Patent Application
20160041376
The field of the invention is devices and methods for the measurement of oil content in water, especially as it relates to the measurement of oil content in water produced from petroleum and natural gas reservoirs.
The global oil industry produces over 300 million barrels of water per day, which amounts to approximately 80% of the liquids produced (Ref. TUV-NEL 2010, Fluor 2012). In offshore production, most of the produced water is discharged into the environment after treatment to discharge standards. A small fraction is re-injected into the formation.
The discharge of produced water is regulated worldwide, with the regulations varying among countries or regions (Fluor, 2012). Oil in water content and toxicity are the two primary regulatory compliance measures. The US regulatory requirements for offshore produced water include oil and grease amount limit (currently 29 mg/L monthly average, 42 mg/L daily max), toxicity test and no free oil discharge, and no sand discharge. The oil and grease measurement is by the EPA 1664A method, which is a gravimetric method using n-hexane solvent extraction and performed in approved laboratories.
Field measurements, both bench-top and online, have also been commonly applied for process monitoring and optimization. Prior art on oil content measurement are represented by the following patents:
In prior art, laser induced fluorescence has only been used for emission magnitude measurement. Imaging analysis has only used with on images obtained by direct lighting and reflection.
In imaging analysis method, the presently available systems for produced water can resolve particles 2-3 microns in size or larger (Tyrie et al. 2005).
The offshore produced water treatment system typically removes oil droplets 3-5 microns and larger, based on the performance of gas induced flotation units as reported by Argonne National Laboratory (Hayes et al. 2004). Finborud et al (1999) discussed that the oil droplet sizes downstream of the first stage separator, and commented that field experience had shown that the oil droplet size distribution often has a peak around 10-15 microns. It can then be estimated from the data provided by Finborud et al (1999) that, if oil droplets larger than 3-5 microns are removed from the produced water by the last stage treatment (for example induced gas flotation with chemical injection), 40% or more of the remaining droplets are smaller than 2 microns.
Therefore an imaging analysis method which can resolve the oil droplets smaller then 2 microns in diameter can improve the accuracy of measurements. Contemplated invention described below is such a system and method.
Contemplated invention is an oil in water content measurement system and method which utilize laser fluorescence microscopy to generate one or more images, and analyze the images to determine the oil droplet content by the number and size distribution of the droplets. The images can also detect oil coated sand particles. The images can be 3-dimensional for configurations intended for high measurement accuracy, and 2-dimensional for configurations where lower accuracy but higher speed of measurement is desired.
Referring to
The stacks of 2-D images are processed by an image processing computing device 8 which can be either at the measurement site or at a remote location. A particularly preferred image processing algorithm is deconvolution to form 3-dimensional (3-D) images of the view volumes. The 3-D images are analyzed to determine the oil droplets' volume content and size distribution. In other applications, the 2-dimensional images are directly used to identify the oil droplets and solid particles.
The inventor has discovered that the fluorescent properties of certain components of oil, such as the Polycyclic aromatic hydrocarbons which emits fluorescent light when experienced excitation by laser light, can be used to produce an image with a microscope. The inventor also discovered that the image can have very high resolution (250 nanometer or even finer), and can be analyzed with an image analysis algorithm to determine the oil droplets' number, size distribution and volume. The inventor further discovered that the method can be used to measure the number, sizes, shape and volume of oil coated solid particles.
The measurement setup of the new method is illustrated in
A water sampling device 2 is inserted to the produced water discharge pipe 1 for a slip stream to be flown through the sample piping 3, valves 4 and 11, measurement section 5 and to discharge. The measurement section is instrumented with a microscope 6 with laser, such as the particularly preferred spinning disk laser confocal microscope with a scanning unit unit with lenslet. The microscope illuminates the view volume with laser beam in a scanning manner. The fluorescence generated by the oil droplets in the sample is captured by the light to electrical signal converter 7, a particularly preferred configuration for which is a CCD (charge-coupled device). The digital signals from the converter are sent to an image processing computing device 8 which can be located either at the site, at a remote location. The image processing utilizes algorithms to improve the image quality if needed, for example using the particularly preferred algorithms of deconvolution, to remove the noise caused by light contributions from out-of-focal plane locations. The processed signals are analyzed to determine the location and size of the oil droplets in the sample. The total volume fraction of the oil droplets and the size distribution are reported through the human machine interface 9.
Many measurement sequences can be utilized with the contemplated invention. An example measurement sequence is as follows:
Many variations of the measurement configuration and image processing method are possible, including:
The above has disclosed the specifics of the contemplated invention to measure oil content in water. It should be apparent to those skilled in the art that many other variations and modifications are possible which are within the spirit of the disclosed invention.
