Method of evaluating cement on the outside of a well casing

A method of logging a wellbore casing and an adjacent formation comprises moving a measurement tool inside a borehole of the casing, wherein the casing is filled with air. Concurrently with moving the measurement tool inside the borehole, the method comprises emitting radioactive energy at an initial energy level from a radiation source of the measurement tool, wherein the radioactive energy is directed toward a wall of the casing and along a travel path from the radiation source to one or more detectors of the measurement tool, measuring energy loss of the radioactive energy at the one or more detectors relative to the initial energy level, and detecting a cement property outside of the casing based on the measured energy loss.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to systems and methods for evaluating cement on the outside of a well casing. More particularly, the invention relates to methods for evaluating the presence, quality, and quantity of cement on the outside of a well casing which is filled with air, for example, the level of the top of the cement surrounding the outside of the well casing.

Description of Related Art

A typical installment of oil or gas well may include a well casing installed in the wellbore. Once the casing is placed in the wellbore, cement is pumped down the borehole of the casing and forced up the outside (backside) of the casing, forming a barrier between the casing and the surrounding earth. The barrier formed by the cement on the outside of the well casing protects the surrounding earth from contamination during service of the well and after the well is abandoned, as well as maintaining the casing in position. The cement barrier can be helpful to protect aquifers in the surrounding earth from the flow of contents from the well.

Title 25, Chapter 78, Subchapter D of the Pennsylvania Administrative Code governs the drilling, operation, and plugging of oil and gas wells in Pennsylvania and is incorporated by reference herein. In particular, 25 Pa. Code § 78.85 governs cement standards and § 78.102 governs the approval of inactive well status. Recently, Pennsylvania has adopted more stringent regulations requiring testing to determine the top of the cement level on the outside of the casing, as set forth in 25 Pa. Code §§ 78.83, 78.83b. Similar laws and regulations may exist in other states and/or jurisdictions. To ensure that the well is environmentally acceptable, the level of the cement on the outside of the casing is verified to be of sufficient height and quality to protect aquifers and other features of the surrounding earth.

Ideally, the cement is pumped into the bore of the casing until it reaches the ground surface of the well on the outside of the casing, such that the cement is visible from the surface. In this case, no special equipment or method is needed to verify the top of cement level. Oftentimes, however, the casing cement is not installed completely to the surface of the well, and, as such, the top of cement level is not visually verifiable. In order to locate the top of cement, specialized equipment and methods are employed to detect the presence or absence of cement on the outside of the casing from the bore of the casing. Typically, apparatuses, systems, and methods for this purpose include a measurement probe which is lowered into the casing and emits electromagnetic, sonic, or nuclear radiation which penetrates the casing. The probe then detects energy loss of the emitted radiation and converts the energy loss into a cement bond log (CBL), which may be analyzed to determine the top of cement level. Additionally, the CBL may be used to analyze qualitative properties of the cement on the outside of the casing.

Heretofore, a severe limitation of the apparatuses, systems, and methods for detecting cement on the outside of a well casing is that the measurement probes are only effective and accurate when used in homogeneous, stagnate liquids. Thus, prior to inserting the measurement probe into the casing, the casing had to be filled with such a medium, generally fresh water with minimum impurities. The necessity of filling a wellbore with liquid prior to inserting the probe adds significant time, cost, and safety concerns to the process of determining the top of cement level.

U.S. Patent Application Publication No. 2016/0053608 to Dowla et al. discloses systems and methods for measuring and/or detecting features of a well casing, such as a casing collar which connects two sections of the well casing. Dowla et al. discloses the use of a measurement tool lowered into a well casing, particularly during live well drilling. Dowla et al. discloses several means of feature detection and logging, including sonic, nuclear, gamma ray, photoelectric, and resistivity. However, Dowla et al. does not consider the use of radioactive logging in an air-filled well casing to determine the top of the cement level.

Radioactive logging using an air medium is known in the art for open bore wells—that is, wells which do not include a casing. However, as of yet, the use of radioactive logging in an air medium has not been adapted to wells which include a casing.

Determination of top of cement level, as well as the quality of the cement, as described above, is necessary not only in new well applications, but also in storage wells and wells which are being plugged and abandoned.

A need exists for systems and methods of determining the presence and quality of cement on the outside of a well casing independent of the borehole medium. Particularly, a need exists for determining the presence and quality of cement when the well casing medium is air.

SUMMARY OF THE INVENTION

In some examples, the present invention generally relates to a method of logging a wellbore casing and an adjacent formation, the method comprising moving a measurement tool inside a borehole of the casing, wherein the borehole is filled with air. Concurrently with moving the measurement tool inside the borehole, the method comprises emitting radioactive energy at an initial energy level from a radiation source of the measurement tool, wherein the radioactive energy is directed toward a wall of the casing and along a travel path from the radiation source to one or more detectors of the measurement tool, measuring energy loss of the radioactive energy at the one or more detectors relative to the initial energy level, and detecting a cement property outside of the casing based on the measured energy loss.

In some examples, detecting a cement property outside of the casing comprises transmitting the measured energy loss to a computing device; and generating, with at least one processor of the computing device, a log of the measured energy loss as a function of depth of the measurement tool in the wellbore.

In some examples, detecting a cement property outside of the casing comprises detecting the presence or absence of cement between the casing and the formation.

In some examples, detecting a cement property outside of the casing comprises detecting the quality of cement present between the casing and the formation.

In some examples, the radiation source comprises Cesium-137.

In some examples, the Cesium-137 has a Curie strength of 1.8 to 2.0 curie.

In some examples, the radioactive energy is a gamma ray.

In some examples, the gamma ray is emitted at an energy level of 660 kilo-electronvolts.

In some examples, moving the measurement tool inside the borehole copmrises lowering the measurement tool into the borehole to a predetermined depth with a caliper arm of the measurement tool retracted, extending the caliper arm to brace the measurement tool against the borehole, and raising the measurement tool from the predetermined depth out of the borehole.

In some examples, the measurement tool has a depth of measurement of up to 6 inches.

In some examples, the measurement tool has a vertical resolution of 10 inches.

The present invention also relates to a system for logging a wellbore casing and an adjacent formation of a wellbore, the system comprising a measurement tool configured to be moved inside a borehole of the casing. The measurement tool comprises a radiation source configured to emit radioactive energy at an initial energy level directed toward a wall of the casing and along a travel path, and one or more detectors configured to measure energy loss of the radioactive energy relative to the initial energy level and generate one or more measurement signals based on the measured energy loss. The one or more detectors are configured to measure energy loss when the wellbore is filled with air. The system further comprises a computing device configured to receive the one or more measurement signals, the computing device comprising at least one processor configured to convert the one or more measurement signals into a graphical log of the wellbore, and a wireline extending between the measurement tool and the computing device, the wireline configured to carry instructions from computing device to the measurement tool and to carry the one or more measurement signals from the measurement tool to the computing device.

In some examples, the radiation source comprises Cesium-137.

In some examples, the Cesium-137 has a Curie strength of 1.8 to 2.0 curie.

In some examples, the radioactive energy is a gamma ray.

In some examples, the gamma ray is emitted at an energy level of 660 kilo-electronvolts.

In some examples, the measurement tool configured to be moved inside the borehole of the casing by lowering the measurement tool into the borehole to a predetermined depth with a caliper arm of the measurement tool retracted, extending the caliper arm to brace the measurement tool against the borehole, and raising the measurement tool from the predetermined depth out of the borehole.

In some examples, the measurement tool has a depth of measurement of up to 6 inches.

In some examples, the measurement tool has a vertical resolution of 10 inches.

In some examples, the computing device is configured to detecting a cement property outside of the casing based on the one or more measurement signals.

These and other features and characteristics of the methods and systems for logging a wellbore casing and an adjacent formation will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification. It is to be expressly understand, however, that the drawings are for the purpose of illustration and description only. In the drawings, like reference numerals designate like components and steps unless noted to the contrary.

DESCRIPTION OF THE INVENTION

As used herein, the term “at least one of” is synonymous with “one or more of”. For example, the phrase “at least one of A, B, and C” means any one of A, B, and C, or any combination of any two or more of A, B, and C. For example, “at least one of A, B, and C” includes one or more of A alone; or one or more B alone; or one or more of C alone; or one or more of A and one or more of B; or one or more of A and one or more of C; or one or more of B and one or more of C; or one or more of all of A, B, and C. Similarly, as used herein, the term “at least two of” is synonymous with “two or more of”. For example, the phrase “at least two of D, E, and F” means any combination of any two or more of D, E, and F. For example, “at least two of D, E, and F” includes one or more of D and one or more of E; or one or more of D and one or more of F; or one or more of E and one or more of F; or one or more of all of D, E, and F.

As used herein, the terms “computer” and “computing device” may refer to one or more electronic devices that are configured to directly or indirectly communicate with or over one or more networks. The computing device may be a mobile device. As an example, a mobile device may include a cellular phone (e.g., a smartphone or standard cellular phone), a portable computer, a personal digital assistant (PDA), and/or other like devices. In other aspects, the computing device may be a desktop computer or other non-mobile computer. Furthermore, the term “computer” may refer to any computing device that includes the necessary components to receive, process, and output data and normally includes a display, a processor, a memory, an input device, and a network interface. An “application programming interface” (API) refers to computer code or other data sorted on a computer-readable medium that may be executed by a processor to facilitate the interaction between software components, such as a client-side front-end and/or server-side back-end for receiving data from the client. A “graphical user interface” or “GUI” refers to a generated display with which a user may interact, either directly or indirectly (e.g., through a keyboard, mouse, touchscreen etc.).

Referring now toFIG. 1, a typical wellbore, generally designated as 1000, for which the method of the present invention is adapted for use, comprises a well casing101extending vertically down the wellbore1000. A cement layer103is located between the outside110of the well casing101and the surrounding earth formation102. The cement layer103extends up the outside110of the well casing101and terminates at a top of cement (“TOC”)104. As may appreciated fromFIG. 1, the TOC104is not readily visible as it hidden between the well casing101and the surrounding earth formation102. The method of the present invention is directed to a method of determining the location of the TOC104using downhole measurement tool(s)2000(seeFIGS. 2-5) situated in the bore of the well casing101.

The bore of the well casing101may be filled with any suitable medium such as air, gas, brine water, or gas-cut fluids. Importantly, the method of the present invention is not reliant on the well casing101being filled with any particular medium in order to determine the location of the TOC104.

To determine the location of the TOC104, a measurement tool2000is inserted into the inside120of the bore of the well casing101. As may be appreciated fromFIGS. 2-5, the measurement tool2000comprises a body such as generally a cylindrical body201, which is attached to a lowering or raising mechanism, such as a wireline3000(seeFIG. 7), such that the measurement tool2000may be lowered into and retrieved from the bore of the well casing101. Optionally, the wireline3000may facilitate communication between the measurement tool2000and an operator5000and/or a computing device4000(seeFIG. 7) located at the surface of the wellbore1000. Alternatively, communication between the measurement tool2000and an operator5000and/or computing device4000can be wireless.

In some examples, the measurement tool2000further comprises a caliper arm202which is extendable and retractable from the body201. The caliper arm202is typically placed in the retracted position, shown inFIG. 3, for lowering into the well casing101. A skid206is located on the measurement tool2000opposite the caliper arm202. In the retracted position, friction between the measurement tool2000and the bore of the well casing101is reduced such the measurement tool2000may be smoothly lowered into the well casing101. The caliper arm202may be placed in the extended position, as shown inFIG. 4, for raising out of the well casing101. In particular, once the measurement tool2000is lowered to a predetermined maximum depth, the caliper arm202is extended to engage the inside120of the bore of the well casing101. This engagement also forces the skid206into contact with the inside120of the bore of the well casing101opposite the caliper arm202. Extension of the caliper arm202can be achieved via an instruction sent from the operator5000and/or computing device4000down the wireline3000, or wirelessly, to the measurement tool2000.

With continued reference toFIGS. 2-5, the measurement tool2000comprises a radiation source203configured to emit radioactive gamma rays toward the well casing101. In a particular configuration in which the wellbore medium is air, the radiation source may comprise, for example, Cesium-137 having a Curie strength of 1.8 to 2.0 curie. The gamma rays are emitted from the radiation source203at a predetermined energy level, for example 660 kilo-electronvolts. The measurement tool2000further comprises one or more detectors204,205. The one or more detectors204,205are positioned along the skid206of the measurement tool2000and are calibrated to measure radioactive energy present at the respective locations of the detectors204,205. In particular, the one or more detectors204,205measure the energy of the gamma rays emitted from the radiation source203after the gamma rays have penetrated the well casing101and the structure on the outside110of the well casing101. As the gamma rays penetrate the well casing101and the structure on the outside110of the well casing101, the gamma rays lose energy. The one or more detectors204,205are calibrated to measure the energy loss of the gamma rays at a predetermined depth perpendicular to the wall of the wellbore casing101. For example,FIGS. 3-4show a short space detector (SSD)204and a long space detector (LLS)205arranged at different locations along the skid206of the measurement tool2000and calibrated to measure at different depths D1, D2, respectively. Further, the spacing of the SSD204and the LLS205determines the vertical resolution of the measurement tool2000. A short gamma ray travel path P1corresponds to the energy loss measurement obtained by the SSD204, and a long gamma ray travel path P2corresponds to the energy loss measurement obtained by the LLS205. As may be appreciated fromFIGS. 3-4, the long gamma ray travel path P1may be longer than the short gamma ray travel path P2. In some examples, the depth of measurement is about 4 inches to about 8 inches, or approximately 6 inches. In some examples, the vertical resolution is about 6 inches to about 14 inches, or approximately 10 inches.

To communicate the energy loss measurements taken by the one or more detectors204,205, each of the one or more detectors204,205generates a measurement signal which is sent via the wireline3000, or wirelessly, to the computing device4000. At least one processor401of the computing device4000may convert the measurement signal generated by the one or more detectors204,205into a graphical or numerical representation of the energy loss at a given location within the wellbore1000. Measurements taken at sequential locations within the well casing101may be used to generate a log610of the wellbore1000as shown inFIG. 6, which may be presented on a GUI generated by the computing device4000. Utilizing the principle that the amount of energy lost from the gamma rays is a function of the material that the gamma ray is passing through, the location of the top of cement104can be identified by a change in the energy measured over the log610of the wellbore1000. Similarly, the location of any casing collars can be identified by a change in the energy measured over the log610of the wellbore1000.

Referring now toFIG. 7, a system diagram of the components necessary to carry out the method of the present invention comprises the measurement tool2000having the radiation source203and one or more detectors204,205. The measurement tool2000may be connected to one end of the wireline3000. Another end of the wireline3000may be connected to the computing device4000, which comprises at least one processor401. An operator5000may communicate through an interface402of the computing device4000. The wireline3000can facilitate communication between the measurement tool2000and the computing device4000and/or the operator5000. Particularly, the wireline3000can carry instructions from the computing device4000to the measurement tool2000, such as instructions to open the caliper arm202, instructions to close the caliper arm202, instructions to emit gamma rays from the radiation source203, and instructions for the one or more detectors204,205to generate a measurement signal. Additionally, the wireline3000can carry a measurement signal generated by the one or more detectors204,205to the computing device4000. Alternatively, the measurement tool2000may communicate with the computing device4000and/or the operator5000wirelessly, without communications being transmitted via the wireline3000.

The step diagram shown inFIG. 8illustrates an example of a method for evaluating cement on the outside110of a well casing101according to the present invention. At step801, the measurement tool2000is moved at a predetermined rate up or down the bore of the well casing101. The rate of movement of the measurement tool2000affects the time necessary to perform the method, and the accuracy of the results. In some non-limiting examples, the measurement tool2000is moved at a rate of about 1,200 feet per hour to about 3,600 feet per hour, or approximately 1,800 feet per hour, although the rate may be adjusted according the desired accuracy of measurement and imposed time constraints. If the measurement tool2000is being lowered, the caliper arm202is retracted. If the measurement tool2000is being raised, the caliper arm202is extended.

The remaining steps of the method occur concurrently with moving the measurement tool2000in the well casing101, and are as follows. At step802, radioactive energy, such as a gamma ray, is emitted from the radiation source203at a predetermined energy level towards a wall of the well casing101. The radioactive energy travels along one or more travel paths P1, P2through the well casing101and the surrounding formation, at which point the energy loss of the radioactive energy is measured by the one or more detectors204,205. At step803, the one or more detectors204,205each generate a measurement signal which is transmitted along the wireline3000, or wirelessly, to the computing device4000. At step804, the at least one processor401of the computing device4000converts the measurement signals into respective data points and generates a graphical or numerical log of the wellbore1000including all previously gathered data points. The log of the wellbore1000may be presented on a GUI of the computing device4000.

In some examples, such as shown inFIG. 8, the method comprises both lowering the measurement tool2000into the well casing101(step801) and raising the measurement tool2000from the well casing101(step805). In such examples, energy loss measurements along the height of the well casing101are taken twice—once during the lowering step801and again during the raising step805. At step806, the at least one processor401of the computing device4000may compare the measurements taken during the lowering step801with the measurements taken during the raising step805to verify the measurements and/or identify anomalous measurements. In other examples, only one of the lowering step801and the raising step805may be performed.

At step807, the location of a feature, such as the TOC104, of the wellbore1000is detected based on the generated graphical or numerical log. The feature of the wellbore1000may be detected either automatically by the at least one processor401of the computing device4000, or manually by the operator5000, by analyzing the measurement signals from the one or more detectors204,205. In some examples, such as shown in the log610ofFIG. 6, the TOC104may be identified by an increase in the amplitude of the measurement signals recorded in the graphical or numerical log610. In such examples, the amplitude of the measurement signals, based on the measured energy loss from the one or more detectors204,205, may be lower when the measurement tool2000is located at a height H within the well casing101where the cement layer103is present on the outside110of the well casing101. The amplitude of the measurement signals may increase when the measurement tool2000is located within the well casing101above the cement layer103. As the measurement tool2000is raised within the well casing101, the computing device4000or the operator5000may detect the TOC104by identifying the point at which the amplitude of the measurement signals increases, indicating that the cement layer103is no longer present on the outside110of the well casing101at the location of the measurement tool2000. Similarly, as the measurement tool2000is lowered within the well casing101, the computing device4000or the operator5000may detect the TOC104by identifying the height H at which the amplitude of the measurement signals decreases, indicating that the cement layer103is present on the outside110of the well casing101at the location of the measurement tool2000.

FIG. 9shows a diagram of example components of a device900. In some examples, the device900may correspond to one or more devices of the measurement tool2000and/or one or more devices of the computing device4000. In some aspects, the measurement tool2000and/or the computing device4000may each include at least one device900and/or at least one component of the device900. As shown inFIG. 9, the device900may include a bus902, a processor904, memory906, a storage component908, an input component910, an output component912, and a communication interface514.

The bus902may include a component that permits communication among the components of the device900. In some aspects, the processor904may be implemented in hardware, firmware, or a combination of hardware and software. For example, the processor904may include a processor (e.g., a central processing unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU), and/or the like), a microprocessor, a digital signal processor (DSP), and/or any processing component (e.g., a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), and/or the like), and/or the like, which can be programmed to perform a function. The memory906may include random access memory (RAM), read-only memory (ROM), and/or another type of dynamic or static storage device (e.g., flash memory, magnetic memory, optical memory, and/or the like) that stores information and/or instructions for use by the processor904.

The storage component908may store information and/or software related to the operation and use of the device900. For example, the storage component908may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, a solid state disk, and/or the like), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, a magnetic tape, and/or another type of computer-readable medium, along with a corresponding drive.

The input component910may include a component that permits the device900to receive information, such as via user input (e.g., a touch screen display, a keyboard, a keypad, a mouse, a button, a switch, a microphone, and/or the like). Additionally, or alternatively, the input component910may include a sensor for sensing information (e.g., a global positioning system (GPS) component, an accelerometer, a gyroscope, an actuator, a radiation sensor, and/or the like). The output component912may include a component that provides output information from the device900(e.g., a display, a speaker, one or more light-emitting diodes (LEDs), and/or the like). The input component910and/or the output component912may correspond to, be included in, or include the measurement tool2000and/or the computing device4000.

The communication interface914may include a transceiver-like component (e.g., a transceiver, a receiver and transmitter that are separate, and/or the like) that enables the device900to communicate with other devices, such as via a wired connection, a wireless connection, or a combination of wired and wireless connections. The communication interface914may permit the device900to receive information from another device and/or provide information to another device. For example, the communication interface914may include an Ethernet interface, an optical interface, a coaxial interface, an infrared interface, a radio frequency (RF) interface, a universal serial bus (USB) interface, a Wi-Fi® interface, a cellular network interface, and/or the like.

The device900may perform one or more processes described herein. The device900may perform these processes based on the processor904executing software instructions stored by a computer-readable medium, such as the memory906and/or the storage component908. A computer-readable medium (e.g., a non-transitory computer-readable medium) is defined herein as a non-transitory memory device. A memory device includes memory space located inside of a single physical storage device or memory space spread across multiple physical storage devices.

Software instructions may be read into the memory906and/or the storage component908from another computer-readable medium or from another device via the communication interface914. When executed, the software instructions stored in the memory906and/or the storage component908may cause the processor904to perform one or more processes described herein. Additionally, or alternatively, hardwired circuitry may be used in place of or in combination with the software instructions to perform one or more processes described herein. Thus, aspects described herein are not limited to any specific combination of hardware circuitry and software.

The number and arrangement of the components shown inFIG. 9are provided as an example. In some aspects, the device900may include additional components, fewer components, different components, or differently arranged components than those shown inFIG. 9. Additionally, or alternatively, a set of components (e.g., one or more components) of the device900may perform one or more functions described as being performed by another set of components of the device900.

While various examples of methods and systems for evaluating cement are provided in the foregoing description, those skilled in the art may make modifications and alterations to these examples without departing from the scope and spirit of the invention. For example, it is to be understood that this disclosure contemplates that, to the extent possible, one or more features of any example can be combined with one or more features of any other example. Accordingly, the foregoing description is intended to be illustrative rather than restrictive. The invention described hereinabove is defined by the appended claims and all changes to the invention that fall within the meaning and the range of equivalency of the claims are to be embraced within their scope.