The Search for Energy: Evaluating a Formation’s Oil Potential

Determining whether a formation contains oil and gas falls under the realm of formation evaluation. Formation evaluation includes the activities the operator does to test a formation for hydrocarbons. The operator must not only know whether hydrocarbons exist, but also whether they exist in ample amounts. A hole may penetrate a formation that contains hydrocarbons; however, if the formation does not contain enough hydrocarbons for the operating company to get its monetary investment back, the company may declare the hole to be dry. Methods of formation evaluation include examining cuttings and drilling mud, well logging, drill stem testing, and coring.

Several techniques are available to help the operator decide whether to complete the well. One of the simplest is looking at the cuttings the drilling mud carries from the bottom of the hole. A geologist can test the cuttings to determine whether they contain hydrocarbons. The mud logger, using various kinds of detection equipment, can also spot hydrocarbons in the drilling mud. An operator probably would not decide to complete or abandon a well using only information from cuttings and mud returns. Careful examination of them, however, can indicate whether the well is likely to produce.

Well logging is a widely used evaluation technique. Many kinds of logging tools are available. Some measure and record natural and induced nuclear, or radioactive, attributes of a rock. Others measure and record the way in which formations respond to electric current. Another log measures and records the speed with which sound travels through a formation. These are only a few on many logs available to operators. By interpreting the recordings, or logs, the operator can usually tell if the well will be a producer.

The operator calls the logging company to the well while the drilling crew trips out the drill string. From a portable laboratory, truck-mounted for land rigs or in a small cabin on offshore rigs, the well loggers lower logging tools into the well on wire line. They lower tools to bottom and then slowly reel them back up. When activated, the tools measure formation properties. The tools transmit the data they gather to the truck or logging shack. There, special recorders and computers store the information. For on-site evaluation, computers in the portable laboratory print the data. These logs give the operator a first look at what a formation may yield. For thorough evaluation, the portable lab can transmit the log’s data to powerful computers located at the central testing facilities. By carefully examining well logs, the operator can determine whether to complete the well. Well logs not only indicate the presence of oil and gas, they also indicate how much may be there.

During the drilling, the operator can run ‘logging while drilling’ (LWD) tools in the drill stem. These instruments incorporate sophisticated electronic devices that sense, transmit, and record formation characteristics as the bit drills ahead. The LWD tool transmits formation information on a pulse the tool creates in the drilling mud. Much as radio waves transmit sound information through air, mud pulses transmit formation information to computers on the surface. The computers analyze and display the information in readouts that experts on the site can interpret and evaluate.

Colorado Energy companies are constantly seeking out oil and testing wells before they drill. This ensures both economic return, and longevity. Heartland Energy Development Corporation evaluates domestic rock formations for oil. Heartland Energy is among the leaders in domestic oil evaluation and production.