36 Measurement and Testing
Viscosity Control and Petroleum-related Operations
Dr. Luc Bellière, Dr. Philippe Burg, Domitille Chantereau and Suzanne M. Stanton 15 rue Nobel- 45700 Villemandeur, France Tel : +33 (0)2 38 85 77 12 • Web :
www.sofraser.com • Email :
instruments@soofraser.com
Petroleum is one of the most important fluids in today’s global marketplace; it remains the primary source of liquid fuels and of rough material for polymerisation industry’s product manufacturing. Viscosity is an important fluid characteristic for many reasons: it can be a functional property; it can be correlated to an exclusive attribute; it can be related to utilisation efficiency; or viscosity can be one indication of how a fluid is handled (pumped, filtered, stirred, etc.). Like most physical properties, viscosity is measured with laboratory analysers or directly in-line. Tis article aims to provide insight into viscosity as it relates to petroleum-related operations.
Drilling mud
While drilling natural gas or oil wells, a fluid called “drilling mud” facilitates the creation of boreholes into the earth. In general, there are two types of mud: water-based and non- aqueous. Various ingredients such as water, gas, chemical solvents, or polymers comprise the formula. Each drilling fluid is chosen by evaluating several concerns and blending is usually done on-site prior to injection in order to adapt the mud’s composition to the drilling environment.
Yield increase Consumption increase Maintenance reduction
Drilling mud is an important element that provides hydrostatic pressure to maintain stability in the wellbore, it cools the drilling head to prevent damage, lubricates tubing and down-hole tools to minimise corrosion, and it minimises formation damage by transporting and evacuating cuttings to the surface. Controlling viscosity and shear rate optimises drilling mud properties and is valuable in terms of location, depth, pressure, geologic properties, and extracted materials. In addition, continuous in- line viscosity measurement at both the entry and exit of the drilling mud keeps fluids inside the well under control, thus preventing injury to both man and environment. The instrumentation used in this process needs to be rugged and resistant to high pressures and high temperatures, as well as reliable even when particles are present.
Extraction
Extraction presents many opportunities for in-line viscosity measurement. Initial recovery focuses on the immediate identification of the pumped product. Well operators monitor viscosity ranges and determine if the product is oil, gas, water, or a mix between the components. The process can be continuously observed and adjusted according to the materials extracted.
Over time, natural well pressure decreases and flow diminishes. In secondary recovery, pressure in the reservoir must be artificially increased in order to preserve fluidity and maintain extraction. In order to supply additional pressure, pseudo-plastic fluids are mixed according to the subterranean environment and injected into the bottom of the well. While these solutions can be made of natural gas, a water / polymer mix, or gas, both viscosity and shear rate must be controlled in order to improve extraction.
When injection no longer provides adequate pressure, thermally enhanced methods heat the oil. At times surfactants are used to alter surface tension between the oil and water within the reservoir. In other situations, microbial blends break down the oil’s hydrocarbon chain. Each method mobilises the oil and brings it to the surface. Throughout each phase of extraction, viscosity control is a key factor in maximising the amount of recoverable oil and securing the good working of the pumping process. The viscosity related instruments used in the extraction process need to be robust and highly resistant to pressure and temperature.
Transport
Pipelines serve various purposes and are commonly classified into three categories. Gathering pipelines are small, interconnected lines that carry crude oil from nearby wells to a processing facility or a treatment plant. Transportation pipelines are huge, over-land networks that transport
Un-burned residues Smokes temperature
Combustion parameter stabilisation Table 1: Performance increase in burning operations
From 1 to 10% From 1 to 10% By 10 Divided by 7
Reduction from 240°C to 200°C 1%
valuable quantities of oil and its derivative products between cities and countries. Distribution pipelines with smaller diameters move products to tanks, storage facilities or the end-user.
Multi-product pipelines transport two or more different products in sequence within the same line. In this scenario, rarely is there a physical barrier between the products.
Instrumentation, data processing, and communication systems are required to support the intricate pipeline structure. Most of these field devices are installed along the lines in key locations such as injection, compressor, pump, block valve, or delivery stations.
Pipeline companies face the challenge of determining product volume according to flow. Viscosity control enhances pipeline transport: viscosity measurement corrects errors by improving the accuracy of the flow rate measure and reflects actual pumped volume. With ever-fluctuating barrel prices, volume precision is crucial. Implementing viscosity control in conjunction with existing field devices optimises valuable assets, with a significant gain in flow measurement precision. In this precise counting operation, the instrumentation needs to prove excellent repeatability in its results, reliability, with no maintenance requirements.
Refining
The first step in refining is separating crude oil into distinct parts by distillation. The separated parts undergo processing, such as cracking, reforming, alkylation, polymerisation, and isomerisation. Blending consists of stocking the residues (heavy fuel, low added value products) by mixing or adding solvents, thereby transforming them into higher value products. Viscosity control allows for precise blending operations where, for example, in the marine industry, maximum residue and minimum product values are required. Refining consists of complex procedures that produce consumable goods such as bitumen, lubricants, heating oil, diesel, and aviation fuels. Each final product is characterised by specific properties, one of which is the viscosity value.
The viscosity index, according to ASTM D2270-04, is a widely used and accepted laboratory measure of viscosity variation due to temperature changes of a petroleum product between 40
April / May 2012 •
www.petro-online.com
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