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Reservoir Fluids

Geochemistry Chemistry

Geochemical characterisation is conducted on Crude oils, Condensates/Volatile Oils, Oil Seeps and Natural Gases.

Crude Oils

The main objective is to assess the following characteristics:

• Determine oil quality
• Identify source rock type, level of thermal maturity, and nature of any alteration processes
• Undertake oil-oil, oil-condensate, and oil-seep correlations
• Define reservoir continuity
• Conduct oil-source rock correlations

Samples which can be submitted for analysis include:

• Subsurface crude oils and condensates/volatile oils
• Surface oils, condensates, and seeps
• Oil impregnated reservoir rock in subsurface and in outcrops

A typical Analytical Package:

• API Gravity
• Sulfur content
• Pour Point/Wax Content
• Whole oil GC, including detailed light hydrocarbons and C15+ n-paraffin and isoprenoid
• Liquid chromatographic (LC) separation - complete or partial
• Quantitative GC-MS of saturate hydrocarbon fraction (Saturate Biomarkers)
• Quantitative GC-MS of aromatic hydrocarbon fraction (Aromatic Biomarkers)
• Stable carbon isotope ratios of saturate and aromatic hydrocarbon fractions

Additional Analyses

• Viscosity
• Saturated hydrocarbon fraction gas chromatography (C10+ GC)
• Aromatic hydrocarbon fraction gas chromatography
• Whole oil stable carbon isotope composition
• Whole oil sulphur isotope composition
• Saturate and/or aromatic hydrocarbon fraction deuterium isotope composition
• Nickel and vanadium content

Interpretation and Reporting

A detailed interpretive report can be generated and provides an assessment of the source organic matter type and maturity at generation/time of expulsion, depositional environment, evaluation of any alteration processes, and possibly geologic age. If multiple oils and evaluated, oil-oil correlation and reservoir continuity can be assessed.

Natural Gases

The primary objectives of analysing gases for geochemistry are:

• Determination of composition of natural gases: hydrocarbons and non-hydrocarbons
• Origin of hydrocarbon gases: biogenic, thermogenic or mixed
• Organic source type and thermal maturity of hydrocarbon gases
• Origin of non-hydrocarbon gases, if present in sufficient quantities

A standard Analytical Package:

• Hydrocarbon gas analysis (C1-C5, C6+)
• Non-hydrocarbon gas analysis (CO2, N2, H2S)
• Stable carbon isotope ratios in C1, C2, C3, C4
• Stable hydrogen isotope ratio in C1
• Stable hydrogen isotope ration in CO2 (quantity permitting)

Interpretation

The standard analytical package with interpretation is adequate for interpretation of hydrocarbon gases. For natural gases with high concentrations of specific non-hydrocarbon gases, additional analyses may be required. GCIRMS can be added to the standard package at the client's request.

Reservoir Geochemistry

Reservoir geochemistry is becoming more and more important to understanding the distribution of liquid hydrocarbons within a reservoir and its compartments (if any).

[A] Reservoir Definition

The main objectives would be:

• Identification and delineation of producing intervals in sandstones or carbonate reservoirs
• Identification and delineation of producing intervals in fractured source rock reservoirs
• Identification of hydrocarbon types
• Definition of gas-oil and oil-water contacts
• Definition of oil quality and producibility
• Organic source type, thermal maturity, and type and degree of alteration

Samples to be utilised would include:

• Sidewall cores
• Conventional core
• Drill cuttings (preserved)

[B] Reservoir Continuity and Related Problems

The main objectives would be:

• Define vertical and lateral reservoir continuity and understand reservoir compartmentalization in oil fields
• Production allocation in commingled or multizone production
• Detection of leakage in commingled production
• Detection of drilling fluid contamination
• Reservoir filling history

Samples to be utilised would include:

• Crude oils and condensates

A typical Analytical Package:

Standard Analysis

• Whole oil GC for reservoir oil fingerprinting (provides light hydrocarbon GC data, C15+ GC data)
• Measurement of smaller naphthenic and aromatic peak pairs (provides the data for the ratio calculations used in the starplots and dendograms)

Optional Analysis

• Quantitative saturate fraction GC-MS
• Quantitative aromatic fraction GC-MS
• Stable carbon isotope ratios

Interpretation

A detailed interpretation can be provided to assess the degree of similarity between liquid hydrocarbons from separate units within the reservoir. Conclusions drawn will aid in evaluation of potential compartmentalisation of the host reservoir.