RU2391684C2 - Method for geoelectric prospecting oil-gas fields with prediction of hydrocarbon saturation - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: pulsed electromagnetic field is excited on the profile under analysis. The overall transient intensity characteristic of the complete electromagnetic field (EMF) is measured in the intervals between pulses of the excitation current. Presence of a hydrocarbon deposit is determined based on comparing the value of the polarisation induced component of the electromagnetic field intensity measured during the intervals between current pulses, with a theoretically calculated value. Further, the value electromagnetic field intensity component arising from the induced polarisation process on a given interval of the linear profile and the background induced polarisation value are measured. The type of hydrocarbon is determined from high or low anomalous of measured induced polarisation parametres relative the background.

EFFECT: more reliable detection hydrocarbon deposits and information content of searching with unambiguous identification the type of hydrocarbons.

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Description

The technical solution relates to geoelectrical exploration methods using evoked polarization (VP) technology for sensing the formation of an electromagnetic field (EMF) in the near field (ZSB) and can be used in the study of a geoelectric section and in the exploration of mineral deposits, including hydrocarbon deposits (HC) and identification their type (separate forecast of oil or gas).

The well-known technology of geoelectrical exploration [6–9] by the ZSB EMF method is based on the study of transient processes occurring in the earth when the EMF is artificially excited by rectangular DC pulses, and includes the excitation of a pulsed EMF and measurement of the transient process in the pauses between current pulses. The geological structure is judged by the field formation curve, which after special processing is presented in the form of a geoelectric section. But the traditional technology of ZSB geoelectro-prospecting has insufficient noise immunity and resolution for the correct implementation of the direct method of mineral exploration. Identification of the type of hydrocarbons in traditional technologies is not possible.

Recently, a number of methods of geoelectro-prospecting [3-6] have been patented, which implement the ZSB with the release of the effect of induction induced polarization (IWP). These technical solutions are based on the experimentally established and theoretically substantiated [1, 7-9]) property of the probing EMF, which consists in the fact that the induced polarization (VP) of the EMF is caused by two components: the VP process and induction induced polarization (IWP). The registration of data using the ZSB-IVP technology and the subsequent processing and interpretation of measurements of the geoelectric section, in comparison with traditional methods, make it possible to obtain a qualitatively new technical result of electrical exploration: to increase the resolution and reliability of the section obtained by isolating the oscillation of the EMF EMP intensity (due to the effects of a finer structure) .

Common signs of geoelectro-prospecting methods [2-6] are: performing geological environment studies along the observation profile by exciting current pulses in the medium under study and determining the field and airspace formation parameters of the medium being studied, constructing a geological section and making judgments about the presence of hydrocarbon deposits from the revealed anomalies of the formation field and VP parameters.

Thus, the method of geoelectrical exploration [3] provides for measuring the electromagnetic field in the pauses between current pulses, determining the parameters of the airspace and the decay time constant of the difference in potentials of the airspace, and constructing time sections from these parameters. The method [2] of electrical exploration when searching for oil and gas fields consists in exciting EMFs, receiving EMF values in the pauses between EMF pulses and processing the data by the method of EMF formation: determining average values and increments over a given interval with subsequent judgment on the presence of oil and gas deposits within the study area, their contours and depth.

However, when implementing the methods [2, 3], adequate complex processing of the entire set of measurements cannot be carried out, and even more so, identification of the type of hydrocarbons in the field.

The method [1] of geoelectrical exploration adopted as a prototype includes excitation of a pulsed electromagnetic field on the studied profile and measurement in pauses between current pulses of the total transient response g (t) in the form of three processes: formation, induced polarization (VP) and induction induced polarization (IWP) depending on time t

g (t) = g _C (t) + g _VP (t) + g _IWP (t),

where g (t) is the intensity of the full electromagnetic field;

g _C (t) is the intensity component of the transition characteristic of EMF formation;

g _VP (t) - component of the EMF intensity due to the process of VP;

g _IVP (t) - component of the IVP intensity EMF,

moreover, the presence of a hydrocarbon field is judged by comparing the values of the components of the ИПП g _ИВП (t) measured in the pauses between current pulses with the theoretically calculated value g _ИВП , _theor (t, ρ), where ρ is the electrical resistivity due to the process of electric shock when the current is turned off .

In the method [1], as in other known methods [2-4], the average values of the measured signals of the geoelectric field are processed, and it is not intended for the analysis of probabilistic-static characteristics of parameter values, which limits its information content and, as a result, the reliability and reliability of detection of hydrocarbon deposits. The main disadvantage of the method [1], as well as other known methods, is the impossibility of identifying the type of hydrocarbon (separate forecast of hydrocarbon saturation: oil or gas).

The essence of the proposed technical solution is to create a method for the search and exploration of oil and gas fields according to the results of measurements of the VP, allowing on the basis of a new search criterion (values of the parameters of the VP relative to the background at a given interval of the measurement profile) to identify the type of hydrocarbon deposits.

The technical solution is based on the dependence of the HC type mapping in the form of extreme values of the VP parameter determined by the results of geoelectric measurements by the authors: oil fields correspond to zones of higher values of the VP parameter above the background, and to gas fields, zones of lower values of the VP parameter relative to the background.

The main technical result of the proposed method is to increase the reliability of detection of hydrocarbon deposits and the information content of the search with an unambiguous identification of the type of hydrocarbons (oil or gas). The method allows for synergy of data processing according to a new search criterion with the traditional technology for identifying anomalies of the type of deposit in the average values of geophysical parameters.

The technical result is achieved as follows.

The method of geoelectrical exploration of oil and gas fields includes the excitation of a pulsed electromagnetic field (EMF) on the studied profile and measurement in pauses between current pulses of the total transient response g (t) in the form of three processes: formation, induced polarization (VP) and induction induced polarization (IWP), depending from time t

g (t) = g _С (t) + g _VP (t) + g _IWP (t), (1)

where g (t) is the intensity of the full electromagnetic field;

g _C (t) is the intensity component of the transition characteristic of EMF formation;

g _VP (t) - component of the EMF intensity due to the process of VP;

g _IVP (t) - component of the IVP intensity EMF,

wherein the presence of hydrocarbon deposits is judged by comparing measured in the pauses between the current pulses of magnitude components TTI g _TTI (t) with the theoretically calculated value g _{TTI, teop} (t, ρ), where ρ - electrical resistivity due EP process at shutdown current .

A distinctive feature of the proposed method is that it additionally measures the values of the parameters of VP g _VP (t, x) at a given interval of distances x of the linear profile and the background value of VP at the same interval, and identification of the type of hydrocarbons with separate forecasting of oil or gas in the identified field is carried out by increased or decreased relative to the background anomalous values of the parameters of the VP.

Figure 1-5 illustrates the essence and technical result achieved by the proposed technical solution:

figure 1 is an example of the manifestation in the geoelectric parameters of the methods of VP, ZSB, secondary seismoelectric effect (SEE) and ZSB-IVP, oil field Kanevskoye, Krasnodar Territory, 2006;

figure 2 is the same for the Shengli-Sea oil deposit, China, 2006;

figure 3 is an example of the manifestation in the geoelectric parameters of the methods of VP and ZSB-VSE for the gas field Beisugskoye, Krasnodar Territory, 2007;

figure 4 - the same in comparison with a seismic section, a gas field in the province of Huabei, China, 2007;

5 is the same in comparison with a seismic section, a gas field, Syria, 2007

Confirmation of the implementation of the proposed method with the implementation of the specified technical result is illustrated by the following examples (Fig.1-5).

Electrical exploration work was carried out on hydrocarbon structures known from seismic data. EMFs were excited by a rectangular rectangular current pulse of 1–3 duration. Measurements of the EMF formation process were carried out channel-by-channel dipole-symmetric multi-channel multi-electrode setup with the number of electrodes 6-8 times the number of channels. To implement the ZSB-IVP method, the intensity of the EMP EMP was recorded in accordance with expression (1), and the oscillations of the EMP for constructing a geoelectric section were isolated from the measured signal of the full EMF by the method described in [1]. The presence of oil and gas fields in the study area and the determination of their contours and depths were carried out (similar to [1]) by comparing the correlation of the results of the analysis of the data of the study area with the characteristics of the known reference (or theoretically calculated g values of the _{IWP, theor} ) of hydrocarbon deposits and / or empty traps.

Identification of the type of hydrocarbons (separate forecasting of oil or gas) in the identified field was carried out according to the measured anomalous values of the parameters of the VP g _VP (t, x) on a given interval x of the linear profile and the background values of the VP on the same interval. According to the increased values of the parameter of the VP of the hydrocarbon field relative to the background, the field was identified as an oil field (Figs. 1, 2), and by the lower values of the parameter of the parameter of the VP, the gas field was identified as a gas field (see Figs.

Empirical data 2006-2008 They confirmed that the features of the proposed method of geoelectrical exploration provide a qualitatively new technical result: increasing the reliability of detection of hydrocarbon deposits and the information content of the search with an unambiguous identification of the type of hydrocarbons (oil or gas) when processing VP measurements using a new search criterion.

BACKGROUND OF THE INVENTION

I. Prototype and analogues:

1. RU 2094829 C1, 10.27.1997 (prototype).

2. RU 2134893 C1, 08.20.1999 (analogue).

3. RU 2231089 C1, 06/20/2004 (analog).

II. Additional sources of prior art:

4. RU 2111514 C1, 05.20.1998.

5. RU 2148839 C1, 05/10/2000.

6. RU 2298210 C1, 04/27/2007.

7. Christmas Eve V.V. High resolution electrical exploration. - Novorossiysk: Publishing House of the Moscow State University named after adm. F.F. Ushakova, 2006, 41 p.

8. Christmas Eve V.V., Nebrat A.G. et al. Theory and practical possibilities of the ZSB-IVP method in the search for oil and gas. - Physics of the Earth, No. 6, 1994, p. 54-56.

9. Electrical Exploration: A Handbook of Geophysics. - M .: Nedra, 1980, p. 329-355, 402-406.

Claims (1)

The method of geoelectrical exploration of oil and gas fields by excitation of a pulsed electromagnetic field (EMF) on the studied profile and measurement in pauses between current pulses of the total transient response g (t) in the form of three processes: formation, induced polarization (VP) and induction induced polarization (IWP), depending from time t
g (t) = g _С (t) + g _VP (t) + g _IWP (t),
where g (t) is the intensity of the full electromagnetic field;
g _C (t) is the intensity component of the transition characteristic of EMF formation;
g _VP (t) - component of the EMF intensity due to the process of VP;
g _IVP (t) - component of the IVP intensity EMF,
wherein the presence of hydrocarbon deposits is judged by comparing measured in the pauses between the current pulses of magnitude components TTI g _TTI (t) with the theoretically calculated value g _{TTI, Thm} (t, ρ), where ρ - electrical resistivity due EP process at shutdown current , characterized in that they additionally measure the values of the parameters of the VP g _VP (t, x) on a given interval of distances x of the linear profile and the background value of the VP on the same interval, and identification of the type of hydrocarbons in the separate forecasting of oil and whether gas in the identified field is carried out at higher or lower relative to the background anomalous values of the parameters of VP

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