Characterisation and monitoring of mineral deposits in down-hole petroleum pipelines.

Christidis, Konstantinos

Abstract

A major problem in the oil and gas industry is the progressive deposition of scales, wax and hydrates in pipelines, causing large production losses over a period of time. The composition and thickness of these deposits vary widely and cannot be reliably quantified at present. Consequently, remedial treatment such as chemical de-scaling etc. are largely based on guess work causing expensive chemical wastage and production shut-downs. This project deals with the study and development of new techniques using ultrasound for the use in down-hole pipelines to identify deposits and assess their thickness, so that effective de-scaling treatments can be implemented. This task involves research into three main aspects namely: characterisation of deposits, monitoring deposit thickness and transmission of data between top-side and down-hole data acquisition systems. The characterisation of mineral deposits in situ involved research into a number of areas, requiring solutions for the effects due to target curvature, surface roughness and temperature. The monitoring of deposits involved the development of an appropriate software algorithm for the graphical presentation of the thickness of the mineral deposits in pipes in real time. The communication between the top-side and down-hole system involved research into analysis and modelling of transmission characteristics of cables for transmission of mixed signals between the down-hole electronic systems with a top-side computer, according to the system requirements. With respect to the characterisation of deposits, the pulse echo response due to curved reflectors were modelled. Close agreement of the model with practical measurements was demonstrated. From these investigations a compensation function was derived which normalises the amplitude response of the received echoes from a curved target, relative to that of a plane reflector of the same material. The effect of surface roughness on the amplitude of reflected echoes was examined, both in time and frequency domains. From this investigation, a correction function was developed to normalise the amplitude response of the received echoes from rough surfaces, relative to that of a smooth reflector. This study further led into the development of a novel ultrasonic spectroscopic technique to assess the gross surface texture of materials. The temperature effect on the amplitude of reflected signals was also investigated. From this investigation a third correction function for the compensation of temperature effect on ultrasonic measurements was developed. All these developments extend the scope of general ultrasonic testing of materials, beyond the specific application in the present project. Having developed the necessary compensation functions, five different techniques were then assessed to identify their potential for material characterisation, namely: the use of Probability Density Function (PDF) analysis of signal decay coefficients, PDF analysis of velocity of sound measurements, the use of neural network, fuzzy logic and knowledge based systems. With respect to monitoring deposits, an adaptive imaging re-construction algorithm was developed to simulate imaging, which maps the cross-sectional profile of the pipeline, in pseudo-real time. A main feature of the software is that it estimates the arbitrary position of the probe array from each frame of data to produce correct cross-sectional images, irrespective of the position of the probe relative to the central axis of the pipe. With respect to data communication, the transmission characteristics of coaxial cables were modelled in order to identify the requirements for the optimal transmission of mixed signals (analogue, digital and power) in a high temperature environment. The effect of temperature differentials to which the cable may be exposed was also mathematically analysed and the conditions for efficient use of cables were made. The simulated results of the mathematical analysis were verified by practical measurements, which showed close agreement. Overall, the main objectives of the project were well achieved, and in some areas exceeding the original specifications. All the main developments were published. The recommendation for immediate future work includes the systematic integration of the techniques developed for field use, in collaboration with the industry.

Citation

CHRISTIDIS, K. 2000. Characterisation and monitoring of mineral deposits in down-hole petroleum pipelines. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2807327

• Thesis Type: Thesis
• Deposit Date: Jun 26, 2025
• Publicly Available Date: Jun 26, 2025
• DOI: https://doi.org/10.48526/rgu-wt-2807327
• Public URL: https://rgu-repository.worktribe.com/output/2807327
• Award Date: Oct 31, 2000