1. HYDROCARBON KITCHEN
An area of the subsurface where source rock has reached appropriate conditions of pressure and temperature to generate hydrocarbons. It is also known as source kitchen, oil kitchen or gas kitchen.The petroleum kitchen is the combinations effects of Temperature-Pressure and time on the lithology.Geothermal Gradient: (thermogenic hydrocarbons)Range: <1-11F/100 feet or 3.3C 100 kmTypical Sedimentary Basins: 1-1.7F/100 feetGood Average: 1.2Oil window : (120-300)F or (50-150)C or about 5,000-20,000 feetIn practice oil below 15,000 ft area. Gas- no practical limit to stable depthCracking of oil to gas controlled by source kerogen and temperatureIn deep basins mostly gas has practical limits related to maturity of source not reservoir.|
Fig.oil window – 60 to 120 degree celsius.
Oil and gas are formed by the thermal cracking of organic compounds buried in fine grained rocks. Type I –Algal (oil prone) sapropelic (Hydrogen rich): The primary source is from algal sediments , such as lacustrine deposits.H/C ratio is greater than equal to 1.5 and O/C < 1. It is also called alginate kerogen containing high concentration of alkanes and fatty acids.
Type II –Mixed: – It consists of abundant moderate length aliphatic chains and naphthenic rings .Ester bonds are common and sulphur is present in some amounts. It is also known as exinite. H/C ratio is between 1 to 1.4 and O/C 0.09 to 1.5.
Type III –Woody (gas prone) humic (Hydrogen poor): The main source of this type of kerogen is continental plants found in thick detrital sedimentation along continental margins. It is also known as vitrinite. It is less favourable for oil generation, but will provide a source rock for gas.
Fig.Van Kravalen diagram.
3. PETROLIFEROUS BASINS OF INDIA
•Category I: Proved petroliferous basins with commercial production •Category II: Sedimentary basins with known accumulations of...