TOP 7 EXPLORATION TECHNIQUES FOR CRUDE OIL

The selection of a drilling site is a tricky and costly affair. Though some visible evidence of a hydrocarbon source, like seepage of oil and gas from the surface, the visual appearance of surface and vegetation, the presence of oil or gas in fountains or rivers, etc., are sometimes used in locating crude oil and gas reserves, and many ancient oil fields were discovered by these events. But, today, such fortunate events are very rare and sometimes may not always be suitable for commercial exploitation. Modern exploration techniques for petroleum use geophysical, geochemical, and geotechnical methods. Exploration of the surface of Earth can be useful for imaging or mapping sub-surface structures favorable for oil and gas accumulation. In the geophysical methods, gravimetric, magnetometric, seismic, radioactive, and stratigraphic studies of the surface are gathered.

exploration technique for crude oil 

 Chemical analysis of the surface soil and rocks is carried out by geochemical methods. Geotechnical methods, such as the mechanical properties of rocks and surfaces, are measured. Remote sensing from the satellite is the most recent development for a low-cost geological survey. Usual geophysical methods include gravimetric, magnetometric, seismic methods, and radioactive methods. Geochemical methods employ chemical analysis of the cuttings (rock samples cut by drilling bit) and core (a narrow column of rock taken from the wall of a drilled hole) of the drilled site

1-GRAVIMETRIC METHOD

The gravity of the earth’s surface varies with distance from the surface of Earth and the type of material, such as salt, water, oil, gas, or mineral matter. The measurement of a small variation of gravity or acceleration due to gravity is recorded with accuracy and the data are converted to retrieve a geological structure of the sub-surface of Earth. A gravimeter is a very sensitive instrument, usually a spring-type balance with high resolution and accuracy capable of detecting a minute variation in gravity. Porous and oil-containing rock layers and salt have a lower density compared to the surrounding non-porous and hard rock layers. Thus, a gravimetric curve is acquired and analyzed for the location of the deposit.

2-MAGNETOMETRIC METHOD

Earth has its magnetic field that varies from one location to another owing to the different structural materials of rocks and also the presence of solar-charged particles received by Earth. A variation of magnetic field strength is recorded by a sensitive instrument, called a magnetometer. Igneous non-porous rocks are found to be magnetic as compared to sedimentary rocks containing organic deposits. Thus, a magnetometric survey can also be used to locate oil deposits. Both the gravimetric and magnetometric methods are done simultaneously to predict a reproducible sub-surface structure. After the zone is confirmed by gravimetric and magnetometric surveys, a seismic survey is carried out for a clear image of the sub-surface structure.

3-SEISMIC SURVEY

This technique uses a sonic instrument over the desired site to correctly locate the prospective basin structure. In this method, a sound signal generated by the explosion method (explorers call them mini-earthquakes, which are artificially created by explosives) is transmitted through the earth’s surface under study, and reflected signals are detected by geophones located at specified positions. The frequency and time of the reflected signal vary with the density, porosity, and type of reflecting surface.

 Various rock deposits at different depths vary with density and porosity. Seismic reflection can measure this change as it travels below the surface. Computer simulation software is used for imaging the sub-surface structure. This is applied to all the surveys for fast and accurate prediction about the oil and gas reserve location, well before a site is finally selected for drilling operations. It is to be noted that exploration has to be deterministic, but the availability of oil and gas is estimated based on probability.

seismic survey

4-REMOTE SENSING METHOD

Solar radiation from the Earth’s surface varies in intensity and frequency depending on the sub-surface property. This observation is collected via satellite to predict the sub-surface structure. To image the sub-surface structure, historical geological data collected previously by gravimetric, magnetometric, and seismic surveys are used. The final image is obtained by geological imaging software (GIS). However, the remote sensing method is not applicable during nighttime or places incapable of reflecting solar radiation, like the ocean surface, which absorbs substantial amounts of solar radiation. However, extrapolation from the land surface in the vicinity of the sea can be accurately predicted but is not applicable for the deep-sea area. A radioactive or gamma-ray survey is also used in the exploration.

 

5-GEOCHEMICAL METHODS

Inorganic contents of surface or shallow cuttings or core are sampled and analyzed for inorganic materials, such as salts and carbonates, which are frequently associated with hydrocarbons. Organic contents or the presence of organic matter are detected by heating a sample in a crucible and the loss of mass of the sample is an indication of the presence of organic matter. The ratio of organic mass to inorganic matter in a sample is used to ascertain the presence of hydrocarbons. Total organic carbon is defined as the carbon present in the organic matter in the sample which is different in inorganic carbon from carbonates. Core samples are examined for porosity, permeability, salt content, organic content, and many other physical and chemical properties.

6-Radioactive:

Equipment and procedures involving radioactive materials have been used within the hydrocarbon exploration and production industry for many years, as well as in other industries and the public health sector. Tracers are routinely used in both the drilling and flow enhancement (stimulation by fracturing) of wells. They may be either chemical or radioactive. There are a considerable number of different radioactive materials used, utilizing either beta or gamma forms of radiation.

There are several purposes to which tracers are applied. In situ logging is used to detect the location of gamma-emitting radioactive tracers (and hence for example the location of the cement, packing, drilling muds, perforating changes, and/or fracturing proppants, or to provide proof of clean-up, depending upon the purpose and means of utilization), while sampling of return/produced fluids for either beta-emitting or chemical tracers is used as a means of evaluating flows and formation clean-up.

 Matters such as well integrity, the precise placement of equipment or identification of target formations, and the extent of fracturing fluid penetration, can be assessed using tracers. It should be noted that not all field operators in Taranaki use radioactive tracers, and likewise, not all uses of radioactive tracers relate to fracturing. As noted above such tracers can be an integral part of a conventional well drilling operation.

 

7-STRATIGRAPHY

Correlations are established between wells, fossils, rock and mud properties, before and during drilling operations for the final prediction, and this technique is known as stratigraphy. But it is important to remember that prediction from exploration may not be correct as far as the location and amount of deposit are concerned. It may happen that the drilling operation may not yield oil or the yield may not be sufficient at the explored site and that the expenditure borne by this work is irrecoverable. Hence, a more accurate determination of the location and economic deposit should be done before investing money in good construction. After confirmation from the test drilled hole, final construction is carried out.