of Geology, Geography and Geoecology

. Reasonable allocation of operational facilities in the context of multilayered reservoirs is the foundation of all scientific and practical work on the development of petroleum fields. The parameters of deposits are subject to changes over the course of develop - ment, and therefore the previously identified system of objects should be updated periodically. This is especially true for offshore mul - tilayered fields, mining which is time-limited due to corrosion of hydraulic structures and high costs for their renewal. In this regard, the rate of using offshore deposits should be quite high not only at the initial stages, but also remain so in subsequent mining periods. Maintaining a high rate of mining is often associated with high material costs (drilling new wells to compact the well network, applying new methods of enhanced oil recovery, etc.), which is not econom - ically viable for the fields in long-term operation. As the practice of mining multilayered fields in Azerbaijan shows, the enlargement of objects allows compacting a mining network while maintaining the total number of wells for a field. At the same time, average daily oil production rates significantly increase as a result having included capacities of contiguous objects. The research aimed at identifying similarities or differences between adjacent horizons of the section of multilayered deposits. Based on the delineated boundaries, there are possibilities of their joint operation as one object, separate or simultaneous-separate operation of wells under appropriate technical conditions. As a result of such measures, all the wells are used rationally and the development rates are increased without additional capital investment. Section of objects of the 3 rd tectonic block of the Neft Daşları offshore field, confined to the Apsheron archipelago of the South Caspian Depression (SCW). The Rodionov’s method was used for a substantial and reliable identification of stratigraphic boundaries. Preliminarily, based on averaged data on 11 parameters, we calculated ꭓ 2 g:m critical value at 95% significance, correspond - ing to m=0.05, which is used to assess the state of boundaries between the horizons. Then, by implementing software, the values for the boundaries of adjacent objects were calculated, comparing which with the critical value allowed for a conclusion about possible joint or separate mining of those productive strata. As a result of the implementation of the corresponding program, the clarity of the boundaries between the objects of the 3 rd tectonic block of the offshore Neft Dashlari field was determined. The need for joint exploita - tion of horizons VII and VIIa, KS 1 and KS 2 , as well as KaS 1 and KaS 2 horizons has been determined, which would optimize the mining of the field and is economically feasible.


Introduction
Azerbaijan is one of the oldest oil producers around the globe. Approximately, the extraction of the Caspian marine deposits has been underway since the mid 20 th century. Within our Republic, search and survey of accumulations of carbohydrate raw material is most promising in the water area of the South-Caspian Depression (SCD), to which a number of large open deposits of oil, gas and condensate are confined, being at various levels of the development. A large number of deposits, situated both inland and in the water area of the sea, are at the late development stages. This stage is characterized by oil degassing, low yield of wells and mining rates.
Exploitation of multilayered fields in general and of each object in particular is carried out based on the designed mining projects. During a technological period, the initial parameters of deposits are elucidated and complemented by new elements. Therefore, those corrections should be introduced to the oil extraction.
As known, during the technological process, the geological-industrial parameters of deposits are also subject to changes, and therefore differences in the parameters of adjacent objects of a section sometimes disappear over time, and sometimes, on the contrary, become starkly contrast. In the first case, those parameters can be classified to one plurality, and unified development of those objects would be the most efficient and practical from the economic standpoint (Abdullayeva, 2001;Bagirov, et. al., 2000Bagirov, et. al., -2002. In general, in the section of deposits, an exploitation object is considered a geological body that consists of one or several contiguous layers, designated according to geological, technological and economic tical need of intensifying neighboring objects of multilayered reservoirs. Therefore, so as to identify distinctness between boundaries of the objects, it is important to use statistical methods that can reliably solve this issue. Thus, we studied deposits of the 3 rd tectonic block of the Neft Daşları field (ND). This field, confined to the Apsheron Archipelago of the SCD, is situated 110 km southeast of Baku ( Fig. 1). Depth of the sea in the area ranges 15-25 m (Fig. 1). The ND field is divided into 6 tectonic blocks, each mined separately (Fig. 2). Within the 3rd block, which was the object of our studies, the productive horizons start from the 4th KaS of the Productive Layer (the Lower Pliocene). From this field, the overall extracted oil has amounted for 15 M T since the start of mining, and the remaining reserves account for 2 M T, which reflects the potential properties of this block. Those deposits, discovered in 1949, have been mined for a long time. Therefore, enhancing oil mining in order to speed up production rates, and mine and use the deposits more completely is a relevant task of industrial geologists. To achieve those goals, first of all, there are needed studies identifying objects of the entire section of the 3rd block, in which the KaS3 and KaS4 are practically not mined and have not been characterized by factual data. Similarities or differences between the productive strata should be identified according to parameteres characterizing them, using methods of mathematical statistics by which a resarcher can accurately solve taks without subjectivity. Identifying distinct boundaries between the objects consists in detecting sharp changes in behaviour of not only just one, but an entire complex of parameters (Rodionov, 1981;Salmanov, 2005Salmanov, , 2007Yanin, 2010;Yanin, 2021;Ibragimov, et. al., 2000).
For this purpose, we collected and systematized a factual material, and calculated averaged values of the parameters of all objects of this block (Table  1). Accordingly, we compiled a matrix of averaged parameters of the deposits. To solve the task, it was reasonable to divide all the parameters into two categories: values of category I parameters that are directly involved in object designation, and category II parameters that do not participate in the modeling, but nonetheless contribute to interpretation of the results from a geological-industrial perspective.
Thus, in category I, we included the following parameters: porosity, permeability, current parameters of deposit mining (current coefficient of oil recovery, average daily oil extraction, average water extraction, water content and reservoir pressure) and current physical-chemical properties of fluids (gas factor, oil density, oil viscosity and general mineralization of water). Category II was comprised of such parameters as total stratum thickness, effective thickness, area of oil bearing and number of producing wells.
For accuracy, we employed the Rodionov's criterion, calculated according to the following formula: , where -mean arithmetic features by j number, calculated for each of the two pluralities, by which a set of n observations is divided; n 1 , n 2 -number of observations in those pluralities; -assessment of the dispersion feature with j number, calculated assuming equilibrium of dispersion of each of the two groups of divided plurality. This assessment is convenient to make according to the following formula: (2) where A 1 and A 2 -pluralities by which T space is divided, having А 1 ∪ А 2 = Т. Function υ(r 2 ) is easier to calculate using the formula below: (3) If the tested hypothesis is correct, υ(r 2 ) would be a random variable, distributed as χ 2 with m degrees of freedom. Thus, hypothesis on uniformity is accepted if (4) and rejected if (5) Such a dichotomic division of the studied complex continues until all the smaller designated more fragmented complexes are uniform (Rodionov, 1981).
As a result of software-performed designation of the objects of the 3 rd tectonic block of ND deposits using the Rodionov's statistical criterion, we calculated values for the boundaries of all adjacent objects, comparing which to the critical values allowed for an unambiguous conclusion on possibility of their combined or separate exploitation.
Critical value of degree of similarity between the objects was with 95% likelihood determined using the Pearson's criterion, resulting in V(r 0 2 ) x 2 0.05;11 =19.7. Also, using the Rodionov's method and necessary software, we determined values for all the adjacent objects of the 3 rd tectonic bock of the multilayered ND deposits. If the obtained values are lower than the critical, then the compared objects can be considered comparatively identical and vice-versa: if they are of greater critical value, then those objects significantly vary between each other. The scheme demonstrates the proposed designation of the exploited objects.
Therefore, according to the results, in all the cases except the boundaries between the 7 th and 7a; KS 1 and КS 2 ; KaS 1 and КаS 2 , the statistical boundaries are reliable V(r 0 2 )>ꭓ 2 g;m . Horizons VII and VIIа, КS 1 and КS 2 , and also КаS 1 and КаS 2 would be practical to unify into a single exploitation object. The conducted geological-industrial comparative analysis of those deposits revealed that the results correspond to the current stage of development.

Conclusions:
1. Using the software algorithm, we calculated critical values and respective values for boundaries of all the adjacent objects of the 3 rd block of the ND deposits, based on which we determined the extent of how distinct they are. 2. The data and the geological-industrial analysis suggest a necessity of involving horizons VII and VIIа, КS 1 and КS 2 , and also КаS 1 and КаS 2. Their further separate exploitation is not economically beneficial. 3. As known, unifying the objects can optimize mining of multilayered long-mined oil reservoirs by effectively using all the wells of the field. Enlargement of the objects can consolidate the mining network, maintaining the general number of wells of the field with no additional expenses required. 4. Enhancement of mining rates of long-mined marine deposits, achieved by increase in mean daily production of oil, should be consistent with measures that would be feasible from both geological and technological-economical standpoints. In oth- КаS 4 er words, maximal possible mining of reserves of offshore deposits should be carried out not only by all existing progressive mining methods but those that are currently economically feasible.