Patent Description:
To drill a borehole in the earth for the recovery of hydrocarbons (e.g., oil and gas), an earth-boring drill bit is mounted on the lower end of a tubular drill string and is rotated. With weight applied to the drill string, also referred to as weight-on-bit (WOB), the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. While the bit is rotated, drilling fluid is pumped from the surface through the drill string and directed out of nozzles in the face of the drill bit into the bottom of the borehole. The drilling fluid exiting the bit is forced from the bottom of the borehole to the surface through the annulus between the drill string and the borehole sidewall.

The drilling fluid, also referred to as drilling mud, performs several functions - maintains a desired pressure within the borehole, cools and lubricates the drill bit, carries rock cuttings to the surface, maintains borehole stability, and transmits hydraulic energy to downhole tools. For example, managing the pressure in the well is important to inhibit the influx of formation fluids into the wellbore, while ensuring excessive wellbore pressure does not fracture the formation and lead to significant drilling fluid loss into the formation. The drilling fluid returning to the surface via the annulus is processed and reconditioned to remove rock cuttings, sand and other solids, as well as to ensure proper mud weight and density, pH, etc. After such processing and reconditioning, the drilling fluid is temporarily stored in mud tanks at the surface, and then pumped back down the drillstring. In this manner, the drilling fluid is continuously recirculated through the drilling system.

As the drilling fluid is circulated through the drilling system, samples of the drilling fluid returning to the surface are continuously taken to identify species of interest (liquids and gases) in the drilling fluid. Typically, the species of interest in the returning drilling fluid to be identified and monitored include hydrocarbons (e.g., methane, ethane, propane, i-butane, n-butane, i-pentane, n-pentane, n-hexane, ethane, propene, etc.), carbon dioxide, hydrogen, helium, sulfur dioxide, benzene, and hydrogen sulfide. In particular, the drilling fluid samples are heated to volatize or vaporize any liquid species of interest in the drilling fluid. Typically, electric heaters are employed to heat the drilling fluid samples. Once volatized and separated from the drilling fluid, the species of interest are transported to analytical equipment for further processing and analysis. This process of removing species of interest from drilling fluid for analytical purposes is commonly referred to as "degassing" or "extracting," with the resulting gaseous samples being called "representative sample gas" as it is generally representative of the species of interest in the returned drilling fluid stream at that particular time. Once the species of interest are removed, the heated drilling fluid is returned to the drilling process. However, the thermal energy in the heated samples of drilling fluid may detrimentally impact the equipment (e.g., pumps) used to transport the drilling fluid back to the drilling process. Moreover, the hot samples of drilling fluid present a potential safety hazard to personnel positioned near the drilling fluid sample return line. <CIT> discloses a device for preparing a fluid, particularly a drilling mud, associated preparation method and associated analysis unit, and <CIT> discloses a solid matrix tube-to-tube heat exchanger.

According to a first aspect of the invention, there is provided a system according to claim <NUM>.

According to a second aspect of the invention, there is provided a system according to claim <NUM>.

For a detailed description of the preferred embodiments of the disclosure, reference will now be made to the accompanying drawings.

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to. " Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms "axial" and "axially" generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms "radial" and "radially" generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

Referring now to <FIG>, an embodiment of an offshore drilling system <NUM> for drilling a subsea borehole <NUM> in an earthen formation <NUM> is shown. In this embodiment, system <NUM> includes an offshore platform <NUM> (e.g., a semi-submersible platform) disposed at the sea surface <NUM>, a subsea blowout preventer (BOP) <NUM> mounted to a wellhead <NUM> at the sea floor <NUM>, and a lower marine riser package (LMRP) <NUM> mounted to the upper end of BOP <NUM>. The upper end of LMRP <NUM> comprises a riser flex joint <NUM> connected to the lower end of a drilling riser <NUM> extending from platform <NUM>. As will be described in more detail below, riser <NUM> takes mud returns from borehole <NUM> to platform <NUM>. Flex joint <NUM> allows riser <NUM> to deflect angularly relative to BOP <NUM> and LMRP <NUM> while hydrocarbon fluids flow from wellbore <NUM>, BOP <NUM> and LMRP <NUM> into riser <NUM>.

Platform <NUM> is equipped with a derrick <NUM> that supports a hoist (not shown). A drill string <NUM> suspended from derrick <NUM> extends from platform <NUM> through riser <NUM>, LMRP <NUM>, BOP <NUM>, and into borehole <NUM>. Drill string <NUM> includes a plurality of drill pipe joints coupled together end-to-end, a bottom-hole-assembly (BHA) <NUM> coupled to the lowermost pipe joint, and a drill bit <NUM> coupled to the lower end of BHA <NUM>. During drilling operations, weigh-on-bit (WOB) is applied as drill bit <NUM> is rotated, thereby enabling drill bit <NUM> to engage formation <NUM> and drill borehole <NUM> along a predetermined path toward a target zone. In general, drill bit <NUM> may be rotated with drill string <NUM> from platform <NUM> with a top drive or rotary table, and/or with a downhole mud motor within BHA <NUM>. Casing <NUM> is installed and cemented in an upper portion of borehole <NUM> extending downward from wellhead <NUM> at the sea floor <NUM>.

An annular space or annulus <NUM> is disposed about drillstring <NUM> and extends from drill bit <NUM> to platform <NUM>. Moving upward from drill bit <NUM>, annulus <NUM> is radially positioned between the sidewall <NUM> of borehole <NUM> and drill string <NUM>, between casing <NUM> and drill string <NUM>, between BOP <NUM> and drill string <NUM>, between LMRP <NUM> and drill string <NUM>, and between riser <NUM> and drill string <NUM>. In other words, annulus <NUM> extends through borehole <NUM>, casing <NUM>, BOP <NUM>, LMRP <NUM>, and riser <NUM>.

Referring still to <FIG>, a drilling fluid supply or circulation system <NUM> disposed on platform <NUM> processes, conditions, samples, and circulates a suitable drilling fluid, also referred to as mud or drilling mud, to cool drill bit <NUM>, remove cuttings from the bottom <NUM> of borehole <NUM> and carry them to platform <NUM> through annulus <NUM>, and maintain a desired pressure or pressure profile in borehole <NUM> during drilling operations. In this embodiment, drilling fluid supply system <NUM> includes a drilling fluid conditioning system <NUM>, a drilling fluid reservoir or tank <NUM>, and a drilling fluid supply or mud pump <NUM>. A drilling fluid return line <NUM> couples conditioning system <NUM> to riser <NUM>, and a drilling fluid supply line <NUM> couples mud pump <NUM> to the upper end of drill string <NUM>. Thus, drilling fluid returning from borehole <NUM> through annulus <NUM> is supplied to system <NUM> via return line <NUM>, and drilling fluid processed and conditioned by system <NUM> is supplied by system <NUM> to drill string <NUM> via supply line <NUM>.

During drilling operations, drilling fluid from tank <NUM> is pressurized by pump <NUM> and sent through fluid supply line <NUM> into drill string <NUM>. The drilling fluid flows down drill string <NUM> and is discharged at the borehole bottom <NUM> through nozzles in drill bit <NUM>. The drilling fluid cools bit <NUM> and carries the formation cuttings to platform <NUM> through annulus <NUM>. The drilling fluid returned to platform <NUM> via annulus <NUM> exits the upper end of riser <NUM> through return line <NUM> and flows into conditioning system <NUM>, which effectively cleans and conditions the drilling fluid before it is circulated back into drill string <NUM>. In particular, conditioning system <NUM> removes undesirable solids from the drilling fluid (e.g., formation cuttings) and removes undesirable gases from the drilling fluid (e.g., dissolved hydrocarbon gases). Such functions are performed in conditioning system <NUM> by equipment known in the art including, without limitation, shakers, desanders, desilters, degassers, mud cleaners, centrifuges, etc. The cleaned drilling fluid flows from conditioning system <NUM> into tank <NUM>. The chemistry (e.g., pH, concentration of corrosion inhibiting chemicals, etc.) and density of the drilling fluid can be adjusted in conditioning system <NUM> or in tank <NUM>. The cleaned and conditioned drilling fluid in tank <NUM> is then supplied by pump <NUM> back down drill string <NUM>. In this manner, drilling fluid is continuously circulated through drilling system <NUM>, cleaned, processed, and conditioned.

Referring still to <FIG>, in this embodiment, drilling system <NUM> also includes a drilling fluid sampling system <NUM> disposed on a skid supported by platform <NUM>. Sampling system <NUM> is in fluid communication with circulation system <NUM> and continuously samples and analyzes drilling fluid returning from annulus <NUM> to identify species of interest within the drilling fluid. In this embodiment, samples of drilling fluid are continuously taken by sampling system <NUM> from return line <NUM> via a sample supply line <NUM> positioned upstream of conditioning system <NUM>, and analyzed samples of drilling fluid are continuously returned from sampling system to return line <NUM> via a sample return line <NUM> positioned upstream of conditioning system <NUM>. Thus, sampling system <NUM> acquires unprocessed samples of drilling fluid returning from annulus <NUM>, analyzes the unprocessed samples of drilling fluid, and then returns the analyzed samples of drilling fluid to return line <NUM> for subsequent processing by conditioning system <NUM>. As noted above and will be described in more detail below, sampling system <NUM> analyzes samples of drilling fluid returned to the surface from annulus <NUM>. However, it should be appreciated that a sampling system (e.g., sampling system <NUM>) can also be provided to analyze samples of drilling fluid being pumped down the drill string (e.g., drill string <NUM>). By analyzing samples of drilling fluid pumped downhole and returned from the borehole, a differential analysis of the species of interest identified, and quantities thereof, can be performed.

Referring now to <FIG>, in this embodiment, sampling system <NUM> includes a heat exchanger <NUM>, a phase separator <NUM>, a heater <NUM>, and a sample degasser <NUM>. Supply line <NUM> continuously pulls samples of drilling fluid from return line <NUM> and flows the samples to phase separator <NUM>. In this embodiment, supply line <NUM> includes a suction tube <NUM> extending through return line <NUM> and having an inlet end 103a disposed in the stream drilling fluid. The drilling fluid in return line <NUM> upstream of conditioning system <NUM> is unprocessed, and thus, contains formation cuttings and other undesirable solids. Thus, in this embodiment, a filter <NUM> is mounted to inlet end 103a to restrict solids from passing into sampling system <NUM>. A sample supply pump <NUM> is provided in supply line <NUM> to pull drilling fluid samples from return line <NUM> and aid in continuously circulating samples of drilling fluid through system <NUM>. The drilling fluid flowing through return line <NUM> and supply line <NUM> has not been heated, and thus, may be described as "cold" drilling fluid. For purposes of clarity and further explanation, the cold drilling fluid flowing through return line <NUM> and supply line <NUM> is designated with reference numeral 80a.

Cold drilling fluid 80a flows from supply line <NUM> into phase separator <NUM> through a drilling fluid inlet <NUM> and exits heat exchanger <NUM> through a drilling fluid outlet <NUM>. Within phase separator <NUM>, any solids in cold drilling fluid 80a (i.e., solids that passed through filter <NUM>) are substantially separated from cold drilling fluid 80a and any gases entrained in the cold drilling fluid 80a (i.e., bubbles in drilling fluid 80a) are substantially separated. The separated solids, designated with reference numeral 80b, are carried by a small amount of cold drilling fluid 80a, exit phase separator <NUM> through a separated solids outlet <NUM>, and are pumped to sample return line <NUM> and into drilling fluid return line <NUM> with a solids removal pump <NUM>. The separated gases, designated with reference numeral 80c, are carried by a small amount of cold drilling fluid 80a, exit phase separator <NUM> through a separated gas outlet <NUM>, and are pumped to degasser <NUM> with a de-aerator pump <NUM>. Gases 80c may include relatively light hydrocarbons that are already in a gaseous state in cold drilling fluid 80a, and thus, are liberated therefrom with relative ease. In particular, cold drilling fluid 80a does not need to be heated to liberate gases 80c via volatilization or vaporization since they are already in a gaseous state. Following separation of solids 80b and gases 80c, the remaining cold drilling fluid 80a exits phase separator <NUM> through a separated drilling fluid outlet <NUM> and flows to heat exchanger <NUM>.

In general, phase separator <NUM> can comprise any suitable device known in the art for separating solids (e.g., solids 80b) and entrained gases (e.g., gases 80c) from drilling fluid (e.g., cold drilling fluid 80a). In this embodiment, phase separator <NUM> is a de-aerator dampener separator (DDS) as developed by Halliburton Energy Services, Inc. of Houston, Texas. Examples of such de-aerator dampener separators are disclosed in <CIT>. In addition, pumps <NUM>, <NUM> may comprise any suitable pumps known in the art for pumping solid-liquid mixtures and gas-liquid mixtures, respectively. In this embodiment, both pumps <NUM>, <NUM> are peristaltic pumps such as Bredel pumps available from Watson-Marlow Pumps Group of the UK, Delasco™ pumps available from PCM USA Inc. of Houston, Texas, and Masterflex® pumps available from Cole-Parmer North America of Vernon Hills, Illinois.

Cold drilling fluid 80a, following separation of solids 80b and gases 80c, exits phase separator <NUM> through outlet <NUM> and flows into heat exchanger through an inlet <NUM>. As will be described in more detail below, within heat exchanger <NUM>, thermal energy is transferred to cold drilling fluid 80a thereby transitioning cold drilling fluid 80a into a pre-heated drilling fluid 80d. Accordingly, inlet <NUM> may also be referred to as cold drilling fluid inlet <NUM>, and outlet <NUM> may also be referred to as pre-heated drilling fluid outlet <NUM>.

Referring still to <FIG>, pre-heated drilling fluid 80d exiting outlet <NUM> of heat exchanger <NUM> flows into heater <NUM> through inlet <NUM>. Within heater <NUM>, pre-heated drilling fluid 80d is further heated to a temperature sufficient to volatize and/or vaporize the species of interest therein. For most drilling operations, the pre-heated drilling fluid 80d is preferably heated to at least <NUM>° C, and more preferably <NUM>° C. The addition of thermal energy transforms pre-heated drilling fluid 80d into "hot" drilling fluid, designated with reference numeral 80e, and volatized and/or vaporized gaseous species of interest 80f, both of which exits heater <NUM> through outlet <NUM>. In general, heater <NUM> can comprise any suitable heater known in the art for increasing the temperature of drilling fluid. In this embodiment, heater <NUM> is an electric heater.

Degasser <NUM> receives separated gases 80c (carried by a small amount of cold drilling fluid 80a and pumped by de-aerator pump <NUM>) through a first inlet <NUM>, and receives the mixture of hot drilling fluid 80e and gaseous species of interest 80f from heater <NUM> through a second inlet <NUM>. Within degasser <NUM>, gases 80c, hot drilling fluid 80e, and gaseous species of interest 80f are recombined, and then gases 80c, 80f are separated from hot drilling fluid 80e. The separated gases 80c, 80f exit degasser <NUM> through a gas outlet <NUM> and flow to an analyzer <NUM> that identifies the species of interest within gases 80c, 80f as described in more detail below. Collectively, gases 80c, 80f may be referred to as "representative sample gas" as they are generally representative of the species of interest in the returned drilling fluid stream at that particular time. The hot drilling fluid 80e exits degasser <NUM> through a hot drilling fluid outlet <NUM> and flows to heat exchanger <NUM>.

In general, degasser <NUM> can comprise any suitable device known in the art for separating gases (e.g., gases 80c, 80f) from liquids (e.g., hot drilling fluid 80e). In this embodiment, degasser <NUM> is a hydro-cyclone degasser. Another example of a degasser that can be used as degasser <NUM> is the QGM Gas Trap available from Diversified Well Logging Inc. of Reserve, Louisiana.

As previously described, analyzer <NUM> receives separated gases 80c, 80f from gas outlet <NUM> of degasser <NUM>. Within analyzer <NUM>, the species of interest in gases 80c, 80f are identified using one or more instruments. In general, any suitable instrument(s) known in the art for identifying gaseous species of interest can be utilized including, without limitation, mass spectrometers, gas chromatographs, total hydrocarbon analyzers, etc. In this embodiment, analyzer <NUM> includes a plurality of instruments <NUM>, <NUM>, <NUM> and a sample collection device <NUM>. Instruments <NUM>, <NUM>, <NUM> and sample collection device <NUM> are arranged in parallel such that each receives a representative sample gas from gas outlet <NUM>. In this embodiment, instrument <NUM> is a mass spectrometer, instrument <NUM> is a gas chromatograph, and instrument <NUM> is a total hydrocarbon analyzer. In addition, in this embodiment, sample collection device <NUM> is a device for periodically (e.g., once an hour, every <NUM> (<NUM> ft. ) of lag depth, etc.) capturing and housing separate and discrete samples of the representative sample gas. For example, sample collection device <NUM> can periodically capture samples of the representative sample gas in separate and distinct sample tubes, which can then be passed off to a third party for independent analysis and identification of the species of interest.

Hot drilling fluid 80e exiting degasser <NUM> flows into heat exchanger <NUM> through an inlet <NUM> and exits heat exchanger <NUM> through an outlet <NUM>. Within heat exchanger <NUM>, the thermal energy within hot drilling fluid 80e is transferred to cold drilling fluid 80a counterflowing through heat exchanger <NUM>, thereby transitioning hot drilling fluid 80e into a cooled drilling fluid <NUM>. Accordingly, inlet <NUM> may also be referred to as hot drilling fluid inlet <NUM>, and outlet <NUM> may also be referred to as a cooled drilling fluid outlet <NUM>. Cooled drilling fluid <NUM> flows from outlet <NUM> of heat exchanger <NUM> through return line <NUM> and into return line <NUM> of circulation system <NUM>. A sample return pump <NUM> is provided in return line <NUM> to pull cooled drilling fluid <NUM> from heat exchanger <NUM> and pump it through return line <NUM> to return line <NUM> of circulation system <NUM>.

In the manner described, samples of drilling fluid are continuously circulated through system <NUM> and analyzed to identify species of interest therein. In this embodiment, heat exchanger <NUM> is provided to simultaneously pre-heat the cold drilling fluid 80a supplied to sampling system <NUM> and cool the hot drilling fluid 80e returned by sampling system <NUM>. This offers the potential to reduce the energy consumption by heater <NUM>, as cold drilling fluid 80a is pre-heated prior to entering heater <NUM>, as well as increase the operating lifetime of return pump <NUM> by reducing the temperature of hot drilling fluid 80e before it passes therethrough. Cooling the hot drilling fluid 80e with heat exchanger <NUM> also reduces safety hazards by decreases the total footprint of the hot drilling fluid circuit within sampling system <NUM>.

Sampling system <NUM> is shown schematically in <FIG>, however, it is to be understood that the various components of system <NUM> are coupled together with fluid conduits (e.g., pipes, hoses, or the like) that place the components in fluid communication and allow samples of drilling fluid to be continuously flowed between the various components. For example, supply line <NUM> comprises a fluid conduit extending from suction tube <NUM> to supply pump <NUM> and a fluid conduit extending from supply pump <NUM> to inlet <NUM>. In addition, a fluid conduit extends from outlet <NUM> of heat exchanger to inlet <NUM>, and a fluid conduit extends from each outlet <NUM>, <NUM>, <NUM> to pump <NUM>, pump <NUM>, and inlet <NUM>, respectively. Further, a fluid conduit extends from pump <NUM> to return line <NUM>, a fluid conduit extends from outlet <NUM> to inlet <NUM>, and a fluid conduit extends from pump <NUM> to inlet <NUM>. Still further, a fluid conduit extends from each outlet <NUM>, <NUM> to analyzer <NUM> and inlet <NUM>, respectively. Moreover, return line <NUM> comprises a fluid conduit extending from outlet <NUM> to return pump <NUM> and a fluid conduit extending from return pump <NUM> to return line <NUM>.

Referring now to <FIG>, heat exchanger <NUM> comprises a core or body <NUM>, a first tubular <NUM> extending through core <NUM>, and a second tubular <NUM> extending through core <NUM> extending through core <NUM> parallel to first tubular <NUM>. Core <NUM> is an elongate generally solid member having a linear central or longitudinal axis <NUM>, a first end 120a, and a second end 120b opposite end 120a. In addition, core <NUM> includes a first through bore <NUM> extending axially between ends 120a, b, and a second through bore <NUM> extending axially between ends 120a, b. Bores <NUM>, <NUM> are parallel to axis <NUM>. As best shown in <FIG>, in this embodiment, core <NUM> has a rectangular cross-section taken perpendicular to axis <NUM>. However, in general, the core (e.g., core <NUM>) can have any cross-sectional geometry including, without limitation, circular, oval, triangular, square, etc..

Referring again to <FIG>, tubulars <NUM>, <NUM> extend axially through core <NUM> between ends 120a, b. In particular, tubular <NUM> is coaxially disposed within bore <NUM> and tubular <NUM> is coaxially disposed within bore <NUM>. Thus, tubulars <NUM>, <NUM> are oriented parallel to axis <NUM> in this embodiment. Core <NUM> is an elongate member having a longitudinal axis. Bores <NUM>, <NUM> and corresponding tubulars <NUM>, <NUM> are parallel and extend linearly between ends 120a, b in this embodiment, whereas in other embodiments, the bores (e.g., bores <NUM>, <NUM>), and associated tubulars (e.g., tubulars <NUM>, <NUM>) can have other geometries. However, in general, the bores and the associated tubulars are preferably spaced apart and oriented parallel to each other as they extend through the core. In one exemplary embodiment, the core is a cylindrical block and the bores (with the tubulars disposed therein) extend helically and parallel to teach other through the core.

In this embodiment, each tubular <NUM>, <NUM> is cylindrical, and has an outer radius R121o, R122o, respectively, and an inner radius R121i, R122i, respectively. Outer radius R121o is the same as the radius of bore <NUM>, and radius R122o is the same as the radius of bore <NUM>. Thus, the outer cylindrical surfaces of tubulars <NUM>, <NUM> contact and engage core <NUM> along the entire length of core <NUM>. In other words, core <NUM> completely surrounds each tubular <NUM>, <NUM>. Further, solid core <NUM> extends between tubulars <NUM>, <NUM>, and thus, there are no voids, gaps, or flow passages between tubulars <NUM>, <NUM>. This enables the direct conduction of thermal energy through core <NUM> between tubulars <NUM>, <NUM>. The inner radius R121i, R122i of each tubular <NUM>, <NUM>, respectively, is preferably between <NUM> (<NUM> in. ) and <NUM> (<NUM> in. ), and more preferably <NUM> (<NUM> in). For most drilling operations, the shortest distance D<NUM>-<NUM> between tubulars <NUM>, <NUM> is preferably greater than or equal to the inner diameter of tubulars <NUM>, <NUM> (i.e., twice the radius R121i, R122i), and less than or equal to three times the inner diameter of tubulars <NUM>, <NUM> (i.e., six times the radius R121i, R122i). For example, if each tubular <NUM>, <NUM> has an inner radius R121i, R122i equal to <NUM> (<NUM> in. ), then distance D<NUM>-<NUM> is preferably greater than or equal to <NUM> (<NUM> in. ) and less than or equal to <NUM>,<NUM> (<NUM> in). Without being limited by this or any particular theory, these preferred ranges for distance D<NUM>-<NUM> offer the potential for efficient heat transfer between tubulars <NUM>, <NUM> through core <NUM>, while maintaining sufficient strength in core <NUM>.

The radially inner surface of each tubular <NUM>, <NUM> defines a drilling fluid flow passage <NUM>, <NUM>, respectively. Inlet <NUM> is provided at one end of flow passage <NUM> and outlet <NUM> is provided at the opposite end of flow passage <NUM>. Inlet <NUM> is provided at one end of flow passage <NUM> and outlet <NUM> is provided at the opposite end of flow passage <NUM>. Inlet <NUM> and outlet <NUM> are disposed at end 120a of core <NUM>, and inlet <NUM> and outlet <NUM> are disposed at end 120b of core <NUM>. Thus, drilling fluid passes through passages <NUM> in the opposite direction as drilling fluid passes through passage <NUM>. In other words, drilling fluids move counterflow through heat exchanger <NUM>.

Referring still to <FIG>, core <NUM> and tubulars <NUM>, <NUM> are preferably made of rigid materials with a relatively high thermal conductivity (W/m*K) to enhance the conduction of thermal energy from hot drilling fluid 80e flowing through passage <NUM> to cold drilling fluid 80a flowing through passage <NUM>, thereby simultaneously pre-heating drilling fluid 80a and cooling drilling fluid 80e. Examples of suitable materials for core <NUM> and tubulars <NUM>, <NUM> including, without limitation, steel, aluminum, and copper. In this embodiment, core <NUM> is aluminum that is cast around stainless steel tubulars <NUM>, <NUM>.

In the manner described, heat exchanger <NUM> allows a metal-to-metal contact between counterflow fluids 80a, 80e, thereby eliminating secondary heat exchange mediums such as oil or water conventionally used in heat exchangers. In addition, heat exchanger <NUM> does not include any moving parts that are often prone to damage and failure. Eliminating secondary heat exchanges mediums and moving parts offers the potential to enhance durability and simplify maintenance as passages <NUM>, <NUM> are easily accessed and can be completely cleaned without concern over hidden ports, dead fluid spaces or unused areas that are susceptible to unseen corrosion. The simplistic design for heat exchanger <NUM> also lends itself well to nondestructive testing and inspection for consistency and reliability purposes, and offers the potential for relatively low cost manufacturing and replacement.

Although drilling fluid circulation system <NUM> and sampling system <NUM> are shown in connection with offshore drilling system <NUM> in <FIG>, it should be appreciated that circulation system <NUM> and sampling system <NUM> can also be used with land-based drilling systems. In addition, although only one heat exchanger <NUM> is shown in sampling system <NUM>, it should be appreciated that more than one heat exchanger (e.g., heat exchanger <NUM>) can be connected in series to further enhance the transfer of thermal energy between cold drilling fluid 80a and hot drilling fluid 80e.

In the embodiment of sampling system <NUM> described above, separated gases 80c exit phase separator <NUM> through a separated gas outlet <NUM>, and are pumped to degasser <NUM> with a de-aerator pump <NUM>. Typically, separated gases 80c include relatively light hydrocarbons that are already in a gaseous state in cold drilling fluid 80a, and thus, are liberated therefrom with relative ease. However, in other embodiments, separated gases 80c are not pumped to degasser <NUM>, but rather, are pumped to sample return line <NUM>. For example, referring now to <FIG>, an embodiment of a sampling system <NUM> that can be used in drilling system <NUM> (e.g., in place of sampling system <NUM>) is shown. Sampling system <NUM> is the same as sampling system <NUM> previously described with the exception that separated gases 80c separated from cold drilling fluid 80a in phase separator <NUM> are pumped to sample return line <NUM> and not pumped to degasser <NUM>. In particular, separated gases 80c exit phase separator <NUM> through a separated gas outlet <NUM>, and are pumped with de-aerator pump <NUM> into sample return line <NUM>, and then pumped through sample return line <NUM> into drilling fluid return line <NUM> with return pump <NUM>. Thus, in this embodiment, separated gases 80c are not supplied to degasser <NUM> and analyzer <NUM>. Rather, in this embodiment, degasser <NUM> only receives the mixture of hot drilling fluid 80e and gaseous species of interest 80f from heater <NUM> through inlet <NUM>. Gases 80f are separated from hot drilling fluid 80e within degasser <NUM>, and then exit degasser <NUM> through gas outlet <NUM> and flow to analyzer <NUM> for analysis and identification of species of interest therein. The hot drilling fluid 80e separated from gases 80f exit degasser <NUM> through outlet <NUM> and flow to heat exchanger <NUM>.

Claim 1:
A system for sampling drilling fluid to identify one or more species of interest within drilling fluid, the system comprising:
a heat exchanger (<NUM>) including a first fluid passage (<NUM>) extending through a first tubular (<NUM>) and a second fluid passage (<NUM>) extending through a second tubular (<NUM>), wherein each fluid passage has an inlet and an outlet, wherein the heat exchanger comprises an elongate core (<NUM>) having a longitudinal axis (<NUM>), a first end (120a), and a second end (120b) wherein the first and second tubulars extend axially through the core from the first end of the core to the second end of the core;
a supply line (<NUM>) coupled to the inlet of the first fluid passage;
a return line (<NUM>) coupled to the outlet of the second fluid passage;
a drilling fluid heater (<NUM>) having an inlet (<NUM>) coupled to the outlet of the first fluid passage
and an outlet (<NUM>); and
a drilling fluid degasser (<NUM>) having an inlet (<NUM>) coupled to the outlet (<NUM>) of the heater, a first outlet (<NUM>) coupled to an analyzer (<NUM>) configured to identify the one or more species of interest, and a second outlet (<NUM>) coupled to the inlet of the second fluid passage,
wherein the heat exchanger is configured to transfer thermal energy from the drilling fluid flowing through the second fluid passage to the drilling fluid flowing through the first fluid passage.