PETROLEUM DEVELOPMENT GEOLOGY WELLSITE GEOL

• Wellsite geology is hybrid of appllied geology on oil and gas well drilling , its study rock cuttings and wireline logs from oil and gas wells to determine what rock formations are

• Wellsite geology is hybrid of

appllied geology on oil and gas well

drilling , its study rock cuttings and

wireline logs from oil and gas wells

to determine what rock formations

are being drilled into and how the

drilling should proceed.

• Wellsite Geologist is geologist in

charge on data acquisition from oil

and gas well drilling operation

They are required to monitor vital

operations during the course of the

well, make sure that the well

program are carried out perform

formation evaluation activities to

ensure the well is drilled and

evaluated in the most safe, efficient

manner, and cost-effective They

also liaise with drilling engineers,

petroleum engineers and mud

logging geologist during the course

JOB PORPOSES

6 MUD & CHEMICAL ENGINEER & CREW

7 CEMENTING ENGINEER & CREW

8 WIRELOGGING ENGINEER & CREW

9 TESTING ENGINEER & CREW

10 OTHER SERVICES ENGINEERS & CREW

11 SUPPORTING CREW

1 Supervision of “Formation Evaluation”

contractors (Mud Logging Geologists, MWD Logging Engineers, Wireline Logging Engineers, Coring and Well Testing Personnel)

2 Logistics concerning the formation

evaluation contractors and their

equipment

3 All safety aspects for the well and

personnel during these evaluation

operations

4 Quality control of all evaluation results

and logs prior to accepting the data or logs from those contractors

5 Providing relevant correlation and well

data to those contractors during their operations

6 Checking all reports and logs from the

evaluation contractors prior to sending them to oil company offices

7 Monitoring and supervising the

collecting, processing and dispatching

of formation evaluation samples

8 Safe-guarding the collection, storage

and transmission of information and reports at the wellsite

9 Wellsite interpretation of the formation

evaluation data

10 Checking and occasionally approving

and signing of service reports and

invoices of the formation evaluation contractors

11 Keeping the drilling superintendent

and operations geologist fully

informed of all formation evaluation operations

Wellsite Geologist should be

completely familiar with all

aspects of the drilling

prognosis Particular attention should be paid to any sections which may require geological decisions.

1 Determination of Primary and Secondary Objectives

2 Determination of Casing Points

3 Detection of Overpressured

Intervals

4 Detection of Lost Circulation Zones

5 Correlation and Detection of Marker Horizons

6 Determination of Geologic Basement or Economic Basement

7 Selection of Logging Run Intervals

8 A complete set of correlation logs and reports should be compiled

9 Near by well’s mudlogs, lithlogs and wireline logs should be used

as sources of information

REGIONAL GEOLOGY PREPARATION

FOR WELLSITE GEOLOGIST

to anticipate if it should deviate from the prognosis

• Nature and depth of basement within the basin

• Geologic age of the section

• Depositional environments and expected lithologies

• Tectonic setting within the basin

• Formation pressure anomalies

• Hydrocarbon occurrences within the basin

• Basin correlations

Wireline Logging Unit

• VSP å Used to “look ahead”, formation top confirmation

• RFT å Fluid sampling, Pressure determination, Oil/Water/Gas

gradients

• Resistivity å Water Saturation, Porosity, Hydrocarbon evaluation

• Density & Neutron å Lithology confirmation, Correlation, Porosity, Overpressure detection, Gas/Oil contacts

• Sonic å Porosity, Mechanical properties, Overpressure

• Dipmeters å Structure, Well trajectory, Facies analysis,

Sedimentology

• Sidewall Cores å Biostratigraphy, Geochemistry, Lithology

confirmation, Hydrocarbon evaluation

MWD/FEMWD unit data

• Directional å Borehole Trajectory (MWD), Dogleg

To ensure satisfactory results, the Wellsite Geologist will be responsible for:

î Existence and depth of known markers

î Top and bottom of each reservoir interval

î Gross & net thickness for each reservoir

interval

î Type of hydrocarbon and hydrocarbon/water

contacts

î Average and range of calculated porosity

and water saturation values for each interval

î Rw in the clean, water-bearing formations

î Propose well test intervals

• THE TEAM å MUDLOGGING CREW:

• MUDLOGGING GEOLOGIST (MUDLOGGER)

• PRESSURE ENGINEER / DATA ENGINEER

• SAMPLE CATCHER

• MUDLOGGING GEOLOGIST å

– CUTTING & CORE DESCRIPTION, HYDROCARBON SHOW,

POROSITY ETC.

• PRESSURE ENGINEER & DATA å

– RECORD, MONITOR & ANALYSE THE DRILLING PARAMETERS SUCH AS ROP, RPM, WOB, TORQUE,

– MUD DATA: MUD TANK LEVEL (MUD LOOS & GAIN), MUD

WEIGHT IN/OUT, TEMPERATURE IN/OUT

– MUD PUMP DATA : CAPACITY, EFICIENCY, VOLUME IN ETC.

• SAMPLE CATCHER å

– COLLECT AND PREPARE SAMPLE FOR MUDLOGGING

GEOLOGIST

• DRY SAMPLE

– obtained from the washed samples collected from the 80-mesh sieve A heat source is used for drying purposes.

– Several precautions when drying samples are:

• DO NOT oven dry oil-based mud samples

• Do not over-dry samples, because they will burn (the burning can be mistaken for oil staining)

• Clay samples should not be oven dried - only air dried

• WET SAMPLE

– collected at the shale shaker Normally the drilling fluid is not

rinsed off.

• GEOCHEMICAL SAMPLE

– These samples require special treatment.

– A bacteriocide (i.e Zepharin Chloride) is necessary to prevent the growth of bacteria which can form additional gas The samples are normally sealed at the wellsite, and shipped separately.

Each lithology should be accurately described, and

that observations recorded in the following order:

a Rock Type g Sorting

b Classification h Luster

c Color i Cementation/Matrix

d Hardness/Induration j Visual Porosity

e Grain Size k Accessories/Inclusions

f Grain Shape l Oil Show Indications

Usually major oil company has own cutting description manual and its

standar legend

COMPARISON CHARTS FOR VISUAL ESTIMATION OF

PERCENTAGE COMPOSITION

EVALUATION OF HYDROCARBON SHOWS

• EQUIPMENTS

– CO2 detection

– H2S detection (in exploration & rich sulfur basin)

– total gas detectors that monitor for N, various sulfides and

H may also be used

• The amount of gas recorded is dependent upon many

variables, including;

– Volume of gas per unit volume of formation

– Degree of formation flushing

– Rate of penetration

– Formation pressure

– Gas trap efficiency

– Gas detector efficiency

– Variability of mud flow rate

• True Zero Gas:

– The value recorded by the gas detectors when pure air is passed over the detection block

(generally done during calibration) To ensure a stable zero mark, the detectors should be zeroed prior to drilling, at casing points, logging points, etc

• Background Zero Gas:

– The value recorded by the gas detectors when circulating, off-bottom, in a clean, balanced bore hole Any gases monitored will be from contaminants in the mud or from gas recycling This value

is the baseline from which all gas readings are referenced for the striplog and mud log, but not plotted on the logs This value will change with respect to changes in the mud system (adding

diesel) and hole size, and should be re-established periodically

• Background Gas:

– This is the gas recorded while drilling through a consistent lithology Often it will remain constant, however, in overpressured formations this value may show considerable variation This is the gas baseline which is plotted on the striplog and mud log

• Gas Show:

– This is a gas reading that varies in magnitude or composition from the established background It

is an observed response on the gas detector and requires interpretation as to the cause Not all gas peaks are from drilled formation, some may occur as post-drilling peaks

• Connection Gases:

– Gas peaks produced by a combination of near-balance/ under-balanced drilling and the removal of the ECD by stopping the pumps to make a connection They are often an early indicator of drilling overpressured formations These should be noted, but not included as part of a total gas curve

• Trip Gases:

– Gas peaks recorded after circulation has been stopped for a considerable time for either a bit trip

or a wiper trip As with connection gases, substantial trip gases can indicate a near balance

between the mud hydrostatic pressure and the formation pressure, they should be recorded but not included as part of a total gas curve

SAMPLE:

MUD LOGGING

WELL 123

SAMPLE: MUD LOGGING

Mud-logging Geologist Corner