Patent ID: 12210133

DETAILED DESCRIPTION

The present disclosure will be described more fully with reference to the accompanying drawings, which illustrate embodiments of the disclosure. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

Embodiments of the disclosure are directed to a determination of a continuous oil density log for a hydrocarbon reservoir accessible via well drilling into the formation bearing the reservoir. Various logging operations may be conducted in the well to generate different logs that characterize the reservoir. The logging operations may generate a carbon-oxygen ratio (C/O) log, a water saturation log, and a porosity log. A continuous oil density log may be determined using the C/O log, the water saturation log, the porosity log, and carbon and oxygen density values of the rock matrix and pore fluids. The continuous oil density log may be used in further characterization and development of the hydrocarbon reservoir, such as well completion, reservoir development (for example, drilling additional wells or extending existing wells), and production optimization.

FIG.1is a diagram that illustrates a well environment100in accordance with one or more embodiments. In the illustrated embodiment, the well environment100includes a reservoir (“reservoir”)102located in a subsurface formation (“formation”)104, and a well system (“well”)106.

The formation104may include a porous or fractured rock formation that resides underground, beneath the Earth's surface (“surface”)108. The reservoir102may be a hydrocarbon reservoir, and the well106may be a hydrocarbon well, such as an oil well. In the case of the well106being a hydrocarbon well, the reservoir102may be a hydrocarbon reservoir defined by a portion of the formation104that contains (or that is determined to contain or expected to contain) a subsurface pool of hydrocarbons, such as oil and gas, coexist with formation connate water. The formation104and the reservoir102may each include different layers of rock having varying characteristics, such as varying degrees of lithology, permeability, porosity, and fluid saturations. In the case of the well106being operated as a production well, the well106may facilitate the extraction of hydrocarbons (or “production”) from the reservoir102. In the case of the well106being operated as an injection well, the well106may facilitate the injection of substances, such as gas or water, into the reservoir102. In the case of the well106being operated as a monitoring well, the well106may facilitate the monitoring of various characteristics of the formation104or the reservoir102.

The well106may include a wellbore110and a well control system (“control system”)112. The control system112may control various operations of the well106, such as well drilling operations, well completion operations, well production operations, or well and formation monitoring operations. In some embodiments, the control system112includes a computer system that is the same as or similar to that of the computer system400described with regard toFIG.4.

The wellbore110(or “borehole”) may include a bored hole that extends from the surface108into a target zone of the formation104, such as the reservoir102. An upper end of the wellbore110, at or near the surface108, may be referred to as the “up-hole” end of the wellbore110. A lower end of the wellbore110, terminating in the formation104, may be referred to as the “downhole” end of the wellbore110. The wellbore110may be created, for example, by a drill bit boring through the formation104and the reservoir102. The wellbore110may provide for the circulation of drilling fluids during drilling operations, the flow of hydrocarbons (e.g., oil and gas) from the reservoir102to the surface108during production operations, the injection of substances (e.g., water) into the formation104or the reservoir102during injection operations, or the communication of monitoring devices (e.g., logging tools) into the formation104or the reservoir102during monitoring operations (e.g., during shut-in or flow well logging operations). In some embodiments, the wellbore110includes cased (“cased hole”) or uncased (or “openhole”) portions. A cased portion may include a portion of the wellbore110lined with casing (e.g., the up-hole end of the wellbore110may be lined with casing pipe which is cemented with the formation). An uncased portion may include a portion of the wellbore110that is not lined with casing (e.g., the openhole, down-hole end of the wellbore110).

In some embodiments, well logging operations are conducted to measure and obtain characteristics of the portions of the formation104surrounding the wellbore110. During a well logging operation, a logging tool114(e.g., including a measurement device) may be lowered into the wellbore110and be operated to measure characteristics of the formation104surrounding the wellbore110as it is moved along a length (or “interval”) of the wellbore110. The characteristics of the formation104may include physical properties of the formation104surrounding the wellbore110. The depth of measurement (or “investigation”) into the formation104(e.g., the distance from the walls of the wellbore110into the formation104for which measurements are acquired) may vary based on the type and parameters of the logging operation. In some instances, the measurements are recorded in a corresponding well log that provides a mapping of the measurements (or values determined therefrom) versus depth in the wellbore110. In some embodiments, the well logging operations for the well106are controlled by the control system112or another operator of the well106.

In some embodiments, a pulsed neutron (PN) logging operation is conducted to generate a C/O log116that indicates C/O characteristics of the formation104, such as carbon-to-oxygen yield ratio (Yc/Yo), as a function of depth in the wellbore110. Pulsed neutron (PN) logging operations typically measure gamma rays generated by absorption of neutrons produced by a neutron source in the surrounding reservoir. A PN C/O logging operation may employ gamma ray spectroscopy measurements to directly sense the presence of carbon atoms in oil and oxygen atoms associated with water. In some instances, C/O logs are derived using gamma ray inelastic spectrometry, for example, based on measurements acquired using a PN logging tool.

The PN logging of the well106may include moving a PN logging tool114aalong a length of the wellbore110to obtain C/O logging data that is used to generate a corresponding C/O log116for the well106. The C/O log116may include mapping of carbon-to-oxygen yield ratio (Yc/Yo) versus depth across a length (or “interval”) of the wellbore110. The C/O log116may be continuous in that it provides a continuous record of values of carbon-to-oxygen yield ratio (Yc/Yo) across the length of the wellbore110.

In some embodiments, a water saturation log118may also be determined. In some embodiments, the water saturation log118is determined using a PN logging operation, by using a “sigma” log from the PN logging data. The sigma log reflects the effectiveness of a formation for capturing thermal neutrons; a higher sigma value indicates greater water saturation and a lower sigma value indicates less water saturation. In some embodiments, water saturation may be determined using the relationship between water saturation (Sw), porosity (ϕ) of the formation rock, and sigma log values. The water saturation log may be continuous in that it provides a continuous record of water saturation across the length of the wellbore110.

In other embodiments, the water saturation log118may be determined by an openhole resistivity, a cased hole resistivity, or dielectric constant logging operation that provides measurements used to determine the water saturation log. The resistivity logging of the well106may include moving a resistivity logging tool114balong a length of an openhole or cased hole portion of the wellbore110to obtain resistivity logging data that is used to generate a corresponding resistivity log for the well106. Resistivity logging measures the electrical resistivity of rock or sediment in and around a borehole. As such, resistivity indicates how strongly the formation (rock and fluids) opposes the flow of electrical current, and can be indicative of the porosity of the formation and the presence of hydrocarbons. For example, resistivity may be relatively low for a formation that has high porosity and a large amount of water, and resistivity may be relatively high for a formation that has low porosity or contains a large amount of hydrocarbons. In some embodiments, water saturation may be determined using the relationship between in-situ electrical resistivity (R) of a porous rock to its porosity (ϕ) and water saturation (Sw) known as Archie's law. In other embodiments, water saturation may be determined from resistivity using additional or alternative techniques. Dielectric constant logging may measure the dielectric permittivity of formation-contained water to determine the water saturation.

In some embodiments, other logging operations, such as nuclear magnetic resonance (NMR) logging, may be performed. The NMR logging tool may generate a magnetic field and pulsed radio frequency (RF) energy, and may collect corresponding NMR data that includes measurements of the resulting induced magnet moment of hydrogen nuclei (protons) contained within the fluid-filled pore space of porous media (e.g., rocks of the formation104) surrounding the wellbore110. In some embodiments, the NMR logging data may be used to generate viscosity data (e.g., including estimates varying values of viscosity (μ) across along a length (or “interval”) of the wellbore110) and a corresponding viscosity log120that includes a mapping of viscosity (μ) versus depth across the length of the wellbore110. The viscosity log120may be continuous in that it provides a continuous record of values of viscosity (μ) across the length of the wellbore110.

A porosity log122may also be generated. In some embodiments, the porosity log118may be generated from NMR logging. In other embodiments, the porosity log118may be generated using other techniques and tools, such as bulk density logging, compensated neutron-porosity (CNL) logging, or the combination of density and neutron-porosity logging. The porosity log may be continuous in that it provides a continuous record of values of porosity across the depth of the wellbore110.

In some embodiments, the control system112stores, or otherwise has access to, well data124. The well data124may include data that is indicative of various characteristics of the well106. The well data124may include, for example, logs for the well106(e.g., the C/O log116, the viscosity log120, or other logs) or other information regarding characteristics of the rock and fluids of the formation104, such as determined or estimated properties of the formation104or the reservoir102. In some embodiments, the control system112determines a continuous oil density log126for the well106based on the C/O log116, the water saturation log118, and the porosity log122for the well106.

In some embodiments, determination of a continuous oil density log for the well106includes the following: (1) conducting logging operations to obtain C/O, water saturation and porosity log data, including: (a) conducting a PN logging operation to obtain the C/O log138(which, for example, defines values of carbon and oxygen yields Yc/Yoof the formation104as a function of depth within the wellbore120), (b) conducting a resistivity logging operation or a PN logging operation to obtain the water saturation log118(which defines values of water saturation as a function of depth within the wellbore120); and (c) conducting a porosity logging operation to obtain the porosity log142(which defines values of porosity) of the formation104as a function of depth within the wellbore120); (2) obtaining carbon and oxygen density values for the reservoir rocks and fluids in the formation; and (3) determining, based on the C/O log138, the water saturation log, and the porosity log, the continuous oil density log126that defines in-situ values of oil density (ρo) as a function of depth within the wellbore120as discussed infra.

The fundamental physical relationship used in C/O logging is based on a mass balance of atomic carbon and oxygen from various sources in the formation. For a formation saturated with oil (o) and water (w) without a borehole, the following Equation can be determined:

YcYo=Vo⁢nc,o+Vl⁢s⁢nc,lsVw⁢no,w+Vl⁢s⁢no,ls+Vs⁢s⁢no,s⁢s=ϕ⁢So⁢nc,o+Vl⁢s⁢nc,lsϕ⁢Sw⁢no,w+Vl⁢s⁢no,ls+Vs⁢s⁢no,ss(1)

Where:Ycand Yoare total carbon and oxygen elemental yields, respectively. Yc/Yomay be a measured C/O ratio (e.g., a ratio of carbon and oxygen (C/O) elemental yields for the given depth), which is regularly acquired, repeatedly, periodically, after the well was drilled to monitor the performance of the reservoir penetrated by the well;nc,ois the atomic carbon density in oil (or oil carbon density or “OCD”), which may be constant or variable from depth to depth for the reservoir or well;nc,lsis the atomic carbon density in limestone (representing carbonate rock matrix), which may be constant for the reservoir or well;no,w, no,lsand no,ssare oxygen densities of water, limestone (representing carbonate rocks), and sandstone, respectively, which may be constants for the reservoir or well;Vlsand Vssare volume fractions of limestone (representing carbonate rocks) and sandstone, respectively, which may be measured values determined by way of an openhole logging or cased hole PN logging operations (e.g., measured values for given depth defined in well data124for the well106based on loggings of the well106);Voand Vw, are volume fractions of oil and water, respectively;Soand Sware saturations of oil and water, respectively (e.g., determined values of oil and water saturation for the given depth), where So+Sw=1; andϕ is the fractional porosity, which is typically a measured value determined by way of an openhole logging operation soon after the well is drilled (e.g., a value of porosity for a given depth determined from logs of bulk density, neutron porosity, or NMR based on loggings of the well106).

Oil saturation So, which is 1−Sw, may be inverted from Equation 1 to derive the following:

So=f⁡(YcYo,ϕ,Vls,Vss,no,w,no,l⁢s,no,ss,nc,l⁢s,nc,o)(2)

In Equation 2, for a reservoir interval with porosity and lithology volumes Vlsand Vss, the following rock and fluid properties can be considered constants; nc,ls, no,ls, and no,ss. Additionally, although the oxygen density of water no,wmay slightly change with water salinity, the salinity effect is minimal; thus, in some embodiments, no,wmay be assumed to be a constant. Carbon and oxygen atomic number density per volume values commonly found in reservoir rocks and fluids are summarized below in Table 1:

TABLE 1CARBON AND OXYGEN DENSITY VALUESIN RESERVOIR ROCKS AND FLUIDSnc, ocarbon density in oil(5.02 × 1022)ρo/(1 + R/12)nc, lscarbon density in limestone1.62 × 1022no, woxygen density in fresh water3.33 × 1022no, ssoxygen density in sandstone5.30 × 1022no, lsoxygen density in limestone4.86 × 1022nca, lscalcium density in limestone1.63 × 1022nsi, sssilicon density in sandstone2.66 × 1022
Where R is the ratio of hydrogen to carbon (H/C) and ρois the oil density.

As mentioned supra, most of the properties in Table 1 may be assumed to be invariant. However, the carbon density in oil may vary due to the compressibility of oil and its structural variability caused by reservoir fluid geodynamics. OCD may be expressed as a function of oil density (ρo) and the ratio of hydrogen to carbon (R), as shown in Equation 3:

nc,o=6.0⁢2⁢3×1⁢02⁢3⁢ρ⁢o1⁢2+R(3)

The hydrogen to carbon ratio (R) in oil may vary independently from oil density and may affect the carbon density by volume of the oil nc,o; as such, the variation in R may not have a significant impact on the saturation calculation as compared to oil density.

Equations 2 and 3 may be solved to derive the continuation oil density (ρo) log across a carbonate reservoir by using the water saturation (Sw) determined from another measurement such as openhole resistivity log or PN log, as follows:

nc,o=YcY0⁢(∅⁢Sw⁢no,w+Vl⁢s⁢no,ls)-Vl⁢s⁢nc,ls∅⁢So(4)6.0⁢2⁢3*1⁢02⁢3(1⁢2+R)⁢ρo=YcY0⁢(∅⁢Sw⁢no,w+Vl⁢s⁢no,ls)-Vl⁢s⁢nc,ls∅⁢So(5)ρo=1⁢2+R6.0⁢2⁢3*1⁢02⁢3⁢YcY0⁢(∅⁢Sw⁢no,w+Vl⁢s⁢no,ls)-Vl⁢s⁢nc,ls∅⁢So(6)

Equation 6 was tested across a reservoir known for its vertical variation in oil properties. For best fit results, a number of iterations were performed with Equation 6 to derive the following, assuming R=1:

ρo=2.1⁢6×(YcY0⁢(∅⁢Sw⁢no,w+Vl⁢s⁢no,ls)-Vl⁢s⁢nc,ls)1⁢02⁢3⁢∅⁢So(7)

Equation 7 was used across an example reservoir to determine a continuous oil density log.FIG.2depicts a composite log200that includes the example continuous oil density log determined from the example reservoir in accordance with an embodiment of the present disclosure.FIG.2includes the following logs: Fluid volumetrics based upon openhole triple combo logs of bulk density, neutron porosity, and resistivity, integrated with NMR data (track202), where the black color represents a heavy oil component and the light green color represents a light oil component; NMR-based viscosity log (track204); resistivity log (track206); and oil density log (track208).

The oil density log (track208) ofFIG.2includes an NMR-based empirical oil density log210in red and an oil density log212in blue that was determined according to the techniques of the present disclosure. The oil density log (track208) also depicts the available PVT sample point214at a depth of 9735 feet. As shown in this track, the oil density log212derived from the techniques of the disclosure as an input exhibits a significant match to the NMR-based empirical oil density log210across the lighter oil fraction zones of the reservoir, yet exhibits superior and more accurate results across the heavier and more viscous oil fraction zones (track204) towards the bottom of the reservoir, representing a significantly better correlation with the NMR-based viscosity log (track204).

FIG.3is a flowchart that illustrates a process300for determining a continuous oil density log and developing a hydrocarbon reservoir based on the continuous oil density log in accordance with an embodiment of the disclosure. In the context of the well106, the operations of the process300may be performed, for example, by the well control system112or another operator of the well106. A processing module of the well control system112may perform one or more of the data processing operations described, such as those directed to determining the continuous oil density log126for the well106. A well operator, such as a control module of the well control system112or well personnel, may operate the well106(or other wells in the formation104) based on the characteristics of the formation104, including those identified in the continuous oil density log126. For example, an operator may operate the well106(or other wells in the reservoir102), or otherwise develop the reservoir102, based on the values of oil density (ρo) of the continuous oil density log126.

As shown inFIG.3, the process300includes conducting logging operations to generate a C/O log, a water saturation log, and a porosity log for a well in a hydrocarbon reservoir (block302). This may include, for example, conducting PN logging of the well106to generate the C/O log for a depth interval of the well, a porosity logging of the well106to generate the porosity log for the depth interval of the well106, and conducting resistivity logging or PN logging of the well106to generate the water saturation log for the depth interval of the well106.

The process300further includes obtaining carbon and oxygen density values for the reservoir rock and fluids (block304). As discussed supra, certain carbon and oxygen density values may be assumed to constant and may use the values described in Table 1.

Next, a continuous oil density log for a well may be determined using C/O log, water saturation log, and other parameters (block306), as described in Equation 7. For example, the continuous oil density log may include a record of the determined values of oil density (ρo) for the depths. For example, the oil density (ρo) for each of the depths of 1000 m, 1001 m, 1002 m and so forth in a wellbore may be determined.

As also shown inFIG.3, the process300may include developing a reservoir based on the continuous oil density log for the well (block308). For example, this may include developing the reservoir based on the determined oil density (ρo) values as various identified depths in the formation. In some embodiments, developing a reservoir includes undertaking operations, such as drilling a well, controlling well drilling operations, plugging back a well, re-perforating a well, controlling well production rates and pressure (i.e., production optimization), controlling well injection rates, injection fluid type, injection pressures, and so forth. For example, operating parameters for a well, such as injection rates or pressures (or production rates or pressures), may be determined based on the oil density (ρo) values of the determined continuous oil density log, and the well may be controlled to operate according to the parameters. For example, the well may be operated to inject fluid into the reservoir at certain injection rates, depths, or pressures, or the well may be operated to produce hydrocarbons from the reservoir102at certain productions rates or pressures. In some embodiments, the continuous oil density log may be provided as an input to petrophysical, geological, and reservoir simulation models to capture the changes in oil properties and enable the generation of more accurate results.

Advantageously, embodiments of the disclosure provide improved accuracy and precision of an oil density log, while providing a potentially deeper depth of investigation into a formation as compared to NMR and PN log measurements and avoiding the uncertainty inherent in NMR logging-based empirical oil density determinations. In contrast to NMR logging, the continuous oil density log determined by the embodiments of the disclosure is more representative of the true formation fluid properties due to the nature of the variables used in the determination and is not affected by the near wellbore logging environment.

FIG.4depicts components of an example computer system400in accordance with an embodiment of the disclosure. The example computer system400may represent a part of or be included with the well control system100discussed supra. In some embodiments, the example computer system400may be in communication with other components of a system for obtaining measurements from a well accessing a hydrocarbon-bearing reservoir. Such other components may include, for example, logging-while-drilling (LWD) systems, measurement-while-drilling (MWD) systems, and other systems that acquire information about hydrocarbon resources. As will be appreciated, such systems may use downhole tools, downhole sensors, drilling components, and other components for acquiring information about subsurface hydrocarbon resources.

As shown inFIG.4, the example computer system400may include a processor402, a memory404, a display406, and a network interface408that may be in communication with a network410. It should be appreciated that the example computer system400may include other components that are omitted for clarity. In some embodiments, example computer system400may include or be a part of a computer cluster, cloud-computing system, a data center, a server rack or other server enclosure, a server, a virtual server, a desktop computer, a laptop computer, a tablet computer, or the like. In some embodiments, the example computer system400is not a part or does not have access to additional computing resources of a computer cluster, cloud computing system, etc., and may be used on-site at a remote wellsite for example.

The processor402(as used the disclosure, the term “processor” encompasses microprocessors) may include one or more processors having the capability to receive and process hydrocarbon resources data, such as the data described in the disclosure. In some embodiments, the processor402may include an application-specific integrated circuit (ASIC). In some embodiments, the processor402may include a reduced instruction set (RISC) processor. Additionally, the processor402may include a single-core processors and multicore processors and may include graphics processors. Multiple processors may be employed to provide for parallel or sequential execution of one or more of the techniques described in the disclosure. The processor402may receive instructions and data from a memory (for example, memory404).

The memory404(which may include one or more tangible non-transitory computer readable storage mediums) may include volatile memory, such as random access memory (RAM), and non-volatile memory, such as ROM, flash memory, a hard drive, any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The memory404may be accessible by the processor402. The memory404may store executable computer code. The executable computer code may include computer program instructions for implementing one or more techniques described in the disclosure. For example, the executable computer code may include continuous oil density log instructions412to implement embodiments of the present disclosure. In some embodiments, the continuous oil density log instructions412may implement one or more elements of process300described above and illustrated inFIG.3.

In some embodiments, the continuous oil density log instructions412may receive, as input, data from various sources. Such sources may be or include logs from logging operations, such as C/O logs and water saturation logs. In some embodiments, example computer system400may access the data via the network410. In some embodiments, the data may be manually input to the example computer system400.

As described herein, the continuous oil density log instructions412may produce, as output a continuous oil density log414. The log414may be stored in the memory404and, as shown inFIG.4, may be displayed on the display406, such as in a graphical user interface.

The display406may include a cathode ray tube (CRT) display, liquid crystal display (LCD), an organic light emitting diode (OLED) display, or other suitable display. The display406may display a user interface (for example, a graphical user interface) that may display information received from the example computer system400. In accordance with some embodiments, the display406may be a touch screen and may include or be provided with touch sensitive elements through which a user may interact with the user interface. In some embodiments, the display406may display the log414in accordance with the techniques described herein.

The network interface408may provide for communication between the example computer system400and other devices and systems via the network410. The network interface408may include a wired network interface card (NIC), a wireless (e.g., radio frequency) network interface card, or combination thereof. The network interface408may include circuitry for receiving and sending signals to and from communications networks, such as an antenna system, an RF transceiver, an amplifier, a tuner, an oscillator, a digital signal processor, and so forth. The network interface408may communicate with networks, such as the Internet, an intranet, a wide area network (WAN), a local area network (LAN), a metropolitan area network (MAN) or other networks. Communication over networks may use suitable standards, protocols, and technologies, such as Ethernet Bluetooth, Wireless Fidelity (Wi-Fi) (e.g., IEEE 802.11 standards), and other standards, protocols, and technologies. In some embodiments, for example, the log414may be provided to other devices over the network410via the network interface408.

In some embodiments, example computer system400may include or be coupled to an input device416(for example, one or more input devices). The input devices416may include, for example, a416, a mouse, a microphone, or other input devices. In some embodiments, the input device416may enable interaction with a user interface (for example, a graphical user interface) displayed on the display406.

The following examples are included to demonstrate embodiments of the disclosure. It should be appreciated by those of skill in the art that the techniques and compositions disclosed in the example which follows represents techniques and compositions discovered to function well in the practice of the disclosure, and thus can be considered to constitute modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or a similar result without departing from the spirit and scope of the disclosure.

Ranges may be expressed in the disclosure as from about one particular value, to about another particular value, or both. When such a range is expressed, it is to be understood that another embodiment is from the one particular value, to the other particular value, or both, along with all combinations within said range.

Further modifications and alternative embodiments of various aspects of the disclosure will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the embodiments described in the disclosure. It is to be understood that the forms shown and described in the disclosure are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described in the disclosure, parts and processes may be reversed or omitted, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description. Changes may be made in the elements described in the disclosure without departing from the spirit and scope of the disclosure as described in the following claims. Headings used in the disclosure are for organizational purposes only and are not meant to be used to limit the scope of the description.