Field Experience with a Subsea Erosion Based Sand Monitoring System
Authors: Braaten Nils A. , Blakset Terje , Johnsen Roy , Birkeland Reidar 
Published: December 2007

Field Experience with a Subsea Erosion Based Sand Monitoring System.

This paper describes the use of an erosion based, subsea on-line sand monitoring system, addressing both use of the probe as a means of optimizing the production, and also as a safety device. Main focus is on the data from the Tordis field, since this was the first installation of the system. Various examples from normal production conditions will be given, including data from maximum sand free rate tests, clean up events as well as correlations between the probe readings and the onset of water production. The correlation between the wear on the probe and piping erosion is also discussed.

Introduction

The production of sand and solids in oil and gas can represent a major problem in terms of erosion and damage to the process system including piping, valves and fittings. Sand production can also lead to a degradation or, in the worst case, a collapse of the reservoir. Unexpected breakdown of the reservoir and water breakthrough can occur, resulting in increased sand content of the well fluid. Process equipment could also fill up due to the settling of sand. In addition to the safety and production technical aspects of unwanted/controlled sand production, the active use of proper on line sand monitoring equipment could also have a cost reducing impact since piping tolerances with respect to erosion may be reduced.

Sand control has in the past been sought mainly through downhole techniques like screens/gravel packs. A gravel pack will, however, limit the production capacity from the reservoir, and it has also been seen to fail with drastic consequences. In addition, the cost of a gravel pack operation can make it desirable to seek for other solutions. The system presented in this article would allow for continuous monitoring of the status of sand production from any type of well, and will serve both as a safety device, and as a tool for optimizing and controlling the oil/gas production. During testing before a well is put into normal production, and at later stages, maximum sandfree rate (MSFR-)tests with on line sand monitoring can be performed to establish the max. acceptable production rates. However, downhole conditions can change over time resulting in sand production, which leads to a need for continuous measurements.

This paper describes experience from use of a an erosion based sand monitoring system. The system does not need any on site calibration (injection of known quantities of sand) to quantify sand contents, and can be used equally well in all flow regimes, single or multiphase, and it has no lower threshold limit for the smallest detectable sand concentration. In addition, erosion rates read directly from the probe elements will be an indicator of the erosion of the piping system itself.

System Description

Sand probe. This sand monitoring system is based on a probe that detects sand production through erosion of sensing elements directly exposed to the fluid. When sand transported by the fluid hits the probe, the sensing elements will be eroded and the following increase in resistance can be continuously measured, and the thickness reduction of the elements can then be easily quantified. Each element is connected to electrical wires and feed with a constant current.

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