Core holder for real-time measurement and visualization

A core holder for core testing includes a body having a cavity. A sleeve is disposed within the cavity. The sleeve defines a chamber to hold one or more core plugs. One or more fiber-optic sensors are disposed at a perimeter of the chamber. Each fiber-optic sensor senses a parameter related to flow of fluid through the chamber. A core testing system includes one or more light sources to provide light to each fiber-optic sensor and one or more light detectors to detect light from each fiber-optic sensor. A method of core testing may include injecting a fluid into one or more core plugs inside the chamber and measuring one or more parameters related to flow of fluid through the one or more core plugs.

BACKGROUND

Core testing is used in the oil and gas industry to investigate various properties of a reservoir, such as porosity, permeability, and fluid saturation. Before performing a core test, one or more core plugs have to be prepared. Typically, this involves taking a cylindrical rock sample from a side of an oil or gas well using a core bit. The rock sample is then cut into multiple pieces, each of which forms a core plug. To conduct a core flooding test, for example, a core plug is commonly placed inside a polymeric sleeve inside a pressurized core holder. The core plug may be saturated with oil and water to simulate real reservoir conditions. The temperature and pressure conditions in the core holder are set to mimic reservoir conditions. While the core plug is under pressure, fluid is pumped through the core plug. The pressure drop and flow rate across the core plug are measured and used to determine various flow properties of the core plug.

In conventional core holders, it is typically not possible to see what is happening inside the core holder in real time without use of complicated machines, such as an x-ray tomography machine. Moreover, conventional core holders do not generally allow for continuous real-time monitoring of parameters, such as temperature, across the core plug.

SUMMARY

A core holder for core testing includes a body having a cavity defined therein; a sleeve disposed within the cavity; a chamber defined within the sleeve, the chamber to hold at least one core plug; and at least one fiber-optic sensor disposed at a perimeter of the chamber, the at least one fiber-optic sensor to sense at least one parameter related to flow of fluid through the chamber. At least a portion of a wall of the body may be made of a transparent material to allow visual monitoring of a condition within the cavity. At least a portion of the sleeve may be made of a transparent material to allow visual monitoring of a condition with the chamber. The at least one fiber-optic sensor may include an optical fiber having a sensing region. The optical fiber may be carried by the sleeve. The at least one fiber-optic sensor may be a fiber-optic temperature sensor, a fiber-optic pressure sensor, or a fiber-optic pressure and temperature sensor. The core holder may include a seal member disposed within the sleeve and positioned to form a barrier between the at least one fiber-optic sensor and the chamber. The core holder may include a first plug disposed at an inlet end of the body. The first plug has a port to permit fluid communication with the cavity from an exterior of the core holder. The core holder may include a second plug disposed at an end of the sleeve proximate the inlet end of the body. The second plug may have a second port aligned for fluid communication with the first port. The core holder may include a plurality of fiber-optic sensors. Each fiber-optic sensor may include an optical fiber having a sensing region. The optical fibers of the plurality of optical fibers may be arranged in parallel on an inner surface of the sleeve. The core holder may include a plurality of fiber-optic sensor. Alternatively, the optical fibers of the plurality of fiber-optic sensors may be arranged to form a loop pattern on an inner surface of the sleeve. An annular space may be defined between the sleeve and the body to hold fluid around the sleeve. The core holder may include at least one port connected to feed fluid into the annular space.

A core testing system includes a core holder having a chamber to hold at least one core plug and at least one fiber-optic sensor disposed at a perimeter of the chamber to sense at least one parameter related to flow of fluid through the chamber; at least one light source connected to the at least one fiber-optic sensor; and at least one light detector connected to the at least one fiber-optic sensor. The core holder may include a body having cavity. The chamber may be defined within the cavity. At least a portion of the body of the core holder may be made of a transparent material. The core holder may include a sleeve disposed inside the cavity. The chamber may be defined within the sleeve. At least a portion of the sleeve may be made of a transparent material. The at least one fiber-optic sensor may be carried by the sleeve. The at least one fiber-optic sensor may be a fiber-optic temperature sensor, a fiber-optic pressure sensor, or a fiber-optic pressure and temperature sensor. The core holder may include a seal member disposed within the sleeve and positioned to form a barrier between the at least one fiber-optic sensor and the chamber. The core testing system may include a pump that is in fluid communication with the chamber.

A method of core testing includes placing at least one core plug within a chamber defined within a core holder; positioning at least one fiber-optic sensor within the core holder and at a perimeter of the chamber; injecting a fluid into the at least one core plug within the chamber; and measuring, with the at least one fiber-optic sensor, at least one parameter related to flow of the fluid through the at least one core plug. Measuring at least one parameter related to the flow of the fluid through the at least one core plug may include measuring changes in a temperature in an environment of the at least one core plug by the at least one fiber-optic sensor. Measuring at least one parameter related to the flow of the fluid through the at least one core plug may include measuring changes in pressure in an environment of the at least one core plug by the at least one fiber-optic sensor.

DETAILED DESCRIPTION

In the following detailed description, certain specific details are set forth in order to provide a thorough understanding of various disclosed implementations and embodiments. However, one skilled in the relevant art will recognize that implementations and embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, and so forth. In other instances, well known features or processes have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the implementations and embodiments. For the sake of continuity, and in the interest of conciseness, same or similar reference characters may be used for same or similar objects in multiple figures.

Embodiments disclosed herein relate to simulating flooding experiments in, for example, the oil and gas industry, to obtain fluid and flow properties. More specifically, embodiments disclosed herein relate to integrating the use of fiber optics technology with a core holder for simulating flooding experiments to determine fluid permeability and flow properties.

It is to be further understood that the various embodiments described herein may be used in various stages of core testing to analyze and measure core plug properties, such as simulating flooding experiments in the oil and gas industry to obtain fluid permeability and flow properties, chemical analysis, hydrocarbon saturation, grain density etc., and in other industries, such as construction and the study of geology. Flooding experiments may refer to core flood testing that may mimic reservoir conditions (i.e., pressure and temperature) on a core plug. For example, a pressure or flow of fluid may be applied across or through the core plug that corresponds to a similar pressure or flow experienced by rock in a reservoir. Initially, the core plug may be disposed in a simulated formation brine, oil, or combination of brine and oil at the start of the core flood test. Fluids, such as crude oil, simulated reservoir brine, drilling muds, acids, and/or other chemicals, may then be injected into the core holder while various measurements of the core and fluid are recorded. Core flood tests recorded measurements and results may then be used to guide mathematical models and extract critical simulation parameters for well operations.

FIGS.1-8show various views of a core holder100in accordance with one or more embodiments. Core holder100may hold one or more core plugs for testing. The term “core plug” will generally refer to a porous body in the general shape of a cylinder. In the oil and gas field, core plugs may be obtained from a rock sample taken from the side of a drilled oil or gas well using a core bit. For illustration purposes,FIGS.4,6, and7show a core plug102within core holder100. For completeness,FIG.8shows that multiple core plugs102of various lengths may be within core holder100in other implementations. For core testing, core holder100may be coupled to testing equipment (not shown). As an example, the testing equipment may include a pump that is operable to inject fluid into core plug(s)102within core holder100. The rate and pressure at which fluid is injected into core plug(s)102may be selected to simulate flooding of a reservoir. In addition, the testing equipment may include or be connected to a computer system (not shown) to store, calculate, and display results from various tests using core holder100.

Core holder100has a body104with an axial axis A (inFIGS.1-4). InFIGS.1-8, body104has a hollow cylindrical shape. However, body104is not limited to this shape. For example, body104may have a tubular shape with other types of cross-sections, such as oval cross-section or rectangular cross-section or square cross-section. As illustrated inFIG.3, body104has a wall106with length L and thickness T. Wall106extends from a first end surface104aof body104to a second end surface104bof body104. Wall106defines a cavity108to hold core plug(s)102. Length L of wall106may be selected based on a length (or lengths) of core plug(s)102(inFIGS.4,6,7, and8) to be disposed within core holder100for testing. For example, if a core plug of some given length is to be arranged inside core holder100, length L of wall106should be at least as long as the length of the core plug. In another example, if multiple core plugs are to be arranged in series inside core holder100, as shown inFIG.8, then length L should be long enough to accommodate the combined length of the multiple core plugs. Similarly, the diameter of cavity108(or inner diameter of wall106) may be selected based on the outer diameter of core plug(s)102to be disposed within core holder100for testing.

In one or more embodiments, wall106may be made from a transparent material to allow visual monitoring of the interior of core holder100. The material of wall106may be, for example, glass, plastic, gypsum plaster, or other transparent and high-temperature-resistant material. The material of wall106may be reinforced or strengthened. In some cases, a transparent window may be formed in wall106rather than forming the entire wall106with a transparent material. Transparency of at least a portion of wall106may allow visual monitoring of flow within cavity108and core plug(s)102during testing of core plug(s)102. For example, testing of core plug(s)102may involve applying heat to core plug(s)102. In this case, the effect of heat on core plug(s)102may be visually monitored from outside core holder100. The material and/or thickness T of wall106are preferably selected to allow wall106to withstand pressures and temperatures that would be encountered during testing of core plug(s)102.

Pressure taps105a,105bmay be formed in wall106. Pressure gauges (not shown) may be connected to pressure taps105a,105bto measure pressure within core holder100. In other cases, other sensors (not shown) may be embedded in wall106for other types of measurements within cavity108. These other sensors may include, for example, temperature sensors, which may allow measurement of temperatures at the boundaries of the core plug(s)102. The measured temperatures may be used to determine temperature across the core plug(s)102and used to adjust heat input to the system.

In one implementation, an inner core holder109(inFIGS.2-8) is disposed inside cavity108. Inner core holder109extends generally in the same direction as axial axis A of body104. The length of the inner core holder109along axial axis A may be selected to be shorter than length L of wall106of body104so that inner core holder109can be fully contained inside cavity108formed by wall106. Although one inner core holder109is shown within wall106, it is possible to have multiple inner core holders109in other implementations. In some cases, the multiple inner core holders109may be arranged in series inside cavity108. In this case, the combined length of the multiple core holders109is preferably shorter than length L of wall106of body104so that the multiple inner core holders can be fully contained inside cavity108.

In one implementation, inner core holder109includes a sleeve110having an inner surface110athat defines a chamber to hold one or more core plug(s)102. Sleeve110may be coaxial with wall106. Sleeve110may be made of a polymeric material or other conformable (or flexible) material. In some cases, the material of sleeve110may be waterproof. Examples of materials that may be used for sleeve110include, but are not limited to, fluorocarbon-based synthetic rubber, polyvinyl chloride (PVC), and flexible gypsum material. Sleeve110has a size and shape to hold one or more core plugs102. To allow visual monitoring of the core plug(s)102within sleeve110, sleeve110may be made of transparent material or have a transparent window. The material of sleeve110may be reinforced.

In one implementation, inner core holder109includes inner end plugs114a,114b(inFIGS.3,5,7, and8), which are disposed at opposite ends of sleeve110. Alternatively, it is possible to provide inner end plugs114a,114bas end caps. Inner end plugs114a,114binclude ports (e.g., through-holes)116a,116b(inFIGS.3,5,7, and8), respectively, to allow fluid communication with the interior of sleeve110and core plug(s)102.

Outer end plugs118a,118b(inFIGS.1,2,7, and8) may be disposed at opposite ends of body104of core holder100. Alternatively, it is possible to provide outer end plugs118a,118bas end caps. The end of body104where outer end plug118ais disposed may be the inlet end of core holder100, and the body104where outer end plug118ais disposed may be the outlet end. The terms “inlet” and “outlet” are relative to where fluid enters cavity108and where fluid exits cavity108, respectively. Outer end plugs118a,118bhave ports119a,119b, which may be aligned with ports116a,116b, respectively, in inner end plugs114a,114b. For core testing, a fluid source (not shown) may be connected to port119a, and a fluid drain (not shown) may be connected to port119b, which would allow fluid to be circulated through core plug(s)102within inner core holder109.

In one implementation, sleeve110(or inner core holder109) is radially spaced from inner surface106aof wall106such that an annular space112is formed between sleeve110(or inner core holder109) and wall106. Fluid may be supplied into annular space112to pressurize core holder100and support sleeve110within cavity108. Flow dynamics in annular space112may be studied to validate fluid behavior in many drilling activities. For example, while injecting a fluid into a formation, the pressure in the annulus is critical to designing certain injection schema. This can be simulated in core testing by structuring the fluid in annular space112to apply hydrostatic pressure around sleeve110at the same pressure value that would be expected during drilling activities. In some cases, wall106may include a first port (not shown) through which fluid can be supplied into annular space112and a second port (not shown) to allow air to escape from annular space112while filling annular space112with fluid. Alternatively, ports (121a,121binFIG.7) may be formed in outer end plugs118a,118bto allow annular space112to be filled with fluid.

In one implementation, inner core holder109includes or carries one or more fiber-optic sensors120(inFIGS.3-8). In one implementation, fiber-optic sensor(s)120are arranged within inner core holder109such that they are positioned at a perimeter of a chamber defined within inner core holder109to hold core plug(s)102. In general, each fiber-optic sensor120may be any fiber-optic sensor120capable of sensing and detecting a desired stimulus in an environment in which the sensor is disposed. In one example, at least one of fiber-optic sensors120may be a fiber-optic temperature sensor. In another example, at least one of fiber-optic sensors120may be a fiber-optic pressure sensor. In yet another example, at least one of fiber-optic sensors120may be a fiber-optic pressure and temperature sensor. In some implementations, an array of fiber-optic sensors120measuring the same stimulus may be carried by inner core holder109. In other implementations, an array of fiber-optic sensors120measuring different stimuli may be carried by inner core holder109.

Referring toFIG.7, as an example, fiber-optic sensor120may include an optical fiber122with a sensing region122a. Sensing region122amay be made of a material (or have a structure) that is sensitive to a desired stimulus in the environment (or chamber) defined within sleeve110. For example, sensing region122amay be sensitive to temperature or pressure or other desired stimulus. In some cases, sensing region122amay be sensitive to more than one stimuli, e.g., both temperature and pressure. Other stimuli that sensing region122amay be selectively sensitive to include, but are not limited to, pressure drop, fluid viscosity, fluid density, and acidity or alkalinity. In the illustrated example, optical fiber122is inserted in a ferrule124. In an example where fiber-optic sensor120is operating in a reflection mode, ferrule124may be connected to a light source126, e.g., a laser source, and light detector128through a connector130. In this example, light source126will generate light that is transmitted to sensing region122aof optical fiber122. The light will be modified by changes in sensing region122adue to interaction of sensing region122awith the environment. The modified light will be reflected back to light detector128through optical fiber122and connector130. In some implementations, end122bof optical fiber122may be shaped or include a coating material or include a lens function to back-reflect light into optical fiber122. Alternatively, as illustrated inFIG.9, fiber-optic sensor120may be configured to operate in a transmission mode, where the modified light from sensing region122ais detected by detector128through end122bof optical fiber122.

In one implementation, optical fiber(s)122of fiber-optic sensor(s)120may be carried by, e.g., attached to or embedded in, inner surface110aof sleeve110, which would place optical fiber(s)122at a perimeter of the chamber defined by inner surface110aof sleeve110. For illustrative purposes,FIG.10shows optical fibers122carried by inner surface110aof sleeve110. The number of optical fibers122(or number of fiber-optic sensors120) carried by inner surface110aof sleeve110may be determined by the desired resolution of the measurements. In one example, optical fibers122may be arranged in parallel and spaced-apart relation along a circumference of inner surface110aof sleeve, with a length of each optical fiber122oriented along a length of sleeve110or along axial axis A, as shown inFIG.10. In some implementations, optical fiber122of fiber-optic sensor120may be arranged to form a single loop pattern or multiple-loop pattern or spiral pattern on inner surface110a. The loop or spiral pattern allows greater coverage of the inner surface110awith a single continuous optical fiber.FIG.11shows an example of optical fiber122(or sensing region122aof optical fiber122) arranged to form a multiple-loop pattern. The multiple-loop pattern may continue along the entire circumference of inner surface110aor may be formed in just a portion of the circumference of inner surface110a. In the case of a spiral pattern, this may resemble forming a thread on inner surface110a. In other implementations, optical fibers122may be arranged to form a grid pattern on inner surface110a, as illustrated inFIG.12. The grid pattern may include some of the optical fibers122extending along a length of sleeve110and others of the optical fibers122extending along an inner circumference of sleeve110.

Fiber optic sensor(s)120provide core holder100with the capability to measure and monitor changes in various conditions within sleeve110, such as pressure and temperature, continuously on real-time basis while testing core plug(s)102. In some embodiments, measurements taken from fiber-optic sensor(s)120may provide useful diagnostic indicators for analysis of fluid flow within core plug(s)102and for identifying in-situ flow, pore connectivity, and other flow parameters on a real-time basis. In one example, fiber-optic sensor(s)120may be temperature sensors that monitor temperature across core plug102. Flow rate changes across core plug102may be inferred from the temperature measurements made by fiber-optic sensor(s)120.

Referring toFIG.13, inner core holder109may include a seal member134that is disposed between core plug(s)102and optical fiber(s)122of fiber optic sensor(s)120to prevent direct contact between optical fiber(s)122and core plug(s)102. Seal member134may have a generally cylindrical shape or other shape to hold one or more core plug(s)102. In this case, the chamber to hold core plug(s)102is now located within seal member134. Seal member134may be made of any suitable sealing material. Alternatively, optical fiber(s)122may be encapsulated in a protective sleeve or bag, such as a polymeric sleeve or bag, which would also serve the function of isolating optical fiber(s)122from core plug(s)102.

FIG.14shows an example core testing setup with core holder100. In the setup, core plug102is disposed inside inner core holder109, which is disposed inside core holder100. Core plug102may be a piece of a rock sample taken from a side of a drilled oil or gas well. The discharge end of a pump136is connected to port119ain outer end plug118a. Port119bin outer end plug118bmay be connected to a drain tank138. Fiber optic sensor(s)120are connected to light source126and light detector128. In addition, light detector128is connected to data acquisition system140, which may be in communication with a computer system142. Core testing may be initiated and controlled from an interface on computer system142.FIG.14shows, for example, that a controller143for pump136and a driver (not shown separately) for light source126may receive control signals from computer system142. Pressure gauges144a,144bmay be connected to (or inserted into) pressure taps105a,105b. Pressure gauges144a,144bmay be connected to data acquisition system140. Prior to conducting testing, annular space112may be filled with pressurized fluid.

To use the setup inFIG.14for core testing, fluid may be injected into core plug102by pump136. The fluid injection can be continuous over a desired measurement period. During this measurement period, the temperature of core plug102(or other stimulus in the environment of core plug102) can be monitored by fiber optic sensor(s)120. The sensing region122aof optical fiber122of fiber-optic sensor120will modulate light passing through optical fiber122as the temperature (or other stimulus) in the environment changes. Light detector128will detect light from optical fiber122and generate a signal that is representative of a characteristic of the detected light, e.g., the intensity of the detected light. Data acquisition system140receives the output of light detector128and may process the output. Computer system142may retrieve the output of light detector128(as well as other data such as output of pressure gauges144a,144b) from data acquisition system140and use the output in computation of various flow parameters related to core plug102.

Benefits of the core testing system using core holder100may include the capability to monitor changes in flow rate within the core plug, estimate water saturation within the core plug, monitor real-time saturation, pressure, and temperature within the core plug, monitor preferred path of water, oil, and gases through the core plug, help in perforation design, provide better estimation for permeability continuous profile, and provide better assessment for enhanced oil recovery (EOR) process and water shut-off jobs. Water saturation can be estimated via measuring the weight of the core plug and the volume of liquid injected into the core plug and produced (i.e., conduct volumetric analysis and material balance of initial and final conditions). This can be supported by sensing changes in pressure drop across the core plug. If necessary, the system can be equipped with advanced logging techniques that can measure resistivity and calculate water saturation using Archie equation. Nuclear magnetic resonance (NMR) is also one of the common logging techniques that can be deployed with the system to measure saturations, measure permeability/porosity profiles, and capture real-time fluid movements inside the core plug.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate that other embodiments can be devised that do not depart from the scope of the invention as described herein. Accordingly, the scope of the invention should be limited only by the accompanying claims.