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What Is a Formation Evaluation?

By Larry Ray Palmer
Updated May 17, 2024
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Formation evaluation is a phrase used to describe the process that determines the viability of a formation to produce oil and other petroleum products. The petroleum exploration process of formation evaluation actually includes several component procedures. Using geological assessments, exploratory drilling, coring, and other procedures, petroleum drilling companies are able to assess the value of a bore hole for production. While the various tests used in formation evaluation can deliver skewed results from time to time, the component tests are considered to be industrial standard practice.

The first step in formation evaluation is geological assessment. Certain geological formations are, statistically, more likely to produce petroleum and other fossil fuel products. Trained geologists look for recognizable formations that are known to yield these resources. When these geological formations are noted, the next step of formation evaluation begins.

Exploratory drilling of bore holes is used to collect soil samples, called cores, and data about the sub-surface formations that may yield petroleum. By using specialized testing equipment in conjunction with the drilling rig, data can be retrieved from the bore hole. This data is then recorded for further evaluation.

Coring is a process of extracting samples of earth from the bore hole. Long, hollow tubes are placed in the drilling rig and then forced into the formation, thus creating a core of earth. This core can then be extracted and studied to determine the presence of petroleum and other fossil fuels.

There are several types of recorded, data logged information evaluation testing. Mud logging tracks the mud and drilling fluid that is brought up by the drilling rig. The contents of the cuttings, including mineral composition, are recorded to determine the presence of petroleum indicators and any possible obstacles to the drilling process.

Electrical logging is another form of data collection that is used in this exploratory drilling process. Small electrical leads are attached to the drilling equipment and lowered into the bore hole. Since most underground geological formations possess water content, these formations are electrically conductive. Petroleum and gas pockets in the rock formations do not conduct electricity in the same manner as water. By recording the way electric current travels through the rock formation, geologists can discover hidden reservoirs of petroleum and gas.

Porosity logging is another component test in the search for petroleum and gases. This type of formation evaluation test may be measured using sound or radiation. The sonic porosity test uses tuned frequency sound waves to find the density of a stone formation. Nuclear porosity testing is accomplished by emitting small amounts of radiation and then tracking its progress into the surrounding geological formations.

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