Drilling - Lecture 5 Notes

Outlines

  • Mod logger and Abbreviation Terms

  • Sample Catcher

  • Mud logger

Learning Outcome

By the end of the Lecture:

  • To understand the fundamentals of drilling fluids.

  • To learn about the Mud functions.

  • To learn about the parameters and tests.

Abbreviations

Operation Abbreviations:

  • R/U: Rig Up

  • R/M: Rig Move

  • R/D: Rig Down

  • R/R: Rig Release

  • M/U: Make Up

  • LCM: Lost Circulation Material

  • WOB: Weight on bit

  • WOC: Weight on cement

  • RIH: Run In Hole

  • TDS: Top Drive System

  • POOH: Pull Out Of Hole

  • BHA: Bottom Hole Assembly

  • CSG: Casing

  • W/T: Wiper Trip

  • DP: Drill Pipe

  • W/L: Wire Line Logging

  • OEDP: Open End Drill Pipe

  • O/P: Over Pull/ton

  • B/O: Break Out

  • TD: Total Depth

Drilling Parameters and Units

  • WOB: Weight on Bit, Unit: Ton.

  • HKLD: Hook Load, Unit: Ton.

  • TRQ: Torque, Unit: Kft.

  • RPM: Rotation Per Minute, Unit: RPM.

  • L-Depth: Lag Depth, Unit: m.

  • L-Time: Lag Time, Unit: Min.

  • SPM: Stroke Per Minute, Unit: SPM.

  • Flow in/out: Flow in/out Gallon per Minute, Unit: GPM.

  • BLKHGT: Block Height, Unit: m.

  • Pit-Act: Pit Active, Unit: bbl.

  • Pit Tot: Pit Total, Unit: bbl.

  • TBR: Total Bit Revaluation, Unit: TBR.

  • I-ROP: Instance Rate of Penetration, Unit: Meter per Hour.

  • A-ROP: Average Rate of Penetration, Unit: Meter per Hour.

  • SPP: Stand Pipe Pressure, Unit: Кра.

Responsibilities of a Sample Catcher

  • Collecting Cuttings: Retrieves rock cuttings at regular depth intervals.

  • Washing & Sieving: Cleans and sieves the cuttings to remove drilling mud.

  • Labeling & Storage: Properly labels and stores samples for further geological examination.

  • Fluorescence Testing: Tests for hydrocarbon indications under UV light.

  • Gas Monitoring: Works with mud loggers to detect hydrocarbon gases in the drilling mud.

  • Maintaining Sample Integrity: Ensures proper handling to avoid contamination.

Mud Logger

  • A Mud Logger is a field geologist responsible for monitoring and analyzing drilling fluid returns (mud) to evaluate subsurface formations, detect hydrocarbons, and ensure drilling safety.

  • They work on-site at oil and gas drilling rigs, collecting and interpreting geological and engineering data in real time.

What Mud Logger Can Do

  • Samples description, analysis, and Interpretation.

  • Hydrocarbons (Oil & Gas) Shows Evaluation.

  • Formation Tops Identification.

  • Lag time check.

  • Determination of zone of interest.

  • Preparation and updating of Master Logs.

  • Casing and Core points determination.

  • Assist the well-site geologist during coring operations.

  • Provide written reports to the Geological Supervisor.

Components of Mud Logging

  • Drilling Mud:

    • Drilling mud (or drilling fluid) is a vital component used to lubricate the drill bit, carry cuttings to the surface, and control formation pressure.

    • Mud loggers analyze the mud’s properties, such as its density, viscosity, and the presence of gas or oil.

  • Cuttings Analysis:

    • Rock cuttings are small particles of rock that are brought to the surface by the drilling fluid.

    • Mud loggers collect and examine cuttings to identify the lithology (rock type), formation boundaries, and potential hydrocarbon zones.

  • Gas Analysis:

    • Gas from the formation is often brought to the surface with the drilling mud.

    • Mud loggers use specialized equipment to analyze the types and quantities of gases (such as methane, ethane, propane, and hydrogen sulfide) present in the drilling mud, which can provide valuable information about the subsurface formation and its potential for oil and gas production.

  • Hydrocarbon Detection:

    • The presence of hydrocarbons in the mud is one of the most important indicators during mud logging.

    • Mud loggers use gas chromatography or flame ionization detection (FID) to detect and quantify hydrocarbons, providing crucial data for reservoir evaluation.

Mud Logging Process

  • Sampling and Collection:

    • Mud loggers collect and examine samples of drilling mud, cuttings, and gas at regular intervals.

    • The samples are analyzed for their geological composition and to identify any signs of hydrocarbon presence.

  • Gas Monitoring:

    • Gas is sampled continuously or periodically from the mud system.

    • Mud loggers use a range of instruments, such as gas detectors and chromatographs, to measure gas concentration and detect specific gases that may indicate productive formations.

  • Cuttings Evaluation:

    • The rock cuttings are analyzed for their mineralogical composition and grain size.

    • They are examined to determine the depth of the well and to correlate with previously drilled sections, identifying new zones of interest.

  • Data Logging and Reporting:

    • All collected data are logged and recorded in real-time.

    • Mud loggers provide detailed reports to the drilling team, including gas readings, lithological interpretations, and other relevant geological data.

    • This information helps inform decision-making on drilling parameters, mud composition, and safety.

Cutting Samples Description and Results

  • Lithology:

    • Rock Type: Identify the type of rock (e.g., sandstone, shale, limestone, etc.).

    • Color: Note the color of the cuttings, both when dry and when wet.

    • Grain Size: Describe the grain size, such as fine, medium, or coarse.

    • Shape and Sorting: Comment on the shape of the grains (e.g., angular, sub-rounded) and how well-sorted they are.

  • Texture:

    • Fabric: Describe the arrangement and orientation of the grains.

    • Porosity: Note the presence and type of porosity (e.g., intergranular, vuggy).

    • Cementation: Indicate the type of cement binding the grains (e.g., calcite, silica).

  • Mineralogy:

    • Mineral Content: Identify the primary minerals present in the cuttings.

    • Accessory Minerals: Note any secondary or accessory minerals.

    • Fossils: Mention the presence of fossils if any are observed.

  • Composition:

    • Matrix: Describe the fine-grained matrix between the larger grains.

    • Cement: Comment on the type and amount of cementing material.

  • Additional Observations:

    • Hardness: Estimate the hardness of the cuttings using the Mohs scale.

    • Reaction to Acid: Test the cuttings with hydrochloric acid to check for the presence of carbonate minerals.

    • Miscellaneous: Note any other significant features, such as the presence of oil stains, sulfide minerals, or unusual inclusions.

How to Describe Cutting

  • Miscellaneous: Note any other significant features, such as the presence of oil stains, sulfide minerals, or unusual inclusions.

  • Example Description:

    • Sample Depth: 2000 meters

    • Lithology: The cuttings are primarily composed of medium-grained sandstone.

    • Color: Light gray when dry, darkening to dark gray when wet.

    • Grain Size: Medium-grained.

    • Shape and Sorting: Sub-rounded grains, moderately sorted.

    • Texture: The cuttings exhibit a well-developed intergranular porosity.

    • Cementation: The grains are cemented with silica.

    • Mineralogy: Dominantly quartz with minor feldspar and trace amounts of mica.

    • Additional Observations: No visible fossils. Cuttings are hard (around 7 on the Mohs scale). No reaction to dilute hydrochloric acid.

  • In the context of drilling, abbreviations are often used to describe cutting samples and their lithology.

Cutting Samples and Abbreviations

  • Common Lithology Abbreviations:

    • Sd: Sandstone

    • Sltst: Siltstone

    • Sh: Shale

    • Lm: Limestone

    • Dol: Dolomite

    • Ch: Chert

    • Gn: Gneiss

    • Sl: Slate

    • Congl: Conglomerate

  • Abbreviations for Describing Cutting Samples:

    • DCS: Describe Cutting Sample

  • Example Abbreviations for Mixed Lithologies:

    • Sd-Dol: Sandstone and Dolomite

    • Sh-Lm: Shale and Limestone

    • Sltst-Sd: Siltstone and Sandstone

    • Lm-Dol: Limestone and Dolomite

Wellsite Geologist: Cutting

  • The cutting samples contribute the basic information about the well.

  • Ditch or cutting samples are the only source of information on lithology, porosity and hydrocarbon shows when unforeseen events preclude wireline logs, cores and sidewalls core samples.

  • Wellsite geologist will make sure to obtaining the most representative cuttings possible under existing conditions.

  • This will require particular care during periods of caving shales, air drilling or under balance drilling, lost circulation, and other hole problems.

  • Wellsite often finds himself at odds with rig personnel whose ultimate aim is to drill the hole as rapidly as possible, often at the expense of obtaining good cuttings.

  • It has generally been found that when the quality of the samples deteriorates to the point that they are unreliable, the drilling and mud program is not being followed by the contractor. This should be brought to the attention of the drilling supervisor.

  • When a compromise cannot be reach and it appears that hydrocarbon shows could be overlooked due to the poor quality of the ditch samples this should be brought to the attention of Management.

  • Collection and Preparation:

    • Every drilling Rig has a shaker screen for separating the cuttings from the mud as they reach the surface.

Wellsite Geologist: Cutting (Continued)

  • The shaker screen may or may not be a good place from which to take cuttings samples.

  • If the mesh size is small enough to remove small cuttings and the well is an area where there is reason to believe that no unconsolidated sand will be encountered, the shaker screen will serve as a satisfactory source of samples.

  • If the shaker screen is used, a broad or box should be placed at the foot of the screen for collection of composite samples.

  • A settling box through which a small portion of the mud is diverted will generally serve to collect more representative samples than those caught from the shaker screen. The use of such a box ensures that a composite sample is collected and afford the surest means of collecting small cutting and finely divided sand.

  • If the drill rate indicates sandstone but none is present in the cutting samples and an increase of loose sand is observe in the de-sanders or de-silter, a settling box should be used.

  • Through zones of lost circulation, such a box provides practically the only means of catching samples while the shaker is by passed. Cuttings will not settle out very satisfactorily, however, from drilling mud of very high density and gel strength.

  • Washing and preparation of the sample of cuttings to be examined is extremely important.

  • In hard rock areas, the cuttings are usually quite easily cleaned. Washing usually is matter of merely hosing the sample in a container with a jet of water to remove the mud film.

Differentiating Between Limestone and Dolomite During Drilling for Mud Logging Geologist

  • Drilling Parameters:

    • Rate of Penetration (ROP): Dolomite is generally harder than limestone, resulting in slower ROP.

    • Drilling Pressure: Increased drilling pressure may indicate dolomite.

    • Cuttings Analysis: Examine drill cuttings for dolomite's characteristic rhombohedral crystals.

  • Chemical Analysis:

    • Calcium-Magnesium Ratio: Dolomite contains magnesium (Mg), whereas limestone is primarily calcium carbonate (CaCO3)(CaCO_3).

    • X-Ray Fluorescence (XRF): Analyze drill cuttings or core samples for Mg and Ca concentrations.

    • Acid Solubility Test: Dolomite reacts slower to hydrochloric acid (HCl) than limestone.

  • Visual Inspection:

    • Color: Dolomite often appears more yellowish or brownish than limestone.

    • Texture: Dolomite can exhibit a sugary or crystalline texture.

    • Fossil Content: Dolomite frequently contains fewer fossils than limestone.

  • Resources:

    • "Baker Hughes Drilling Fluids and Mud Logging Manual"

    • Journal of Petroleum Science and Engineering

    • "Limestone and Dolomite Identification Using Drilling and Logging Data" (Vol. 172, 2019)

Calcimetry / Dolomimetry

  • Rock Identification

    • Limestones / Silts, Sands characterization

    • % Calcite (after 1 minute) 95 to 100, % Silt, Sand 0 to 5: Limestone

    • % Calcite (after 1 minute) 50 to 95, % Silt, Sand 5 to 50: Silty, Sandy Limestone

    • % Calcite (after 1 minute) 5 to 50, % Silt, Sand 50 to 95: Calcareous Silt, Sand

    • % Calcite (after 1 minute) 0 to 5, % Silt, Sand 95 to 100: Silt, Sand

    • Limestones / Clays, Shales characterization

    • % Calcite (after 1 minute) 95 to 100, % Clay, Shale 0 to 5: Limestone

    • % Calcite (after 1 minute) 65 to 95, % Clay, Shale 5 to 35: Argillaceous Limestone

    • % Calcite (after 1 minute) 35 to 65, % Clay, Shale 35 to 65: Marl

    • % Calcite (after 1 minute) 5 to 35, % Clay, Shale 65 to 95: Calcareous Clay, Shale

    • % Calcite (after 1 minute) 0 to 5, % Clay, Shale 95 to 100: Clay Shale

    • Limestones / Dolomites characterization

    • % Calcite (after 1 minute) 90 to 100, % Dolomite (after 15 minutes) 0 to 10: Limestone

    • % Calcite (after 1 minute) 50 to 90, % Dolomite (after 15 minutes) 10 to 50: Dolomitic Limestone

    • % Calcite (after 1 minute) 10 to 50, % Dolomite (after 15 minutes) 50 to 90: Calcareous Dolomite

    • % Calcite (after 1 minute) 0 to 10, % Dolomite (after 15 minutes) 90 to 100: Dolomite

Oil Show

  • The presence of liquid hydrocarbons in the mud or inside the cuttings is characterized by:

    • The direct or natural fluorescence

    • The odour and colour

    • The distribution: staining and bleeding

    • The solvent fluorescence

  • Shows are ephemeral, because liquid hydrocarbons are highly volatile and are a function of:

    • Mud weight

    • Mud type (WBM or OBM)

    • Bits used

    • Flushing while drilling (overbalance)

    • Sample washing
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