Karst is developed by the dissolution of soluble rock caused by an active fluid flow. It significantly increases the porosity and permeability compared to the matrix system. Active flowing along the top, bottom and edges of the lenses near the coastline leads to the formation of pores of meters scale because of the dissolution of the rocks. All this must be considered when constructing a geological model for further effective development of the field. A new approach in karst extraction and modeling is implemented using factor analysis. The first stage consists of a selection of large karst geobodies using seismic data. Inversion seismic volume (an inversion for acoustic impedance) is used for the extraction of geobodies. In addition, a variety of seismic volume attributes is used to extract karst geobodies, and then a resampling of these seismic attributes is done. After that synthetic logs for all wells with non-matrix properties on the attribute parameters were obtained. Geobody extraction followed by its export to the properties of the geological model is carried out. The second stage includes the extraction of karst using well data, such as core, well logs, mud losses intervals and CHCD (closed hole circulation drilling). Then factor analysis is used to examine the link between the values of different variables and determine the best correlation between the parameters and groups. Based on these data karst flags on wells are generated. As a result, generated discrete karst log is scaled up and distributed throughout the geological model using a 3D trend of geobodies property in Petrel software. The percentage of karst in geobody is based on well data. The size and distribution of karst are based on field analogues and published materials on outcrops analogues. Porosity logs within karst intervals are created and distributed in the 3D model using a stochastic algorithm. Own methodology of karst model construction is presented, especially new approach in karst extraction and modeling is applied using multivariate statistical analysis - factor analysis. Factor analysis is multivariate method applied to study the link between the values of variables. It is assumed that the known variables depend on fewer unknown variables and random errors. The implemented mathematical apparatus is confirmed with real data on the well.
Generative potential and thermal maturity for Upper Palaeozoic source rocks from the south-eastern edge of Precaspian Basin were determined using Rock–Eval. A high hydrocarbon source rock generative potential and high degree of thermal maturity for the Lower Permian, Mid-Carboniferous strata have been revealed based on 39 rock samples. TOC values of 0.4–5.5% have been obtained for mature source rocks. Integrated geochemical analysis determined from Rock–Eval studies combined with 1D basin modelling was utilized in order to reconstruct thermal evolution for the Upper Palaeozoic source rocks. Calibrated 1D models for three wells had been constructed to understand petroleum system. For two deep exploration wells (Nur-1 and Tassym SE-1), which penetrated pre-salt strata at the depths of 5.7 and 7 km, respectively, the impact of salt diapirism on timing of maturation was modelled. Type II kerogen was used, which is based on previous palaeogeographic studies. The stratigraphic framework and major stages of geodynamic evolution were analysed. Salt-related structural traps in post-salt strata have been described based on 3D seismic data, and additional intra-salt sediment packages have been delineated. Discovered producing oil fields in the Upper Triassic and Jurassic–Cretaceous stratigraphic sections are mainly confined to the four-way dip structural closures above the steep flanks of salt structures. Based on burial and thermal modelling, the maturation and generation behaviour of kerogen Type II below salt-related minibasins and close to thick salt diapirs were inferred. For Lower Permian SR with type II kerogen, the generation peak (maturity over 50%) occurs in Middle to Late Jurassic. For predominantly carbonate and terrigenous-carbonate Mid-Carboniferous marine SR, generation peak occurs earlier below salt withdrawal minibasins. Implications for deeper hydrocarbon prospectivity were made for the study area, and methodology for evaluating hydrocarbon potential adopting 1D basin modelling technique and geochemical data is presented.
Tengiz field is one of the largest oil fields in the world. Reservoir is an isolated carbonate structure of a big area and big thickness. High heterogeneity caused by complex heterogenic and structural history of reservoir rises many uncertainties and makes characterization of reservoir extremely complicated. This fact alongside with big area and high hydrocarbon column of reservoir may make some of reservoir characterization techniques less effective. In this work was examined application of alternative Hydraulic Flow Units technique of distribution of permeability values for model. HFU technique divides reservoir to discrete units, which have lateral continuity and confirm lithological and facial heterogeneity of reservoir. This technique compared with classic porosity vs permeability correlations. Application of different permeability models were examined and compared through its effect on history matching of bottom hole pressures of Tengiz field simulation model. Additionally, was examined performance of two hydrodynamic simulators (E300 and Intersect) at conditions of big number of cells and high heterogeneity of reservoir.
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