The ApplicATion of BiogeophysicAl sTudies in The seArch for oil fields

The article gives an analysis of qualitative and quantitative indices of biogeophysical anomalies (BGPh-anomalies) recorded over oil deposits, obtained as a result of experimental and methodological work on the oil fields studied in detail. By the degree of intensity and complexity of the BGPh-anomalies registered in digital form with special equipment developed by the authors, a set of qualitative and quantitative features has been developed that make it possible to determine the genetic type of the structural trap of the identified oil deposit, and, under favorable conditions, the depth of its occurrence. BGPh-anomalies of the “tectonic fault” type, their influence on the “oil deposit” type of BGPh-anomalies have been studied. The limiting values of the watercut in the exploited oil reservoir are determined, when exceeding, the oil reservoir ceases to create a BGPh-anomaly such as “oil deposit”, which can be used for the areal monitoring of oil fields. The minimum thickness of the oil-saturated reservoir is determined, which creates an anomaly of the “oil deposit” type. Based on this analysis, it is assumed that the BGPhanomalies arise only over oil deposits, potential for industrial development.


Academic note
In the academic journal, the millennium was marked by the discovery of a large silver field in Germany by dowsers, after which a thaler with a frame was released (Maksimov, 1970).Acknowledgment of dowsing merits in the XVIII century was the decree of Catherine II to include divining rod in the Petrozavodsk's coat of arms (Frantov, Glebovsky, 1987).
The beginning of publications about the possibility of using the divining rod method for the water search in the USSR refers to the beginning of the twentieth century.Here the work of Professor I.A. Kashkarov of the Tomsk Polytechnic Institute should be noted, as well as the works of V.A. Guskov, I.I.Ginzburg.
In 1973 the International Society for the Study of Instrumental Research of Biofields was organized, where the questions of dowsing were also considered.
The Ministry of Geology of the USSR organized in 1967 a meeting at the All-Union Institute of Mineral Raw Materials on dowsing with the participation of eight institutes, where the terms BPhE(biophysical effect) and BPhM (biophysical method) were approved.
The first All-Union seminar on BPhE was held in 1968, the second -in 1971, in Moscow, the third -in 1976 in Tomsk, the fourth -in 1979 in Riga, the fifth -in 1981 in VSEGINGEO.The results were 445 publications in the collections of the library of the Academy of Sciences of the USSR; a bibliography on BPhE was compiled.In the 1980s, the effect of the biolocation method was fully recognized by the USSR Academy of Sciences.
A letter from Academician O.A. Ovchinnikov, vicepresident of the Academy of Sciences of the USSR, notes: "The Academy of Sciences of the USSR have considered issues related to the dowsing method and finds that the application of this method will yield appreciable savings in the national economy, and the need for its further study does not cause doubts" (Sochevanov, 1984).
In the work "Biogeophysical method of prospecting and exploration of oil fields", a working hypothesis of the origin of Biogeophysical (BGPh) anomalies over oil deposits is given, based on the electromagnetic nature of this phenomenon (Mardanov et al., 2015).
In the work "Electromagnetic field as a cause of the emergence of the biophysical effect", references are given to the connection of BPhE with electromagnetic fields and ionization of air (Sochevanov et al., 1975).

introduction
At present, the seismic survey method, aimed at finding positive structures, is the most generally recognized and reliable method for searching for oil fields.However, seismic exploration has one significant drawback: in identified seismic structures, oil may not exist, and the seismic structures themselves may be false, caused by velocity anomalies in the overlying sediments.Therefore, recently there has been an increased interest in methods aimed at direct search for oil deposits.Such methods include the biogeophysical method.
Biogeophysical method, which in previous centuries was called "Divining rod method" was widely used in the Middle Ages, in particular, most of the ore deposits of gold, silver, copper, lead, antimony, iron, coal in Western Europe were discovered thanks to the application of this method (Maksimov, 1970, Sochevanov et al., 1987).In ancient times the BGPh method was called dowsing, this phenomenon was known more than 4000 years ago.It boils down to the fact that some people, when passing over aquiferous or ore zones, observe a deviation or rotation of a clamped woody branch in the hand.
Recent studies show that biogeophysical anomalies can be detected not only over ore deposits, but also over oil fields (Mardanov et al., 2015).
For direct searches for heavy oil fields, JSC "Tatneft" in May 28, 2014 received patent No. 2551261 "Method for mapping structural uplifts in the upper part of the sedimentary cover and predicting heavy oil deposits".Summary of the invention: Electromagnetic waves emit and receive signals reflected from the interfaces of the sounded medium.Herewith structural maps of the uplift, as well as temporary seismic sections of the reflected boundaries of the upper part of the sedimentary cover are preliminarily constructed; geophysical studies of the wells, core materials are studied.
Another method of direct searches for hydrocarbon deposits is the overvoltage prospecting method, patent No. 2391684 dated April 22, 2008."Method of geoelectric exploration of oil and gas fields with the forecast of hydrocarbon saturation".
In contrast to the biogeophysical method, the radar method of patent No. 2551261 has a significant drawback -a narrow field of application, requiring detailed study of the field by drilling, seismic survey, and the patent No. 2391684 drawback is a low resolution for all electrical survey methods, low reliability.

Methods and technology of the Bgph method
At present, the authors have developed and applied the original technique and technology for the production of BGPh-studies of oil, which allows recording anomalies using a semi-automatic digital recorder combined with a GPS sensor.Depending on the intensity of the biophysical field, the frame in the hands of the operator performs a rotational motion with a certain force.The recorder converts this rotational force into millivolts, which allows the resulting material to be digitized and processed promptly using a specially designed computer program.With the use of the developed technology, it became possible to digitally quantify the level of intensity of BGPh-anomalies.Since the intensity of the BGPh-field is not obtained directly by measuring electromagnetic or other geophysical parameters, but indirectly, on the resultant maps, the intensity is denoted in conventional units (cu).This allows not only to identify and delineate oil deposits, but also to distribute the studied area according to the degree of prospects into several categories.The most promising can be considered those areas where the identified intense GGPh-anomalies such as "oil deposit" coincide with the positive seismic structures of the target oil-bearing horizons.

interpretation of the results of Bgph-studies
With the increase in the number of areas studied by the BGPh-method in the search for oil deposits, the authors made significant progress in interpreting the results of the field survey.During the last six years, experimental, methodical and production work was carried out at 57 facilities located mainly in the Volga-Ural oil and gas province.
In order to resolve the interpretation issues in 2014-2015, the BGPh-method was carried out in two detailed areas of the Alekseevsky and Bavlinsky oilfields located on the south-eastern slope of the South-Tatar Arch.
2.1.The first polygon for solving the problems of interpretation of the BGPh-anomalies was the experimental and methodological work on the central part of the Alekseevsky oil field, which is being developed for more than twenty years (Fig. 1).
The unified oil deposit, which is in operation for more than 20 years, according to the data of the BGPh-study is divided into two parts; the division occurs along a tectonic fault line 150-250 meters wide, coinciding with the riverbed of the Kuehlga River, with a steep northern side.
All wells, of which industrial oil is currently produced, are in the outline of the BGPh-anomaly such as "oil deposit".Wells that, because of the water cut in the reservoir, have been transferred to the reservoir pressure maintenance regime, are located behind the outlines of the BGPh-anomalies.
In the central part of the BGPh-anomaly such as "oil deposit", a zone with an intensity of 60-80 cu is allocated; this zone corresponds to the contour of oil deposits in the carbonate Devonian sediments D3fm, which are located under the reservoir in the Tournaisian sediments C1t.
Only in one well No. 6440, which is located outside the BGPh-anomaly such as "oil deposit", oil is produced with a flow rate of 4m 3 /day and it is located near the tectonic fault.This corresponds to the hypothesis of the origin of BGPh-anomalies over oil deposits, according to which the BGPh-anomaly from the tectonic fault breaks the BGPh-anomaly over the oil deposit (Mardanov et al., 2015).2.2.The second polygon for solving the problems of interpreting the BGPh-anomalies was pilot works at the Sabanchinsky oil field developed since 1974.The map compiled on the basis of the results of the BGPh-studies is shown in Fig. 2.
On the area of BGPh-studies, according to the available geological information, it was assumed initially that there is one vast oil deposit with a complex configuration.As a result of the work, six BGPhanomalies of the "oil deposit" type of various sizes were identified.
In the central part, an extensive BGPh-anomaly with an intensity of 30-50 cu was found, within which one zone with an increased intensity of values and two zones of absence of the BGPh-anomaly of the "oil deposit" type was identified.After applying the revealed contours of anomalies to the development map of the field, it was found out that zones of anomaly absence within the deposit can be caused either by the absence of industrial oil (insignificant thickness of oil-saturated reservoir, with low reservoir properties -as in wells 2196,1749,2159,2158) or the presence of "washed" productive zone in the area of wells 2163, 2165.20 years ago, at the beginning of operation they produced oil up to 5t/ day, but then, due to watering, they were transferred to the reservoir pressure maintenance regime.In the center of "oil-free zone" there are wells 2163, 2165.In the well 2161 the water-cut is 83%; in the well 2172 the water-cut is 92.4%.
A zone with an increased intensity of 50 to 70 cu was found in the area of well 2168, and in the very center of this zone the intensity of the BGPh-anomaly reaches a maximum value of 90 cu.After the conducted pilot works, the following features were emerged: -zone with an intensity of 50-70 cu is caused by an oil deposit of increased thickness in the Tulskian-Bobrikovian deposits C1; -zone with an intensity of 90 cu refers to a deeper, terrigenous Devonian D 3 .Its dimensions are small -200x200 meters.At the same time, it is known that several producing wells from the terrigenous Devonian deposits are exploited in this region, and the BGPh-studies, however, only note medium-intensity anomalies related to the lower Carboniferous.The explanation of this phenomenon is that these wells have been producing oil for many decades, and the water cut of the production reaches 98-99%.With such a wateroil ratio, the operator of BGPh-studies does not reveal the oil deposit.
As a result of the pilot production works conducted at the Sabanchinsky field, the following was revealed: -BGPh-studies conducted on the area of old deposits, identify areas with industrial oil, where the water cut of the products does not exceed 75-80%; -The BGPh-method under favorable conditions makes it possible to determine the presence of a second, more deep-lying oil deposit under the upper deposit and to contour it; -The presence in the geological section of several oil-saturated reservoirs with an interval of several

determination of the quality of oil reservoirs
In 2015, BGPh-studies were carried out at Shuganskoy, Komuninsky, and Pokrovsky uplifts of the Muslyumovsky section of OJSC Mellyaneft to clarify the contours of the developed deposits and identify new oil deposits.All the tasks were successfully solved.It is interesting to consider the results of drilling a horizontal well 186g, the horizontal part of the trunk of which is beyond the boundary of the BGPh-anomaly of "oil deposit" type (Fig. 3).According to the logging conclusion, the oil saturation of the С1tl reservoir in the horizontal part of the trunk with length of 130 meters is in the range of 55-60%, clay content -from 4.5 to 7.5%.As a result of the well tests, it was possible to obtain only a small amount of technical water, there is no inflow of reservoir fluid.At the same time, it is known that production wells No. 179, 180, 182 and 185, located in the central part of the oil deposit, have penetrated the oil-rich reservoir С 1 tl with clay content not exceeding 3.5%, and oil has been successfully produced for a long time.Thus, we can assume that the BGPh-method allows to indirectly determine reservoir properties of the formation.

The fact that within the oil reservoir of the structural type, identified by seismic prospecting and drilling, the BGPh-method identifies zones of BGPh-anomaly absence, can be explained by a change in reservoir properties -in terrigenous rocks by increased clayiness, in carbonate reservoirs -by dense areas.
After analyzing the results obtained and comparing them with the geological structure and hydrodynamic parameters of the studied sections of the fields, the following conclusions can be drawn.
1.At present, the technical level achieved at LLC NPF LOZA allows to register the BGPh-anomalies in digital form, continuously along the working profile.The intensity of the BGPh-anomaly is measured in conventional units (cu), in the range from 0 to 100 cu.As experience shows, gradation is enough in five intervals with values: 0-20; 20-40; 40-70; 70-90 and above 90 cu.
2. BGPh-anomaly such as "oil deposit" appears almost vertically over the outer contour of the oil deposit, with an accuracy of 50-100 meters.
3. In a detailed study of an oil field in long-term operation, local zones with high water cut (over 80%) are allocated as zones of absence of an "oil deposit" anomaly.
4. If the injection is located inside the oil reservoir contour, the area that is "washed" by injected water is allocated as a zone of absence of an "oil deposit" anomaly.
5. The fact that within the oil reservoir of the structural type, identified by seismic prospecting and drilling, the BGPh-method identifies zones of absence of the BGPh-anomaly, can be explained by a change in reservoir properties -in terrigenous rocks by increased clayiness, in carbonate reservoirs -by dense areas.
6.If the thickness of the oil-saturated reservoir is less than 1.5-2 meters, it is not allocated as an "oil anomaly".
7. In some cases, inside the BGPh-anomaly such as "oil deposit" with an average intensity of 30-40 cu, zones are allocated with an intensity of 60 cu, and sometimes up to 90 cu.This happens in those cases when one or several oil deposits are located under one deposit, several hundred meters deeper.For example, in the case of a fragment of the Alekseevsky field (Fig. 1), discussed above, a zone with an intensity of 30-50 cu refers to the contour of the oil deposit in the sediments C1kz, and the anomaly with an intensity of 60-80 cu along the contour coincides with the contour of oil deposits in the carbonate sediments of the Upper Devonian (D 3 fm).

Identification of tectonic faults
When searching for oil deposits by BGPh-studies, anomalies such as "tectonic fault" are often detected.This occurs as follows: an anomaly of the "oil reservoir" type disappears, after some distance an anomaly of the "tectonic fault" type appears.The width of the zone of the tectonic fault is from several meters to hundreds of meters.Quite often the anomaly "oil deposit" ends on a tectonic fault.If the oil anomaly is extensive, an anomaly of the "oil deposit" type appears again after the "tectonic fault" anomaly.The width of the absence zone of "oil deposit" anomaly along the tectonic fault in most cases coincides with the steep slopes of ravines.
The explanation of this phenomenon is possible: it is well known that ravines and rivers occur in places of tectonic faults.Anomalies of the "tectonic fault" type are mainly confined to ravines and river valleys.It is generally believed that a zone of destruction is formed along the inclined (subvertical) plane of the tectonic fault, where, due to the displacement of the rock layers, fragmentation occurs, and the rock cracks become more fractured.Hydrothermal streams circulate for a long time along this subvertical zone of destruction, which cause secondary mineralization in the nearfault zone.Ultimately, this leads to the formation of an inhomogeneously densified subvertical plane.The presence of such an anomalous object screens the anomaly emerging above the oil deposit (Fig. 1, 3).Since destruction and secondary mineralization in the tectonic fault zone does not occur in the same way everywhere, a screen that prevents the formation of a BGPh-anomaly also arises of different qualities.Therefore, the zone of absence (screening) of the oil anomaly along the tectonic fault varies in width.
In the scientific literature devoted to the study of tectonics in the Volga-Ural oil province, the identification and tracing of tectonic faults within oil deposits has not yet been systematized and described.Modern seismic exploration does not notice small faults as a result of multiple summation of traces.This can be clearly seen from the time cuts applied to seismic records, where tectonic faults from seismic exploration, above the terrigenous Middle Devonian, are practically not distinguished.Geochemistry gives some scatter of data that is "spread out" over the area.It is known that discrete methods of fixation cannot uniquely identify small faults, especially when there is no vertical displacement of the seams.The BGPh-method allows to continuously trace the nature of the change in the anomalies of the "tectonic fault" type and as a result, it makes it possible to isolate both large tectonic faults having a deep origin, and neotectonic ones having a local character.

effectiveness of the use of Bgph-studies
To illustrate the effectiveness of the use of BGPhstudies in forecasting the prospects of seismic structures, a few more examples are given below.
Tlanchi-Tamaksky section is located to the west of the village of Tat.Suksi in the Aktanyshsky district.In 2013, as a result of the studies carried out by the BGPh-method, one large anomaly of the oil deposit type was singled out with the aim of predicting the oil prospect of the Tlanchi-Tamaksky section.The size of the detected anomaly is 4х2 km, in the central part of the anomaly there is a section of increased intensity, with a high degree of prospects, with dimensions of 1x1.5km.The design well No.300 is located within the anomaly (Fig. 4).
petrovsky section of the Bavlinsky field is located to the south-west from the village of Petrovka in the Bavlinsky district.In 2014, as a result of the research carried out by the BGPh-method, an anomaly of the "oil deposit" type with two intensive areas and a size of 0.6x1.0km was singled out for the prospective evaluation of oil prospectivity by the design point for well No.1130.The design drilling point is located within the intensive zone of the oil anomaly (Fig. 5).A forecast was made about the prospects for identifying oil-saturated reservoirs in the Lower Carboniferous and Devonian sediments.
In addition to the above examples, there are still a significant number of studies that confirm the high efficiency of the BGPh-method in the search for oil deposits, these works are included in Table 1.
Table 1 includes 97 investigated structures at 37 sites.Based on the results of wells testing, including previously drilled wells, the success rate of 141 wells is 94%.In addition, on the territory of the Samara, Orenburg, Ulyanovsk, Perm, Chelyabinsk and Kurgan Regions and in the Republics of Tatarstan, Bashkortostan, an additional study was conducted on 14 licensed sites, the results of which, for reasons of confidentiality of information, are not included in Table 1.Orekhovsky license section, forecasting the seismic structures 28 seismic structures were analysed on the total area of 120 sq.km.Among them 21 oil anomalies were identified on the 20 structures and 8 structures were without anomallies 35 wells drilled after the BGPh-studies are located on the studied area.Among them 27 wells correspond to the BGph-studies results, 8 wells with oil production were drilled beyond the anomalies 77

Fig. 2 .
Fig. 2. Results of the BGPh-studies at the Sabanchinsky field

Fig. 3 .
Fig. 3. Results of the BGPh-studies on the Pokrovsky uplift

Fig. 4 .
Fig. 4. Results of the BGPh-studies at the Tlanchi-Tamaksky section.Note: Well No. 300 was drilled in the spring of 2014, the oil deposit in C1bb was penetrated.The total capacity of oil-saturated reservoirs is 10 m

Table 1 .
Results of the BGPh-studies on identification of objects that are promising for oil reserves