Page 14 - Treating Oilfield Emulsions

Segment III
Chapter 9

Sampling Procedures

Petroleum Extension-The University of Texas at Austin
A 11 oil delivered to pipeline companiesis su~ included. Inaddition to automatic sampling, API
.l"\.. ject to their testing. Therefore, to assure recommends three manual procedures suitable
that the oil will be accepted, the producer should for sampling tanks that contain crude oil: thief
sampleand test theoil in thesamemanneraspre­ sampling, bottle sampling, and tap sampling.
scribed by the pipeline company that purchases
it.Theproceduresfor taking samplesand making Thief Sampling
. water and sediment tests vary from field to field
Probably the most common method of obtain­
and company to companyand mustbeagreed on
ingsamplesofcrudeoil in lease tanks isbymeans
by both the buyer and the seller. Any agreement
of a thief. A thief is a round tube, with a uniform
found to be mutually acceptable serves the pur­
cross section, that has a capacity dependent on
pose.
the size of the sample required (fig. 46). It is
The Measurement Coordination Department
suspended by a chain or rope at its upper end; a
of the American Petroleum Institute has pu~
lished standards for measuring, sampling, and
testing petroleumand petroleumproducts. These
standards reflect procedures that are considered
acceptable in the absence of any specific agree­
ment between the buyer and the seller of crude
oil; they are not intended to conflict with or
supersedeanycontractualagreemententered into
betweenthebuyerand the seller. The material for
this chapter is drawn from API, Manual of Petro­
leum Measurement Standards (MPMS), chapter 8,
section 1, Manual Sampling of Petroleum and Petro­
leum Products, and chapter8, section 2, Automatic
Sampling of Petroleum and Petroleum Products.
The basic principle ofany sampling procedure
is to obtain a sample or a composite of several
samples that is truly representative of the oil in a
tank or other container. The sample can then be
tested to determine properties that have a bear­
ing on the measurement of the oil sampled. Two
basic sampling methods are available: tank, or
TUBE
manual, sampling; and automatic sampling. If,
however, a tank's contentsare not homogeneous
from the top to the bottom, or if certain other
conditions are not met, automatic sampling is
recommended. For tank sampling to be accept­
able, the contents of the tank must be homoge­
neousand (1) the tank must contain a heavycom­
BOTTOM
ponent (such as water), which dearly separates CLOSURE
from the main component, (2) the tank must be
equipped with either a swingsuctionora weiron
the outlet that prevents shipment of the heavy
component, and (3) the tank samples must be
taken so that none of the heavy component is Figure 46. A tubular tank thief

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