GeoBaikal 2020

To obtain the correct information about the petrophysical properties of rock core samples under investigation and to create the foundation for NMR logging interpretation it is essential to carry out laboratory NMR investigations of the core, which contains the same fluids in its pore space as does the formation bottom-hole area (characterizing the NMR logging investigation radius). To carry out measurements of cavernous rock core samples in NMR-relaxometer GeoSpec DRX-HF an integrated procedure of CT and NMR investigations was implemented using the construction from caprolon, which allows preserving caverns filled with the fluid during the investigations. The resonance frequency of NMR-relaxometer GeoSpec DRX-HF, working at 2.3 MHz, aligns with the downhole instrument; therefore, T2 cut-off and T2 cavernous cut-off values obtained using this instrument, if required, may be applied for NMR logging results interpretation. Obtained with the usage of calculated cut-offs NMR logging values of cavernous porosity possess a nice correlation with the CT data. It is proved by the cavernous porosity data obtained by FMI. The suggested by us complex CT and NMR method is primarily recommended to estimate the cavernous porosity on core samples.

Traditionally simultaneous (Model based and Sparse Spike) inversion is used for prediction of reservoir properties such as saturation, porosity and permeability. However, in the case of geological sediments with high acoustic contrasts as carbonate reservoir in East Siberia the usual method is sometimes useless. In this paper, the method of stratigraphic simultaneous inversion is presented which helps to improve the quality of inversion in the high-contrast sediments. Technical algorithm, results of interpretation, advantages/disadvantages of this method are discussed.

The seismo-geological analysis while drilling horizontal wells and side-tracks was developed and successfully deployed on one of the super-giant oil fields of the Siberian Platform. Reservoir rocks of faulted and fractured Precambrian carbonates were influenced by multiple episodes of tectonic activity, subsequent erosion and deep burial, complicated by intensive diagenetic processes, involving wide spectrum of different processes from development of giant karst zones to fine-scale leaching and stilolitization. During pre-drilling stage a large number of seismic attributes were analyzed to identify and interpret all kinds of seismic anomalies, which run across planned well trajectories. These anomalies are often interpreted as faults, fracture and karst zones, leaching intervals, etc. During drilling stage such zones are often confirmed by lost circulation, drill bit drops, LWD logs anomalies and other events. During production stage these disintegration zones are on one hand considered as sweet spot areas in terms of reservoir properties and hydrocarbon saturation and production, but on the other hand have increased risks of water and gas breakthrough. Therefore, good understanding and spatial mapping of such anomalous zones in carbonate reservoirs by 3D seismic methods are critically important for successful well drilling as well as for overall decrease of field development costs.

The development of extra-viscous oil fields requires the use of effective methods using modern technologies. One of them, as the most technologically advanced and economically feasible, is the method of steam and thermal impact on the formation - SAGD. This technology needs high-quality and timely control over the process of steam injection into the reservoir. This problem is successfully solved worldwide by seismic monitoring. Based on a change in the elastic properties of the rock in the reservoir due to a decrease in fluid viscosity, monitoring studies the patterns of propagation of the field of elastic waves in the area of steam injection. However, this raises the problem of the repeatability of seismic monitoring conditions due to the variability of surface conditions from seasonal factors such as weather and seasons. These variations can be significant and exceed expected responses from changes in the reservoir. This paper presents an overview of the problems of variability of the upper part of the section during seismic monitoring and some results of our research, which were devoted to studying variations in the elastic properties of the upper part of the section at different times of the year for several years.

The horizontal anisotropy of the geoelectric section usually did not attract the attentiojn of geophysicists and was considered as a secondary parameter. Often, due to the use of axially symmetric systems of electromagnetic sounding, its investigations in this case is fundamentally impossible.However, a number of recent studies have shown that horizontal anisotropy of rock’s physical properties is an important indicator of tangential tectonic stresses. To quantify the effect of anisotropy on the MTS data using a 2-dimensional modeling program, a series of theoretical calculations was carried out. Two versions of the models were considered: macro- and microanisotropic. The calculations showed that the MTZ curves are sensitive to the influence of horizontal anisotropy of the geoelectric section. But taking into account the significant influence of near-surface inhomogeneities on the MTS curves, it should be determined that the assessment of horizontal anisotropy by the TEM - MTS complex is possible only for deposits of the oversalt complex.

The paper is devoted to several variants of geometric 3-D inversions of EM data with finding the parameters of conductivity and chargeability of a geolelectrical model. The first variant is based on two-stage 3-D inversion, at the first stage of which, the 3-D conductivity structure is recovered with separating the signals of EM and IP fields. At the second stage (of the first variant), the chargeability parameters are recovered with the use of residual signals obtained as subtraction of EM signals, which are computed for the conductivity model obtained at the first stage, from the observed data. In the second variant of 3-D inversion, we perform the simultaneous search of conductivity and chargeability distributions and, if it is necessary, the parameters of decay function. In both variants, the block structures are used for the initial model parameterization, and the vector of parameters includes x-coordinates of borders between the blocks, y-coordinates of borders between the rows of blocks as well as the electro physical parameters within the blocks. The workability of both approaches is demonstrated on the synthetic data for the 3-D geoelectrical model, which is constructed on the basis of the 3-D inversion results of DNME-data obtained on one of the North Pre-Caspian oil fields.

A special feature of the problems associated with the study of mineral resources is the incompleteness of knowledge about studied objects. It can be caused both by insufficient quantity of the geological and geophysical data, high variability of the geological parameters or combination of these factors. To minimize the risks of making erroneous technological and investment decisions it is necessary to assess the existing uncertainties. Traditionally such assessment is based on multivariate geological modeling. In order to obtain reliable information, it is important that the model gives an unbiased estimate, i.e. it does not bring a systematic error in all decisions obtained. But how can one be sure that the model is reliable if the real geological parameters are unknown? Calibration of the model based on initial data by resampling methods with small amount of initial information is problematic. In this situation the risk of making wrong decisions is inevitable, but it can be reduced by strictly controlling the modeling tools used and avoiding those of them that tend to introduce systematic error into the model. Studying the behavior of the tools used can be based on computational experiments. The proposed work represents the results of such research.

Comprehensive studies on the hydrocarbons potential prospects of Signalnaya area, located in the water area of the Mddle Caspian Sea within the boundaries of the western part of Khvalensko-Sarmatsky uplift zone, are presented. The studies are based on the results of seismic survey, lithofacies and paleotectonic analysis, differetional-normallized method of electricfl prospecting (DNME), aimed at solving the problem of direct prediction of hydrocarbon deposits. His approach allowed to identify Signalnaya non-anticlinal trap and to substantiate its hydrocarbons potential prospects.

The integration of gravity and magnetic studies and seismic data after object-oriented re-processing allows us to clarify the geological structure of objects of the pre-Jurassic complex. Characteristic patterns have been identified, which are confirmed by exploration drilling.

The trend for the complexity of potential oil and gas exploration prospects is obvious. The current complicated situation in oil and gas markets dictates financial caution to the companies investing in oil and gas exploration. The existing approach used by the industry for exploration projects assessment through EMV calculation has several weak points related to subjectivity of forecasts and risk evaluation. The criticism and suggestion for economics assessment in current distressed conditions are given.