Geothermal Pipeline Deposit Measurement Using Gamma Ray Absorption Technique

Abstract

Pipe scanning using gamma ray absorption techniques was applied to geothermal brine line with scale deposits at Mahanagdong Sector Leyte Geothermal Production Field. The equipment used consisfed of a Cesium-l37 source and Nal (Tl) scintillation detector. The source arm and detector of the pipe scanner are adjusted so that these were positioned at opposite sides of a pipe, and the slit of the source holder is aligned with the Nal crystal of the detector.

Gamma scanning was done at three different orientations- horizontal, vertical and diagonal ( 45") of a pipe section. Measurements were done at 3 points, upstream, middle, and downstream of a section of a pipe at 2.5 meters interval. A total of 18 test points were scanned.

Results of the experiment showed that pipe scanning using gamma ray absorption technique can be used to predict scale deposit thickness in closed and properly drained pipes. However, presence of varying levels of brine in the pipe significantly alters the results of gamma scan measurements, and can be interpreted as scale deposits.

Horizontal measurements gave the most linear correlation between actual and calculated measurements. This observation is expected because the probability that the pipe is void of brine at horizontal orientation is greater than any other orientation. The only factor that may have affected the accuracy of horizontal measurements is the scale bulk density that may vary from location to location.