GENERALIDADES DEL PETRLEO

Petroleum: is a dark, viscous, foul smelling liquid, a mixture of solid, liquid and gaseous hydrocarbons with traces of salt, rock particles and water.

-Composition: Complex mixture of hydrocarbons, chiefly alkanes.

-Formation: Petroleum is believed to have been originated from the remains of sea organisms. The micro organisms have largely contributed to the formation of petroleum. Due to the effect of heat, pressure and catalytic action of anaerobic bacteria, the buried remains of sea organisms decomposes very slowly forming petroleum.

-Occurrence of petroleum: Petroleum occurs in nature, trapped between two layers of impervious (non-porous) rocks, usually under the sea. Natural gas collects above the surface of petroleum.

-Mining of petroleum: Petroleum is brought to the surface by drilling a hole in the Earth's crust and sinking pipes deep down through the impervious cap rock. Natural gas first comes out under high pressure. Then, petroleum is pumped out, collected in tanks and transported, for further processing.

Mud logging is the creation of a detailed record (well log) of a borehole by examining the cuttings of rock or brought to the surface by the circulating drilling medium (most commonly mud). Mud logging is usually performed by a third-party mud logging company. This provides well owners and producers with information about the lithology and fluid content of the borehole while drilling.

Mud logging, also known as hydrocarbon well logging or gas logging, entails gathering qualitative and semi-quantitative data from hydrocarbon gas detectors that record the level of natural gas brought up in the mud. Chromatographs are used to determine the chemical makeup of the gas.

Other properties such as drilling rate, mud weight, flowline temperature, oil indicators, pump pressure, pump rate, lithology (rock type) of the drilled cuttings, and other data are recorded. Sampling the drilled cuttings, usually under the direction of the wellsite geologist, must be performed at predetermined intervals.

The main purpose is to identify all hydrocarbon indications from the rock samples and from the oil and gas entrained in the drilling mud. Gas detected in the mud can be interpreted to be:

1. liberated gas 2. recycled gas 3. produced gas 4. contamination gas 5. trip gas

Only liberated gas indicates a possible prospect; the others merely confuse the analyst. This data, combined with the gas composition determined from a chromatograph, assists in the location of oil and gas zones as they are penetrated. The breakup of the gas shows into these categories reduces the chance of misinterpretation of a gas kick on the mud log.

Another important use of these logs is well safety, since overpressured zones, lost circulation, and gas kicks will be recognized quickly and remedial action taken.

Total gas in the mud is measured in units of parts per million, but does not represent the actual quantity of oil or gas in the reservoir. Total gas is separated in a chromatograph. The most common gas component is methane (C1). Heavier hydrocarbons, such as C2 (ethane), C3 (propane), and C4 (butane) may indicate an oil or a "wet" gas zone. Heavier molecules, up to C7 may be recorded.