The Origins, Migration and Trapping of Petroleum and Exploring For It

During certain geologic ages, when the climate was suitable, petroleum began as organic material derived from plants and animals which grew in abundance. As these organisms went through their cycles of growing and dying, buried organic material slowly decayed and became our present-day fossil fuels: oil, gas, coal and bitumen. Oil, gas and bitumen were dispersed in the sediments (usually clay-rich shales). Over millions of years, these organic-laden shales expelled their oil and gas under tremendous pressures from the overburden. The oil and gas migrated into permeable strata below or above them, then migrated further into traps that we now call reservoirs. It’s interesting to note that the word “petroleum” is derived from the Latin words for “rock” (petra) and “oil” (oleum), indicating that its origins lie within the rocks that make up the earth’s crust.