (e.g. 1 foot (300 mm) as the nozzle is moved through the fill.)
A second motor can be provided at the tip of the pump tool to rotate the pump nozzle as is shown in
Features can be added at or around the pump nozzle to mechanically agitate the fill as the nozzle is rotated.
In another embodiment, pump hydraulic power can be used to create a slow reciprocating motion of the nozzle (via a low power turbine for example), that can assist mobilisation of the fill using features such as those described above.
The limitation of how far the pump could be pushed in the well is usually the helical lockup of the CT in a deviated well. One way of circumventing this limitation is to combine an electric borehole tractor to pull the pump to depth, and then disengage and deactivate it to allow pumping while pulling the CT and pump back towards the surface. Hydraulic tractors can also be used when flowing in ‘standard’ (i.e. down the CT) circulation. However, their flow requirements can tend to increase BHP, which may be undesirable in very low pressure reservoir conditions.
The pump can also contain a flow-diverter above it, commanded from the surface via optical or electrical means, that would allow opening ports to the annulus to flow through the CT in cases when well control or CT cleaning is required. Once the CT has been cleaned, or any obstructions have been removed, the flow-diverter can close the ports and normal ‘reverse’ circulation can resume.
Even without the flow-diverter described above, flowing in the ‘standard’ direction from the surface can also be used to clean the filter of accumulated pebbles by ejecting them further up the wellbore and then moving the tool back down to the fill and proceeding with the clean-out operation.
It will be appreciated that the various techniques described above can be combined to give the described advantages. Other changes can be made while staying within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06290733.2 | May 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/03679 | 4/26/2007 | WO | 00 | 2/20/2009 |
