Basic concepts of oil exploration

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1. Text “Basic concepts of oil exploration”

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Text “Basic concepts of oil exploration”

Oil and gas geology is a branch of geology which can be defined as “a science of searching oil and gas deposits”, though geologists often work on the development of such deposits after their discovering. The usage of last achievements of geological science in oil and gas prospecting and exploring don’t except, nevertheless, the element of chance; only one of seventy wells drilled for searching of new oil and gas deposits leads to commercially profitable discovery. That’s why only large companies have geological services and many others engage petroleum geologists as consultants.

Geologists gradually realized relationship between natural oil and gas occurrence and rock structure and in 1915 oil geology was formed as a separate science. Since that time a number of specialists in oil and gas exploring increased and nowadays thousands of geologists are busy with oil and gas searching. In order to explore oil and gas deposits successfully, it is necessary to determine exact conditions favorable for deposits formation. As you know oil exploration has two stages: prospecting and searching. Prospecting stage in its turn consists of tree steps.

The first step includes regional works which are held in the basins with non-established oil-and-gas content with the help of aeromagnetic, geological and gravimetric survey, geochemical investigation of waters and rocks, profile area crossing by seismic prospecting, drilling of key and parametric wells. The aim of this step is to establish regions for further prospecting work.

The second step consists of more detailed investigation of reservoir zones by means of detailed gravimetrical prospecting, subsurface-contour, electrical and seismic survey and geological drilling. On the third step exploratory wells are drilled in order to discover the deposits. Primary exploratory wells are drilled on maximum depth. The upper store is to explore firstly and then come deeper ones. This work leads to the storage estimation.

Searching stage is a completion phase in geological process. Its main purpose is preparation for exploration. In the process of searching, deposits are to be contoured, lithologic composition and hydrocarbon saturation must be defined. On completing searching works storage is accounted and recommendations on deposit introduction to exploitation are given. Searching effectiveness depends on deposit discovering ratio. Gravimetrical methods of oil and gas exploring are based on weak variations of attracting force, defined by different rock properties. Gravity is less above salt dome because salt has less density than surrounding rocks; but it is more above anticlines as dense rocks of foundations are closer to the surface.