Read the text and translate it into Russian.                                           Factors Considered in Petroleum Geology

                                          Factors Considered in Petroleum Geology

  Exploring for petroleum was once a matter of good luck and guess work; now petroleum explorationists use many technical and scientific principles to guide them. Today, surface and subsurface geological studies drive the discovery of oil and gas. Aerial photographs, satellite images, and various geophysical instruments provide information that helps to determine where to drill an exploratory well. Then specialists examine the rock fragments and core samples brought up while drilling the exploratory well and run special tools into the hole to get more information about the formation underground. Examining, correlating, and interpreting this information make it possible for the petroleum prospector to accurately locate subsurface structures that may contain hydrocarbon accumulations worth exploiting.

       Thus, petroleum geology refers to the specific set of geosciences that are applied in searching for hydrocarbons. Petroleum geology is principally concerned with the evaluation of key elements in sedimentary basins, namely: source, reservoir, seal, trap, timing of maturation, migration.

       In terms of source analysis, several facts need to be established. Firstly, the question of whether there actually “is” any source rock in the area must be answered. Delineation and identification of potential source rocks depends on studies of the local stratigraphy, paleogeography and sedimentology to determine the likelihood of organic-rich sediments having been deposited in the past.

       The existence of a reservoir rock (typically, sandstones and fractured limestones) is determined through a combination of regional studies, stratigraphy and sedimentology (to quantify the pattern and extent of sedimentation) and seismic interpretation. Once a possible hydrocarbon reservoir is identified, the key physical characteristics of a reservoir that are of interest to exporationists are its porosity and permeability, which are determined by different logging methods.

       The seal, or cap rock, is a unit with low permeability that prevents escaping of hydrocarbons from the reservoir rock. Analysis of seals involves assessment of their thickness and extent.

       The trap is an arrangement of rock layers that contains an accumulation of hydrocarbons, yet prevents them from rising to the surface. The trap consists of an impermeable layer of rock above a porous, permeable layer containing the hydrocarbons. Traps come in all shapes, sizes, and types.

       If the likelihood of there being a source rock is thought to be high, the next matter to address is the state of thermal maturity of the source, and the timing of maturation. Maturation of source rocks depends strongly on temperature, as the majority of oil generation occurs in the 60° to 120° C range. Gas generation starts at similar temperatures, but may continue up beyond this range, perhaps as high as 200 C. In order to determine the likelihood of oil/gas generation, therefore, the thermal history of the source must be calculated. This is performed with a combination of geochemical analysis of the source rock and basin modeling methods.

       The oil source rock is not the oil reservoir rock; the movement of the oil from the former to the latter is known as primary migration. Movements of oil and gas within the reservoir rock are referred to as secondary migration. Careful studies of migration reveal information on how hydrocarbons move from a source to a reservoir and help quantify the source of hydrocarbons in a particular area.

       Thus, the discovery of new plays and reassessment of old ones can be a long and costly process. A scientific approach greatly increases the chances of success and this requires the selection of the methods appropriate to the problem to be solved.

 

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