CHAPTER 2- Physical and Chemical Properties of Hydrocarbons Gas Dry Gas Methane Wet Gas Ethane, Butane… Condensate *gaseous in subsurface liquid at surface Liquid H/C- oil, crude oil, crude Plastic H/C- asphalt & related… Solid H/C- Coal and Kerogen Gas Hydrates- ice crystals containing H/C Natural Gas- mixture of H/C and non H/C in gaseous phase or in solution with crude oil

Gases Dissolved- in solution with other liquids in reservoir Associated- gas cap gas- in gas phase above liquid Non associated- little or no crude in reservoir Organic vs inorganic Wet vs Dry Gas- dry <0.1 g/mcf Sweet vs Sour- H2S in sour gas

H/C gases- major constituent - H/C paraffin series CH4 most common, C2, C3, … Ethane, butane (the inferior gas), propane all common All others uncommon

Methane- swamp gas, fire damp- Coal mine shale gas- drillers term Genesis- *mantle *biogenic gas *thermogenic gas 20% of natural gas produced is Biogenic (methane only)

Inert Gases He, Ar, Ra He- 5 ppm in atmosphere up to 8% in reservoirs He-rich deposits derived from U, Th, Ra- i.e. granites and shales- basement rock Natural production rate from parent low, expulsion and transport rate high Panhandle Hugoton Field, gas processing plant since 1929, contains 1.86% He

Nitrogen *inorganic- volcanic in origin *organic- degradaton of ammonia and nitrates shallow diagenesis Fig. 2.2 97% N 2% He 1% CO2 Atmospheric N also Trapped in connate gas

Hydrogen H- rare – highly reactive and mobile 1.36 TCF found in Mississippian Age sediments in Kansas 40% H, 60% N, CO2, Ar, CH4- thermogenically mature, never escaped CO2- Biogenic and Volcanic major constituent of volcanic gas 3CH4 + 6O2 = 3CO2 + 6H2O CaCO3 + H2 = Ca+ + H2O + CO2- Acids flowing through limestones

H2S Free gas and highly soluble Major concern when drilling- kills people on rigs in the USA several times a year Highly corrosive to steel- sour gas and oil Low H2S- bad, drives production costs up- have to scrub out High H2S- good, produce S Volcanic and biogenic origin CaSO4 + 2CH2O = CaCO3 + H2O + CO2 + H2S 2CH2O = organic matter Also associated with carbonates and Pb-Zn deposits and deep basin brines Anydrite  calcite- exothermic- hot enough to mobilize Pb-Zn sulfide brines

Crude Oil Mixture of H/C in a liquid phase which remains a liquid at the surface Yellow, green, brown, black Wide variety of viscosities Most lighter than water Vary in Specific Gravity Chemistry- C, H, V, Ni,… no two oils the same. Ponca Crude, 234 compounds

Hydrocarbons- cont. Paraffins- alkanes- straight chain carbon with branching n < 5 gas at surface 5 < n 1< 5 liquid at surface n> 15 grade into solid wax for given molecular wt. Straight chain higher boiling point than isomers Isomers-branching

Naphthenes Aromatics Cyclo alkanes- single bond All liquids at surface Benzene ring structure Liquid at surface Occurrence: Toluene>xylene>benzene

Hetero compounds Organic compounds containing O, N, S & metals, acids, esters, Ketones, phenols, alcohols In younger oils- fatty acids, isoprenoids, naphthenic and carboxylic acids Sulfur also common, both as H2S and other phases Nearly any ions found in sedimentary minerals can be found in crude Va & N occur as organometallics generally in porphyrin- derived from chlorophyll and hemoglobin Metals most often associated with resins Sulfur and asphaltene fraction most common in shallow, younger, degraded crude.

Classification of Crude Oil Many classification schemes *engineering based- refineries Physical properties: viscosity boiling pt refractive index molecular wt density

Classification of Crude Oil *geochemical based- maturation, genesis, and history and other geoparameters of occurrence. Molecular structure: key to source and geological history

Classification of Crude Oil Paraffins, Naphthenic and intermediates based on distillation factors time and temperature Tissot and Welte (1978) used ratio between para & naph & aromatics Oils vary not only w/ age, but w/ variatin in source and degree of Degradation- degradatin causes wide variations , esp. w/shallow oils

Gas Hydrates