Cross quality control for mud logging measurements

Abstract

A method for mud logging includes performing a first gas measurement on a first gas sample obtained from circulating drilling fluid on a drilling rig using a first gas chain; performing a second gas measurement on a second gas sample obtained from the circulating drilling fluid on the drilling rig using a second gas chain; defining a quality control window for the first gas measurement from the second gas measurement; and cross-mass controlling the first and second gas measurements by comparing the first gas measurement to a mass control window.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of European Application No. 23306710.7 filed on October 5, 2023, the entire contents of which are incorporated herein by reference. Background Art

[0003] When drilling a well for producing hydrocarbons, drilling fluids are usually circulated through the well for many purposes. For example, drilling fluids are usually intended to provide pressure to underground formations, cool and lubricate the drill bit, flush cuttings from the drill bit and transport them to the ground, and provide hydraulic power to various downhole tools. Drilling fluids also usually transport formation fluids and dissolved formation gases to the ground. Such gases can be released by the drill bit when the drill bit cuts the formation, and can include various alkane gases, such as methane (C1), ethane (C2), propane (C3), butane (C4), pentane (C5), etc.

[0004] The released gases are typically collected and evaluated at the surface while drilling (e.g., via gas chromatography). Such gas measurements can be used to monitor drilling operations and various safety concerns, as well as to evaluate the potential productivity of the reservoir and the wellbore being drilled. During some drilling operations, two independent gas collection and measurement systems are used to collect and measure the released gases. While such independent systems can provide valuable insights into the drilling operations and the contents of the reservoir, there is room for further improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] For a more complete understanding of the disclosed subject matter and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0006] Figure 1 An example drilling rig including the disclosed system for taking mud logging measurements is depicted.

[0007] Figure 2 Another embodiment of a surface system for taking mud logging measurements is shown.

[0008] Figure 3 An example block diagram of the disclosed crossover quality control is depicted.

[0009] Figure 4A and 4B (collectively, FIG. 4 ) depicts a flow chart of an exemplary mud logging method employing the disclosed quality control method.

[0010] Figure 5A and 5B (collectively, FIG. 5 ) depicts an exemplary mud log generated using the method disclosed in FIG. 4 .

[0011] Figure 6 An exemplary mud log is depicted, which further illustrates the disclosed embodiments and certain advantages thereof. DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure include methods and systems for making and evaluating drilling fluid gas composition measurements. In one exemplary embodiment, the disclosed method includes making a first gas measurement on a first gas sample obtained from a circulating drilling fluid on a drilling rig using a first gas chain; making a second gas measurement on a second gas sample obtained from a circulating drilling fluid on the drilling rig using a second gas chain; defining a quality control window for the first gas measurement based on the second gas measurement; and cross-quality controlling the first and second gas measurements by comparing the first gas measurement to the quality control window.

[0013] Figure 1 An example drilling rig 20 is depicted, which includes a system 80 for making mud logging measurements (e.g., for cross-checking first and second parallel mud logging measurements). The drilling rig 20 can be positioned above a subsurface formation (not shown). The drilling rig 20 can include, for example, a derrick and a lifting device (also not shown) for raising and lowering a drill string 30, which, as shown, extends into a wellbore 40 and includes, for example, a drill bit 32 and one or more downhole measurement tools 38 (e.g., logging while drilling tools or measurement while drilling tools) in a bottom hole assembly (BHA) above the drill bit 32. Suitable drilling systems (e.g., including drilling, steering, logging and other downhole tools) are well known in the industry.

[0014] The drilling rig 20 also includes a surface system 50 for controlling the flow of drilling fluid used on the drilling rig (e.g., for drilling the wellbore 40). In the depicted example drilling rig, the drilling fluid 35 can be pumped downhole (as depicted at 92), for example, via a conventional mud pump 57. The drilling fluid 35 can be pumped, for example, in route through a riser 58 and a mud hose 59 to the drill string 30. The drilling fluid 35 typically exits the drill string 30 at or near the drill bit 32 and creates an upward flow 94 of mud that passes through the wellbore annulus 42 (the annular space between the drill string and the wellbore wall). The drilling fluid 35 then flows through the return conduit 52 to the mud pit system 56, where the drilling fluid 35 can be recirculated. It should be understood that the terms drilling fluid and mud are used synonymously herein.

[0015] The circulating drilling fluid 35 is intended to perform a number of functions during the drilling operation, one of which is to transport drill cuttings 45 to the surface (in an upward flow 94). The drill cuttings 45 are typically removed from the return mud via a shale shaker 55 (or other similar solids control equipment) in a return conduit (e.g., immediately upstream of the mud pit 56). Gases released or generated during drilling may also be transported to the surface in the circulating drilling fluid. These gases, which may be dissolved in the mud or dissolved in the form of bubbles, are typically removed from the drilling fluid, for example, via one or more degassers 54a, 54b located in or near a header box 53, which is immediately upstream of the shale shaker 55 in the example depiction. The drill cuttings 45 and the extracted gas are typically examined at the surface to assist the drilling operation and evaluate the formations through which the drilled wellbore passes.

[0016] As known to those of ordinary skill in the art, formation gas can be released into the wellbore 40 via the drilling process (e.g., by crushing the formation rock through the mechanical action of the drill bit), and can also migrate into the wellbore 40, for example, via fractures in the formation rock. The drilling process can also produce gas, for example, via drill bit metamorphism (DBM). Once in the wellbore, the gas can be transported to the surface via the drilling fluid (in the upward flowing fluid 94). The gas can be dissolved (dissolved) in the drilling fluid and / or in the form of bubbles, and can be sampled in the surface system, for example, via one or more drilling fluid degassers 54a, 54b and / or headspace gas probes. The disclosed embodiments are not necessarily limited to how the gas is sampled.

[0017] Further references Figure 1 , the drilling rig 20 may also include a testing facility 60 (e.g., a mud logging system or laboratory trailer including one or more instruments suitable for performing various measurements on sampled gases in the drilling fluid). In the illustrated embodiment, the testing facility 60 has an instrument arrangement (e.g., a gas chromatograph) configured to measure the composition of the formation gas. The facility may also include a system 80 configured to perform mud logging measurements including the disclosed quality control procedures. The system may include the instrument arrangement, or may be configured to receive gas composition measurements from the instrument arrangement (e.g., a gas chromatograph). Of course, the testing facility 60 may include many other testing instruments known to those of ordinary skill in the art, as well as computer hardware and software configured to evaluate gas composition measurements and various drilling and environmental parameters. The hardware may include one or more processors (e.g., microprocessors) that may be connected to one or more data storage devices (e.g., a hard drive or solid-state memory) and a user interface. It will be further understood that the disclosed embodiments may include processor executable instructions stored in the data storage device. The disclosed embodiments are of course not limited to the use or configuration of any particular computer hardware and / or software.

[0018] Of course it should be understood that Figure 1 A land drilling rig 20 is depicted, but the disclosed embodiments are equally applicable to land drilling rigs or offshore drilling rigs. As known to those of ordinary skill in the art, an offshore drilling rig typically includes a platform deployed on top of a riser that extends from the seafloor to the surface. A drill string extends downward from the platform, through the riser, and through a blowout preventer (BOP) located on the seafloor into the wellbore. The disclosed embodiments are expressly not limited in these respects.

[0019] Figure 2 Another view of a portion of the surface system 50 is depicted. As described above, the return conduit 52 is configured to carry the drilling fluid 35 (sometimes including gas bubbles 37) from the wellbore 40 to the mud pit 56. The exemplary system 50 includes a first degasser 54a and a second degasser 54b, for example, deployed in or near a header box 53, which is immediately upstream of the shale shaker 55 and the mud pit 56. In this example configuration, the degassers 54a, 54b are configured to remove gases (referred to in the industry as gas bleed) from the drilling fluid emerging from the wellbore 40. A small volume of drilling fluid can be circulated through each of the degassers 54a, 54b, where they are agitated and optionally heated to remove alkanes and other gases from the fluid volume. Although the disclosed embodiments are not limited in this regard, it should be appreciated that the first degasser 54a can provide gas primarily for evaluating drilling operations and various safety concerns, and the second degasser 54b can provide gas for evaluating the potential productivity of the reservoir and the wellbore being drilled. In such operation, as described in more detail below, the first and second degassers 54a, 54b are connected to respective first and second gas measurement devices and provide independent measurements of the wellbore gas composition.

[0020] It should be understood that the degasser 54a, 54b may include substantially any suitable degasser, for example, including a vacuum degasser, a centrifugal degasser, and an impeller degasser. The degasser may also be configured to heat the drilling fluid 35 to promote enhanced degassing of the fluid. The disclosed embodiments are not limited to the type of degasser employed. It should also be understood that the first and second degassers 54a, 54b do not necessarily (and typically do not) include the same type of degasser. In other words, the first degasser 54a is typically (although not always) of a different type and configuration than the second degasser 54b.

[0021] like Figure 2As further depicted in , in an example embodiment, the degassers 54a, 54b can be piped directly to a mud logging unit or a rig lab 60 (e.g., as depicted at 65a, 65b), for example, to automatically deliver sampled gas for composition testing. In addition, although not shown, the system 50 may include one or more pumps (e.g., suction or booster pumps) configured to pump sampled gas from one or more degassers 54 and / or gas probes to the lab 60. Of course, the disclosed embodiments are not limited to any sampling, pumping, or gas delivery configuration.

[0022] Figure 3 An example block diagram 100 of a disclosed mud logging configuration is depicted. In the depicted embodiment, independent quality control (QC) procedures are implemented for multiple drilling and mud logging equipment. For example, various drilling parameters can be measured at 102. Independent QC of these measurements can be provided at 104. The drilling parameters can be measured using various rig equipment and can include, for example, weight or load on the drill bit (WOB), rotation rate (RPM) of the drill string, measured torque, penetration rate while drilling, drilling fluid flow or pumping rate, and mud pool volume or depth. QC of these drilling parameters can include checking the measured values ​​against predefined specification limits and calibrating the sensors used to make the measurements.

[0023] Various drilling fluid parameters may be measured at 106. Independent QC of these measurements may be provided at 108. The drilling fluid parameters may include various American Petroleum Institute (API) measurements, such as mud density; viscosity and gel strength; oil, water, low gravity solids, and weighting material concentrations; pH and alkalinity; elemental concentrations of calcium and chlorides; and electrical stability. These properties may be measured using various rig or laboratory equipment that may have independent QC procedures (e.g., at 108). As with the above parameters, QC of drilling fluid parameters may include checking the measurements against predefined specification limits and calibrating the sensors used to make the measurements.

[0024] The block diagram 100 further includes a first gas chain, which includes a first degasser 112 and a first measuring device (such as an analyzer of a GC device) 116 and a second degasser 122 and a second measuring device (such as an analyzer of a GC device) 124. As described above, each of the first and second degassers may include a degasser of substantially any suitable type and configuration, for example, including vacuum degassers, centrifugal degassers and impeller degassers and heated degassers. The first analyzer 116 and the second analyzer 126 can be configured to quantify the amount of light alkanes and optional other gases (e.g., olefins and alcohols) in the gas sample. In a preferred embodiment, these measuring devices quantify at least the following light alkane gases: methane (C1), ethane (C2), propane (C3), normal butane (nC4), isobutane (iC4), normal pentane (nC5) and isopentane (iC5), however, the disclosed embodiments are not limited in this regard. In other embodiments, the gas measurement device can quantify C1 to C8 as well as aromatic compounds such as benzene and toluene, cyclic compounds such as cyclopentane, methylcyclohexane, and inorganics such as hydrogen, helium, carbon monoxide, and carbon dioxide.

[0025] In an exemplary embodiment, the first gas chain can include a standard gas service, such as ReservalFlex (available from SLB), which is configured for monitoring the safety of drilling operations, and the second gas chain can include an advanced gas service, such as FlairFlex service (available from SLB), which is configured for monitoring the composition of the reservoir. The Flairflex service provides laboratory quality gas composition measurements of reservoir fluids during drilling and can be used for hydrocarbon and fluid contact identification and inter-well and intra-well fluid phase mapping. It should be understood that the disclosed embodiments are not limited to use with any particular gas chain configuration. In addition, the analyzers 116, 126 can include substantially any suitable gas measurement equipment, including, for example, GC-FID, GC-TCD, GC-MS, MS, adsorption spectroscopy (e.g., IR, MID) and / or Raman spectroscopy.

[0026] The first and second gas chains may be independently quality controlled, for example, such that the first degasser 112 may be independently quality controlled at 114, the first analyzer 116 may be independently quality controlled at 118, the second degasser 122 may be independently quality controlled at 124, and the second analyzer 126 may be independently quality controlled at 128. Independent quality control procedures for the first and second degassers 112, 122 may include, for example, evaluating various degasser parameters relative to corresponding threshold-based alarms. These degasser parameters may include, for example, the flow rate of drilling fluid through the degasser, the drilling fluid level in the degasser, the drilling fluid temperature in the heated degasser, the impeller speed in the impeller degasser, and the vacuum level in the vacuum degasser. The various degasser sensors may also be calibrated from time to time to ensure accurate measurements.

[0027] The quality control procedures for the first analyzer 116 and the second analyzer 126 may include evaluating various analyzer parameters relative to corresponding threshold-based alarms. These degasser parameters may include, for example, gas sample line pressure, analyzer pump pressure, analyzer exhaust flow, and analyzer detection head oven temperature. In addition, the first analyzer 116 and the second analyzer 126 may be calibrated using a control sample including one or more alkane gases of known amounts (or concentrations). The calibration may include determining peak heights and / or peak areas corresponding to individual alkane gases, and further determining coefficients such that the estimated composition of the control sample is close to or equal to its known composition.

[0028] Further references Figure 3 , the disclosed embodiments also include cross-quality control checks, in which first and second gas measurements are quality controlled relative to each other. For example, gas composition measurements made by a first gas chain (a first degasser and a first analyzer) may be quality controlled relative to gas composition measurements made by a second gas chain (a second degasser and a second analyzer). Similarly, gas composition measurements made by the second gas chain may also be quality controlled relative to gas composition measurements made by the first gas chain. In such embodiments, the cross-quality control check may define an expected operating window (e.g., an expected range of amount or concentration) for a selected measured gas component in one gas chain (e.g., C1, C2, C3, iC4, nC4, iC5, or nC5) relative to a corresponding measured gas component in another gas chain. The disclosed cross-quality control checks may provide advance warning of problems associated with either gas chain, and may further advantageously assist an operator in quickly identifying and remediating such problems.

[0029] Now turn to Figure 4A and 4B(collectively, FIG. 4 ) depicts a flow chart of example methods 150 and 200 for mud logging. The methods 150 and 200 may be performed, for example, while drilling a subterranean wellbore. Figure 4A In the embodiment of the present invention, a first amount of a selected alkane gas in a circulating drilling fluid may be measured at 152 using a first gas train (e.g., a first degasser and a first gas analyzer), and a second amount of the selected alkane gas may be measured at 154 using a second gas train (e.g., a second degasser and a second gas analyzer). In an exemplary embodiment, the first gas measurement and the second gas measurement may be made substantially simultaneously at 152, 154 while drilling the wellbore. At least one crossover quality control window may be defined at 156. For example, a first crossover quality control window may define an expected operating window (e.g., an expected amount range) of the first gas measurement made at 152 relative to the second gas measurement made at 154. Similarly, a second crossover quality control window may define an expected operating window of the second gas measurement made at 154 relative to the first gas measurement made at 152. At 158, the first gas measurement and the second gas measurement may be cross-quality controlled, for example, by comparing the first gas measurement to the first quality control window and / or comparing the second gas measurement to the second quality control window. The method 150 may optionally further include adjusting the first gas measurement or the second gas measurement at 160 when the comparison at 158 ​​is unfavorable. Unfavorable means that the first gas measurement is not within the first quality control window and / or the second gas measurement is not within the second quality control window.

[0030] exist Figure 4B In the method 200, different first and second gas samples may be obtained from the circulating drilling fluid used when drilling the wellbore via different first and second degassers at 202. Corresponding first and second gas measurements may be performed on the first and second gas samples at 204 to obtain first and second amounts of selected alkane gases (and optionally other gases). An expected ratio of the first and second amounts (e.g., the first amount to the second amount or the second amount to the first amount) may be determined at 206. First and second (or upper and lower) limits may be defined at 208 based on the expected ratio determined at 206, thereby defining a crossover quality control window. At 210, the first and second gas measurements may be crossover quality controlled, for example, by comparing one or both of the first and second gas measurements to corresponding quality control windows (or multiple windows). The method 200 may optionally further include adjusting a procedure for obtaining one or both of the first and second gas samples or a procedure for performing the first and second gas measurements at 212 when the comparison at 210 is unfavorable (e.g., when the first and second measurements are out of specification with respect to each other).

[0031] A gas sample may be obtained in a gas measurement, for example, as described above with respect to Figure 2 and Figure 3 As described, gas measurements may be made using substantially any suitable degasser and gas analyzer (measurement device) such as a GC measurement device. Gas measurements may include the amount or volume fraction of various alkane gases such as C1, C2, C3, iC4, nC4, iC5, and nC5, as well as other common wellbore gases. Furthermore, the disclosed cross-quality control may be performed for any number of measured gases, for example, for each of the measured gases or for some selected subset of the measured gases.

[0032] Continuing with reference to FIG. 4 , defining a crossover quality control window may include determining an expected relationship between a first gas measurement and a second gas measurement, for example, an expected relationship between a first quantity measured using a first gas chain and a second quantity measured using a second gas chain. The expected relationship may be described, for example, as an expected ratio of a first quantity to a second quantity (e.g., a first quantity to a second quantity or a second quantity to a first quantity). In an exemplary embodiment, the ratio may be related to a ratio of a drilling fluid flow rate through a first degasser to a drilling fluid flow rate through a second degasser. This may be expressed mathematically, for example, as follows:

[0033]

[0034] Where R represents the expected ratio, F1 and F2 represent the calibrated or quality controlled drilling fluid flow rates through the first degasser and the second degasser, and C represents a coefficient that takes into account other factors other than the drilling fluid flow rates that may affect the expected ratio. It should be understood that when the first degasser and the second degasser are operated in parallel (e.g., Figure 2 The resulting gas composition measurements should have similar trends (over time or depth), but may differ in magnitude primarily (but not exclusively) attributable to different degasser flow rates. The exact ratio may vary due to temperature, mud rheology, degasser deployment location, and other factors that may be considered by the coefficient C.

[0035] In an exemplary embodiment where the first gas chain comprises a standard gas chain configured to monitor wellbore safety and the second gas chain comprises an advance gas chain configured to assess reservoir contents, the drilling fluid flow rate through the first degasser may be greater than the drilling fluid flow rate through the second degasser (e.g., by a factor in the range of about 2 to 8). In such an embodiment, it may be expected that the first gas chain measures a greater amount of measured gas than the second gas chain. During normal operating conditions, the measured gas amounts may be related by the aforementioned ratio, for example, as follows: M1 = R·M2 where M1 and M2 represent the first gas measurement and the second gas measurement.

[0036] First and second (or upper and lower) crossover quality control limits, above and below the expected ratio, may be defined at 208, for example, as follows:

[0037] L1=R+Δ

[0038] L2=R-Δ (2)

[0039] Where L1 and L2 represent the first and second crossover quality control limits and 2Δ defines the quality control window width (such that the ratio defines the center of the control window). At 210, the first gas measurement and the second gas measurement may be cross-quality controlled, for example, by comparing one or both of the first gas measurement and the second gas measurement to a corresponding quality control window (or windows). This may be expressed mathematically, for example, as follows:

[0040] (R-Δ)·M2 <M1<(R+Δ)·M2

[0041]

[0042] Note that in order to obtain the upper limit or window value of the first gas measurement value M1, the second gas measurement value M2 can be multiplied by the first coefficient (R+Δ) and in order to obtain the lower limit or window value of the first gas measurement value, the second gas measurement value can be multiplied by the second coefficient (R-Δ). Similarly, in order to obtain the upper limit or window value of the second gas measurement value M2, the first gas measurement value M1 can be divided by the second coefficient (R-Δ) and in order to obtain the lower limit or window value of the second gas measurement value, the first gas measurement value can be divided by the first coefficient (R+Δ).

[0043] The disclosed embodiments are now described by the following non-limiting hypothetical example. In this particular example, the first gas chain and the second gas chain may include a standard gas service, such as ReservalFlex (available from SLB), which may be configured for monitoring the safety of drilling operations, and an advance gas service, such as FlairFlex service (available from SLB), which may be configured for monitoring reservoir contents. The degasser in the standard configuration may pump drilling fluid at a flow rate of approximately 1500 mL / min, while the degasser in the advance configuration may pump drilling fluid at a flow rate of approximately 300 mL / min. Based on equation (1) above, the ratio R=1500 / 300=5 may be calculated (e.g., when coefficient C is approximately 1). The first and second limits may be calculated from equation (2). For example, when Δ=1, the limits may be equal to 6 and 4. Equation (3) may then be used to perform cross-quality control on the standard gas measurements and the advance gas measurements, ensuring that the following conditions apply:

[0044] 4.AG <SG<6·AG

[0045]

[0046] Wherein SG denotes a measurement value made using a standard gas service (first gas measurement value) and AG denotes a measurement value made using an advanced gas service (second gas measurement value).

[0047] Figure 5A and 5B (collectively, FIG. 5 ) depict example well logs 240 and 250 illustrating the disclosed embodiments. In these figures, the first gas measurement and the second gas measurement of the above examples (e.g., in parts per million of methane - C1) are plotted on the horizontal axis, and time or depth is plotted on the vertical axis. Figure 5A Recorded are the standard gas measurement SG at 242 and the upper and lower crossover quality control limits at 244 and 246. In this example, the upper crossover quality control limit is equal to six times the advance gas measurement value and the lower crossover quality control limit is equal to four times the advance gas limit. Figure 5B The advance gas measurement AG at 252 and the crossover quality control upper and lower limits at 254 and 256 are recorded. In this example, the crossover quality control upper limit is equal to one-fourth of the standard gas measurement value, and the crossover quality control lower limit is equal to one-sixth of the standard gas limit. It should be noted that in this example, each of the gas measurements remains within the crossover quality control specification of the other.

[0048] Figure 6 An example well log 260 is depicted that further illustrates the disclosed embodiments and certain advantages thereof. The depicted well log 260 is similar to Figure 5B The log depicted above is that it records the advanced gas measurement AG at 262 and the previously described crossing quality control upper and lower limits at 264 and 266. Figure 6 Also included is a cross quality control alarm track 270 that indicates when the lead gas measurement is within the cross quality control specification (shown as light gray at 272) and when it is outside the cross quality control specification (shown as dark gray at 274). It should of course be understood that the cross quality control alarm track can provide a colored indication, such as green when the measurement is within the cross quality control specification and red when the measurement is outside the cross quality control specification. Figure 6 Also included is the well log 280 of the advance gas degasser mud flow at 282 and the corresponding degasser flow alarm track at 290, where light gray indicates that the degasser mud flow is within specification at 292 and dark gray indicates that the flow is out of specification at 294 (of course, the alarm track can also use green and red to indicate flow rates within and out of specification).

[0049] In the depicted example, both the advance gas measurement and the advance gas degasser mud flow are within specification early in the operation, as indicated in the alarm tracks at 272 and 292. As the mud logging operation progresses, the advance gas measurement is observed to drop below the crossover quality control lower limit at 268, thereby triggering a change in the alarm track, as shown at 278. At a similar time or depth, the degasser mud flow log indicates a change in flow behavior beginning at 284, however, the change in flow behavior has not yet triggered a flow alarm. The alarm is not triggered until a later time or depth when the degasser flow drops below the threshold at 286, and thereby triggers a flow alarm, as indicated at 296. In this example, the fixed threshold degasser flow alarm 290 is not triggered until after the crossover quality control alarm 270 is triggered. It can be seen that the crossover quality control and corresponding alarms can provide early warning of system errors (such as degasser fouling in this example), and therefore can provide more timely troubleshooting.

[0050] It should be understood that the present disclosure includes many embodiments. These embodiments include but are not limited to the following embodiments.

[0051] In a first embodiment, a method for mud logging includes performing a first gas measurement on a first gas sample obtained from a circulating drilling fluid on a drilling rig using a first gas chain; performing a second gas measurement on a second gas sample obtained from a circulating drilling fluid on the drilling rig using a second gas chain; defining a quality control window for the first gas measurement based on the second gas measurement; and cross-quality controlling the first and second gas measurements by comparing the first gas measurement to the quality control window.

[0052] A second embodiment may include the first embodiment wherein taking the first gas measurement and taking the second gas measurement comprises measuring a composition of the at least one alkane gas using a gas chromatography device.

[0053] A third embodiment may include any one of the first to second embodiments, wherein the first gas chain includes a first degasser and a first gas measurement device, and the second gas chain includes a second degasser and a second component measurement device.

[0054] A fourth embodiment may include any one of the first to third embodiments, further comprising adjusting the first gas measurement or the second gas measurement when the first gas measurement is outside the quality control window.

[0055] The fifth embodiment may include any one of the first to fourth embodiments, wherein performing a first gas measurement includes obtaining a first gas sample from the circulating drilling fluid using a first degasser, and performing a first gas measurement on the obtained first gas sample; and performing a second gas measurement includes obtaining a second gas sample from the circulating drilling fluid using a second degasser, and performing a second gas measurement on the obtained second gas sample.

[0056] A sixth embodiment may include any one of the first to fifth embodiments, wherein a first gas measurement is independently quality controlled; a second gas measurement is independently quality controlled; defining includes defining a quality control window for the first independently quality controlled gas measurement based on the second independently quality controlled gas measurement; and cross quality control includes comparing the first independently quality controlled gas measurement to the quality control window.

[0057] A seventh embodiment may include any of the first to sixth embodiments, wherein defining the quality control window includes determining an expected ratio of the first gas measurement to the second gas measurement.

[0058] An eighth embodiment may include the seventh embodiment, wherein the expected ratio is equal to a coefficient multiplied by a ratio of a drilling fluid flow rate through a first degasser used to obtain the first sample to a drilling fluid flow rate through a second degasser used to obtain the second sample.

[0059] A ninth embodiment may include any one of the seventh to eighth embodiments, wherein defining the quality control window further comprises defining a first control limit and a second control limit according to the expected ratio to define the quality control window.

[0060] A tenth embodiment may include the ninth embodiment, wherein the expected ratio defines a center of the quality control window.

[0061] In an eleventh embodiment, a system for mud logging includes a first degasser configured to obtain a first gas sample from a circulating drilling fluid; a second degasser configured to obtain a second gas sample from the circulating drilling fluid; a first gas measuring device configured to perform a first gas measurement of a component of the first gas sample; a second gas measuring device configured to perform a second gas measurement of a component of the second gas sample; and a processor configured to: receive the first gas measurement and the second gas measurement; define a quality control window for the first gas measurement based on the second gas measurement; and cross-quality control the first and second gas measurements by comparing the first gas measurement to the quality control window.

[0062] The twelfth embodiment may include the eleventh embodiment, wherein the first gas measuring device includes a first gas chromatography device, which is configured to measure the composition of at least one alkane gas in the first gas sample, and the second gas measuring device includes a second gas chromatography device, which is configured to measure the composition of at least one alkane gas in the second gas sample.

[0063] A thirteenth embodiment may include any of the eleventh to twelfth embodiments, wherein the processor is further configured to generate a log depicting the first gas measurement and the quality control window.

[0064] A fourteenth embodiment may include any one of the eleventh to thirteenth embodiments, wherein defining the quality control window further comprises determining an expected ratio of the first gas measurement to the second gas measurement, wherein the expected ratio is equal to a coefficient multiplied by the ratio of the drilling fluid flow rate through the first degasser and the drilling fluid flow rate through the second degasser.

[0065] A fifteenth embodiment may include any one of the eleventh to fourteenth embodiments, wherein defining the quality control window further comprises defining a first control limit and a second control limit according to the expected ratio to define the quality control window.

[0066] In a sixteenth embodiment, a method for mud logging includes obtaining a first gas sample and a second gas sample from a circulating drilling fluid while drilling a subsurface wellbore using corresponding independent first and second degassers; performing first and second gas measurements on the corresponding first and second gas samples obtained using independent first and second gas analyzers; determining an expected ratio of the first and second gas measurements; determining a first cross-quality control limit and a second cross-quality control limit based on the expected ratio to define a quality control window; and cross-quality controlling the first and second gas measurements by comparing the first gas measurement with the quality control window.

[0067] A seventeenth embodiment may include the sixteenth embodiment, further comprising adjusting the first gas measurement or the second gas measurement when the first gas measurement is outside the quality control window.

[0068] An eighteenth embodiment may include any one of the sixteenth to seventeenth embodiments, wherein the first degasser and the second degasser are independently quality controlled; the first gas analyzer and the second gas analyzer are independently quality controlled; the first gas measurement and the second gas measurement are independently quality controlled; the second gas measurement is independently quality controlled; and the cross quality control includes comparing the first independently quality controlled gas measurement with a quality control window.

[0069] A nineteenth embodiment may include any of the sixteenth to eighteenth embodiments, wherein the expected ratio is equal to a coefficient multiplied by a ratio of a drilling fluid flow rate through the first degasser to a drilling fluid flow rate through the second degasser.

[0070] A twentieth embodiment may include any one of the sixteenth to nineteenth embodiments, wherein the expected ratio defines a center of the quality control window.

[0071] Although the crossover quality control of mud logging measurements has been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims

1. A method for mud logging, comprising: performing a first gas measurement on a first gas sample obtained from circulating drilling fluid on the drilling rig using a first gas chain; performing a second gas measurement on a second gas sample obtained from circulating drilling fluid on the drilling rig using a second gas train; defining a quality control window for the first gas measurement based on the second gas measurement; and The first gas measurement and the second gas measurement are cross-quality controlled by comparing the first gas measurement to the quality control window. 2 . The method according to claim 1 , wherein the first gas chain comprises a first degasser and a first gas measuring device, and the second gas chain comprises a second degasser and a second composition measuring device.

3. The method according to claim 1, wherein: The first gas measurement is independently quality controlled; The second gas measurement is independently quality controlled; The defining includes defining a quality control window for the first independently quality controlled gas measurement based on the second independently quality controlled gas measurement; and Crossover quality control involves comparing the gas measurement of the first independent quality control with the quality control window.

4. A system for evaluating downhole gas composition measurements, the system comprising: a first degasser configured to obtain a first gas sample from a circulating drilling fluid; a second degasser configured to obtain a second gas sample from the circulating drilling fluid; a first gas measurement device configured to perform a first gas measurement of a composition of the first gas sample; a second gas measurement device configured to make a second gas measurement of a composition of a second gas sample; and A processor configured to: receiving a first gas measurement and a second gas measurement; defining a quality control window for the first gas measurement based on the second gas measurement; and The first gas measurement and the second gas measurement are cross-quality controlled by comparing the first gas measurement to the quality control window.

5. A system according to claim 4, wherein the first gas measurement device includes a first gas chromatography device, which is configured to measure the composition of at least one alkane gas in the first gas sample; and the second gas measurement device includes a second gas chromatography device, which is configured to measure the composition of at least one alkane gas in the second gas sample.

6. The system of claim 4, wherein defining the quality control window further comprises determining an expected ratio of the first gas measurement to the second gas measurement, wherein the expected ratio is equal to a coefficient multiplied by a ratio of a drilling fluid flow rate through the first degasser and a drilling fluid flow rate through the second degasser.

7. A method for mud logging, comprising: while drilling a subterranean wellbore, obtaining a first gas sample and a second gas sample from a circulating drilling fluid using respective independent first and second degassers; Performing first gas measurement and second gas measurement on the obtained corresponding first gas sample and second gas sample using independent first gas analyzers and second gas analyzers; determining an expected ratio of the first gas measurement to the second gas measurement; determining a first crossover quality control limit and a second crossover quality control limit based on the expected ratio to define a quality control window; and The first gas measurement and the second gas measurement are cross-quality controlled by comparing the first gas measurement to the quality control window.

8. The method of claim 7, further comprising adjusting the first gas measurement or the second gas measurement when the first gas measurement is outside the quality control window.

9. The method according to claim 7, wherein: The first degasser and the second degasser are independently quality controlled; The first gas analyzer and the second gas analyzer are independently quality controlled; The first gas measurement and the second gas measurement are independently quality controlled; The second gas measurement is independently quality controlled; and Crossover quality control involves comparing the gas measurement of the first independent quality control with the quality control window.

10. The method of claim 7, wherein the expected ratio defines a center of the quality control window.

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