Method and apparatus for washing an upper completion

The cleaning of a wellbore which has a casing in its upper part and a reservoir liner at its lower end by running only one string into the wellbore to cement the liner in place and to clean both the liner and the upper part of the well. Thus, the entire well is made ready for completion in a single trip.

FIELD OF THE INVENTION

This invention relates to the washing of a cased length of a hydrocarbon production well or water injector well, above the reservoir liner and in particular to a method and apparatus for achieving such washing efficiently and making savings on the amount of time needed for the washing operation.

BACKGROUND OF THE INVENTION

When a hydrocarbon well, or water injector well is drilled, casing is installed in the upper region of the well and then, normally, a reservoir liner is run into the well on drill pipe equipped with a reservoir liner hanger. Once the reservoir liner hanger is in place, cement is displaced into the reservoir liner and back up the annulus outside the reservoir liner, cementing it in position, and the liner is left filled with drilling mud. At this stage mud is circulated in the casing to remove residual cement, metal swarf, etc. The drill string is removed and a special cleanout string run in to the end of the reservoir liner. The casing and reservoir liner are then washed out with various fluids, and the portion of the casing in which the production packer is to be set is further cleaned with a scraper device. The well is thereby put into a suitable state to be filled with completion fluid and completed. The well cleanout string is relatively delicate since it must be narrow enough to extend through the reservoir liner. Because it is delicate it needs to be run in slowly.

Casing wash tooling is specially designed for the operation. It is designed to be rotated in the well; this is necessary in order to achieve effective washing. Since the well may be highly deviated, the string tends to lie on the lower side of the casing and, in the absence of rotation, only the region above the string will be effectively washed.

The casing wash tooling is also specially designed to carry out a so-called inflow test to check that there is no leakage of fluid from the reservoir liner or into the reservoir or production casing/liner. The casing wash process takes many days with associated cost and it is desirable to reduce this. The process is also risky since the thin cleanout string which passes down the reservoir liner is delicate and easily damaged.

BRIEF SUMMARY OF THE DISCLOSURE

According to the invention a process for washing a wellbore comprises passing a drill string, including a reservoir liner hanger running tool, down a cased wellbore to install a reservoir liner in an uncased distal portion of the wellbore; displacing cement into the reservoir liner annulus by passing completion fluid through the drill string and reservoir liner; without first removing the drill string from the wellbore, performing an inflow test on the reservoir liner; and washing the interior of the casing by passing wash fluid through the drill string and into the casing, whilst rotating the drill string.

Also according to the invention, an apparatus for washing a cased wellbore comprises a drill pipe having an assembly fitted to a distal end thereof, the assembly comprising: a reservoir liner hanger and reservoir liner hanger running tool; and an inflow test tool capable of forming a sealed connection between the drill string and the reservoir liner or reservoir liner hanger, for performing an inflow test on the reservoir liner.

DETAILED DESCRIPTION

Referring firstly toFIG. 1, a wellbore1comprises an upper, cased part2underneath which is a reservoir liner3. Extending through the wellbore approximately to the junction between the upper part2and reservoir liner3is a drill string4. At the distal end of the drill string is an assembly comprising a reservoir liner hanger5, associated reservoir liner hanger running tool10, which inFIG. 1is connected to the reservoir liner hanger, and a ball valve6. The assembly also comprises a scraper tool for cleaning a section of the interior of the casing above the reservoir liner hanger5. At the distal end of the reservoir liner is a burst disc. The scraper tool and burst disc are omitted from the drawings for clarity. They are standard components whose design and functionality will be familiar to anyone of ordinary skill in this field. The function of all these components will be described below. At the distal end of the drill string4is an inflow test seal, also omitted from the drawings for clarity and whose function will be explained below.

At the stage illustrated inFIG. 1, the reservoir liner3has been placed by the drill string4at a desired depth. The reservoir liner hanger5has not yet been set. The wellbore is filled with drilling mud7to balance/control the well pressures. In an alternative method, the reservoir liner hanger is set before the cement is displaced.

Referring toFIG. 2, a cementing job is now performed by introducing cement into the drill string4. A volume of cement sufficient to fill the annulus around the reservoir liner3is introduced into the drill string4, immediately followed by a cleaning plug and completion fluid8(in this case, brine). As the completion fluid displaces the cement through the reservoir liner3, the cleaning plug substantially prevents cement being left on the reservoir liner interior wall.

An appropriate volume of completion fluid8is pumped down the drill string4to displace all the cement into the annulus of3. Cement filling the annulus is shown at9inFIG. 2. At this point the drill string4and the entire length of the internal bore of the reservoir liner3are filled with brine8. The reservoir liner hanger will now be set, anchoring the reservoir liner3to the upper, cased part2and creating a continuous seal between these.

The drill string4is then withdrawn slightly so that its distal end, with the reservoir liner hanger running tool10, is detached from and right above the reservoir liner hanger5. This action closes the ball valve6by pulling a shifting tool past a shifting profile (a technique for actuating down-hole components which is well known in this field). This state is shown inFIG. 3. The ball valve6keeps the completion fluid8in the reservoir liner3separated from the upper, cased well volume2above, i.e. prevents debris from the upper part of the well from falling into the reservoir liner. The closing of the valve6is not limited to pulling a shifting tool past a shifting profile, but could also be achieved by a clock timer, pressure pulses, or any other technique known generally in this field. The ball valve6could be replaced by any suitable type of mechanical valve, e.g. a flapper valve, but a ball valve is preferred because the ball valve can also act to prevent fluid flow in the opposite sense, e.g. as a barrier in case of a leak in the reservoir liner.

The ball valve6is actuated by the drill string being withdrawn, and this helps prevent the completion fluid in the reservoir liner from becoming contaminated with solid material from above.

In a modified apparatus and method, the ball valve6is not present, nor circulation is started. The inventor believes that the process for cleaning of the upper completion, as described below, is so short (perhaps of the order of 2 hours) that this will give rise to very little, if any, solid material falling into the reservoir liner even if no valve is present. The short time for the cleaning operation means that there may be insufficient time for the drilling mud to heat up appreciably; it is when the drilling mud becomes hot (i.e. is heated to the temperature of the formation which can be around 150 degrees Celsius or more) that solids (e.g. barite) tend to settle out of the mud, so for this reason also the valve6may not be necessary. With circulation started any debris from upper part of the well will not permitted entering the reservoir liner3.

The casing scraper tool (not shown in the drawings) that was previously collapsed in the reservoir liner expands to scrape the production casing string that hosts the reservoir liner hanger5. The drill string4is rotated and/or reciprocated, which causes the scraper tool to scrape clean a portion of the interior of the casing the portion which will receive a production packer at a later stage in the completion of the well.

Drilling mud is continuously circulated, with the drill string rotating, to clean heavy debris from the upper part of the well, above the reservoir liner hanger. Debris such as cement and metal swarf can be removed by the heavy drilling mud. Rotation of the drill string ensures that the entire inner surface of the casing above the reservoir liner hanger is cleaned.

After circulation of mud, the rotation of the string is stopped and an underbalanced fluid is circulated down the drill string. This is shown inFIG. 4. The inflow seal is stung into a polished bore receptacle (“PBR”) of the reservoir liner hanger. Although the inflow seal and PBR are not shown as such in the drawings, inFIG. 4it can be seen that the end of the drill string is engaged once more with the liner hanger and a seal at the end of the drill string is schematically shown at12.

The PBR need not be part of the liner hanger and may alternatively be provided on another part, above or below the liner hanger assembly. PBRs are well known in themselves and their structure and function will be apparent to one of ordinary skill in this field.

Together the inflow seal and PBR provide a temporary seal between the drill string and reservoir liner, isolating the interior of the drill string4and reservoir liner3from the annulus between the drill string and casing2.

Once the seal between the drill string and PBR/reservoir liner is engaged, the underbalanced fluid causes the reservoir liner to be underbalanced to the reservoir allowing the inflow test of the reservoir liner.

The underbalanced fluid in the drill string is created by displacing some of the mud in the string with a light oil or base oil, shown at13inFIG. 4, having a density lower than the completion fluid. If fluid in the drill string is detected coming to surface, this is an indication of a leak in the reservoir liner. It is important to conduct such an inflow test prior to completing the well.

In an alternative method, which saves time but is less safe because the degree of underbalance cannot be controlled, the mud in the drill string is simply displaced to completion fluid and the inflow test then done.

After the inflow test, the inflow seal is disengaged from the PBR and the underbalanced fluid in the drill pipe is circulated out of the well. The upper part of the wellbore is washed with a wash train comprising a sequence of different fluids as is well known in this field. During this process the drill string is rotated. Rotation of the drill string throughout the washing provides for efficient displacement. The casing scraper tool may be employed again (or alternatively for the first time) at this point in the process. Reciprocation of the drill string causes the scraper to scrape the casing where the production packer for the upper completion will be placed and set after the drill string is retrieved.

Finally the upper part of the wellbore is displaced to completion fluid8and the drill string withdrawn. This is shown inFIG. 5.

The process described avoids the running of a separate cleanout string either to clean the reservoir liner or to clean out the upper part of the wellbore. Several days of rig time can be saved as well as avoiding the hazardous process of running a narrow cleanout string into the reservoir liner, which is prone to failure by buckling.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.