What is Sampling & Analysis?

Sampling and analysis in the oil and gas industry is the process of taking numerous small grabs of oil and gas field samples and performing a variety of tests on them to confirm the product quality and that they comply with the government regulations such as the analysis procedure, and what the resulting compositions are to be recorded. There are specific rules for where and how to sample and when to report hydrocarbon liquids as a liquid or a gas equivalent volume. Accurately sampling natural gas, crude oil, and condensates on-site for laboratory analysis is crucial to generating quality data.

Why is Sampling & Analysis Performed in the Oil and Gas Industry?

Oil and gas sampling and analysis is performed to test the components of the product. Many impurities and contaminants can be found in oil and gas which affects the equipment, the environment, and the economy. These analyses can be used in both diagnostic and preventative scenarios. Sampling and Analysis need to be performed to stay compliant with the province’s energy regulations. If the sampling and analysis frequency wasn’t followed, or the analysis wasn’t used or updated within the required time frame, then energy regulators can assign non-compliance events which can result in less revenue and incorrect royalty payments.

How are Field Samples Taken?

Crude Oil

A representative composite sample of oil for analysis is crucial.  Even the smallest error can result in a loss of thousands or possibly millions of dollars. Sampling is a serious matter for crude oil sales. The equipment used in sampling should be focused on the concept of taking a sample from the pipeline, which is correctly representative of the product. This is done by taking a sample from the flowing conditions or replicated flowing conditions of the stream.

Sampling from non-flowing streams or equivalent will not provide an accurate or high-quality sample. Various sampling locations may present many difficult obstacles that must be avoided or reduced as much as possible to preserve the sample accuracy. The main point of crude oil sampling is to determine the quality of the oil at the custody transfer point. The purpose of a crude oil sampling system is to grab a small representative portion of the product that contains the water, oil, and contaminants in the same proportion as is flowing in the stream.

When sampling crude oil, the pipeline must be conditioned so that the point of sample is representative of the composition of the pipeline. The sampling device has to be able to sample the product under pipeline conditions such as temperature, pressure, viscosity, and contaminants. Samples must be taken safely and handled cautiously. If samples are collected without using proper procedures the sample may become distorted, which would give an inaccurate result once analyzed at the lab. Careful consideration should also be taken with the type of container used for all oil and gas samples. This is why it is crucial for sampling to be performed by a highly trained field professional.

Natural Gas

Natural Gas sampling is performed to determine the total gas composition, hydrocarbon dew point, specific gravity, and the value of the gas. Three techniques are normally used to collect gas samples; continuous composite sampling, continuous online sampling, or spot sampling.

The sample should be taken from the center 1/3 r/d of the pipeline. If the sample is to be transported, a sample cylinder should be used to maintain the sample in the same condition as in the pipeline. If vapor or liquid is in the gas stream the liquid needs to be eliminated before the sample is introduced to on-line analyzers. This will prevent damage to the instrument. The sample collection and storage equipment should be stainless steel to prevent the elements in the gas from being absorbed.

Types of Oil and Gas Analysis

There are different tests for every oil and gas product, the main types of analyses that are performed are:

• Compositional gas analysis (C7+ and extended gas analysis)
• Routine oil analysis
• Hydrocarbon liquid analysis, both atmospheric and pressurized (C7 or C30)
• Standard, extended and complete water analysis
• Trace sulphur analysis
• Field H2S analysis

Crude Oil Analysis

• Heavy/light crude oil analysis
• API and specific gravity
• Asphaltenes
• BS&W
• Viscosity at various temperatures
• Flashpoint
• Freeze-point
• Total and trace sulfur content
• Free water and trace content (Karl Fischer)
• Wax content
• Pressurized Water-cut analysis
• Hydrocarbon Analysis

Dry Gas and Liquid Hydrocarbon Analysis:

• Routine gas analysis (hydrocarbons up to C7+ or C10+ and extended), He, H2, CO2, N2, H2S, calculated pseudo-critical properties, gross heating value, relative density, and molecular weight.
• Atmospheric or pressurized hydrocarbon liquid analysis (including total sample and C7+ relative densities, molecular weights and total sample gas equivalency factors).
• Trace sulphur analysis 
• Reid vapor pressure.
• GIS and/or GOR determinations 

Oilfield Water Analysis:

• Standard, extended and complete water analysis
• Compatibility testing 
• Trace and total sulphur analysis
• Water scaling tendencies 
• Corrosion water
• Metals by atomic absorption spectroscopy
• Glycol analysis
• Amine analysis
• Polymer concentration in water
• Impinger analysis for H2S in SAGD gas/steam vapour streams
• Sampling and Analysis is a critical aspect of your business. Sampling takes expertise and careful examination. Failure to use the correct techniques can negatively affect revenue, compliance, equipment, and the health and safety of the environment. 

Overview of Routine Core Analysis

Retrieval and analysis of cores are essential to all phases of the petroleum industry. Cores offer the only opportunity to obtain intact, vertically continuous samples that allow the visual examination of depositional sequences and variations in reservoir character. Properly analyzed cores provide data available from no other source; these data should provide direct evidence of the presence, quantity, distribution, and deliverability of hydrocarbons. Cores are essential to understanding the nature of the pore system in the potential reservoir unit. The knowledge gained from cores enhances our ability to predict reservoir performance and to select procedures to maximize profitable hydrocarbon recovery.