The present invention relates to a method of pressure testing a plugged well extending into a hydrocarbon bearing formation. The invention also relates to a method of plugging a well, for example, by placement of a high quality sealant, to facilitate subsequent pressure testing.
Oil and gas wells have in general three different purposes, as producers of hydrocarbons, injectors of water or gas for reservoir pressure support or for depositing purposes, or as exploration wells. At some point it is likely to be necessary to satisfactorily plug and seal these wells, e.g. after the wells have reached their end-of life and it is not economically feasible to keep the wells in service (so-called “plug and abandon”), or for some temporary purpose (e.g. “slot recovery”). Plugging of wells is performed in connection with permanent abandonment of wells due to decommissioning of fields or in connection with permanent abandonment of a section of well to construct a new wellbore (known as side tracking or slot recovery) with a new geological well target.
A well is constructed by a hole being drilled down into the reservoir using a drilling rig and then sections of steel pipe, casing or liner are placed in the hole to impart structural integrity to the wellbore. Cement is placed between the outside of the casing or liner and the bore hole and then tubing is inserted into the casing to connect the wellbore to the surface. For ease of reference, all of these entities inserted into the well are referred to here as “tubulars”. When the reservoir is to be abandoned, either temporarily or permanently, a well barrier must be established across the full cross-section of the well. This is generally achieved by removal of the tubulars from the well bore by pulling the tubulars to the surface or by section milling. Well barriers are then established across the full cross-section of the well, in order to isolate the reservoir(s) and prevent flow of formation fluids between reservoirs or to the surface. It is necessary to remove the tubulars from the wellbore in the case that proper quality of the sealant (e.g. cement) behind the tubular(s) cannot be determined.
To save having to remove an entire length of tubular from a well, a tool may be inserted into the well to cut the tubulars at a point beneath that at which the plug is to be formed, and only the upper detached part of the tubulars removed from the well. It is also possible to use a milling tool to mill away a part of the tubulars at the location where the plug is to be formed.
Attempts have been made to increase the efficiency of the method of abandonment. For example, GB2407835 describes wellbore sealing wherein explosive charges are used to perforate a lower end of the tubing and then sealing fluid is pumped through the perforations so as to plug the well around the bottom end of the tubing. A similar approach is described in WO2012096580.
U.S. Pat. No. 2,591,807 relates to an apparatus that uses relatively low and high velocity explosive charges spaced at opposing ends of a container full of cement for placing in a zone of a wellbore whereby, upon ignition, cement is forced downwardly and outwardly to release cement into the cavity between the tubing and formation. U.S. Pat. No. 2,696,258 and U.S. Pat. No. 2,696,259 relate to an apparatus for depositing cement in a zone wherein the cement is contained within an elongated container and a gas generating charge is ignited to displace the cement through a lower outlet of the container into the zone. The charge expands the container into sealing contact with the casing, while at the same time rupturing the end of a tubular body to release cement into the wellbore.
Regulations may require that an abandoned well be plugged so as to seal the well over at least some specified longitudinal extent, e.g. greater than 50 metres. An improperly abandoned well is a serious liability so it is important to ensure that the well is adequately plugged and sealed. However, as it can be difficult to accurately determine the quality of a well plug, regulations will typically over specify plug requirements by some significant margin. In any case, even when a plug meets the specified requirements there may be a risk of failure for any number of reasons.
In order to determine the integrity of a well plug it is desirable to perform pressure testing. This is relatively easy to achieve from above the plug. However, it is currently not possible to perform pressure testing of a plug from below.
It is an object of the present invention to provide an improved method of testing the integrity of a well plug. It is a further objective to provide a method of plugging a well to facilitate such improved testing.
According to a first aspect of the present invention there is provided a method of plugging a well extending into a hydrocarbon bearing formation to facilitate temporary or permanent abandonment of the well. The method comprises forming two or more plugs within the well, the plugs being formed at longitudinally spaced apart locations whilst providing a fluid communication path from a region above the topmost plug to the or each space between adjacent plugs. This configuration facilitates pressure testing of one or more of the plugs by conducting fluid through said path.
The method may comprise partially or completely filling the or each space intermediate adjacent plugs with a permeable material or void making material or device. The permeable material may be a particulate material, for example sand or proppant.
The step of providing a fluid communication path may comprise locating one or more pressure testing tubes within the or each plug located directly above an intermediate space.
The method may further comprise pressure testing one or more of the plugs by conducting fluid through said path. The method may further comprise plugging the fluid communication path subsequent to a pressure testing procedure.
According to a second aspect of the present invention there is provided a method of pressure testing a plug formed during plugging of a well using the method of any one of the preceding claims. The method comprises passing a fluid through said fluid communication path in order to establish an elevated or reduced pressure within one or more spaces intermediate the adjacent plugs, and monitoring the pressure or leakage between the plugs and/or monitoring pressure above or below one or more of the plugs to determine plug integrity.
As has already been discussed above, it is often necessary to either temporarily or permanently plug a well, extending into a hydrocarbon formation, in order to prevent fluids from leaking out of, or indeed into, the formation. This is commonly achieved by forming a cement plug within the well. Other materials, such a epoxy resins, may be used instead of cement. Typically, in order to achieve seal with sufficient integrity, a plug may extend over many tens of meters.
During preparation of the well for plug formation, a plug support or base 8 is located within the well, typically with the remaining tubulars. A cementing tubular 9, used to deliver cement or other sealant to the plug locations, may remain within the well after plug formation. [In this case, the cementing/sealant tubular will probably be filled with sealant or other mechanical devices in order to maintain plug integrity.]
Turning now to the pressure testing itself, this involves introducing fluid into the space 10 via the pressure testing tube 11. This fluid could, for example, be drilling fluid or other liquid material. The fluid is introduced to the tube 11 at the surface, e.g. from a support platform or other vessel, using appropriate valves and pumps, and fills the space 10, e.g. filling the voids within the permeable material. The fluid pressure at the surface is monitored, e.g. to ensure that it can exceed the highest possible pressure that might arise beneath the plug. This allows the pressure in the intermediate space 10 to be calculated. Alternatively, pressure sensors may be located within the intermediate space and data fed back to the surface, e.g. to allow pressure increase and decrease within one or more spaces to be monitored. Appropriate sensors are mounted on the testing tube 11. These sensors could be, for example, pressure sensors, chemical sensors, optical sensors, acoustic sensors, etc, or indeed any combination of these sensor types. The sensors are configured to determine the integrity of the upper plug 2, and possibly to some extent the integrity of the lower plug 3, during and after application of the elevated pressure to the intermediate space 10.
Whilst
It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/051942 | 1/31/2013 | WO | 00 |