BENDING-STRAIN SLUG DETECTION SYSTEM FOR A PIPELINE
Publication Date: 2002-Mar-07
The IP.com Prior Art Database
The present invention measures the length and speed of liquid slugs propagating along a pipeline transporting gas plus liquid phase fluids. Development was motivated by multiphase petroleum production, where advance warning of a slug arrival at the first-stage separator is invaluable, as it allows time for action to be taken to avoid a shut-down in the event of a particularly long slug.
BENDING‑STRAIN SLUG DETECTION SYSTEM FOR A PIPELINE
The present invention measures the length and speed of liquid slugs propagating along a pipeline transporting gas plus liquid phase fluids. Development was motivated by multiphase petroleum production, where advance warning of a slug arrival at the first‑stage separator is invaluable, as it allows time for action to be taken to avoid a shut‑down in the event of a particularly long slug.
Previous approaches which been used have included:
a. Measurement of natural frequency of span of pipe. See attached SPE paper 30663 on SYMINEX slug detection system.
b. Measurement of sound propagation and attenuation across pipe interior.
c. Measurement of capacitance across an electrically non‑conducting segment of pipe. (Does not work for all‑steel pipe.)
d. Measurement of gamma ray attenuation
Gas and liquid in the multiphase flow of unprocessed petroleum production will distribute into any of several different flow regimes depending upon the flow rates of the gas and liquid. The slug flow regime consists of liquid slugs, which fill the pipe for significant lengths, separated by gas pockets. Slug flow produces large fluctuations in the gas and liquid flow rates at the pipeline outlet. These flow rate fluctuations can produce upsets of the processing facilities. Advance warning of the length and velocity of a slug allows time for mitigating action to be taken to avoid an upset. The invention described herein measures slug length and velocity by sensing weight‑induced strains in the pipe as the slug passes instrumented pipe segments. Important criteria this invention ideally satisfies is that it be man‑portable, inexpensive, non‑invasive and dependable. Development of this technology to date indicates that it will meet these criteria.
PRINCIPLE OF OPERATION
The basic concept of this invention is to measure (continuously) the bending strain at four or more equally spaced stations along a straight, unsupported span of the pipeline (see Fig. 1). Strain readings are then considered in triplets, that is, groups of three adjacent stations referred to as a measurement group. For a certain class of weight distributions, the total weight contained within the pipe segment spanning the measurement group can be calculated from the three strain readings. Specially, for the (1, 2, 3) measurement group in Fig. 1, it may be shown that
Pd2 = total weight of contained fluid between stations 1 and 3
ε1, ε 2, ε 3 = the bending strains at the outer surfaces of the pipe wall at
stations 1, 2, and 3 respectively.
K = constant
Similarly, for the (2, 3, 4) triplet,
where the definitions are analogous to those above. The constant K is best obtained from a calibration as will be described below. In general, it may be slightly different for the two triplets, so separate calibrations should be performed for each.
The magnitude of increase in Pd2 will reveal when a slug has entered the (...