SHALED-OUT BERRIAS-HAUTERIVIAN SUITE IN YAMAL AND RELATED STRATIGRAPHIC TRAPS

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 12, December 2018, pp , Article ID: IJCIET_09_12_079 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed SHALED-OUT BERRIAS-HAUTERIVIAN SUITE IN YAMAL AND RELATED STRATIGRAPHIC TRAPS Kurkin A.A, Yankova N.V, Kuznetsov V.I and Stulikov S.K NOVATEK NTC, 50 let VLKSM st., 53, Tyumen, Russia, Kornev V.A. Industrial University of Tyumen, Volodarskogo st., 38, Tyumen, Russia, ABSTRACT The resources of oil and gas in Yamal peninsula can be substantially increased by identifying new objects in the Neocomian interval. As a result of detailed seismic and well data interpretation of the Neocomian interval in the southwest part of Yamal of the Akhskaya suite has been allocated Berrias-Early Hauterivian thickness, composed mainly of mudstones, clays and siltstones in the west. Along the boundary of the distribution of the stratum in the form of seismic anomalies are located the pinch-out traps of the layers of the later traditional clinoforms of the western fall on the roof of the rising stratum. The productivity of this type of non-anticlinal traps is confirmed by drilling in a number of areas. Key words: traditional clinoforms, non-anticlinal traps Cite this Article: Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A, Shaled-Out Berrias-Hauterivian Suite in Yamal and Related Stratigraphic Traps, International Journal of Civil Engineering and Technology, 9(12), 2018, pp INTRODUCTION According to official estimates, Yamal has colossal amounts of hydrocarbon resources: 10,400 billion cubic meters of gas resources and 220 million tons of oil. More than a third of gas resources are concentrated in small structural traps of the Aptian-Albian-Cenomanian complex (Figure 1), where a small percentage of the exploration drilling success is observed in Yamal and Gydan [1]. There were no large reliable structural uplifts left for exploratory drilling in Yamal. At the same time, relatively low official estimates of the resources of the Neocomian deposits, including the Achimov strata, seem to be underestimated. In the south of Yamal, large editor@iaeme.com

2 Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A deposits are discovered in this interval - Rostovtsevskoye and Novoportovskoye. There have also been received hydrocarbon inflows from the objects that are not on the state balance sheet in many other areas: Malyginskaya, Syadorskaya, Pyasadayskaya, Verkhnetiuteiskaya, Khambateiskaya, Sredneyamalskaya, Yuzhno-Nurminskaya. Hence follows the conclusion that the resource base of Yamal can be substantially increased by identifying new promising non-anticlinal objects in the Neocomian interval. So, in general, in the Yamal-Nenets Autonomous District, in the course of geological prospecting and generalizing work over the past years, the resources of the Achimov hydrocarbon play increased by 30-50% [2]. Figure. 1. Distribution of reserves and gas resources by intervals in the southeast of Yamal As one of the priority promising directions for the search for new non-anticlinal traps, the south-eastern part of the peninsula should be considered (Figure. 2), where the Neocomian interval has a particularly complex, two-level structure, and in places it is heavily sanded (the so-called Novoportovskaya suite). Here, seismic sections distinguish the reflecting boundaries of not only the traditional, northwestern, but also the southeastern and northeastern dip (Figure 3). Assumptions about the presence of promising objects in the zone of "interference" of clinoforms of a receding dip were expressed back in the late 1980s by A.L. Naumov, V.S. Sosedkov [3], and others. Here modern researchers distinguish promising traps of the barrier type [4]. For a correct resource assessment, it is necessary to generalize the results of previous work to a single model. The fact is that most of the prospective traps on the state balance were identified on the basis of a 2D seismic survey 25 years ago, using methodically different approaches and dispersed throughout the vast area of Yamal. Previously performed generalizing works were based on a regional network of profiles and were aimed at identifying major promising zones within the regional and zonal Neocomian cyclites. There are no published modern generalizing works that take into account and preserve the degree of detail of the field survey materials. The goal of this work was to study the features of the Neocomian interval structure, search and map perspective non-anticlinal objects in the southeast of the Yamal peninsula on the basis of the creation of a single detailed seismogeological model. 2. METHODS Initial data for the seismogeological framework were drilling materials of 170 wells, 2D seismic profiles with a total length of over 20,000 linear km, reprocessed in accordance with modern methods, as well as 3D surveys in the Malo-Yamalskiy and Novoportovskiy subsoil plots. A detailed well and seismic correlation of the Neocomian interval was carried out - 13 reflecting horizons were traced, the boundaries of their propagation and wedging were mapped, structural maps were constructed. From the thickness maps and visually from the seismic sections, geomorphological boundaries were determined - the upper ("brows") and the lower bends of the clinoforms editor@iaeme.com

3 Shaled-Out Berrias-Hauterivian Suite in Yamal and Related Stratigraphic Traps It should be noted that identification of geomorphological boundaries is difficult due to the "flatness" of Yamal's clinoforms associated with the conditions of their formation. Most of the Neocomian deposits of the Yamal peninsula belong to the Barremian complex and in the south of the peninsula - to the Late Hauterivian [5]. This is the last cycle of lateral filling of the basin, which is characterized by a great distance from the eastern provenance area and shallower sedimentation conditions. Figure 2. Map of the clay Berrias-Hauterivian interval thicknesses (Voskhodnaya suite) On the basis of paleogeomorphological and attribute analyses of seismic data, taking into account borehole materials, zones of supposed accumulation of sand material in unda-, fondo-, and clinothems were identified. The zones were distinguished according to two main criteria: the presence of geologically significant thickness swellings and/or seismic anomalies. Anomalies were mapped using attribute analysis, as well as visually in seismic sections editor@iaeme.com

4 Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A Figure. 3. Seismic section along the line 1. The location is marked in Fig RESULTS. CLAY BERRIAS-HAUTERIVIAN THICKNESSES IN THE SOUTH-WEST OF YAMAL. A distinctive feature of the structure of the Neocomian deposits in Yamal, as it was already said, is the presence of the reflecting boundaries of the southeastern and northeastern dips on seismic sections, which can not be identified with traditional clinoforms of the western dip of the Akhskaya suite (Fig. 3). As a result of detailed correlation, these "anomalous" reflecting boundaries were singled out into a separate suite. Let us call it Berrias-Hauterivian; the rationale for the age of the core is given below. It was singled out according to the characteristic pattern of seismic recording - plane-parallel, gently sloping wedges; traditional clinoforms are attached to the roof of the suite; as well as by well data. In the interval of this thickness, reservoirs were not found in any well. The greatest thicknesses of the described suite are observed in the vicinity of the Shchuchinskiy protrusion and the Nurminskoye uplift and are more than 400 m (Figure 2). According to the core analysis, this suite is represented by black and dark gray platy micaceous mudstones, and in the west by gray siltstones, with impregnations of pyrite, suggesting deep-sea marine sedimentation conditions. Age biostratigraphic determinations were made using microfauna and ammonites in the wells Zapadno-Yarotinskaya 301, 302, Malo-Yamalskaya 3002, Yuzhno-Nurminskaya 8 (Fig. 4), Rostovtsevskaya 94. Age varies widely from Berrias to Hauterivian. Thus, this clay suite accumulated earlier than the traditional Neocomian clinoforms, which, as noted earlier, are of the Late Hauterivian age in the south of Yamal. This is confirmed by the seismic image of the investigated sediments. In the zone between the Nurminskiy and Nulmuyakhinskiy (Rostovtsevskiy) uplifts, it is clearly visible that the foundation of the later clinoforms of the western dip has been wedged to the roof of the Berrias-Hauterivian suite by characteristic seismic facies of the downlap, as well as by "bright spots" corresponding to sand layers accumulating in the zones of wedging (Fig. 5). It should be noted that the roof of the complex is displayed rather arbitrarily on temporary sections at times. Thus, in the zone between the Nurminskiy and the Khambateiskiy uplifts, the downlap is worse. This can be explained by similar acoustic properties - in this zone, the fondoform parts of western-dip clinoforms are probably also shaled out. The thickness map between the first cover Neocomian Arctic pack and the roof of the considered thickness illustrates the paleorelief of the bottom of the Neocomian basin at the time of accumulation of traditional clinoforms (Fig. 6). Obviously, in the relief of the bottom of the paleobasin a structural nose was pronounced, "sticking out" in the zone of maximum thickness of the clay strata - in the region of the Nurminskiy uplift editor@iaeme.com

5 Shaled-Out Berrias-Hauterivian Suite in Yamal and Related Stratigraphic Traps What is the geological interpretation, the origin of this suite? Some researchers, for example, V.S. Sosedkov, interpreted this complex as western clinoforms of the eastern dip, Ural-Paihoy ablation [3]. Indeed, the composite seismic section in Fig. 4 shows the source of ablation of the complex under study - the Shchuchinskiy protrusion. This is evidenced by gently sloping wedges inside the suite, dipping in the northeastern direction. However, clinoforms are clearly traced only closer to the source of ablation, and when at a distance from it to the east, they sharply become more flattened out and move into a plane-parallel pattern of the seismic record. In most of the area, east of the Voskhodnaya well, pronounced clinoforms are not prominent within the suite. This is due, apparently, to the low rate of sedimentation and the clay composition of the sediments. According to A.A. Nezhdanov, the Berrias-Early Valanzhinian Medvezhiya suite [6] is identified within the territory under consideration, which stretches from the Kara Sea through the western part of Yamal to the south in the form of a linear zone of increasing thickness parallel to the Urals to the territory of the Khanty-Mansi Autonomous District, where it enters the Tutleimskaya suite. It is mainly composed of bituminous mudstones. On seismic sections to the south and north of Yamal this suite clearly differs from the clinoforms of the eastern dip. Its origin is associated with tectonic phenomena: deflection, accumulation of sea clays, and subsequent uplifting during the Late Cimmerian folding. At least the lower part of the isolated clay complex in the south-west of Yamal can be identified with the Medvezhiya suite. According to the age determinations in the wells of the Zapadno-Yarotinskaya area, the upper part is of the Hauterivian age (Fig. 4). Figure. 4. Seismic section along the line 2. The location is marked in Fig editor@iaeme.com

6 Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A Figure. 5. Seismic section along the line 3 without (above) and with interpretation (below). The location is marked in Fig. 6. Thus, the Berrias-Hauterivian shaled-out suite in question has the characteristic features of both proposed models: in the west at the Shchuchinskiy protrusion, it can be interpreted as clinoforms of the eastern dip, passing into the Medvezhiya thickness in the east. In this connection, the authors propose to separate this complex into a separate thickness as part of the Akhskaya suite. The suite has a local distribution in the south-west of Yamal. The name could be given by the wells where age determinations exist and the core from this interval is described: Yarotinskaya, Nurminskaya, Nulmuyakhskaya, but they are already occupied. Therefore, it is proposed to name the thickness Voskhodnaya - by the well 3021 of the same area, which penetrated the interval at full capacity. The lithological composition of the suite is mudstones, clays; siltstones are found in the west. The age is Berrias-Early Hauterivian. At the bottom, the suite is underlain by the Tithonian Bazhenov and Callovian- Kimmeridgian Nurminskaya suits, which are also mostly shaled-out. Late Hauterivian- Barremian clinoforms of the western dip with sandy layers wadge to the thickness from above. It should be noted that some authors sometimes refer the lower part of the suite in question to the Bazhenov suite, for example, in the Zapadno-Yarotinskaya area [4]. But in this interval, Berrias siltstones, and not Bazhenov mudstones, are identified by the core Effect on the distribution of sand material. Based on the above, the following model for the development of the Neocomian interval is obtained. At the end of the Jurassic - the beginning of the Neocomian in the area of the modern Novoportovskaya and Sredneyamalskaya structures during the Late Cimmerian folding, the growth of paleouplift was experienced, and between them a saddle formed in the Nurminskaya area. Within this saddle, in the Berrias - Early Hauterivian, marine clayey sediments from the Shchuchinskiy protrusion were deposited. It is interesting to note that at the beginning of the formation of the Jurassic deposits, right in the area of the modern Nurminskiy uplift, a zone of unloading of the sedimentary material from the elevated zone in the South-West was recorded for the paleovalley, clearly identified in thicknesses and seismic sections, associated with deep faults. Thus, the inherited character of the development of the area during the entire Jurassic and early Neocomian is manifested editor@iaeme.com

7 Shaled-Out Berrias-Hauterivian Suite in Yamal and Related Stratigraphic Traps Figure 6. Promising traps of the western-dip clinoform bed wedging on the roof of the Voskhodnaya suite By the end of the Hauterivian, when the clinoforms of the western dip approached the Yamal peninsula, a paleoprotrusion formed by Berrias-Hauterivian clay sediments was formed in this region. Its formation can be associated with both overcompensation of the relief during the accumulation of distal parts of the Ural clinoforms of the eastern dip, and with the tectonic uplift. The latter may be due to local compression at the southern end of the deep faults of the Nurminskiy megaswell as a result of a right-sided shift along them. The clay Berrias-Hauterivian Voskhodnaya suite played a huge role in the distribution of the sedimentary material of the later Neocomian clinoforms and predetermined the increased content of the sand component in the South of the peninsula. The formed paleoprotrusion in the area of the Malo-Yamalskaya and Nurminskaya areas (Fig. 6) served as an obstacle to the distribution of sediments, the so-called lateral paleoswell [3]. This caused the formation of terraces in the slope of the clinoforms of the western dip and shallow, favorable conditions for the accumulation of reservoirs of the so-called Novoportovskaya suite. This explains the abnormally high sandiness of the bottoms of the Akhskaya suite at the Novoportovskoye and Rostovtsevskoye deposits located on the southern slope of the rising sequence. At the same time, in the zone of maximum thicknesses of the Voskhodnaya suite, the bottom part of the editor@iaeme.com

8 Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A Achskaya suite is absent, since there was no accommodation for its accumulation - this case includes the Nurminskiy uplift Influence on oil and gas potential. Promising traps. Despite the fact that the Voskhodnaya suite is completely shaled-out, it had a direct impact on the distribution of hydrocarbon deposits. It was noted above how the thickness predetermined the accumulation of reservoirs and, accordingly, the formation of the deposits of the Novoportovskoye and Rostovtsevskoye fields. The above-mentioned deposits are confined to structural uplifts in the modern plan. However, the purpose of this paper is to search and map traps of a non-anticlinal type. In the area under consideration, hydrocarbon inflows were obtained from the Neocomian interval in wells drilled under unstructured conditions - YuzhnoNurminskaya 8, Sredneyamalskaya 13, 14, Khambateiskaya 57 and wells in the west of the Nulmuyakhinskaya area. We have established that these deposits are confined to traps of wedging out of reservoirs of clinoforms of the western dip on the roof of the shaled-out Voskhodnaya suite (Fig. 6). These traps are characterized by anomalies of the wave field in the zones of wedging (Fig. 7). Figure 7. Seismic sections along lines 4 and 5. The location is indicated in Fig. 6. The reservoir in promising traps has a different genesis, depending on which part of the western dip clinoform is wedged to the roof of the Voskhodnaya suite: in the east it is the classic deep-water Achimov alluvial fans (the Khambateiskaya deposit), and in the west - shelf layers (a trap to the west of the Sredneyamalskaya area). As a result, as it was assumed by A.L. Naumov and V.S. Sosedkov, along the entire distribution boundary of the western Neocomian wedge, according to our interpretation - the Voskhodnaya suite, the development and localization of promising traps of wedging out of clinoforms of the western dip were established (Fig. 6, 7). All localized seismic anomalies opened by the wells are confirmed by drilling in part of the presence of the reservoir. Due to this fact, unidentified anomalies should also be considered promising zones of development of sandstones. It should be noted that these zones should not be directly associated with the presence of deposits, since "bright spots" on seismic sections do editor@iaeme.com

9 Shaled-Out Berrias-Hauterivian Suite in Yamal and Related Stratigraphic Traps not necessarily indicate the prospectivity of the trap, but may be associated with a watersaturated reservoir, or with "dense" reservoir sections where there are no industrial inflows of HC. Thus, the selected objects require further research in the course of detailed seismic surveys. Similar promising traps are also localized in the northeast of Yamal, where the boundary of the distribution of the Voskhodnaya suite extends (Fig. 2), in particular, in the Syadorskaya area. To the west of the considered territory, a similar promising trap of wedging out in the shelf layer in the Yarkhutayakhskaya area is predicted. The Voskhodnaya suite also had a negative effect on the filling of the hydrocarbon traps - a powerful clay interval served as a cap isolating the Cretaceous reservoirs from the Jurassic oil and gas source rocks. This explains, in particular, the water content of the Neocomian strata of the Malo-Yamalskaya area. 4. CONCLUSIONS As a result of the creation of a single seismogeological model on the basis of detailed seismic and borehole correlation of the Neocomian interval in the southwest of Yamal, the Berrias - Early Hauterivian Voskhodnaya suite composed predominantly of marine mudstones was identified as part of the Akhskaya suite. Its thickness reaches more than 400 m. The reflecting boundary - the wedge of the eastern dip, counter to the traditional Neocomial clinoforms - is associated with the roof of the thickness. The thickness was formed before the accumulation of traditional clinoforms. Its formation is related both to the tectonic factor and to the precipitation progradation in the northeastern direction from the Shchuchinsky protrusion. This suite served as a side support for the accumulation of clinoforms of the western dip and predetermined the abnormally high content of the sand component in the south of the peninsula. This explains the formation of powerful reservoirs and deposits of hydrocarbons in the lower reaches of the Akhskaya suite of the Novoportovskoye and Rostovtsevskoye deposits. Along the boundary of the thickness distribution in the form of seismic anomalies, traps of wedging of the clinoform beds of the western dip on the roof of the Voskhodnaya suite are localized. The productivity of this type of non-anticlinal traps is confirmed by drilling in the Yuzhno-Nurminskaya, Sredneyamalskaya, Khambateiskaya, and Nulmuyakhinskaya areas. Returning to the question of estimating the resource base, as a result of the refinement of the structure of the Neocomian, the resources of the studied territory are redistributed as follows (Fig. 1). The maximum amounts of resources are shifted from the Aptian-Albian-Cenomanian and Jurassic complexes to non-anticlinal traps of the Neocomian interval, including the Achimov. It is recommended to take this into account when planning geological exploration works in Yamal. REFERENCES. [1] Kurkin, A.A. Reasons for the non-confirmation of structural objects in exploratory drilling in the Yamal and Gydan petroleum region / A.A. Kurkin // Exposition Oil Gas No. 5 (58). - pp [2] Borodkin, V.N. Characteristics of the geological structure and oil and gas potential of the Achimov oil and gas play in Western Siberia / V.N. Borodkin, A.R. Kurchikov. - Novosibirsk: Publishing House of the SB RAS, p. [3] Sosedkov, V.S. Refinement of structural charts and schemes for depositions of the cover of the northern part of the West Siberian lowland on the basis of generalization of additional geophysical information. Report on the results of the work of the thematic team 103/ editor@iaeme.com

10 Kurkin A.A, Yankova N.V, Kuznetsov V.I, Stulikov S.K and Kornev V.A / V.S. Sosedkov, V.P. Chetvertnykh, Yu.N. Surkov - Labytnangi: PGO "Yamalgeofizika", [4] Kislukhin, I.V. Features of the geological structure and oil and gas content of the Jurassic- Neocomian deposits of the Yamal peninsula / I.V. Kislukhin; ed. by I. I. Nesterov. - Tyumen: Tyumen State Oil and Gas University, p. [5] Gorbunov, S.A. Regional system of correlation and indexation of the Achimov reservoirs in the north of Western Siberia / S.A. Gorbunov [et al.] // Exposition Oil Gas No.6 (52). - pp [6] Nezhdanov, A.A. Influence of the Late Cimmerian folding on the stratification of the Early Neocomian deposits of Western Siberia / A.A. Nezhdanov [et al.] // Exposition Oil Gas No.7 (60). - pp editor@iaeme.com