Hydrocarbon Liquid, Produced Gas, Mud Gas, and Side Wall Core Sampling Procedures

Oil Samples

Production samples should be collected at the well head. Well head samples are preferable to header samples, because even header samples may be contaminated by leaking valves, corrosion inhibitor, etc.  Flush the sampling point, since taps and needle valves are dead spots in the flow stream and may contain non-representative fluids. Samples should be collected in glass bottles or metal cans, avoiding contact with any plastic and avoiding contact with any oil-contaminated sampling equipment.  Plastic bottles contain plasticizers that contaminate the sample. It is NOT necessary to try to separate oil from water, or to try to break emulsions. Minimum sample sizes for archival purposes are 2 drams (~ 4 ml), but larger containers up to quart size are preferred.

After sample collection, the containers should be tightly sealed, and should be labeled with:

• The sampling date and time (ESSENTIAL)
• The well name (ESSENTIAL)
• The field name (ESSENTIAL)
• The sampling point (well head, or header, or separator, etc.) (ESSENTIAL)
• Other location information (OPTIONAL. Possible information might include: country, state, county, basin, latitude/longitude, and/or section/township/range, etc.)
• Operator (OPTIONAL)
• Depth(s) (OPTIONAL)
• Test number (OPTIONAL)
• Reservoir (name and/or lithology and/or age) (OPTIONAL)
• GOR. (OPTIONAL)

Condensate Samples

Extra care to avoid contamination should be taken when sampling condensates because they typically have low biomarker concentrations and can be easily contaminated by fluids left in the separator from a previous test.  To minimize contamination, start with clean equipment and sample near the end of the test. If a condensate is waxy, it should be sampled near the well head upstream of any suspected wax precipitation in the flow lines. 

RFT Samples

RFT samples are often vented at the surface, thereby losing the gas fraction of the sample. If a DST or PVT sample will not be taken over the interval, any RFT chamber that is believed to contain hydrocarbons should be vented into an evacuated cylinder as described below in order to preserve the gas for possible future analysis.

Produced Gas Samples

Produced gas samples can be taken at the well head, from the production stream, or from a test separator.  If associated gas is sampled from an oil well, the sample should be taken upstream of the stock tank (e.g., the test separator) rather than from the top of the stock tank.  Samples should be taken in 300 ml metal cylinders (supplier information can be obtained from OilTracers LLC Dallas; 214-584-9169). Cylinders should have been sent evacuated!  If not, evacuate them, and sample as follows: 

1. Locate appropriate sampling port for taking gas sample. A location on or as near as possible to the primary separator is preferred. Avoid low spots in the offgas line for taking gas samples to keep from collecting condensed liquids. Locate appropriate fittings required to rig a sample line from port to cylinder. Check sampling port gas pressure to ensure it is less than 1800 psi. In the unlikely event that sampling port gas pressure exceeds 1800 psi, the pressure needs to be reduced with an additional regulator. 
2. Remove plug from sample cylinder valve. Purge sample line with gas to blow any liquids out of the sampling line by cracking valve on sampling port.  Loosely hook up fitting at end of sampling line to sample cylinder and purge again; tighten fitting while purging. Open valve on sampling port all the way. 
3. Open valve to sample cylinder. Confirm that cylinder was originally evacuated by listening for hissing sound as cylinder fills. Wait a minute or so to allow pressures to equilibrate, then close valve on sample cylinder.  Close valve on sampling port; disconnect sampling line from cylinder. 
4. Plug cylinder valve and label cylinder with date, time, well name, test number, separator temperature and pressure, perforation depths, and GOR.  Record cylinder number in sampling notes (number is stamped on cylinder). 

Mud Gas Samples

Mud gas is sampled from the mudlogging gas line during drilling. Samples are collected in one of two ways:

1. Using IsoTubes, a product of Isotech Laboratories. Contact OilTracers LLC or Isotech Laboratories for sampling procedures.
2. CALI-5-Bond gas bags.

Sampling instructions for gas bags are as follows (instructions courtesy of Humble Instruments and Isotech Laboratories):

1. 1. Remove the metering valve assembly from the sampling kit and, if necessary, clean any old Teflon tape off of the pipe threads on the valve-snubber fitting with a brass brush. Wrap at least two layers of Teflon tape onto the threads (wrap clockwise while looking at the end of the fitting).
2. Attach the metering valve assembly to a valve or gauge port on the well to be sampled and snug it down with a wrench. If possible, the sample should be collected from the gas-oil or gas-water separator to avoid collection of liquid. The stainless steel fittings provided in the sampling kit are rated for use up to 5,000 p.s.i.g.
3. Check to see that the metering valve is fully closed, and then open the valve on the sampling port. If sampling in an area where high hydrogen sulfide concentrations are possible, it is a good idea to connect a piece of vinyl tubing to the pressure release valve, direct the other end of the tubing away from the work area, and tape the end in place. If the metering valve is accidentally opened too fast, this precaution will direct the gas away from you.
4. Slowly open the metering valve until you can just hear a slow flow of gas from the luer-hub bag connector. Adjust the flow so that there is little or no gas escaping from the pressure release valve. An alternative method is to hold your thumb over the end of the bag connector to seat it and then open the metering valve until you just hear the pressure release valve start to chatter. If properly adjusted, when you remove your thumb from the bag connector, gas will no longer flow out the release valve.
5. Remove a gas bag from its shipping container and while the gas is still flowing slowly, insert the luer hub into the luer-fit valve on the gas bag with a slight twisting motion. Inserting the luer hub depresses the valve stem and opens the valve. The tapered design of this fitting allows for a leak-tight friction fit.
6. Let the bag fill slowly. The pressure-release valve releases at about 1 psig and this will prevent over-pressuring of the bag. However, to allow space for expansion during shipment, the bag should only be filled to about 2/3 of capacity.  The bag is properly filled when it is about 1.5 inches thick.
7. It only takes a couple ounces of pressure to fill one of these gas bags. But, if even that amount of pressure is not available, a sample can be collected using a rubber squeeze-bulb hand pump. Pump it a few times to purge air from the bulb and then attach the outlet to a gas bag.  The bag can be filled with about fifteen or twenty squeezes of the bulb.
8. Once the bag is filled, remove the fitting from the bag (be careful because if the fitting is pressed into the valve too tightly, the top of the valve can separate from the main valve body when attempting to remove the fitting). Although these bags are durable, they can be damaged if not handled properly. Be careful not to crease or puncture the bags.
9. Record the pertinent information on the tag attached to the bag, and return the bag to the shipping container. If the concentration of methane in the sample exceeds 5%, it must be shipped as a hazardous material in the proper container with HazMat shipping labels.
10. Return the samples to the laboratory for analysis as soon as possible. Use of an express shipper is recommended.

Typically, samples are collected at regular sampling intervals. The interval is well specific, but the example below is typical:

• 1st Depth Range: casing point to top of target -30 m intervals 
• 2nd Depth Range: target interval - 5 m intervals 
• 3rd Depth Range: 30 m intervals
• Shows: should be sampled at 3-5 m intervals for the duration of the show (e.g., 20 m show = 4 bags).

Each bag should be labeled with well name, depth of sample, date, time, and total gas units recorded.  For example, 

    Prudhoe Bay State -1 
    3656æ MD 
    11-5-82
    13:15 hrs
    220 units

Any important notes should also be labeled on the samples, e.g. first sample below casing, mud weight increased, mud additive added etc. Samples should be packaged in HAZMAT shipping containers according to US Department of Transport regulations (IATA UN3167), labeled with appropriate Flammable Gas stickers, and sent air freight as soon as possible to a laboratory specified by OilTracers LLC.

Side Wall Cores

Immediately following collection, side wall cores (SWC) should  be handled as follows.  All of the elements in this protocol have two goals:

1. to minimize evaporation of light ends from the samples, and 
2. to avoid contamination of the samples with plasticizers or other organic substances.

After being removed from the bullet, the SWC should immediately be wrapped tightly in tin foil, and placed back in the SWC jar.  Additional, crumpled foil can be added to the jar to prevent the SWC from excessive movement during transit. The exterior of the jar lid should be wrapped tightly with Teflon tape.  The jar should then immediately be put in the freezer.  When it is time to ship the samples, they should be shipped frozen, by putting them in a cooler along with dry ice.  If dry ice cannot be used for shipping, then frozen gel-packs or frozen plastic bottles of water can be used.

For shipping instructions, contact Mark McCaffrey
tel: (214) 584-9169, e-mail: mccaffrey@OilTracers.com
or Mark Beeunas
tel: (520) 247-8957, e-mail: beeunas@OilTracers.com

Ordering Information for Sample Containers¹

Item	Purpose	Fisher Cat. No.	Qorpak No.	Unit	Price
16 oz. Amber Bottle (wide mouth)	Oil storage/shipping	03-320-8E	7922	case	$74.00
16 oz. Amber Bottle (narrow mouth)	Oil storage/shipping	03-320-4D	7922	case	$74.00
16 oz Clear Bottles	Oil storage/shipping	03-326-3J	7914	case	$74.00
8 oz Amber Wide Mouth	Oil storage/shipping	03-320-8D	7934	case	$74.00
8 oz Clear Wide Mouth	Oil storage/shipping	03-321-1B	7968	case	$63.00
4 oz Amber Wide Mouth Bottles	Oil storage/shipping	03-320-8C	7933	case	$65.00
4 oz Clear Wide Mouth	Oil storage/shipping	03-321-1A	7967	case	$51.00
1 oz Amber Wide Mouth	Oil storage/shipping	03-320-8A	7930	case	$45.00
1 oz Clear Med. Rounds	Oil storage/shipping	03-320-11A	7981	case	$101.00
16 oz Narrow Mouth Ultra Clean Bottle	Condensate Storage	03-321-9A	8683	case	$106.00
4 oz Med. Round Ultra Clean Bottle	Condensate Storage	03-321-7F	8614T	case	$78.00
48-400 TFE Lined Cap	Condensate Storage	02-883-3N	5211/100	pack	$157.00
1 pt cans (narrow mouth)	Oil shipping	04-667A	-	case of 246	$472.50
1 qt cans (narrow mouth)	Oil shipping	04667B	-	case of 196	$238.00
2 oz Whirl Pak Bags	Solid splits	01-812-6A	-	pack	$45.00
6 oz Whirl Pak Bags	Solid splits	01-812-6B	-	pack	$45.00
3x5" Sampling Envelopes	Dry solid splits	56775-039**	-	pack of 500	$14.95
300mL Gas Cylinder(SS,1800psi max)	Gas storage	304L-HDF4-300***	-	1	$84.60
1/4" Valve (Need 2/cylinder)	Gas storage	SS-1RM4***	-	1	$43.00
1/4" Caps (Need 2/cylinder)	Gas storage	SS-4-CP***	-	1	$5.30
Ultra One lab gloves (size L)	Sample Handling	11-387-56D	-	pack of 50	$10.25
Ultra One lab gloves (size L)	Sample Handling	11-387-56D	-	cs of 10 pk	$90.00

¹ Fisher telephone no.: 1-800-766-7000; VWR telepnone no.: 1-800-932-5000

**This item is purchased from VWR and not Fisher

*** This item is purchased from our local Swagelok Distributor. Discounts on quantity are available.