Pipeline Blockage Location by Strain Measurement Using an ROV
Authors: Rogers L.M. 
Published: October 2008

ABSTRACT
The paper describes an ROV based inspection method for locating a blockage in a marine pipeline. The method measures changes in the hoop strain in the pipe corresponding to changes in the internal fluid pressure. The device latent applied for), converts radial extension or compression of the pipe into axial compression or tension respectively of a load cell. It allows the use of a high sensitivity axial strain sensing element to measure the hoop strain in the pipe. By pressurizing the pipe at positions upstream and downstream of the blockage and measuring the resulting hoop strain, the bounaimies of the blockage can be accurately defined. The device can be installed and recovered by ROK the signals being relayed to the surface via the ROV's umbilical. The method has been used successfully to locate and define the extent of a blockage in a deepwater oil flowline running from a satellite well system to a production platform, allowing the planning of eflective remedial action. i%e results of the strain measurements were found to be fully consistent with the contents of the pipe determined by subsequent sectioning. Key features of the hoop strain &vice include rugged design, high sensitivity, ease of attachment and recovery by ROV with the need for minimal cleaning and for access only to a sector of the pipe, typically Y4 the circumference.

INTRODUCTION
As exploration moves into colder, deeper waters and efforts are made to extend the recoverable resource using existing production facilities, wax dropout in marine pipelines is becoming more problematic. It has been encountered in the North Sea, in deepwater wells off Brazil and in other locations worldwide. The composition of crude oil is a complex mixture ofAlkanes (saturated hydrocarbons) ranging in molecular size from methane (MJV 16) to waxy solids (h4W &gt;100 & MP &gt;90 deg. C)Alkenes (unsaturated hydrocarbons)Aliphatic and Aromatic HydrocarbonsSulphure and Nhrogen CompoundsOther Fluids and Solids (water, grit, metals)
The alkanes are the predominant fraction of most crude oils, the low molecular weight compounds up to C12 (petrol, diesel, kerosene) being the most valuable, Above C12, the alkanes become progressively less volatile and more viscous. Above Cl 6 (or C20 depending on the Authority) the Akanes are collectively called tariffs or waxes.
Fields very enormously in their proportion of high molecular weight compounds and can even vary within the same well. As the molecular weight increases, the paraffin's tend to solidify by forming microcrystalline aggregates which precipitate out of the cnude oil. progressively Initially this solidification is held back by the presence of smaller alkanes which act as parting solvents. However, above C40, these aggregates grow in size and eventually settle onto the solid surfaces of flowlines, separators, tanks, etc.
The down hole temperature in an oilwell can vary from near ambient (in shallow wells) to around 100 deg. C in deep wells. As the oil flows from the well it can cool gradually or rapidly depending on the presence of water.