Patent Application
20090314499
The field of the invention is multi-string wells that require removal of a string without killing the well.
For a variety of reasons wells can have multiple strings. One more recent example involves steam assisted gravity drainage (SAGD) installations used to recover tar sands from shallow formations. These installations use wells in combination. An injection well extends horizontally through a formation and is used to deliver steam into the formation to get the tar sands into a flowing condition as the heat added reduces viscosity. The production well is also run horizontally in the same formation and is generally below the injection well. The heated tar sands, from the steam from the injection well, flow into the production well for removal to the surface and further processing.
Those skilled in the art will appreciate that normally without steam injection, there is no flow in the producer well W. In order to make the tar sands flowable the producer well needs to be heated from the injector well and from steam delivered to the producer well. This is a very slow process that can take months. Once the producer well is at temperature it is full with steam and condensate. If the ESP 24 develops a problem and needs to be removed the well W first had to be killed with water added from the surface 34 before a wellhead (not shown) could be removed so that the ESP 24 could come out. If the wellhead were simply removed and the well W were still live, the condensate in the open hole 20 would experience a pressure reduction and flash to steam and come out at the surface 34 since the wellhead was no longer in position. This would create a very dangerous condition at the surface. The alternative no available is killing the well with fluid before taking off the wellhead so that the flashing of condensate doesn't occur at the surface and possibly injure personnel. The problem with killing the well is that it takes so long to reheat it after it cools and it potentially does not produce as well even after it is put back in service after a months long warm up.
The present invention seeks to provide a way to remove the ESP 24 without having to kill the well W. The downhole equipment is reconfigured to provide a seal between the casing and the slotted liner and another seal between the guide string and the inside of the slotted liner. The guide string features internal seal bores and a ported sub or a sleeve type valve that allows flow to the ESP for production but cuts off flow to the ESP when the concentric string which could hold instruments is moved with respect to its surrounding guide string. With the well isolated below the ESP the production string with the ESP at its lower end can be pulled without killing the well as will be explained in detail below.
U.S. Pat. No. 6,328,111 is relevant to inserting an ESP into a live well that has a single string.
A multi-string well has an electric submersible pump (ESP) that can be removed without killing the well. A slotted liner is sealingly secured externally to casing and internally to a guide string that remains in the wellbore when the ESP is removed. A ported sub is part of the guide string and a concentric string which could hold instruments string that moves relatively to the guide string can selectively allow flow in an annulus between them and to the ported sub or that annulus between the guide and concentric string which could hold instruments can be blocked off by manipulation of the concentric string to close the ported sub. With the lower portion of the well now blocked off, the wellhead can be removed so that the ESP can come out with the production string. The device has particular application to steam assisted gravity drainage (SAGD) systems as well as other downhole applications.
Starting at the uphole end, the guide string 116 features internal seal bores 124 and 126 followed by a landing shoulder 128. Below that is a sliding sleeve ported sub 130 shown in the open position in
On the concentric string 122 there is a no go 136 shown resting on shoulder 128 in
Arrows 144 indicate how flow that got through the slotted liner 106 progresses through the perforated sub or screen 132 as indicated by arrow 146, Once inside the perforated sub 132 flow is free to pass through the open ports 148 as indicated by arrows 150 and then into the ESP 100 as indicated by arrows 152. In the
As stated before, the concentric string 122 is shiftable at the surface using hydraulic cylinders 154 that are connected to pistons 156 which are in turn connected to yoke 158 that supports the concentric string 122. Concentric string 122 is sealed at 160 in wellhead 162. Locally available hydraulic pressure can be applied and removed to attain the positions of
Those skilled in the art will appreciate that the preferred embodiment of the present invention uses the strings normally in a producer well in a SAGD system and allows ESP removal without killing the well. More broadly the present invention is an isolation system in multi-string wells to allow a string and associated equipment to be removed without killing the well. While SAGD is an illustrated application other downhole multi-string well configurations can have the benefit of the present invention. While a sliding sleeve valve is illustrated and operated with a shifting tool other valve types are contemplated for example flappers and 90 degree ball valves to mention a few.
In SAGD service, the system keeps the basic components of a production string with an ESP at its lower end and a guide string for the concentric string. At the same time with some reconfiguration of the guide and the instrument strings the open hole portion of the producer well can be selectively isolated to allow removal of the wellhead and the production string with the ESP without having to kill the well. This allows the producer well to be kept warm while the ESP is replaced and minimizes subsequent performance degradation in putting a killed well back on line. The warm up that would otherwise take months is also dramatically shortened saving the operator workover costs and allowing production to resume that much sooner. The illustrated assembly can also be used in an injection well with the flows reversed in direction and the ESP replaced with another downhole tool.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
