Substantiation of paleohydrodynamic sedimentation modes and identification of missed oil-and-gas saturated areas that are promising for additional exploration of the Lower Cretaceous deposits of the Albian stage of the Achikulak oil field according to geophysical well logging data

In the development of the oil and gas complex, the improvement of methods for studying the patterns of distribution of hydrocarbon deposits is of particular importance. At the same time, scientific research can be carried out in different directions. These include increasing the resolution of various methods of borehole and areal geological and geophysical studies of lithological features and oil-and-gas content, developing new approaches to interpreting well logging results, analyzing the productivity of poorly studied regions and areas of the section, identifying low-amplitude folds and non-anticlinal deposits. The development of hydrocarbon deposits in the Stavropol Territory has been going on for many decades, which has led to reduction of deposits within medium and large anticlinal uplifts. Therefore, the main attention is now paid to the prospect for low-amplitude and small-size uplifts and traps of the non-anticlinal type, which include lithological and stratigraphic ones.

BIOSTRATIGRAPHIC CHARACTERIZATION OF THE CRETACEOUS DEPOSITS OF THE SAN-PEDRO MARGIN OF DRILL HOLES K1 AND K2 OF BLOCK KL: PALEOENVIRONMENT IMPLICATION

The KL block studies was carried out the eastern part of the San Pedro margin, it has an area of 2034 km2 with a water depth varying from 500 to 2750 m with two probings (K1 and K2).The objective of this work is to carry out a biostratigraphic and paleoenvironmental study based on the associations of planktonic and palynomorphicmicrofauna in the formations of the KL block boreholes. From a lithological point of view, the base of the boreholes generally comprises alternating limestone and argillite, very fine to fine grained quartz sandstone. Its upper part is overlain by claystoneinterbedded with limestone, silstone and siliceous cemented sandstone and alternating claystone, medium to coarse grained sand and siliceous cemented quartz sandstone. The Albian is determined by the presence of the species Ticinellamadecassiana. The Cenomanian is identified by the micropalaeontological assemblages composed of Globigerinelloides spp., Guembelitria spp., Hedbergella spp., Hedbergelladelrioensis, Globigerinelloides bentonensisandLoeblichella cf. hessi. The Turonian is based mainly on the species Hedbergellaplanispira, Heterohelixmoremani and Whiteinella archaeocretacea. The Early Senonian is characterized by associations of species (Hedbergellasp, Hedbergella cf. delrioensis, Buliminacrassa and Whiteinella baltica) and palynomorphs (Proteaciditestienabaensis, Odontochitinacostata, Odontochitinaporiferaand Tricolpites sp). The roof of the Campanian is known by the association of the palynomorph (Trichodinium castanae) and the microfossil (Gaudryina cretacea) The Maastrichtian is highlighted by the associations composed of species Rzehakina epigona fissistomata, Rzehakina minima, Plectina lenis, Reophax duplex, Reophax pilulifera, Reophax globosus, Gaudryina pyramidata and Afrobolivina afra) and palynomorphic species (Andalusiella gabonensis, Cerodinium granulostriatum and Palaeocystodinium australinium). All the micropalaeontological data coupled with those of the microfaunas make it possible to envisage a depositional environment of the internal platform type with continental influence on an external platform.

The Upper Cretaceous deposits structure of Western Siberia

As the title implies the article presents the results of many years comprehensive research of the Western Siberian Upper Cretaceous stratigraphy (without Cenomanian). The volume of Upper Cretaceous formation, their biostratigraphic and lithological characteristics are discussed. Based on the analysis of new materials (lithological, biostratigraphic, well geophysics investigation data, magnetostratigraphic, seismostratigraphic), the regional correlation scheme of formations, members and beds has been refined. A new model of correlation schemes, a scheme of facies zoning, and reasonable changes in the nomenclature of the Upper Cretaceous formations are proposed. The Slavgorod and Ipatovo horizons have been replaced by a single Berezovo horizon. Specific properties description of the new suites, established at the first (Okhteurievo, Tagul, Bolshaya Laida, Nizhnaya Agapa), have been done.

Types of river sources of the thin-grained aluminosilicaclastics for the Jurassic and lower cretaceous deposits of the West Siberian megabasin

Background. The lithogeochemical features of fine-grained detrital rocks (mudstones, shales, and fine-grained siltstones) allow, with a certain degree of success, the main parameters of the formation of sedimentary sequences to be reconstructed. These parameters include (primarily in terms of their REE and Th systematics) the types of river systems supplying thin terrigenous suspension in the sedimentation area: the rivers of the 1st category – large rivers with a catchment area of more than 100,000 km2; 2nd category – rivers feeding on the products of erosion of sedimentary deposits; 3rd category – rivers draining mainly igneous and metamorphic rocks; and 4th category – rivers carrying erosion products of volcanic associations.Aim. To reveal, based on the analysis of interrelationships between such parameters as (La/Yb)N, Eu/Eu* and the Th content, the types of river systems that fed the Jurassic and Lower Cretaceous deposits of the Shaim oil and gas region (OGR) (Sherkalinsky, Tyumen, Abalak and Mulymya formations) and the region of the North Pokachevsky field of the Shirotnoe Priobye region (Sherkalinsky, Tyumen and Bazhenov formations, Lower Cretaceous deposits).Materials and methods. The ICP MS data for almost 100 samples of mudstones and fine-grained clayey siltstones were used to analyse the features of distribution of lanthanides and Th in the Jurassic and Lower Cretaceous clayey rocks of the Shaim OGR and the area of the North Pokachevsky deposits. Individual and average composition points for formations, members and layers were plotted on the (La/Yb)N-Eu/Eu*, (La/Yb)N–Th diagrams developed by us with classification areas of the composition of fine suspended material of modern rivers of different categories.Results and conclusion. The results presented in the article showed that during the formation of the deposits of the Shaim OGR in the Early and Middle Jurassic, erosion affected either mainly sedimentary formations or paleo-catchment areas that were very variegated in their rock composition. In the Late Jurassic, the source area was, most likely, a volcanic province, composed mainly of igneous rocks of the basic composition, and located within the Urals. This conclusion suggested that the transfer of clastic material from the Urals to the Urals part of the West Siberian basin “revived” much earlier than the Hauterivian. The Jurassic-Lower Cretaceous section of the vicinity of the North Pokachevsky field was almost entirely composed of thin aluminosilicaclastics formed due to the erosion of volcanic formations. These volcanic formations were located, as followed from the materials of earlier performed paleogeographic reconstructions, probably within the Altai-Sayan region or Northern Kazakhstan. Thus, the supply of detrital material in the considered territories of the West Siberian basin had a number of significant differences in the Jurassic and early Cretaceous.

Lithological models of reservoir rocks for upper cretaceous deposits in East Caucasian Region

The article describes the results of lithological and petrophysical investigations that would be a base for characterization of reservoir rocks in Upper Cretaceous deposits. These investigations include thin sections description, SEM and NMR analysis. As found that three main factors have constrained final quality of reservoir rocks: 1) depositional settings favorable for coccoliths and chalk sedimentation; 2) late diagenesis changes – compaction and recrystallization degree; 3) fracture intensity.

Practical Application of the Mineralogical Mapping Method for Stratigraphy of the Cretaceous Deposits of Southern Primorye (Russian Far East)

Highly ordered mixed-layer formations of chlorite–smectite (corrensite) and mica–smectite (rectorite) were found in the volcanogenic–sedimentary rocks of Southern Primorye. They have shown a rather narrow “living” time interval (Cretaceous–Paleogene). The associations of corrensite and rectorite with chlorite, mica, kaolinite, and laumontite have great value in labeling. Their study would determine the time and thickness parameters of sedimentation conditions, the nature of the transformation stages, the physicochemical and climatic parameters of the accumulation of the depositional material, and the geological history and stratigraphic construction of Mesozoic–Cenozoic volcanogenic–sedimentary rocks of the Primorye Region.

Microfacies and Depositional Conditions of Jurassic to Eocene Carbonates: Implication on Ionian Basin Evolution

In order to decipher the paleo-depositional environments, during the Late Jurassic to Early Eocene syn-rift stage, at the margins of the Ionian basin, two different areas with exposed long sequences have been selected, Kastos Island (external margin) and Araxos peninsula (internal margin), and were examined by means of microfacies analysis and biostratigraphy. On Kastos Island, based on lithological and sedimentological features, the following depositional environments have been recognized: an open marine/restricted environment prevailed during the Early Jurassic (“Pantokrator” limestones), changing upwards into deep-sea and slope environments during the Late Jurassic and Early Cretaceous (Vigla limestones). The Upper Cretaceous (Senonian limestones) is characterized by a slope environment, whereas during the Paleogene, deep-sea and toe of slope conditions prevailed. In Araxos peninsula, Lower Cretaceous deposits (“Vigla” limestones) were accumulated in a deep-sea environment; Upper Cretaceous ones (Senonian limestones) were deposited in slope or toe of slope conditions. Paleocene limestones correspond to a deep-sea environment. In Araxos peninsula, changes occurred during the Cretaceous, whereas on Kastos Island, they occurred during the Paleocene/Eocene, related to different stages of tectonic activity in the Ionian basin from east to west.