33. Describing and logging oil shows

A. Degree of oil stain

1. No visible oil stain

2. Spotty oil stain

3. Streaky oil stain

4. Patchy oil stain

5. Uniform oil stain

B. Colour of oil stain

1. No visible oil stain

2. Light brow oil stain

3. Medium brow oil stain

4. Dark brow oil stain

5. Black asphalt residue (dead oil)

C. Degree of oil fluorescence

1. No visible oil fluorescence

2. Spotty oil fluorescence

3. Streaky oil fluorescence

4. Patchy oil fluorescence

5. Uniform oil fluorescence

D. Colour of oil fluorescence

1. No visible oil fluorescence

2. All shades of blue

3. All shades of yellow

4. All shades of gold

5. All shades of brow

E. Degree of cut

1. Excellent

2 Strong

3. Moderate

4. Slight

5. Very slight

F. Colour of cut

1. All shades of Yellow

2. All shades of brown

G. Degree of cut fluorescence

1. Instantaneous

2. Fast

3. Streaming - poor, fair, good.

4. Slow.

5. Crush- poor, fair, good.

B. Colour of cut fluorescence

1. Bright (colour) residual ring - live oil

2. Medium (colour) residual ring - live oil

3. Dull (colour) residual ring - live oil

4. Dark brown or black non-fluorescent ring - dead oil

- EXAMPLE:

SS: CLR-WH, F-MGN, MOD SRT, SBANG,HD, W/CAIC CMT, HI GLAUC, FRI, GD POR, W/ 50% STK, LT BRN O STN, STK,BRI YEL FLU, STRG YEL STRM CUT, BRI YEL RING.

= Sandstone: Clear to white, fine to medium grained, moderately sorted, subangular, hard, with calcareous cement, highly gluconitic, friable, good porosity, with 50% streaky, light brown oil staining, streaky, bright yellow fluorescence, strong yellow streaming cut, bright yellow ring.

NOTES Of CAUTION

1. Many rocks, notably Limestone and dolomite, exhibit mineral fluorescence, it is important to distinguish this from oil fluorescence. When solvent is placed on cuttings showing only mineral fluorescence, nothing happens - the Solvent remains clear, and no fluorescent residual ring is left on the dish after evaporation.

2. Care should be taken not to confuse oil staining with contamination of sample by pipe dope, rig grease or fluorescent mud additives. If in doubt, contamination should be checked under UV light for comparison.

3. Before using chlorothene to determine oil shows, check the solvent for contamination. Pour some onto a clean spot dish and allow evaporation, If a fluorescent ring forms then it is contaminated and should be discarded immediately to avoid logging false oil shows.

4. Before a spot dish is used it should be checked for contamination. under UV light. The correct method of cleaning a spot plate is to wash it with powdered soap, rinse it thoroughly to remove soap, and stand on end to allow evaporation of water. (soap and some towel fibers exhibit fluorescence).

5. Chlorothene must be stored or transported in glass bottles with bakellte tops and foil liner, or in tin cans for larger quantities.

For sample analysis, chlorothene should be kept in glass bottles with glass stoppers. Plastic containers, and rubber stoppers and droppers will eventually dissolve and contaminate the chlorothene, therefore, they should not be used.

6. Oil shows can be evaluated in oil base mud especially with cores. Ditch cuttings of lower permeability oil bearing rocks can also be noticed, regardless of the mud system by carefully searching with the fluoroscope for contrasts between the fluorescence of the oil mud and that of any natural oil.

DEFINITION OP TERMS

Several of the common terms which are normally found in descriptions of shows may carry different meanings for the person who wrote them than for the person reading them.

An attempt at standardizing definitions is made here.

1. STAINING: The color added to a rock by oil or organic material remaining in pores or coating the grain surfaces. This color must be described independently of the background color of the rock, which is a composite color compared of the colors of the various minerals which make up the rock.

2. FLUORESCENCE: The ability of the oil on or in the cuttings to absorb ultraviolet rays and give off visible light. Care must be taken to ensure that the fluorescence reported for a show is a hydrocarbon fluorescence and not caused by minerals.

3. CUT: Solubility of the oil in the sample. A cut is obtained by exposing cuttings to a solvent such as chlorothene or carbon-tetra-chloride. This cut fluorescence is the estimated amount of fluorescing material that streams from the sample as observed under fluorescent light, or the fluorescent ring remaining on the dish after the solvent has completely evaporated,

4. LIVE OIL: Oil which has a high percentage of volatile (gas) in solution to that it is mobile in the reservoir.

5. DEAD OIL: Oil in the reservoir which has little or no gas in solution.

6. RESIDUAL OIL: Particulate oil in a sample Which generally occurs as black particles disseminated throughout the smaller pores of the sample. Residual oil may be bitumen, pyrobitumen or biowaxes.

7. BITUMEN (Asphalt-Tar): A generic term applied to most natural inflammable substances composed principally of a mixture of hydrocarbons substantially free of its volatile compounds. It generally occurs in samples as a heavy, viscous, semi-solid black residue. Bitumen will not exhibit any visual fluorescence under fluoroscope, but its cut may do. It can be dissolved by benzene, chlorothene and carbontetrachloride. Bitumen melts and flow at temperatures above 130 F.

8. PYROBITUMEN: A material resembling bitumen, but composed primarily of carbon. It exhibits no fluorescence or cut and it is totally insoluble in any solvent. As opposed to bitumen, it only melts at very high temperatures

BIOVAXES: When an oil is attached by bacteria, the ending product is an unusual high-melting wax This biowax is black (due to asphaltnes), has no fluorescence and insoluble. · The physical appearance may.be similar a hand black shoe polish. Visually, one may have difficulty distinguishing between pyrobitumen and biowaxes in rock samples.

Distinguishing "live” oil from "dead" oil

A highly interpretative method of defining Live from Dead oils is as follows:-

To determine weather live oil occurs , the cuttings are put in a dish of water, placed under an ultraviolet light and viewed through a microscope while crushing the Samples. This operation is best performed by using a “Corvascope”.

The data obtained by use of this method in conjunction with such parameters as staining, fluorescence and cut can then be combined to distinguish between the two types of oil.

A) When the oil moves rapidly to and spreads onto the surface of water; it is live oil trapped in the smaller pores of the cuttings.

B) If the oil moves slowly out of the cutting but Still spreads on the surface; it is live oil occurring in a tight rock.

C) Oil which moves slowly to the surface and does not spread but remains in droplets, is dead oil.

D) No oil moves from the crushed cuttings:-

1- Gas - light to no stain, weak fluorescence, no cut

2- Live oil - water-wet - high porosity and permeability, light stain, fluorescence and cut, flushed and gas expansion,

3- Bitumen - dark stain and cut.

4-. Pyrobitumen and biowaxes - black stain, no fluorescence or cut.

OIL FLUORESCENCE (AFTER LYNCH)

A.P.I. GRAVITY	COLOUR
BELOW 15 °	BROWN
15 ° - 25°	ORANGE (GOLD)
25° - 35°	YELLOW / CREAM
35° - 45°	WHITE
Over 45°	BLUE / WHITE /. VIOLET

Miscellaneous tests For hydrocarbons