RU1802101C - Method for detection of oil and gas-bearing terrigenous formations - Google Patents

Abstract

Usage: in petroleum geology to study the sections traversed by wells, to identify and evaluate hydrocarbon reserves, as well as to obtain information on the progress of development of oil and gas fields. The inventive measure the apparent electrical resistivity before and after exposure to the formation, the impact on the formation is carried out by injection of an aqueous solution of sodium tetraborate, and repeated measurements are performed during the existence of a colloidal system formed by the interaction of formation water and sodium tetraborate, and the lifetime of the colloidal system and the required concentrations of sodium tetraborate are determined by mixing its aqueous solution and the formation water samples under formation conditions JVI's. 1 wp

Description

The invention relates to petroleum geology and can be used to geologically study sections drilled by wells, to identify and evaluate hydrocarbon reserves (HC), as well as to obtain information on the progress of field development.

The aim of the invention is to increase the efficiency of the method in the conditions of deposits with a high content of iron and low salinity of water.

The method is based on the following provisions ..

Typically, oil and gas saturated formations are characterized by positive anomalies of apparent electrical resistivity {p. However, when sedimentary rocks contain highly conductive ore ferrous minerals (pyrite, magnetite, etc.) in amounts of more than 5%, p substantially decreases. If in this case the produced water is weakly mineralized, then the RK decreases even more, up to the disappearance of a significant anomaly. Under these conditions, conventional electrometry does not unambiguously isolate oil and gas saturated formations.

. It should be noted that iron-bearing deposits have a characteristic color of brownish and reddish tones, which allows them to be distinguished in section by core or sludge.

When sodium tetraborate is introduced into the studied interval, the following processes occur.

An aqueous solution of sodium tetraborate, which is an electrolyte, penetrates into the reservoir containing hydrocarbons, as a result of which

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The conductivity of this interval increases, and pk decreases by about an order of magnitude.

In the water-saturated part of the section, the reverse process occurs. When sodium tetraborate interacts with formation waters, complex ions are formed, which are compounds of boron ions with calcium magnesium, iron, etc., which are contained even in weakly mineralized formation waters. As a result, a colloidal system forms in the form of a white friable flocculent precipitate. In this case, there is a decrease in the number of free ions, which leads to a decrease in electrical conductivity and an increase in arr. It has been experimentally established that, depending on the concentration of sodium tetraborate, the life time of the colloidal system can be 6-7 hours. After this, the LCR system decays and is restored to its original value. The appearance of a negative anomaly / OK during repeated electrometry during the existence of the colloidal system indicates the presence of an oil and gas bearing formation.

The method is implemented as follows.

After a prospective non-detection of the hydrocarbon section of the section, composed of red sediments, is carried out, standard logging is carried out and pk is measured. Samples of produced water are taken by section and their salt composition is determined. The necessary concentration of sodium 35 tetraborate in solution is selected in a laboratory simulation to ensure the formation of a colloidal system under reservoir conditions20

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x After that, a solution of the indicated concentration is pumped into the investigated part of the section, and repeated measurements / Ec are carried out over the lifetime of the colloidal system. By the appearance of a negative anomaly / Ek, they conclude that there is an oil and gas bearing formation ..

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Forumula and zobret-n and

Claims (2)

1. A method for identifying oil and gas saturated terrigenous strata in a well, including stimulating the formation, measuring along the wellbore and comparing apparent resistivities before and after impacting and revealing oil and gas saturated formations by the pattern of changes in apparent resistivities, characterized by, so that in order to increase the efficiency of the method under conditions of development of deposits with a high iron content and low salinity of the formation water, the formation is affected by then injecting aqueous sodium tetraborate to form a colloidal system in the water-saturated part of the section of the well, and re-measuring the apparent electrical resistivity is carried out during the life of the colloidal system. 2. The method according to claim 1, wherein the time of existence of the colloidal system and the concentration of the sodium tetraborate solution are determined by sampling. formation water and mixing them with an aqueous solution of sodium tetraborate of various concentrations at formation pressure and temperature.