Quantifying occurrence of deformation bands in sandstone as a function of structural and petrophysical factors and their impact on reservoir quality: an example from outcrop analog of Productive Series (Pliocene), South Caspian Basin

Deformation bands (DB) are known to influence porosity and permeability in sandstones. This study aims to predict the occurrence of DB and to quantify their impact on reservoir properties based on field measurements in the steeply dipping limb of a kilometer-scale fold in Yasamal Valley, western South Caspian Basin. An integrated approach of characterizing bands and their effect on reservoir properties included measurements of natural gamma radioactivity and permeability using portable tools, along with bed dip and the count of DB across distinct facies. A set of core analyses was performed on outcrop plugs with and without bands to estimate the alteration of rock properties at the pore scale. Interpretation of outcrop gamma-ray data indicates the absence of bands in Balakhany sandstones containing shale volume greater than 18% for unconsolidated and 32% for calcite-rich facies. A high amount of calcite cement appears to increase the number of DB. A poor, positive trend between bed dip and DB concentration was identified. We show that net to gross, defined as the thickness fraction of sandstone bound by mudstones, is among the parameters controlling the occurrence of bands. Samples containing a single DB show a 33% and 3% decrease in permeability and porosity, respectively, relative to the host rock. We reveal a new set of lithological and petrophysical factors influencing DB occurrence. This study offers a direct tool that can be applied in subsurface reservoir analogs to predict the occurrence and concentration of DB and estimate their influence on rock properties.

Features of the distribution of the suspended form of iron in the water column of the Caspian Sea

Статья посвящена изучению распределения железа в водной взвеси Среднего Каспия. Актуальность работыопределяется необходимостью оценки естественного состоя­ния морской среды и фиксации ее базового состояния (в том числе различных форм химических элементов) для дальнейшего использования с целью мониторинга экологической ситуации на шельфе Каспийского моря в условиях интенсификации геологоразве­дочных работ и разработки месторождений нефти. Цель работы. Установить характерные особенности поведения взвешенного железа в водах Среднего Каспия. Материалы и методы работы. Изучался материал, отобранный в 1989-1990 годах в ходе выполнения рейсов исследовательских судов. Принадлежащих Каспийскому НИИ рыбного хозяйства, до начала освоения нефтегазовых месторождений. Он представлен отфильтрованными частицами взвеси из 178 проб воды, взятых из различных слоев водной толщи на 63 станциях. Определение содержаний железа проводилось на спектрографе PGS-2 способом испарения. Результаты работы. Минимальные концентрации взвешенной формы железа в поверхностном слое водной толщи установлены на участке внутреннего шельфа и подводного склона котловины Среднего Каспия, что связано с выносом твердых частиц дрейфовыми течениями. Концентрации взвешенной формы железа в поверхностном слое возрастают к середине моря, что обусловлено стягиванием взвешенных частиц центростремительными силами циклонального течения. Придонный слой отличается повышенными концентрациями взвешенной формы железа. Возле дельт рек они связаны с оседанием выносимых с суши твердых частиц. Аномально высокие содержания взвешенной формы железа в придонном горизонте центральной части Среднекаспийской котловины, фиксируемые на отдельных станциях, обусловлены поступлением железа с эманациями донных грязевых вулканов и его коагуляцией в условиях щелочной среды. В целом, с увеличением глубины наблюдается последовательный рост концентраций взвешенной формы железа. Это связано с изменением солености и усилением вертикальной стратификации (уменьшением солености поверхностного горизонта и увеличением солености глубоких слоев). Это приводит к коагу­ляции и флокуляции органических и металлор­ганических коллоидов и переводу растворенного железа во взвесь The article is devoted to the study of the distribution of iron in the water suspension of the Middle Caspian Sea. The relevance of the work is determined by the need to assess the natural state of the marine environment and fix its basic state (including various forms of chemical elements) for further use in order to monitor the environmental situation on the shelf of the Caspian Sea in the conditions of intensification of exploration and development of oil fields. Aim. To establish the characteristic features of the behavior of suspended iron in the waters of the Middle Caspian. Materials and methods. The material selected in 1989-1990 during the voyages of research vessels was studied. owned by the Caspian Research Institute of Fisheries, before the development of oil and gas fields. It is represented by filtered suspended particles from 178 water samples taken from various layers of the water column at 63 stations. Determination of iron content was carried out on the PGS-2 spectrograph by evaporation. Results. The minimum concentrations of the suspended form of iron inthe surface layer of the water column were established on the section of the inner shelf and the underwater slope of the Middle Caspian basin, which is associated with the removal of solid particles by drift currents. The concentrations of the suspended form of iron in the surface layer increase towards the middle of the sea, which is caused by the contraction of suspended particles by the centripetal forces of the cyclonic current. The bottom layer is characterized by increased concentrations of the suspended form of iron. Near river deltas, they are associated with the subsidence of solid particles carried out from the land. Abnormally high concentrations of suspended iron in the bottom horizon of the central part of the Middle Caspian basin, recorded at individual stations, are due to the influx of iron with emanations of bottom mud volcanoes and its coagulation in an alkaline environment. In general, with increasing depth, there is a consistent increase in the concentrations of the suspended form of iron. This is due to a change in salinity and an increase in vertical stratification (a decrease in the salinity of the surface horizon and an increase in the salinity of the deep layers). This leads to coagulation and flocculation of organic and organometallic colloids and the transfer of dissolved iron into suspension.

Petroleum Systems Modeling and Hydrocarbon Migration and Oil Potential Assessment of the Southern Side of Pre-Caspian Basin, Kazakhstan

An active oil system is recognized from the data in the Tengiz-Primorsky uplift zone of the southern edge of the Pre-Caspian Basin in stratigraphic ascending and structural traps of the Famennian carbonate reservoir. This area is considered one of the most high-yeilding gas provinces in Kazakhstan. However, the timing of the displacement and migration of hydrocarbons depending on the formation of traps remains unclear. To reduce this uncertainty, an attempt was made to analyze a cross-sectional model that takes into account seismic structural interpretation and data from the Ansagan 1 well to simulate history, temperature, sourcerock maturity and pressure regimes over geological time. The displacement of hydrocarbons from the original rocks and further HC migration were modeled using 2D reservoir fluid flow modeling based on the Darcy flow equation. The main blocks of the source rocks correspond to the Devonian complex with the influence of algal lipids or organic matter enriched in lipids (type I kerogen). The maturity trend increases from east to west due to higher burial. The general objectives of this article were to set goals and determine the level of detalization of the research; selection and preparation of input data, filling the model with information, restoring the basin immersion history, calculating the thermal model, and determining the maturity of source deposits, calibrating the thermal model, calculating HC emigration; assessment of migration routes.

Seismic Facies Analysis of Lower Productive Series of Gurgan-Deniz Field in South Caspian Basin with the Aid of Seismic Attributes

Drilled for the first time in 1946 and one of the oldest fields in the South Caspian Basin located in the western part of Apsheron sill, Gurgan-Deniz has been subject to redevelopment. A 3D seismic survey, conducted over the area for the first time, has been interpreted, analysing the lower Productive Series with regard to seismic facies and prospectivity. The facies analysis allows for better understanding of eustatic levels in the region and depositional environments of lower Productive Series in the area. A composite seismic attribute Sweetness and an RGB blend of Spectral Decomposition have been applied to the 3D volume, as well as to the interpreted stratigraphic surfaces. With the aid of the attributes and petrophysical well description, direct and indirect facies interpretation have been carried out. First, considering reflection parameters such as parallelism, continuity and hummockiness, as well as sedimentary features. Subsequently, reaching conclusions on depositional processes, environments, and geological evolution. Finally, analysing field prospectivity and migration pathways. Eight seismic facies have been identified by analysing stratigraphic horizons representing the tops of Kalin Suite (KaS), Pre-Kirmaky Sand Suite (PK) and Kirmaky Suite (KS). Facies have been interpreted as mass-flow deposits, amalgamated channel systems, channel and bar systems, sheetflow and floodplain deposits in a varying lacustrine-fluvial environment. KaS has been deposited following a sea- level drop and increased sediment inflow from Palaeo-Volga. The origin of the mass-flow facies is thought to be related to the increase of sedimentation speed, as well as tectonics decreasing the terrace stability. PK shows evidence of further sea-level drop and shows mainly fluvial depositional environment. Starting from KS, sea level has started to rise, once again showing mixed depositional environment. Attribute anomalies have been explored in the lower wing of the anticline structure in PK and KaS. A 3-way trap and possible migration pathways generate considerable risks.

Influence of Secondary Alterations on the Structure of the Pore Space of the Upper Permian Carbonate Deposits of the Northern Side Zone of the Caspian Basin

The analysis of the facies distribution of reservoirs within the Moscow-Artinskian sedimentation rim within the Northern part of the Pre-Caspian Basin was carried out. The Teplovsko-Tokarevskaya group of deposits is a chain of carbonate structures stretched in the sub-latitudinal direction. They are consist mainly of bioherm structures, which include tubifytes, foraminifera, crinoidea, ostracods, ostracods, etc. From the lithological point of view, the reservoir rocks are represented by dolomite-limestone differences-from organic limestones to secondary chemogenic dolomites. The influence of facies distribution and secondary dolomitization on the structure of the pore space remains controversial and requires detailed study. The concepts of secondary dolomitization were analyzed and one of the concepts of the formation of secondary dolomites and anhydrites was used to justify the facies distribution: Zones of secondary transformation (dolomitization) form a sweet spots zone in the Artinskian carbonate horizon when high-salinity (Mg2+) waters from the Filippovsky horizon carbonates are infiltrates to Artinskian carbonate. As a result of the discharge of elision waters during digenetic dehydration of gypsum. After the anhydride overlaying of the Artinskian carbonate structure, several regressive-transgressive cycles occurred, which formed a sequence of consistent dolomite-limestone and gypsum layers in the Filippovskian time. During the diagenesis water contained in the gypsum was dehydrated into the permeable zones in carbonates of the Filippovsky horizon, followed by unloading in the region of the Artinskian horizon. Evaporite sedimentation of chemogenic carbonates and gypsum created a condition for the subsequent infiltration of sulphate and magnesium waters in the direction dip formation angle. The source of magnesium is the water remaining after the precipitation of gypsum and carbonates in the Filippovskian time.