bottoms-up mud sample

Bottoms-up mud sample collection procedure and field show evaluation at the WCSB wellsite requires the mud logger to collect the lag sample at the precise moment it arrives at the surface flowline based on the calculated bottoms-up time, then subject the sample to a standardized sequence of visual, ultraviolet fluorescence, and solvent cut examinations to classify the hydrocarbon show by type, intensity, and fluid phase before reporting the result to the company man and geologist for drilling decisions, because a correctly timed and thoroughly examined bottoms-up mud sample provides the most representative indication of formation fluid type and show intensity of any sample collected during the drilling program. The bottoms-up mud sample at a WCSB wellsite is physically collected from the possum belly (the settling tank immediately downstream of the shaker) or from the bell nipple flowline using a 1-liter sample jar at the calculated bottoms-up time, which is the elapsed circulation time in minutes equal to the annular volume from bit to surface divided by the pump output per minute; the collected sample is a composite of the drilling fluid that was in contact with the formation at the time of bit penetration and therefore carries the fluorescent hydrocarbons, formation water, and gas extracted from the formation during drilling, with the sample quality degrading if collected more than 15 to 30 minutes after the calculated bottoms-up arrival because further dilution by circulating mud reduces the hydrocarbon concentration in the sample toward background. In WCSB conventional oil exploration wells in the Cardium, Viking, and Mannville formations, the bottoms-up mud sample fluorescence examination under long-wave ultraviolet light (365 nm UV lamp) is the primary field screening tool for oil shows: crude oil fluoresces with a characteristic color and intensity that depends on its API gravity (light crude oils at 35 to 50 API fluoresce pale yellow to white; medium crude at 25 to 35 API fluoresces yellow to orange; heavy crude at below 25 API fluoresces brown to dull orange; condensate and very light crude can fluoresce pale blue-white to white), and the fluorescence color provides the mud logger and wellsite geologist with a rapid field estimate of the reservoir oil gravity before laboratory analysis is available. The cut test adds a second diagnostic dimension to the field show evaluation: a small portion of the mud sample is placed in a watchglass, 1 to 2 mL of a solvent (traditionally white gasoline, now typically heptane or odorless mineral spirits for safety) is added and swirled to dissolve any oil present in the sample, and the solvent-mud solution is re-examined under UV light; a streaky or bloomy fluorescence in the cut solution confirms the presence of extractable crude oil and distinguishes a genuine oil show from fluorescent drilling fluid additives or naturally fluorescent formation minerals that may produce false positive UV readings on the uncut sample. Understanding the bottoms-up mud sample collection timing calculation for WCSB lag sample accuracy, the fluorescence color classification system for WCSB crude oil API gravity estimation, the cut test procedure and interpretation for distinguishing genuine oil shows from background fluorescence, the show intensity classification scale used in WCSB mud log reports (no show, trace, fair, good, very good, excellent), and the regulatory reporting requirements for show identification gives WCSB mud loggers, wellsite geologists, and company men the field evaluation framework to make real-time drilling decisions from bottoms-up sample data before laboratory analyses are available.

• Bottoms-up sample timing calculation and lag correction for WCSB horizontal wells: The lag time for a WCSB horizontal well bottoms-up mud sample must account for the full annular volume from the bit through the lateral, through the curve, and up the vertical section to surface; the annular volume calculation uses the same capacity tables as the well control kill sheet, with each casing and open-hole section contributing its specific annular volume per metre based on casing ID and drill pipe OD. For a WCSB Montney horizontal well at 6,200 m measured depth with a 1,800 L/min circulation rate, the annular volume is approximately 47 m3 (7.6 L/m average annular capacity) and the lag time is 47,000 L / 1,800 L/min = 26.1 minutes; the mud logger starts the stopwatch when the bit penetrates the formation of interest and collects the bottoms-up sample at 26.1 minutes at the possum belly. Lag correction for pump stroke count is more accurate than time-based lag in WCSB horizontal wells where pump rate changes during connections introduce timing errors; 47,000 L / 9.3 L/stroke = 5,054 strokes at the mud logger's stroke counter is the more reliable bottoms-up target in WCSB horizontal programs where connection time adds to lag uncertainty.
• Fluorescence examination technique and color classification for WCSB crude oil show evaluation: The fluorescence examination of a WCSB bottoms-up mud sample requires a calibrated 365 nm UV lamp (minimum 4 watts) held 10 to 15 cm above the sample jar in a darkened examination area; the mud logger and geologist observe both the fluorescence color and intensity, recording both on the mud log. WCSB Cardium oil (typically 38 to 45 API) fluoresces pale yellow-white with a weak to moderate intensity that is easily distinguished from the brown-orange fluorescence of Mannville heavy oil (18 to 25 API) or the brilliant white to pale blue-white fluorescence of Montney condensate (above 50 API NGL). The fluorescence intensity is graded on a 5-point scale: 1 (trace, barely visible against background), 2 (weak, clearly visible but dim), 3 (moderate, bright but not brilliant), 4 (strong, brilliant and easily visible), 5 (very strong, blindingly bright, characteristic of saturated reservoir). A WCSB mud log reporting fluorescence as "good yellow-white fluorescence intensity 3-4 on cut" indicates a Cardium-type medium to light crude oil show of commercial interest requiring follow-up core or DST evaluation.
• Cut test procedure and solvent selection for WCSB mud sample show evaluation: The cut test for WCSB bottoms-up mud sample evaluation uses a 5 mL spoonful of the sample material placed in a 10 cm diameter watchglass; 2 mL of heptane (n-C7, preferred for safety and consistent solvency) is added and the mixture is stirred with a glass rod for 30 seconds, then allowed to settle for 1 minute before UV examination. A positive cut result shows fluorescence blooming outward from the mud particles into the solvent layer as dissolved oil distributes throughout the heptane, with the bloom color matching the expected crude gravity; a negative cut (no bloom, solvent remains dark under UV) indicates that the UV fluorescence on the uncut sample was produced by fluorescent drilling fluid components (synthetic base oil in WCSB OBM wells) or naturally fluorescent formation minerals such as calcite cement veins or sparite in Devonian carbonates. In WCSB oil-base mud wells, the cut test interpretation requires a reference sample of the base mud alone to establish the background fluorescence level from the synthetic oil carrier, and only fluorescence in the cut sample that exceeds background by at least two intensity grades is recorded as a genuine hydrocarbon show.
• Show classification and mud log reporting standards for WCSB regulatory submissions: WCSB mud log show classification uses a standardized terminology required by AER for all Alberta wells: "No Show" (no fluorescence, no cut response), "Stain" (very faint fluorescence on uncut only, no cut bloom), "Trace Show" (faint fluorescence with weak cut bloom, non-commercial), "Fair Show" (moderate fluorescence with positive cut bloom, warrants geological evaluation), "Good Show" (strong fluorescence with vigorous bloom, commercial reservoir candidate), "Excellent Show" (brilliant fluorescence with immediate strong bloom, strong commercial indication). The mud log submitted to AER must record the show classification at each bottoms-up sample depth, the fluorescence color and intensity grade (1 to 5), the cut test result (positive/negative/background), and the mud logger's qualitative assessment of oil gravity from fluorescence color. WCSB operators drilling in H2S zones must additionally classify any gas shows from the H2S sensor readings accompanying the bottoms-up sample, with H2S concentration in ppm reported at the time of sample arrival to correlate gas influx with formation depth.
• Bottoms-up mud sample preservation and dispatch for laboratory geochemical analysis in WCSB exploration wells: When a bottoms-up mud sample from a WCSB exploration well shows a fair to excellent oil show on field examination, the mud logger preserves a 500 mL split of the sample in a sealed glass jar with no headspace for laboratory gas chromatographic (GC) analysis and whole oil geochemical fingerprinting. The sample must be stored at 4 degrees C from collection to dispatch (within 4 hours) to prevent light hydrocarbon evaporation; loss of C1-C5 components before GC analysis introduces negative bias in the oil API gravity estimate and can misrepresent the GOR of the show fluid. WCSB exploration operators specify that any bottoms-up sample with fluorescence intensity grade 3 or above be preserved and dispatched to the laboratory within 8 hours of collection, with the mud logger recording the sample collection time, temperature at collection, and any delays in cold chain custody on the chain-of-custody form that accompanies the sample to the laboratory for the geochemical correlation report used in the well's final geological evaluation.

Bottoms-Up Show Classification Triggering Core Decision on WCSB Cardium Exploration Well

A west-central Alberta Cardium exploration well was drilling through a 12 m gross sand interval at 2,240 m depth when the mud logger collected the bottoms-up sample at the calculated lag of 1,820 strokes (22 minutes at 1,650 L/min). Visual examination of the sample showed oil-stained cuttings with cream to pale yellow coloring; UV fluorescence examination showed brilliant yellow-white fluorescence with intensity grade 4 on the uncut sample. The cut test with heptane produced an immediate strong fluorescence bloom with a yellow-white color consistent with 38 to 44 API crude, graded as positive intensity 4. The mud logger reported "Good Show, yellow-white fluorescence intensity 4, positive cut intensity 4, estimated 38 to 44 API" to the company man and geologist within 5 minutes of sample collection. Based on the field show classification and the sand gamma ray response showing GR below 40 API units on the LWD real-time log, the company man made the decision to call for a core barrel run over the 12 m interval. The core recovered 9.8 m of productive Cardium channel sand with average porosity 14% and oil saturation 68%, subsequently tested at 28 m3/day on a 48-hour DST, confirming the bottoms-up show classification as a reliable field indicator that justified the $85,000 core barrel cost.

Related Terms

Bottoms-up mud sample is the primary entry covering lag sample collection for H2S monitoring and gas chromatographic show evaluation; this companion entry covers field fluorescence examination and cut test procedure, UV color interpretation for API gravity estimation, and AER mud log reporting standards for WCSB wells. Mud logging is the wellsite service responsible for collecting and evaluating bottoms-up mud samples; the mud logger calculates lag time, performs UV and cut examinations, classifies the show, and records results on the mud log per AER standards. Fluorescence is the optical property of crude oil under ultraviolet light that enables field show classification; fluorescence color correlates with crude oil API gravity and lets the WCSB geologist estimate reservoir fluid type before laboratory analysis is available. Oil show is the field classification assigned based on bottoms-up mud sample fluorescence and cut test results; show grade from trace to excellent determines whether the program proceeds, requests a core barrel, or triggers a DST. Lag time is the calculated circulation delay that determines when the bottoms-up sample arrives at surface; accurate lag calculation from annular volume and pump output is the prerequisite for a representative sample that correctly correlates hydrocarbon shows to formation depth.