Patent ID: 12222273

DETAILED DESCRIPTION

Embodiments of the present disclosure are described below in detail with reference to the accompanying figures. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the claimed subject matter. However, it will be apparent to one having ordinary skill in the art that the embodiments described may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

Embodiments disclosed herein relate generally to systems and methods for testing porosity evolution in a rock sample using a photothermal laser to target and heat selected material in the rock sample. The photothermal laser may be designed to emit a selected wavelength that corresponds to an absorption peak of the selected material in the rock sample, such that when the photothermal laser irradiates the rock sample, the selected material in the rock absorbs the laser emission and is heated.

By using a photothermal laser to heat selected material in a rock sample, material held in the rock's pores may be targeted and selectively heated without heating the surrounding rock matrix. For example, kerogen is a naturally occurring organic material that may be found in the pores of a source rock. Typical organic constituents of kerogen include algae and woody plant material. Depending on the type of kerogen, kerogen may go through a thermal maturation process that yields oil or gas. As kerogen is heated and goes through thermal maturation, kerogen may change in color (e.g., from yellow-orange to brown to black). According to embodiments of the present disclosure, by using a photothermal laser to selectively heat kerogen within a rock sample, the kerogen may undergo thermal maturation without adversely affecting other materials in the rock sample (e.g., clays), which may allow investigation of porosity evolution in the rock sample as a result of kerogen thermal maturation.

According to embodiments of the present disclosure, a testing device used for monitoring porosity evolution in a rock sample may include a photothermal laser that may selectively heat pore material in the rock sample. The testing device may also include monitoring equipment that may be used to monitor the porosity evolution in the rock sample as the pore material is selectively heated with the photothermal laser.

For example,FIG.1shows an example of a system100for testing a rock sample102that includes a testing device110according to embodiments of the present disclosure. The testing device110may include at least one photothermal laser120mounted inside a body112of the testing device110and positioned to be directed toward the rock sample102.

A photothermal laser120may be designed to emit a beam with a selected wavelength that may target and heat a specific material distinguished by color within the rock sample102. According to embodiments of the present disclosure, a photothermal laser120may be a diode laser, where an electrical current may be directed to a diode to create lasing conditions at the diode's junction. Recombination in the diode material may result in emission of radiation with a particular wavelength according to the diode material used. In other words, different diode material may emit radiation having different wavelengths. Thus, a photothermal laser120may be designed to emit a selected wavelength by selecting the corresponding diode material to emit the selected wavelength. For example, if a selected material in a rock sample102has a black color, which may absorb wavelengths ranging from 400-700 nm, a photothermal laser may be designed to emit a wavelength between 400-700 nm by selecting corresponding diode material to form the photothermal laser. When targeting selected material that has an absorption curve that overlaps with a color of non-selected material in the rock sample, the photothermal laser may be designed to emit a beam with a wavelength that corresponds to an absorption value for the color of the selected material and that does not correspond to an absorption value for the color of the non-selected material.

In some embodiments, more than one photothermal laser120may be provided, where each photothermal laser120may be designed to emit a different selected wavelength. By providing multiple photothermal lasers120with different emission wavelengths, multiple phases of organic material may be targeted for heating. This may allow, for example, for continuous thermal maturation of organic material within a rock sample.

The rock sample102may be held on a sample stand114provided inside the testing device body112. The sample stand114may include a stage, or platform, on which the rock sample102may be held. According to embodiments of the present disclosure, the sample stand114may be movable, e.g., using a motor115. For example, the sample stand114may be rotatable about a central axis116and/or may be axially movable up and down along the central axis116.

In some embodiments, a capping stand118may also be provided in the body112, where the capping stand118may be co-axially aligned with the sample stand114and axially spaced apart from the sample stand114. The capping stand118may be used to hold the rock sample112in place on the sample stand114, where the rock sample112may be sandwiched between the sample stand114and the capping stand118. In some embodiments, the capping stand118may be rotatable about the central axis116(e.g., using a separate motor117or the same motor115used to rotate the sample stand114), where the capping stand118may rotate in the same direction and at the same speed as the sample stand114to rotate a rock sample being held between the two stands. In some embodiments, the capping stand118may be axially movable along the central axis116(in addition to or alternately to being rotatable), where axial movement of the capping stand118may apply a load to the rock sample112, e.g., for providing uni-axial stress on the rock sample102and/or for holding the rock sample102in place during testing. In some embodiments, a rock sample102may be provided on a sample stand114in a testing device without a capping stand118.

As shown inFIG.1, the sample stand114and the capping stand118may extend into the interior of the testing device body112to hold a rock sample102inside the body112. In some embodiments, the testing device body112may be a framed structure, e.g., having one or more frames that support equipment of the testing device, where the interior of the body112may be open to the environment around the testing device. In some embodiments, the testing device body112may be an enclosed structure, e.g., having walls that are capable of fully enclosing the interior of the body112. When a testing device body112is an enclosed structure, the body112may include one or more removable walls that act as a lid (which may open and close to allow access inside the body112) or may include one or more other type of sealable port that may open and close to allow access inside the body112.

According to embodiments of the present disclosure, a photothermal laser120may be mounted directly, or indirectly, to a wall or a frame of the body112. In some embodiments, the photothermal laser120may be mounted on tracks113in the body112, where the photothermal laser120may be moved to different positions in the body112along the tracks113. The tracks113may extend axially along the testing device110(such that the photothermal laser120may be axially moved along the body112) and/or may extend circumferentially around the testing device110(such that the photothermal laser120may be moved circumferentially along the body112). In some embodiments, a photothermal laser120may be manually moved to different locations in the body112. In some embodiments, the photothermal laser120may be fixed in a single location along the testing device body112.

According to embodiments of the present disclosure, at least one of the sample stand114and the photothermal laser120may be axially movable within the body112, such that the sample stand114and the photothermal laser120are axially movable with respect to each other. Additionally, or alternatively, the sample stand114may be rotationally movable and/or the photothermal laser120may be circumferentially movable around the body112, such that the sample stand114and the photothermal laser120are rotationally movable with respect to each other.

By providing at least one of a movable sample stand114and a movable photothermal laser120, the rock sample102and the photothermal laser120may be movable with respect to each other during testing, which may allow the photothermal laser120to radiate multiple portions of the rock sample102. For example, the photothermal laser120and rock sample102may be axially moved with respect to each other to allow the photothermal laser120to radiate the entire axial length of the rock sample102. According to embodiments of the present disclosure, relative movement between the rock sample102and the photothermal laser120may be used to direct a beam from the photothermal laser120to contact the entire (or almost all of the) rock sample102. In such manner, the entire amount of the selected material in the rock sample102may be uniformly heated by the photothermal laser120. For example, in some embodiments, the rock sample102may be rotated and the photothermal laser120may be moved axially while the photothermal laser120directs a beam toward the rock sample102in order to uniformly heat selected material in all parts of the rock sample102. In some embodiments, the rock sample102may be rotated and moved axially while the photothermal laser120directs a beam toward the rock sample102from a stationary position in order to uniformly heat selected material in all parts of the rock sample102.

As selected material in the rock sample102is heated with the photothermal laser120, pressure may be applied to the rock sample102. In some embodiments, a pressure representative of a downhole pressure may be applied to simulate downhole conditions in a formation represented by the rock sample102. For example, a pressure of up to about 20,000 psi may be applied to the rock sample102while it is being irradiated with the photothermal laser120.

According to embodiments of the present disclosure, pressure may be applied to the rock sample102using a pressure unit provided with the testing device110. The type of pressure unit used may be selected based on the type of pressure applied to the rock sample102. For example, in the embodiment shown inFIG.1, the pressure unit may be formed by the combination of the sample stand114and the capping stand118, where at least one of the sample stand114and the capping stand118is axially movable to apply uniaxial stress (represented by arrows119) to a rock sample102sandwiched between the sample stand114and the capping stand118.

In other embodiments, a pressure unit may include a pressure vessel and/or a pressure pump to generate triaxial stress on the rock sample. For example,FIG.2shows an alternative embodiment of the testing device110including a pressure unit, where the pressure unit includes a pressure vessel105for applying triaxial stress on a rock sample. The pressure vessel105may include a sleeve106, a base107positioned at a lower end of the sleeve106, and a cap108positioned at an opposite, upper end of the sleeve106. A rock sample may be confined inside the pressure vessel105between the base107and cap108. Axial stress (represented by arrows119) may be applied in the axial direction, e.g., using a piston, and confining pressure (represented by arrows109) may be applied in the radial direction, e.g., using confining fluid, to a rock sample confined in the pressure vessel to provide triaxial stress pressure on the rock sample. The pressure vessel sleeve106may be made of a material that allows a photothermal laser and an imaging device to transmit through the sleeve.

In some embodiments, a pressure vessel may be selected from various types of high pressure, high temperature (HPHT) reactors for inducing different processes in a rock sample (e.g., in situ pyrolysis of organic matter in shale, decarbonation of limestone, and alkali-driven geopolymerization of aluminosilicates). As a first example, a reactor system may include an internally-heated pressure vessel with a maximum pressure rating of 34.5 MPa at 510° C. The reactor system may be a 1 L volume bolted closure autoclave heated by a 200 W ceramic refractory heater. Samples may be jacketed by annealed copper tubing to separate the pore fluid and confining pressures and thermally isolated by cylindrical alumina spacers on either end. As second example, a reactor system may include a standard pressure vessel (e.g., general purpose vessels sold by PARR Instrument Company such as their Series 4760 General Purpose Pressure Vessel) with an external heater selected for small batch reactions (including caustic solutions) at pressures and temperatures up to 20 MPa and 350° C., respectively.

According to embodiments of the present disclosure, various types of standard pressure vessels known to be used for rock measurements may be used in conjunction with testing devices (e.g., including a photothermal laser and scanner system) described herein. In some embodiments, standard pressure vessels may be used in conjunction with testing devices described herein without modifying the standard pressure vessel.

As selected material in the rock sample102is heated with the photothermal laser120, porosity evolution within the rock sample102may be monitored using one or more monitoring devices in the testing device110. For example, according to embodiments of the present disclosure, a testing device110may include one or more different types of sensors which may be used to monitor properties indicating porosity evolution in the rock sample102as it is targeted by the photothermal laser120.

In some embodiments, one or more sensors may be attached to the rock sample102to monitor characteristics of the rock sample102as it undergoes testing. For example, as shown inFIG.1, velocity and strain sensors104may be attached to the rock sample102to measure changing forces and deformation of the rock sample102during testing. Such measurements may be used to determine the effects of changing porosity in the rock sample102on the elastic properties of the rock as porous material is heated by the photothermal laser.

In some embodiments, one or more chemical sensors111may be provided in the testing device110to measure a chemical composition in the testing device110. For example, a chemical sensor111may be mounted on a wall or other support structure in the testing device110. In some embodiments, chemical sensors111may be used in combination with enclosed testing devices, where one or more chemical sensors111may be enclosed inside a testing device body112. Enclosing a chemical sensor111within a testing device110during testing of the rock sample102may improve detection of chemicals generated during the testing.

Different types of chemical sensors111may be used to detect different chemicals. For example, in embodiments where a kerogen pore material (e.g., type III kerogen material) is targeted and heated by the photothermal laser120, the kerogen may generate a hydrocarbon gas. When the hydrocarbon gas escapes the rock sample102, a chemical sensor111capable of detecting hydrocarbon gas may detect changing amounts of the hydrocarbon gas in the testing device environment released from the rock sample102. In such manner, the chemical sensor111may indicate gas formation from the rock sample102, which may be used in analysis of the porosity evolution in the rock sample102as it is targeted by the photothermal laser120.

Additionally, according to embodiments of the present disclosure, porosity evolution within the rock sample102may be monitored using one or more imaging devices. For example, according to embodiments of the present disclosure, a testing device110may include an imaging device, such as a computed tomographic (CT) imaging device (e.g., a conventional CT scanner, a micro-CT scanner, nano-CT scanner, or synchrotron CT scanner) to visualize rock-pore systems in a rock sample102. A CT scanner may be used to take measurements (e.g., x-ray measurements) around the rock sample102to produce different cross-sectional images corresponding to different slices of the rock sample102. The cross-sectional images may be layered together and processed to generate 3-dimensional (3D) volumes between the layers and form a digital model of the rock sample, which can reveal the internal features of the rock sample102. In some embodiments, for example, a micro-CT scan may provide a non-destructive technique for 3D imaging of the pore space in the rock sample102at a resolution of several microns.

For example, as shown inFIGS.1and2, a testing device110may include a micro-CT scanner130having an x-ray source132and at least one x-ray receiver134. The x-ray source132and x-ray receiver(s)134may be arranged around the testing device110in a position to take images of a rock sample102held on the sample stand114as selected material in the rock sample102is heated with the photothermal laser120. For example, an x-ray source132and an x-ray receiver134may be spaced apart from and positioned around opposite sides of the sample stand114and rock sample102. X-rays from the x-ray source132may be transmitted through the rock sample102and recorded by the x-ray receiver(s) as a 2-dimensional (2D) image (a CT scan). CT scans may be taken by the micro-CT scanner130as the x-ray source132rotates around the rock sample102, or as the rock sample102rotates within the source beam. For example, the x-ray source132and the x-ray receiver134may be rotatable around the sample stand, e.g., via a track system around a perimeter of the testing device body112. In such embodiments, the body112of the testing device may have a circumferential perimeter around which the micro-CT scanner130may be moved. By taking CT scans as the rock sample102and micro-CT scanner130are rotated relative to each other, a series of CT scans may be taken of part of or the entire rock sample102. Serial CT scans from the micro-CT scanner130may then be compiled together to construct a 3D digital model of the rock sample102.

Resolution of the generated 3D digital model may be, for example, on the millimeter to micron to sub-micron scale, depending on the CT device used. Petrophysical calculations, such as porosity and permeability, depend on, for example, the segmentation of pixels into rock vs. pore. Segmentation may be difficult if some of the pores are smaller than the resolution of the micro-CT scanner130. Bulk density of the rock sample102may be computed from x-ray attenuation coefficients, which is a characteristic of the rock material used to identify one or more rock material segments in the rock sample, and thus help in identifying the pore structure of the rock sample102.

Images taken by the imaging device may be sent to a computing system140for processing, as shown inFIG.1. Any combination of mobile, desktop, server, router, switch, embedded device, or other types of hardware may be used for the computing system140. For example, as shown inFIG.3, the computing system140may include one or more computer processors302, non-persistent storage304(e.g., volatile memory, such as random access memory (RAM), cache memory), persistent storage306(e.g., a hard disk, an optical drive such as a compact disk (CD) drive or digital versatile disk (DVD) drive, a flash memory, etc.), a communication interface312(e.g., Bluetooth interface, infrared interface, network interface, optical interface, etc.), and numerous other elements and functionalities.

The computer processor(s)302may be an integrated circuit for processing instructions. For example, the computer processor(s) may be one or more cores or micro-cores of a processor. The computing system140may also include one or more input devices310, such as a touchscreen, keyboard, mouse, microphone, touchpad, electronic pen, or any other type of input device.

The communication interface312may include an integrated circuit for connecting the computing system140to a network (not shown) (e.g., a local area network (LAN), a wide area network (WAN) such as the Internet, mobile network, or any other type of network) and/or to another device, such as another computing device.

Further, the computing system140may include one or more output devices308, such as a screen (e.g., a liquid crystal display (LCD), a plasma display, touchscreen, cathode ray tube (CRT) monitor, projector, or other display device), a printer, external storage, or any other output device. One or more of the output devices may be the same or different from the input device(s). The input and output device(s) may be locally or remotely connected to the computer processor(s)302, non-persistent storage304, and persistent storage306. Many different types of computing systems exist, and the aforementioned input and output device(s) may take other forms.

Referring again toFIG.1, a computing system140may be connected to one or more components of a testing device110, including, for example, testing components used to perform testing/apply testing parameters to a rock sample102and detecting components used to detect or sense resulting parameters from the testing.

For example, the computing system140may be connected to testing components, such as the photothermal laser120, a pressure unit, and/or a stand114,118. The computing system140may be connected to a controller of a testing component in order to control the testing component using the computing system140. For example, the computing system140may send instructions to a controller of the photothermal laser120to operate the photothermal laser120, including, for example, to control the position/orientation of the photothermal laser120and to control the frequency and duration of emitting a beam from the photothermal laser120. In some embodiments, the computing system140may be connected to a controller of a pressure unit to operate the pressure unit, including, for example, to control the amount of pressure applied to a rock sample and timing for when pressure is applied. For example, the computing system140may send instructions to a pressure unit controller to correspond operation of the pressure unit with the photothermal laser to apply pressure to a rock sample while being heated with the laser. In some embodiments, the computing system140may be connected to an operating component (e.g., a controller or motor) of a stand to operate the stand, including, for example, to rotate or axially move the stand (e.g., sample stand114and/or capping stand118).

By using a computing system140to operate testing components in a testing device110, testing may be done automatically and according to a preset program. For example, the computing system140may send instructions to the testing device110to concurrently apply a preselected pressure to a rock sample, emit a beam from a photothermal laser120on the rock sample, and move the rock sample (via rotational and/or axial movement of a stand holding the rock sample).

Additionally, the computing system140may be connected to one or more detecting components of the testing device110, such as sensors (e.g., chemical sensors111and/or velocity and strain sensors104), the micro-CT scanner130, and/or other imaging device provided in the testing device110. Data collected from one or more of the detecting components of a testing device110may be sent to the computing system140for processing. In some embodiments, the computing system140may send instructions for operation of a detecting component. For example, the computing system140may send instructions to a controller of the micro-CT scanner130to operate the micro-CT scanner130, including, for example, to control the position of the micro-CT scanner130relative to a rock sample held in the testing device110and timing for taking images of the rock sample as the micro-CT scanner130and rock sample are moved relative to each other.

In some embodiments, data collected from a detecting component may be used to make a decision in controlling a component in the testing device110. For example, when an image is taken by a micro-CT scanner130, the computing system140may send instructions to the micro-CT scanner130or a stand (e.g., sample stand114and capping stand118) to rotate before taking another image. In some embodiments, the computing system140may send instructions to the testing device110to reduce pressure applied to a rock sample102after receiving data from velocity and strain sensors104on a rock sample indicating a failure in the rock sample102.

Software instructions in the form of computer readable program code to perform embodiments of the disclosure may be stored, in whole or in part, temporarily or permanently, on a non-transitory computer readable medium such as a CD, DVD, storage device, a diskette, a tape, flash memory, physical memory, or any other computer readable storage medium. Specifically, the software instructions may correspond to computer readable program code that, when executed by a processor(s), is configured to perform one or more embodiments of the disclosure. For example, the computing system140may include software programs to perform methods disclosed herein, including processing images taken of a rock sample102in a testing device110and generating a 3D digital model of the rock sample102from images taken of the rock sample102.

Referring now toFIG.4,FIG.4shows an example of a method400according to embodiments of the present disclosure. One or more steps shown may be omitted or repeated. According to embodiments of the present disclosure, a computing system (e.g.,140inFIG.1) may be used to perform one or more steps of the method400using a testing device (e.g.,110inFIG.1orFIG.2).

As shown, the method400may include providing a rock sample on a stand in a testing device (step410). The rock sample may be a rock representative of a downhole formation, where the rock sample may include organic matter contained within pores of the rock. For example, the rock sample may be a shaley rock containing clay, cement, fluids, and organic matter (e.g., kerogen or other hydrocarbon material).

A photothermal laser may be provided in the testing device and oriented to emit a beam to the rock sample (step420). The photothermal laser may be designed to emit a beam with a selected wavelength that corresponds to an absorption peak of organic matter in the rock sample, such as kerogen.

The photothermal laser may irradiate the rock sample with the beam to selectively heat the organic matter within the rock sample (step430). In some embodiments, the rock sample may be rotated and/or moved axially as the rock sample is irradiated by the photothermal laser, such that the photothermal laser may irradiate all or most of the organic matter within the rock sample. By irradiating the rock sample with a beam having a wavelength that corresponds with an absorption peak of a selected material in the rock sample (e.g., a selected organic material), the selected material may be heated by the beam without heating other rock material (e.g., clays). For example, selective heating from a photothermal laser may target the darkest components in a rock sample such as kerogen to stimulate thermal evolution and hydrocarbon production without destroying clays or evaporating bounding water in the rock sample.

According to embodiments of the present disclosure, pressure may be applied to the rock sample while the rock sample is selectively heated by the photothermal laser. For example, a pressure that is within a range of a downhole pressure may be applied to the rock sample in order to simulate a downhole condition. Pressure may be applied to the rock sample using a pressure unit provided with the testing device.

The porosity of the rock sample may be monitored as the selected material (e.g., selected organic matter) is heated (step440). For example, chemical sensors may be provided in the testing device to sense chemical changes in the testing device as the selected material is heated. In some embodiments, changes in elastic properties of the rock sample may be measured as the selected material is heated using velocity and strain sensors positioned around the rock sample in the testing device.

According to embodiments of the present disclosure, monitoring the porosity of the rock sample as the selected material is heated may include taking images of the rock sample, for example, taking x-rays of the rock sample using a CT scanner. Image data may be used to generate a 3D digital model of the rock sample showing the porosity of the rock sample.

In contrast to rock testing devices conventionally used to characterize rock under elevated temperatures representative of downhole conditions, devices and systems according to embodiments may use a photothermal laser to selectively heat small portions of a rock sample rather than the entire rock sample. Using testing devices according to embodiments of the present disclosure, a photothermal laser may heat selected material within a rock sample without damaging other, non-selected material in the rock sample. Such devices and methods may be useful, for example, when testing clay-rich source rocks, where pyrolysis may be performed on the kerogen (from heating via a photothermal laser) without heating up the clay or damaging the water bounds they carry. Testing devices disclosed herein may also be equipped with sensors to detect any chemical changes and elastic properties in real-time, e.g., using chemical sensors, velocity, and strain sensors. Additionally, a CT scanner may be used to monitor the porosity evolution as a result of the increase in temperature from the photothermal laser, including, for example, porosity evolution from heating kerogen beyond the oil and gas windows.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.