surveyed location. The results of the geologic survey are not conclusive and only offer a possibility of finding petroleum reservoirs. The rate of success of finding petroleum reservoirs using geologic surveys alone has been historically low. Currently, geologic surveys are used together with other geophysical surveys to provide higher rates of success in finding petroleum reservoirs.
Geophysical Surveys
are mainly four types of geophysical surveys used in the industry: gravity survey, magnetic survey, seismic survey, and remote sensing.gravity survey is the least expensive method of locating a possible petroleum reservoir. It involves the use of an instrument, a gravimeter, which picks up a reflection of the density of the subsurface rock. For example, because salt is less dense than rocks, the gravimeter can detect the presence of salt domes, which would indicate the presence of an anticline structure. Such a structure is a candidate for possible accumulation of oil and gas.magnetic surveyinvolves measurement of the magnetic pull, which is affected by the type and depth of the subsurface rocks. The magnetic survey can be used to determine the existence and depth of subsurface volcanic formations, or basement rocks, which contain high concentrations of magnetite. Such information is utilized to identify the presence of sedimentary formations above the basement rocks.seismic survey involves sending strong pressure (sound) waves through the earth and receiving the reflected waves off the various surfaces of the subsurface rock layers. The sound waves are generated either by using huge land vibrators or using explosives. The very large amount of data collected, which include the waves travel times and characteristics, are analyzed to provide definitions of the subsurface geological structures and to determine the locations of traps that are suitable for petroleum accumulation.type of survey is the most important and most accurate of all of the geophysical surveys. Significant technological developments in the field of seismic surveying have been achieved in recent years. Improvements in the data collection, manipulation, analysis, and interpretation have increased the significance and accuracy of seismic surveying. Further, the development of three-dimensional (3D) seismic surveying technology has made it possible to provide 3D descriptions of the subsurface geologic structures.sensing is a modern technique that involves using infrared, heat-sensitive, color photography to detect the presence of underground mineral deposits, water, faults, and other structural features. The sensing device, normally on a satellite, feeds the signals into special computers that produces maps of the subsurface structures.
Exploratory Drilling
data collected from the geologic and geophysical surveys are used to formulate probable definitions and realizations of the geologic structure that may contain oil and / or gas. However, we still have to determine whether petroleum exists in these geologic traps, and if it does exist, would it be available in such a quantity that makes the development of the oil / gas field economical? The only way to provide a definite answers is to drill and test exploratory well (s). Exploratory well, known as the wildcat well, is drilled in a location determined by the geologists and geophysicists. The well is drilled with insufficient data available about t...
