Reservoir Rock Laboratory Course (1st Ed.)

1. Petrophysics

2. Coring and Plugging

1. Without Distillation methods

2. Soxhlet Extraction method

3. Dean-Stark Distillation-Extraction

4. Conclusions and Recommendations

Cleaning and Saturation DeterminationObjectives:

Cleaning and drying the core samples

Introduction and Theory:Before measuring porosity and permeability,

the core samples must be cleaned of residual fluids and thoroughly dried.

The cleaning process may also be a part of fluid saturation determination.

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Direct Injection & centrifugal methods

Direct Injection of SolventThe solvent is injected into the sample in a continuous

process.

The sample is held in a rubber sleeve thus forcing the flow to be uniaxial.

Centrifuge FlushingA centrifuge which has been fitted with a special head

sprays warm solvent onto the sample.

The centrifugal force then moves the solvent through the sample.

The used solvent can be collected and recycled.

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Gas Driven method

Gas Driven Solvent ExtractionThe sample is placed in a pressurized atmosphere of

solvent containing dissolved gas.The solvent fills the pores of sample.

When the pressure is decreased, the gas comes out of solution, expands, and drives fluids out of the rock pore space.

This process can be repeated as many times as necessary.

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Soxhlet extractor

A Soxhlet extractor is a piece of laboratory apparatus invented in 1879 by Franz von Soxhlet.

It was originally designed for the extraction of a lipid from a solid material.

Typically, a Soxhlet extraction is only required where the desired compound has a limited solubility in a solvent, and the impurity is insoluble in that solvent.

Soxhlet mechanism

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Soxhlet Extraction Apparatus

A Soxhlet extraction apparatus is the most common method for cleaning sample, and is routinely used by most laboratories. As shown in the Figure, samples to be cleaned are placed in a porous thimble inside the Soxhlet.

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Procedure

Electric or gas heaters are used to vaporize the solvent. The hot vapors meet the samples in the thimble and

dissolve the oil and water.

Vapors are condensed and cover the sample until over-flown back to the solvent flask.

The extraction process continues for several hours and is terminated when no more oil remains in the samples. This is recognized when the condensing vapors remain

clean because no oils is left in the cores to be dissolved.

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Remarks

After the extraction, samples are dried in an electric oven. Sometimes vacuum may also be applied to the oven.

A complete extraction may take several days to several weeks in the case of low API gravity crude or presence of heavy residual hydrocarbon deposit within the core.

Low permeability rock may also require a long extraction time.

The dried samples are kept in a desiccator sealed with grease and has some moisture absorbents at its bottom.

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Dean-Stark apparatus

The Dean-Stark apparatus or Dean-Stark receiver or distilling trap or Dean-Stark Head is a piece of laboratory glassware used in synthetic chemistry to collect water (or occasionally other liquid) from a reactor. It was invented by E. W. Dean

and D. D. Stark in 1920 for determination of the water content in petroleum.

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Dean-Stark distillation procedure

The Dean-Stark distillation provides a direct determination of water content.

The oil and water area extracted by dripping a solvent, usually toluene or

a mixture of acetone and chloroform, over the plug samples.

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Calculation of water and oil content

In this method, the water and solvent are vaporized, recondensed in a cooled tube in the top of the

apparatus and the water is collected in a calibrated chamber.

The solvent overflows and drips back over the samples.

The oil removed from the samples remains in solution in the solvent. Oil content is calculated by

the difference between the weight of water recovered and the total weight loss after extraction and drying.

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direct-injection, centrifugal and gas driven-extraction methodsThe direct-injection method is effective, but slow.

The method of flushing by using centrifuge is limited to plug-sized samples. The samples also must have sufficient mechanical

strength to withstand the stress imposed by centrifuging.

However, the procedure is fast.

The gas driven-extraction method is slow. The disadvantage here is that it is not suitable for poorly

consolidated samples or chalky limestones.

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Distillation methods

The distillation in a Soxhlet apparatus is slow, but is gentle on the samples. The procedure is simple and very accurate water content

determination can be made.

Vacuum distillation is often used for full diameter cores because the process is relatively rapid. It is also frequently used for poorly consolidated cores

since the process does not damage the sample.

The oil and water values are measured directly and dependently of each other.

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solvents

In each of these methods, the number of cycles or

amount of solvent which must be used depends on the nature of the hydrocarbons being removed and the solvent used.

Often, more than one solvent must be used to clean a sample.

The solvents selected must not react with the minerals in the core.

The commonly used solvents are:AcetoneBenzeneBenzen-methol AlcoholCarbon-tetrachlorideChloroformMethylene DichlorideMexaneNaphthaTetra ChloroethyleneTolueneTrichloro EthyleneXylene

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1. (KSU) M. Kinawy. “Reservoir engineering laboratory manual" Petroleum and Natural Gas Engineering Department, King Saud University, Riyadh (2009).

2. “Soxhlet Extractor.” Wikipedia, the free encyclopedia 5 July 2014. Wikipedia. Web. 22 July 2014.

3. “Dean-Stark Apparatus.” Wikipedia, the free encyclopedia 5 July 2014. Wikipedia. Web. 22 July 2014.