Sampling device with diamond-like carbon coating

Abstract

A diamond-like carbon coating is provided on a metal interior surface of a sample chamber of a well fluid sampling apparatus to render the sample chamber substantially impervious to the absorption of at least H2S, mercury, and / or mercaptans. The coating is a dense, amorphous, diamond-like carbon with an sp3 content greater than about 65% and is composed of about 70 percent (%) carbon, 30 percent (%) hydrogen. The coating may be applied over the surface in one or more layers by a suitable method, e.g., plasma assisted chemical vapor deposition or a PAVCD process, and is between about 10 and about 20 microns thick. One or more of the layers of the coating includes a small percentage of silicon to increase both the adherence to the metal interior surface of the sample chamber and the absorption resistance of the coating. The resulting sample chamber provides H2S, mercaptan, and mercury retention of greater than about 95% of the original concentration in samples stored up to 14 days.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is related to and claims the benefit of U.S. Provisional Patent Application 61 / 104,116, filed on Oct. 9, 2008, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention generally relates to sampling devices for oilfield reservoir fluids that allow sampling and measurement of trace amounts of H2S, and is specifically concerned with a diamond-like carbon coating applied over the internal surfaces of the sampling chamber of such devices that renders the chamber substantially impermeable (or non absorbent) to H2Sand able to withstand acid and alkaline fluids.[0004]2. Discussion of the Background[0005]Existing sampling technology preserves samples above reservoir pressure ensuring representative pressure / volume / temperature (PVT) analysis. However, for chemical or trace element analysis some components of the samples are lost due to ph...

AI Technical Summary

Benefits of technology

[0009]Therefore, there is a need to develop sampling devices that can be used to sample oilfield fluids that have traces of H2S and are able to measure the H2S. There is further a need to develop a sampling device having an internal coating that can withstand alkaline chemical environment and that also has superior mechanical wear resistance. To these ends, the present invention provides a well fluid sampling device (or tool) including a sample chamber for receiving and holding a sample well fluid that has been coated with a diamond-like coating (DLC). The coating employed in the inventive sampling device substantially prevents absorption of H2S as well as of other components such as mercury and mercaptan into the walls of the sampling device. The same coating can also be used likewise in any type of sampling and analysis devices, such as sampling bottles, flow lines and associated equipment, gas chromatographs, mercury analyzers, etc. The coating is also chemically resistant to both acid and alkaline environments, provides scratch resistance, and allows for representative compositional analysis of the samples taken even of very small trace amounts of components, even after many long days of storage.

[0010]One embodiment of the invention is directed to a well fluid sampling apparatus, which comprises a sample chamber for receiving and holding a sample well fluid, and a diamond-like carbon coating (DLC) provided on an interior of the sample chamber that is preferably between about 10 and about 20 microns in thickness. The coating substantially prevents absorption of at least one of H2S, mercury, and a mercaptan therethrough.

[0011]The DLC coating is preferably dense, amorphous, diamond-like carbon with an sp3 content greater than about 65% and has a composition comprising about 70 percent (%) carbon and about 30 percent (%) hydrogen. The coating substantially prevents absorption of at least one of H2S, mercury, and a mercaptan through it.

[0012]The well fluid sampling apparatus is provided with a substantially chemically inert sample chamber which is achieved by applying the DLC coating of the invention to the material of the sample chamber (usually a non-corrosive metal such as stainless steel or a nickel alloy steel). The apparatus may also be referred to herein as a “tool” or “sampling device”. The apparatus may be lowered to the required depth in the well where a well fluid sample is admitted to the sample chamber, which is subsequently sealed. The tool is preferably arranged so that pressures inside and outside the sample chamber remain substantially equal during and after sample taking. The sample may be subjected to post-sampling pressurization to keep the sample in its original single-phase state. The substantial chemical inertness of the sample chamber avoids removal of reactive components of the well fluid from the sample by chemical reaction with the material forming the sample chamber (conventionally a metal). This enables accurate assessment of new wells without the need for extended flow testing. Equalization of pressures inside and outside the sample chamber enables the material of the sample chamber to be selected for its chemical inertness rather than for mechanical strength to resist forces otherwise arising from pressure imbalances.

Problems solved by technology

However, for chemical or trace element analysis some components of the samples are lost due to physical or chemical processes, most of which are time dependent.

Many of the components will react with the walls of sampling tools / sample bottles and / or decompose with time.

However, all such coatings are generally deficient as a barrier to H2S, mercaptans, and mercury and may crack due to elastic deformation of the sampler.

This is generally satisfactory in terms of H2S barrier, but is deficient in terms of mechanical resistance and chemical resistance to alkaline environments.

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