Rig-Up for Pressure Control

The present invention relates to a method for creating and verifying a thermite-based downhole well barrier in a well. The present invention also relates to a system for creating and verifying a thermite-based downhole well barrier in a well. The present invention also relates to a method for providing a thermite-based downhole barrier in a well.

To meet governmental requirements during plugging and abandonment (P&A) operations in a well, a deep-set barrier must be installed as close to the potential source of inflow as possible, covering all leak paths. A permanent well barrier shall extend across the full cross section area of the well, including all annuli, and seal both vertically and horizontally in the well. Normally cement is used for the purpose of P&A operations.

Recently, an alternative method of performing P&A operations has been invented, using a heat generating mixture, e.g. a thermite mixture. Thermite is normally known as a pyrotechnic composition of a metal powder and a metal oxide. The metal powder and the metal oxide produce an exothermic oxidation-reduction reaction known as a thermite reaction. A number of metals can be the reducing agent, e.g. aluminium. If aluminium is the reducing agent, the reaction is called an aluminothermic reaction. Most of the varieties are not explosive but may create short bursts of extremely high temperatures focused on a very small area for a short period of time. The temperatures may reach as high as 3000° C.

WO 2013/135583 discloses a method of abandoning a well by melting surrounding materials, such as pipes, cement and formation sand, the method comprising the steps of; providing an amount of a heat generating mixture, the amount being adapted to perform the desired operation, positioning the heat generating mixture at a desired position in the well, igniting the heat generating mixture, thereby melting the surrounding materials in the well.

In traditional P&A operations, the barrier is formed by cement placed either inside casing and tubulars, or homogeneous across the entire cross section. In addition, cement is also positioned above the cross section interval inside of the tubulars at a distance of 30-50 m. In cemented P&A operations the barrier may be tested by performing a pressure test of the well volume above the plug. However, this may not always be possible, for example where the well above the barrier is influenced by the P&A operation.

In the thermite-based barrier formed by the method of WO 2013/135583, the heat generating mixture, e.g. the thermite mixture, when initiated, for example by ignition, will burn with a temperature of up to 3000° C. and melt a great part of the proximate surrounding materials, with or without the addition of any additional metal or other meltable materials to the well. The surrounding materials may include any material normally present in the well, such as tubulars, e.g. casing, tubing and liner, cement, formation sand, etc. The heat from the ignited mixture will melt a sufficient amount of said materials. When the heat generating mixture has burnt out, the melted materials will solidify forming a sealing barrier comprising melted metal, cement, formation sand, etc. against the well formation.

In some tests of the above method, the heat generating mixture was based on iron oxide and aluminium. It was found that a fluid path was formed through the casing above the sealing barrier. Hence, even if the method is creating a sealing barrier, a conventional pressure test of the sealing barrier cannot be used to verify the barrier, as pressurized fluid on the upper side of the barrier during the test will flow from the casing and out to the annulus outside of the casing.

Moreover, while the prior art P&A operations based on cement allow the use of sensors for measuring various parameters at the location of the barrier during the operation, the temperature of the prior art P&A operations based on thermite does not allow such sensors at the location of the barrier during the operation, as sensors will be damaged by the heat.

One object of the present invention is to provide a method and system for verification of such barriers.

NO 20200795 A1 discloses a thermite reaction charge, comprising bismuth oxide, Bi2O3 and a fuel metal comprising aluminium. This thermite reaction charge is adapted to react at a relatively faster reaction rates. It also discloses a method of sealing a well with a rock-to-rock cross-sectional well barrier, where the well comprises a downhole completion comprising at least a casing.

The above types of P&A operations are relatively new, and there is therefore a need to verify the quality of the barrier.

One object of the present invention is therefore to provide a method for verifying a thermite-based barrier.

One object of the present invention is to provide a method for performing a plug and abandonment operation with the bismuth-based thermite mixture in a safe and reliable way.

The present invention relates to a method for creating and verifying a thermite-based downhole well barrier in a well, wherein the method comprises the steps of:

In one aspect, the thermite-based downhole well barrier is a rock-to-rock cross-sectional well barrier extending across the entire cross section of the well bore. The term “rock-to-rock cross-sectional well barrier” is used herein to denote that the well barrier is in contact with and bonded to the rock formation and thus blocks the entire cross-sectional area of the well bore.

In one aspect, the barrier is formed by melting of and subsequent solidifying of at least parts of the surrounding materials in the well as a result of the heat generating process. The surrounding materials may comprise casing, cement, sand, gravel, and/or cap rock. The barrier may further comprise remnants of the well tool used for transportation of the heat generating mixture into the well.

The term “verifying”, “verification” etc. is used herein to denote a process where a measured parameter is compared with an expected parameter and where it can be determined that the integrity of the well barrier is intact by comparing the measured parameter with the expected parameter. Typically, the comparison is done by comparing the difference between the measured parameter and the expected parameter. If the absolute value of the difference is below a predetermined threshold value, then the well barrier is determined to be intact, while if the difference is above a predetermined threshold value, then the well barrier is determined not to be intact.

The term “determining that the integrity of the well barrier is intact” is used herein to denote a process where it is determined that it is likely that the integrity of the well barrier is intact. As is known, the overall purpose of a P&A operation is to provide an eternal, 100% sealed well. In some situations, it is required to monitor an abandoned well for a period of time, for example by means of gas detectors, in order to ensure that there is no leakage. According to the present invention, it is achieved that the monitoring may be omitted, or the number of abandoned wells needing monitoring can be reduced.

In one aspect, the expected parameter is representative of an expected fluid pressure and/or an expected fluid flow at the upper location of the well as a function of time, at least from time of ignition of the heat generating mixture.

In one aspect, the expected parameter is a mathematical model of the expected fluid pressure and/or expected fluid flow at the upper location of the well as a function of time.

In one aspect, the method comprises the step of determining the expected parameter based on:

In one aspect, the generic expected parameter comprises measurements of parameters from one or more previous operations.

In one aspect, the generic expected parameter comprises measurements of parameters from one or more previous operations performed in a controlled environment.

In one aspect, the generic expected parameter comprises measurements from one or more previous operations performed in a controlled environment in the form of a test cell with a test environment similar to a real well environment.

The test environment may have a temperature and/or a pressure similar to a real well environment. The test environment may have a well design similar to a real well design. The well design of the test environment may be a down-scaled version of a real well design or a full-scale version of a real well design.

The term “real well” is here used to denote a generic well. Hence, the real well is not the well in which the thermite-based downhole well barrier is to be created in.

Hence, the generic expected parameter can be used as basis for determining the expected parameter for a number of different wells as long as some specific well parameters for the well in which the thermite-based downhole well barrier is to be created in, are known.

Alternatively, it is possible to perform one operation in a controlled environment for each well in which the thermite-based downhole well barrier is to be created in, where the well design and test environment are selected to be as close to the each well as possible. However, this will not be very efficient. In addition, at least some of the specific well parameters must be used. As the test cell typically has a height being much lower than the height of actual wells, and due to a possible reduced scale of the well design of the test environment, the specific well parameters for the actual well will still be necessary for converting the generic expected parameter to the expected parameter.

In one aspect, the parameter representative of pressure and/or fluid flow at an upper location of the well as a function of time is measured as a relative pressure and/or as a relative fluid flow as a function of time.

In one aspect, the upper location of the well is defined as the upper section of the well below the well head and/or the topside of the well. The topside of the of the well here includes the well head. The upper section of the well below the well head is a location at which sensors are not damaged by the heat from the heat generating process. For practical purposes, the upper location will typically be immediately below the well head, i.e. 0-10 meters below the well head and/or on the topside of the well, for example adjacent to the well head.

In one aspect, the first peak area is a positive peak, i.e. a pressure increase over time or a fluid flow increase over time.

In one aspect, the heat generating mixture comprises a first constituent and a second constituent, wherein the first constituent comprises bismuth oxide and wherein the second constituent comprises aluminum or an aluminum alloy. The heat generating process is often referred to as an exothermic process.

In one aspect, the method comprises the step of identifying the first peak area of the expected parameter.

It is assumed that the first peak area of the measured parameter is a result of gas produced in the initial phase of the heat generating process, i.e. during the reaction between the first constituent and the second constituent. As discussed above, the temperature may reach as high as 3000° C. in a relatively short period of time.

In one aspect, the method comprises the steps of:

In one aspect, the step of identifying the maximum points comprises:

It should be noted that a maximum point has an amplitude and a point of time.

In one aspect, the step of comparing the points in time comprises:

In one aspect, the predetermined time threshold is 0-20 seconds, preferably, the predetermined time threshold is 0-10 seconds.

In one aspect, the step of identifying the maximum points comprises:

In one aspect, the step of comparing the amplitudes comprises:

In one aspect, the step of identifying the first peak area of the measured parameter comprises:

In one aspect, the first time interval is 1-240 seconds measured from the time of ignition, preferably 10-240 seconds measured from the time of ignition, even more preferred between 10-120 seconds measured from the time of ignition.

In one aspect, the first time interval is dependent on the depth of the desired location in the well. Hence, by using the depth of the desired location in the well, the first time interval may be made shorter. Hence, if the first peak area of the measured parameter and/or the first peak area of the expected parameter are found by signal processing, a shorter time interval may reduce the signal processing time.

In one aspect, the amplitude for the maximum point within the first peak area of the expected parameter is a pressure increase of 120-150 Bar.

In one aspect, the time for the maximum point within the first peak area of the expected parameter is determining the first time interval.

In one aspect, the method comprises the steps of:

The initial maximum points may be defined to be within the first peak areas.

The expected parameter may be a continuous function. However, it should also be noted that the expected parameter may also be a discrete function. The expected parameter may be a plot of a data set. The expected parameter may also be represented as a set of time-dependent properties.

In one aspect, the method comprises the steps of: