Features of Tyumen Formation facial structures according to the spectral decomposition

A.V. Butorin (Gazprom Neft),R.R. Zinnurova, Gazpromneft-NTC

Источник: Журнал «Нефтяное хозяйство»

To date, the problem of finding new development targets becomes all the more urgent. This question is especially acute in regard to relatively depleted fields where the main reservoirs are highly drilled. In this case, the number of possible sites for drilling of new wells is reduced every year, which in addition to declining production makes the development of the asset economically less attractive.

One way to address the emerging problem may be development of edge parts, or searching for the so-called “oil remnants” unaffected by development. Such decisions are always connected to high risks, as it is often difficult to model behavior of fluids in the late stage of development. Another possibility to give a second wind to the field is a search for new development targets on previously unconsidered parts of the section. This decision can potentially solve the problem of “worked-out” asset, but such way often requires comprehensive study of all accumulated geological and geophysical data, as well as additional costs of exploration stage. The topic of searching for new “horizons” will be discussed in this article on the example of Noyabrsk region in West Siberian sedimentary basin.

In most cases, West Siberian fields development is focused on Lower Cretaceous sedimentary cover, in some cases interest of geologists extends even down to Vasyugan layers formed below Bazhenov formation. The most frequently developed Lower Cretaceous deposits are associated with Neocomian shelf sediments — relatively shallow sediments accumulated in the shelf stops. As a result, sand bodies formed under similar conditions of sedimentation are characterized by considerable size and stable properties along the section. Similar conditions of sedimentation for the section of Noyabrsk region observed in the accumulation of Vasyugan suite in the Upper Jurassic. Lower Cretaceous and Upper Jurassic shelf deposits are the most traditional development targets in this region of Western Siberia.

Most researchers have identified a number of classes of possible “promising” development targets which can postpone the evening of a field:

1) Cenomanian deposits

2) Achimov deposits

3) Tyumen formation

4) Triassic complex

5) Deposits of basement

The first class is represented by continental Upper Cretaceous deposits, in this area this complex is represented by the layers of PK group. Most often, these sediments are gas-saturated and associated with large gas deposits PK1. Oil-saturation is less common, additionally adequate geological modeling is hampered by complexity of their structure. A positive factor is the large number of transit wells revealing this complex, as all Noyabrsk region targets lie much deeper. However, significant oil deposits have not been detected in this complex despite of high drilling.

The second class includes clinoform complex deposits — deep-sea sediments formed in a bottom and slope of shelf terraces. Prospects for this type of deposits discussed by geologists for decades. The major difficulty of its development is associated with rapid change of properties in both vertical and lateral direction, which is due, primarily, with complex environment of sedimentation and development of system of channels and submarine fans.

The third class, represented by the Tyumen suite, can also be considered as a promising center, able to solve arising problems of worked-out assets. This stratigraphic units is Middle-Upper Jurassic deposits, underlying Vasyugan suite, and formed in a “continent-sea” transition zone. Tyumen deposits are regionally distinct complex represented all over the area, so their study is an extremely urgent task in terms of further development.

The latter two promising complexes are not considered in connection to Noyabrsk region due to significant depth of the Triassic complex and basement rocks.

Thus, the most promising complexes that can provide the resource base replenishment of depleted fields are Achimov and Tyumen deposits. This study considers Jurassic complex of Tyumen suite. The main disadvantage of Tyumen deposits is relatively low studied rocks drilling data — complex lies below the deepest target of Vasyugan complex, so the data on the structure and saturation of the Middle Jurassic rocks are often presented only in the sections of deepest wells. In this case, the factual information about the geological structure is extremely discrete, and the main role in the study of the Tyumen deposits is given to methods of areal seismic exploration. Seismic methods in this case just have to help geologists estimating internal structure of the prospective Jurassic complex and reveal its facial structure.

The purpose of this study is to investigate Tyumen deposits using interconnection of wells and seismic data. The focus is on the choice of the optimal algorithm for the study of the wave field to address the detailed geological problems.

The article primarily intended to show the experience of the Gazpromneft NTC, LLC in studying Tyumen deposits in Noyabrsk region of Western Siberia. The article provides an analysis of the most successful solutions used for the analysis of the wave field in the target range, allowing to predict facial structure of the complex with a high degree of confidence, which in turn is an important step in the study of the productive interval. The experience is invariant, i.e. not tied to “specific” requirements of the given data, so it can be applied to other deposits of the studied basin, which solves fairly important problem — the dissemination of knowledge.

The purpose of this study is to compile a regional facial map of Tyumen sediments in order to identify the most promising areas for further exploration, including exploratory drilling.

To achieve this purpose it is necessary to perform the analysis and interpretation of available geological and geophysical data, including seismic 2D / 3D data and well information (logs, core).

As part of the study of seismic data the primary role given to 3D surveys, due to the complex structure of the studied complex. In total there are 17 cubes on the area under consideration, with a total area of 20 000 sq. km. Carrying out this study required the creation of a single project, which would bridge the gap between all the available seismic data through a system of regional lines. Tied surveys interpreted later in order to obtain a single structural map for Tyumen deposits.

The total number of wells is approximately 23 thousand wells, but only 180 reveal deposits under study. Thus, it can be concluded relatively poor knowledge of Tyumen complex of the wells data.

The relevance of this study is primarily associated with a significant potential of Tyumen deposit in terms of its oil content. Identification of the main structural features of the complex will eventually solve an important issue of replenishment of the resource base of Noyabrsk region. The region is mainly characterized by deposits in the final stages of development, so the search for new perspectives become increasingly pressing issue.

Geological structure of Tyumen suite

Formation of productive strata of the Tyumen suite, to which in this territory belongs U2-3 complex, occurred in a transition zone between continental and marine facial environments. The accumulation of stratigraphic complex occurred in Middle Jurassic time. This period of geological history within the region of Western Siberia is characterized by extensive spread of continental sedimentation conditions. Sea conditions are observed in the northern part of the sedimentary basin. Areas of abandoned sea characterized by the development of numerous freshened overgrown ponds, where accumulation of silt and peat occurs. Subsequently, these reservoirs lead to the development of coal members in section of complex U2-3 that is well fixed on the drilling data. The southern part of the West Siberian basin is a vast alluvial plain with a large variety of low-lying landscape, which occasionally were filled by sea. The northern part of the basin is characterized mainly by shallow sea depositional environment.

Studied Noyabrsk region occupies an intermediate position and is attached to the development system of the complex transition between continental and marine sediments. In wells sections coal seams can be detected which reflect the temporary presence of stagnant conditions during the time of the regression stages. Thus, the geological development of the area suggests the presence of delta complex, characterized by the development of a complex system of channels through which removal of sediment occurred from the continental part of the reservoir to the sea.

The lithological composition of Tyumen deposits is a classic one for Western Siberia — rocks are clastic sediments complex, occasionally with carbonaceous units.

As mentioned above, facial sedimentation conditions of Tyumen suite formation in the studied area include the development of a complex delta system, reflecting a transition zone between the continental conditions in the south of the basin, and mostly sea in the north. However, in practice the allocation of facial environments within the section characterizing the geological development of the area may not always be realized. Moreover additional uncertainty is influenced by discrete nature of spatial well data — deposits opened only in 180 wells over the studied area, while not always satisfactory core material can be obtained (core recovery is about one percent).

Thus, the Tyumen deposits can be characterized as poorly studied from geological point of view — borehole data is not capable today to provide a decrease in geological uncertainties. Tyumen deposits at the time of exploration and drilling exploration wells were not earmarked, so information is more random in nature which in conjunction to given characteristics of the geological structure could result in an incorrect assessment of the structure and prospects of the complex.

Weak representation of borehole data leads to the fact that the leading role in the study of Tyumen complex nowadays is given to areal seismic methods which are capable to provide primary facial differentiation of the area, thereby to identify main patterns of reservoir properties distribution of Tyumen complex.

Studying Tyumen deposits on seismic data

Volatile nature of the Tyumen deposits leads to a complex structure of the wave field within this complex, which is primarily due to reflection coefficients changes. From the resolution point of view channels within Tyumen deposits appear as thin layers, i.e. cause reflection interference from the top and bottom, which makes difficult their detection on seismic sections.

Considered in this study Tyumen deposits are confined to reflecting horizons J2-J3, which belong to the upper part of the stratigraphic unit. On the wave field the stratigraphic top of J2 and J3 complexes has not explicit reflection on dynamic parameters, as the aged carbonaceous mudstone layer is a stable reflector here, since it provides significant acoustic contrast. Formation of aged carbonaceous strata obviously marks a period in the geologic history of the region under study when sedimentation conditions were favorable for the accumulation of carbonaceous matter, i.e. in the period of time when the territory of the Noyabrsk region was filled with swampy low lands providing conditions for accumulation of such deposits.

Allocation of channels and associated lithological bodies is possible by studying dynamic properties of the wave field, which include amplitude, phase, frequency, etc. Variety of dynamic properties leads to the fact that the inventory of modern seismic geophysics has a big number of algorithms which can provide information on the wave field. In this regard, there are several of the most common methods:

1) Amplitude analysis — based on the study of wave field amplitudes distribution along the reflecting surface. In this case, presence of geological object should change amplitude and phase of the signal that is reflected in the assessment of the amplitude.

For the analysis purpose a variation of assessment directly along the reflector can be used, or by using a window sized in consistency with the studied geological object and reflection.

In the first case, an important aspect of the analysis is the quality of reflecting horizon tracking — inconsistency between existing interpretation and characteristic points of the signal may lead to an incorrect assessment of the amplitude and false geological interpretation.

The second algorithm using a calculation window includes a large number of mathematical operations of signal evaluation to obtain an assessment of the amplitude characterizing the studied interval of the wave field.

The main requirement for detecting of geological structure features of Tyumen suite formation is the relationship between reflection coefficient and facial conditions. In other words, the presence of geological bodies in the context should change interference response of the wave field exceeding noise level. Otherwise, such change might be “invisible” in terms of the standard analysis during seismic exploration.

Unfortunately, typical channel capacity within Tyumen deposits is beyond the resolution of the wave field, the entire capacity of the complex J2-J3 varies within 50-75 ms. Thus, the complex structure of the studied complex leads to the interference character of the wave field.

2) Inversion analysis — based on the assessment of acoustic impedance, obtained from the wave field by applying the inversion operation. The acoustic-based inversion approach is based on the low-frequency models derived from log data on speed of propagation of longitudinal waves and rock density. Low-frequency model is used for calculation of synthetic wave field. The inverse solution is sought by changing of the acoustic model in order to minimize the residual functional between synthetic and real wave field. The model which provides a minimum difference with the actual wave field is taken as the final acoustic impedance.

Analysis of the acoustic impedance data can be performed in a similar way as on the standard amplitude analysis, which is provided the use as an assessment along the reflector and thus obtaining an integral evaluation.

As shown by the study of the acoustic properties from borehole data, presence of the channel system leads to a reduction in acoustic impedance. Thus, there are the preconditions for using the method of inversion in the study of the geological structure of Tyumen suite formation.

3) Spectral approach — based on the study of changes in spectral parameters of the wave field. According to the theory of spectral decomposition, the frequency parameters of the anomalies can be observed in the interference reflections from the top and bottom of the reservoir. Confirmation of this thesis is observed in many studies, including the fundamental article by G. Partyka.

To perform spectral decomposition the most widely used two algorithms: the discrete Fourier transform and continuous wavelet transform. Since the core of the Fourier transform is infinite harmonic function, this method is not well suited for the study of non-stationary processes, such as wave field. Moreover, the use of the Fourier transform requires a certain analysis window, rather “thin” for the emergence of geological effects. However, in this case, some subjectivity is introduced in the solution of the spectral decomposition. Based on the above-described drawbacks of the Fourier decomposition algorithm, the most preferred step is wavelet transform. In this case, window is not required — duration of the wavelet depends on its frequency content and is controlled by scale factor. In addition this property appears as a “shift” — reflecting the spatial position of wavelet within seismic trace. Scale and shift input allow a much more detailed view of the spectral parameters of the wave field.

Another feature of spectral decomposition method is usage of a special method of the results visualization — the RGB-mixing algorithm. This algorithm uses three input spectral parameters, each assigned to a color — red, green or blue. The amplitude of frequency parameter corresponds to intensity of the assigned color and thus the lowest amplitude corresponds to black, and the highest spectral value corresponds to the maximum color saturation. As part of the algorithm input spectral harmonics are combined in a single array, so each discrete output array (cube or map) is characterized by three values of the amplitude. Discrete color is determined by three-dimensional RGB palette.

This visualization scheme allows simultaneous analysis of three different frequency parameters, with a high degree of color differentiation.

Theoretically, as channel systems act as areas of interference, spectral decomposition is the most suitable method for analyzing seismic data. However, it should be noted that the loss of the sign of the frequency parameters leads to some limitation of the possibility of predicting acoustical properties of the geological environment.

Detecting channel systems upon seismic data

As described in the previous section, inventory of geophysics contains generally three approaches to study of Tyumen deposits, each characterized by its positive and negative sides. Based on method limitations it’s rather difficult to make a clear choice in favor of a certain technic, so it was decided to conduct a comparative analysis and empirically opt for a more informative algorithm.

For this purpose, we can consider an example of structure analysis of Tyumen deposits in one of the fields included in Noyabrsk group of fields. For this purpose, we calculated following maps:

1) RMS amplitude map with 10 ms window;

2) Minimal acoustic impedance map with 10 ms window;

3) Spectral RGB-map for harmonics 15-25-35 Hz.

Joint analysis of the information received reveals following patterns. Amplitude and acoustic impedance maps are characterized by similar details of the internal structure of Tyumen deposits. Detecting thin channel systems is observed both in the amplitude levels and in lower values of acoustic impedance. However, the most detailed picture of the internal structure of the studied range is obtained using spectral approach to studying the wave field — thin channels are detected which cannot be identified using standard approaches of the wave field analysis.

Fig. 1. The comparison of amplitude map (A), impedance map (B) and spectral RGB-map ©

This thesis is well confirmed by visual comparison of maps. To verify the resulting hypotheses about more informative spectral approach similar analysis was performed for several fields — one of which is included in Noyabrsk group of fields, another is located further to the south in Khanty-Mansiysk region.

Fig. 2. The comparison of amplitude map (A) and spectral RGB-map (B) for deposit in Khanty-Mansiysk region

Analysis of the obtained information allows us to make an unambiguous conclusion about the most detailed spectral approach compared to standard methods of seismic data analysis. At the same time such detail is the general trend of Tyumen deposits, regardless of the geographical location of the region. The main requirement is the presence of wave field interference on thin geological objects.

However, the method of spectral decomposition is poorly studied at the moment, there is a large number of examples of its successful application, but the study of factors affecting the nature of the anomalies in wavelet transform is absent. In this regard, the continued use of the method requires some research on the main factors leading to changes in the spectral parameters of the wave field. This issue is addressed in the theoretical part of this study, which will be revealed in the next section.

The study of spectral effects on the model data

The simplest and most intuitive way to study a technique is to perform the modeling. In this case, we will solve the problem with a priori known, given decision that allows us to analyze obtained results more fully.

For this purpose, we built two acoustic models of wedging formation, which can be conventionally called as “intrusion model” and “overlap model.” Wedge model is a good opportunity to consider the effect of change in reservoir capacity on spectral characteristics, as it allows us to evaluate the change as enhancing the effect of interference in the framework of the “intrusion model” is considered acoustically contrast wedge placed in an isotropic medium. “The model of overlap,” describes the case of a gradual change in the acoustic properties of the section. Both models have been given a change of acoustic impedance along the wedge; this technique allows us to trace the influence of changes in the geological properties to the spectral characteristics of the wave field.

Fig. 3. Intrusion model (left) and overlap model (right)

These models were used to calculate synthetic wave field, in this case Ricker impulse with dominant frequency of 30 Hz has been selected as the signal source. The resulting wave field is applied to the input of the wavelet transform algorithm to estimate spectral characteristics of 15, 25 and 35 Hz.

The obtained estimates of harmonic wave field allowed to build a three-dimensional RGB-cube to analyze patterns of change of color anomalies in various models of the geological environment.

Fig. 4. Analysis of spectral anomalies in “intrusion” model

Fig. 5. Analysis of spectral anomalies in “overlap” model

Analysis of the data model allows us to make several important conclusions:

1) Spectral anomalies occur in the interference reflections from the top and bottom of the wedge. At the same time brightness and intensity of the anomalies is not uniform in the section — in the roof and bottom parts anomalies are less pronounced, the maximum color differentiation is observed in the median portion of the wedge. Thus, brightness of the anomaly may indicate the spatial position of the interfering object. This consequence is extremely important in the future use of the method in the context of real geological environments, which are often represented by a set of interfering objects located at different stratigraphic levels.

2) The acoustic properties of the reservoir does not affect the nature of spectral anomalies — analysis of median cross sections of the wedge allows us to establish that the structure of the color anomaly remains unchanged regardless of the relative acoustic impedance of the wedge. The acoustic properties of the reservoir only affect the brightness of the anomaly — it is obvious that the smaller the amplitude of the acoustic reflection contrast will be lower because of the smaller reflectance. Also, the acoustic properties of the reservoir affect the time of onset of interference; it is obvious that in a hard, i.e. high-speed, wedge interference occur earlier than in a soft wedge. Therefore, we can assert that the same spectral anomalies will occur at equal time capacity layers regardless of their acoustic properties. The development of this thesis to the real environment leads to the conclusion that two lenses filled with sandstone and clay will have the same spectral anomalies at equal time capacity. On this basis, the use of spectral anomalies for lithological separation of the studied sediments is impossible without the involvement of some additional data.

3) “Intrusion model” is characterized by the highest brightness in the area of the interference. This model corresponds to the case where reflection from the top and bottom are characterized by opposite-polarity.

4) “Overlap model”, in contrast, is characterized by attenuation of spectral parameters in the area of interference. This model meets the “normal” speed law — a gradual increase of in the impedance downwards the section. In this case, reflection from the top and bottom is characterized by the same polarity. It should be noted that these conclusions are essential as well for the case of gradual decrease of the acoustic impedance.

Thus, we can conclude that different display of channels (bright and dim channels) may be associated with different geological structure, i.e. different models of relations between the channel and the host geological environment are observed.

Summarizing performed theoretical study, we can conclude that the method of spectral decomposition allows detailed mapping of objects acting as local regions of interference. At the same time the opportunity to assess relative acoustic properties of similar geologic bodies is lost. Therefore, the most appropriate use of spectral decomposition is in combination with other methods of analysis of the wave field, as well as research of GIS and core. In this case comprehensive and detailed assessment and interpretation of existing geophysical data are possible.

Understanding the causes of spectral anomalies allows us to determine possibilities and limits of applicability of the method. This aspect is an important step in the study of a relatively new method of spectral decomposition.

Comparison of spectral and standard approach.

Practical application of the information obtained as the result of modeling assumes , the calculation of the regional RGB-mixing map for interval of Tyumen deposits. For this purpose spectral harmonics of 15, 25 and 35 Hz were estimated on all available seismic cubes. The choice of this frequencies combination is based on another theoretical study carried out in Gazpromneft NTC, but is not mentioned in this article, and to date is not published. Cross-linking of all areas was carried out at map level, this approach yielded the most detailed view of the internal structure of Tyumen deposits complex.

To increase accuracy of prediction and interpretation, in addition to spectral maps in regional scale, we have drawn a map of RMS amplitude of all available seismic areal data. The necessity of this map has been proved in the previous section. In addition to amplitude maps, for some explorations with conditioning log data (P-wave and dencity) inversion transformation was performed that allowed us to obtain additional acoustic impedance maps estimating minimum impedance in a narrow window.

Joint analysis of information on acoustic impedance and spectral RGB-map allows us to perform a qualitative interpretation of the geological structure. Spectral map provides a good detection of thin objects and acoustic impedance map allows us to evaluate properties of detected bodies. However, it should be noted that the use of a standard approach to dynamic interpretation can not provide such fine details.

An important aspect of this study is aggregation of seismic data obtained from existing wells GIS data and core material.

Fig. 6. The resulting spectral map of the study region

Geological interpretation of the results

Unfortunately Tyumen deposits can be considered as poorly understood at the moment, there are 23 thousands of wells for the whole Noyabrsk region, Tyumen deposits opened only in 180, while not all wells are characterized by the presence of well-preserved core material.

Paleofatial detail model is based on the study of existing core material. Layers J2-J3 formed within the tidal delta. Basic lithotypes has been determined characterizing the conditions of accumulation of the Tyumen Formation: sandstones of delta channels, carbonaceous mudstones of intradelta areas (lagoons, swamps, etc.), silty sandstones of alluvial shafts. The rocks are marked abundant macrofossils of flora, plant detritus, traces of bioturbation, inclusions of pyrite and siderite. It is worth noting that in the core samples of the formation J2 marine bivalves and foraminifera can be observed which indicates the increasing influence of the sea during the deposits storage process.

Selecting channel facies as a result of core description is insufficient, so during interpretation of facial conditions the result of seismic interpretation has to be taken into account.

In order to assess the prospects of the channel facies sediments and associated areas, statistical analysis of correlation between availability of channel according to seismic data and the effective capacity of the complex J2, J3 was carried out. Obviously, in the wave field only the “resistant” channels can be observed that have evolved within a sufficiently long in geological terms or deposition conditioned a significant amount of sediment characterized by excellent acoustic properties.

Fig. 7. Example of combination well and seismic data

To assess the influence degree of channels on effective capacity of the complex, all of the observed channels on the spectral RGB-map were allocated individual polygons. Then the evaluation function of distance to the nearest polygon was introduced, thus each well received an estimate reflecting its position relative to the selected channel. After that, all the wells were placed on a single cross-plot with axes of the distance to the channel and the effective capacity of the complex. For ease of interpretation averaging of the effective capacity was performed on the basis of 500 meters, i.e. estimate was performed on the intervals 0-500, 500-1000 meters and so on, the maximum significant distance was limited to 6000 meters from the channel.

Fig. 8. Statistical estimation of most probable thickness of channels

As we can see from the plot distribution of points forms a triangle, gradual reduction in the maximum effective power of the distance from the channel part can be observed. Thus if we consider the average values for the intervals, then there is a unique linear dependence of the effective capacity on the distance from the channel.

It should be noted that this relationship does not allow a quantitative assessment of the observed areas prospects, but rather indicates a greater probability to observe a more powerful collector next to the channel than at a distance. Obviously the development of transport channels in a delta plain, accompanied by the deposition of a facies complex, which do not have the necessary acoustic contrast or capacity for display on the wave field, so geological approach based on the actualism principle is a necessary step at the present level of knowledge of Tyumen deposits.

For example, the actualism principle can be illustrated in relation to one of the fields included in Noyabrsk region.

Fig. 9. Modern analogue of tide-dominated delta

Conclusions and further recommendations.

The carried out study results in an assessment of existing algorithms for the analysis of the wave field to solve the problem of facial zoning of Tyumen sediments in Noyabrsk region of the West Siberian basin.

The spectral approach is shown to provide the best results for the analysis of the wave field compared to more conventional amplitude and inversion analysis. However, the spectral data preferentially reflect only a change in the effective capacity of the reservoir in the interference region, at the same time changes of acoustic impedance have no significant effect on the nature of the anomalies of the spectral decomposition. This thesis has been shown by the example of the two models of wedge formation, which generally describe well the possible variety of existing environments.

The main result at this stage of the study is regional maps (RGB, amplitude and acoustic impedance map), which reflect the complex structure of the studied Tyumen complex. The maps show the development of a complex system of channels of sediment transport, developing within the delta plain — periodically flooded areas, corresponding to the transition from continental to marine conditions of sedimentation.

As the statistical analysis shows, the wells located closer to the channel according to the observed seismic data are characterized by higher probability to open more powerful area of effective thickness. While the distance from the channel increases, the probability of significant volume of the reservoir gets lower.

The relevance of the study is primarily associated with the need to find and involve new facilities into development in order to maintain the level of oil production at the fields in the final stages of development. This problem is relevant to many fields in Noyabrsk region and in Western Siberia as a whole, as depletion of reserves in the region is about 70 percent. This Tyumen deposits are characterized by extremely weak study, with a significant depth of their occurrence, i.e. there is no transit wells, as well as the complex structure of the complex from the geological point of view. In this context, this work aims to solve the second problem related to decrease in the uncertainty of the geological structure of the complex. The gradual accumulation of knowledge and the application of new technologies of analysis of seismic data will reduce the risks associated with the development of stratigraphic complex. At the moment it is possible to extend boreholes running on Vasyugan deposits or deep drilling of pilot hole in the development of overlying facilities.

This study is an initial step in the detailed studying of the of Tyumen sediments in Noyabrsk region, it reflects the ending stage of conceptual modeling of the complex, i.e. identifying basic laws of the structure and productivity of Tyumen Formation rocks. For more reliable results detailed study of the borehole data is required to analyze and review interpretation of core samples, conducting recheck of the wells without fracking in the end of the past century, tests of the existing wells. All these activities will gradually reduce the risks and uncertainty, and thus bring the full-scale development of this complex within Noyabrsk region.

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