Vol 20, No 2 (2020)
- Year: 2020
- Articles: 9
- URL: https://ered.pstu.ru/index.php/geo/issue/view/118
Abstract
The development of differentiation methods for porosity, permeability and petrographic properties depending on the facies is analysed. The influence of structure (as per Dunham classification) on the changes in porosity and permeability, including the use of full-size core samples, has been studied in depth. Permo-Carboniferous deposit of Usinskoye field has been selected as the study target. Reservoir properties of the strata under study are highly heterogeneous: along with highly porous and cavernous rocks there are low-porous and cracked varieties in the section, which applies to rocks of different lithological composition. Porosity and permeability properties were analysed for more than 9000 standard core samples and ca. 1.000 full-size core samples, factoring in the scale effect and including microfractures, large caverns and rock matrix, commensurate with sample sizes. Analysis of maximum variation range is of particular importance for structurally complex carbonate reservoirs. Furthermore, based on the conducted lithologic, petrographic and petrophysical studies, the Authors identified four types of reservoirs and eight different types of lithogenesis, for each of which geological and physical parameters were estimated. Based on the cumulative correlation plots, four zones of heterogeneity were identified, that are subject to the influence of properties of core samples of different lithogenesis types. From the petrographic and petrophysical research findings, the influence of various petrotypes/lithotypes on changes in porosity and permeability of reservoirs was studied for Usinskoye field for the first time. Following all the conducted experiments, it has been established that the rocks of the Permo-Carboniferous deposit of the Usinskoye field show extreme heterogeneity of porousity properties that vary over a wide range. In this connection, ‘core to core’ petrophysical correlations shall be differentiated depending on the structure of void space and lithology of rocks.
 |  |
Abstract
The problem of obtaining reliable seismic data from water-logged areas is considered. Raw hydrocarbon deposits of the northern territories in Perm Krai are very promising assets, yet rather complex for geological study, as they are located in difficult surface conditions. Seismic surveying being the most detailed and reliable remote-sensing method of geological study of subsurface resources, the modern 3D seismic surveys require covering a much larger surface area with a survey grid than that occupied by the search object in depth. Wetlands significantly attenuate seismic waves, which results in obtaining the data that is complex for further geological interpretation, and also significantly constrain technical and methodological aspects of the research, while it is impossible to avoid the impact of difficult surface conditions in the area of hundreds of square kilometers. In order to estimate the possibility of obtaining high-quality data under such conditions, extensive test surveys were conducted using various types of seismic wave recording and excitation equipment. The analysis is presented and the possibility of solving this problem with the help of modern seismic survey methods is estimated. The study has touched upon the technology of obtaining primary data and the stage of processing the information for its further geological interpretation. Such innovative instruments as Geoton impulsive seismic vibrator and GS-ONE high-sensitivity geophones were reviewed. As a result, conclusions were made on certain advantage of an explosive energy source over an impulsive one, especially at wetland strata directly. At the same time, Geoton seismic vibrator features high ecological compatibility and safety, which allows for its wide application at seismic survey operations in populated areas. From the results of the test survey data processing, the best quality and detail level of the wave pattern recorded by single geophones has been noted. Following the findings of the conducted study, recommended practice guidelines have been given for seismic surveys in wetland conditions and at areas with high environmental and safety requirements.
| |
Abstract
The results of geomechanical simulation for problem-solving in the provision of accident-free well-drilling are considered. There is a need to develop a numerical 3D geomechanical model for the field under study with the subsequent stability calculation of producing wells. The operations area is located offshore in the Baltic Sea. Further to a brief description of the field, the results of collection and audit of initial data for the simulation are presented. A method of one-dimensional geomechanical simulation on reference wells was studied, including determination of dynamic and static elastic strength characteristics of rocks, calculation of pore pressure, and vertical and horizontal stress. Well stability calculations based on the 1D geomechanical simulation results were obtained and analysed. Next, the results of three-dimensional geomechanical simulation were analysed: determination of limits and development of the model’s structural framework, geometry testing, filling the grid with mechanical properties, as well as calculation of the total stress tensor by finite element method (FEM). The results of 1D and 3D modeling were compared. From there, a numerical 3D geomechanical model for the field under study was developed. The next step was to calculate wellbore stability for projected wells. Additionally, volumes of pressure gradients of drilling mud absorption, rock caving and hydraulic fracturing at various inclination angles and drilling directions were calculated. Recommendations have been developed for accident-free well construction in the field under strudy, including real-time support and update of the geomechanical model during drilling. The results obtained and the operations method can be used in the design and construction of wells in other fields subject to regional specifics.
| |
Abstract
The development of Upper Permian deposit of high-viscosity oils is planned with the use of thermal methods of oil recovery enhancement: cyclic steam simulation of wells. A simulator allowing to calculate changes in thermal properties of rock fluids, as well as to solve the equations of heat and mass transfer should be used for reservoir simulation. Cyclic steam treatment was simulated using CMG STARS, a numerical simulator with a wide range of applications, including simulation of thermal processes. The cyclic steam stimulation takes place in three main stages: the steam injection phase; the soak phase; and the production phase. The number of cycles were selected by calculation based on the optimal operation of a well. Calculations with 7, 5 and 3 cycles were conducted to determine the optimal number of cycles. Prediction calculations of the well operation without steam cycling stimulations were conducted, as well. The calculation results revealed the operation mode with the highest cumulative oil production. When estimating the efficiency of cyclic steam stimulation of wells using hydrodynamic simuation, dependencies on a number of geological and physical parameters, including steam dryness, formation thickness, steam injection rate, and impregnation duration, were obtained By the results of numerical experiments, conclusions have been made and recommendations have been given on individual approaches to selection of optimal parameters of cyclic steam stimulation for each individual well, subject to its structure and features. Using factor analysis, the most optimal parameters for cyclic steam stimulation of wells of Upper Permian deposit of Usinskoye field were selected. For reference, three predicted options of well operation were calculated. Technical and economic indicators of the efficiency of the well operation options in Upper Permian deposit of Usinskoye field, which provide for the well operation in natural conditions and multiple CSS jobs at the basic and recommended options, were estimated.
| |
Abstract
As the stock of wells at a late stage of operation is on the increase, there is a growing need to introduce new integrated technologies aimed at watercut reduction. The reduction of watercut consequentially enables long-term operation of the watercut well stock, increasing the recovery of remaining oil reserves. Polyacrylamide is the most avaibale and applicable agent for solving the conformance control problems. Summing up the international and domestic practice, the efficiency of application of various modifications of methods with the use of polyacrylamide to reduce watercut of wells has been analysed. Such injection technologies as conventional polymer waterflooding, in situ gels, colloidal dispersion gels, and pre-cross-linked gels have been reviewed. Cross-linked polymer gels are three-dimensional structures in which polymer chains are cross-linked by either ionic or covalent polar bonds. Depending on the particle size, they are divided into macrogels (from 100 µm to several cm) and microgels (from 0.1 to 30 µm). The application of macro- and microgels, compared to in situ compositions, significantly reduces the risks of polymer chains destruction induced by mechanical, chemical and thermal factors. Based on the analysis findings, recommendations on the use of various modifications of polymer injection have been developed, subject to geological and technological conditions of development of production facilities. In order to reduce the watercut of well production it is recommended to use macrogels in the fields under reservoir conditions with permeability exceeding 500 mD, microgels at permeability ranging from 100 to 500 mD, and colloidal dispersion gels - at permeability from 10 to 100 mD. To improve the development efficiency, advanced technologies shall be timely adjusted to geological and technological conditions, and field trials shall be performed at domestic fields.
| |
Abstract
Oil recovery enhancement methods, mostly chemical ones, are widely applied in the course of development of oilfield hard-to-recover hydrocarbon reserves. Each reservoir stimulation technology features certain application conditions depending on the reservoir’s initial geological and physical parameters and the current state of its development. A methodological approach to determination of rock oil permeability and displacement coefficients when testing compositions of technologies of physical and chemical methods of oil recovery enhancement based on laboratory studies of rheological properties of various grades of acrylamide polymer is presented. The methods have been developed in accordance with the requirements for core study. The list of equipment and basic characteristics of the filtration system, as well as the procedure for preparing working fluids and reservoir models for laboratory studies are presented. Laboratory research of rheological properties of gel systems was conducted subject to specifics of the technological process of preparation of components of viscoelastic composition at wellhead and its subsequent injection into formation. For this purpose, to determine the rheological characteristics of gel systems a specialised rheometer was used that allowed to record in a dynamic mode the data on changes in viscosity properties of the tested polymer systems prepared on the models of fresh, produced and Cenomanian waters in the well-formation pressure-temperature conditions. Based on the findings of laboratory studies it was shown that the trial injection of cross-linked compositions based on polyacrylamide (PAA) of FP-107 and Poly-T-101 grades that are able to increase manifold the final viscosity of polymer composition (2-3 times, and more) with temperature rise in low-salinity waters (produced and Cenomanian waters) enables greater process efficiency compared to acrylamide grade FP-307 that is currently used in the Company’s fields.
| |
Abstract
A practice of hydraulic fracturing in carbonate deposits at Komi Republic and Nenets Autonomous District fields is considered. Over three hundred jobs were perfomed since 2012 with the wide application of hydraulic fracturing technology in carbonate reservoirs. A significant share of remaining recoverable reserves in carbonate deposits dictates the need for bringing them into development and increasing their recovery rates, in particular, through hydraulic fracturing. As permeability and porousity of candidate wells are gradually deteriorating, maintenance of a stable level of the hydraulic fracturing process efficiency is ensured through introduction of new technologies and optimisation of conventional ones. The problems of hydraulic fracturing implementation are closely related to the principal issues of field development and specifics of carbonate reservoir structure. The key tasks in hydraulic fracturing have been defined subject to structural features of carbonate reservoirs and ongoing development issues, including: increase in fracture conductivity; increase in coverage by area and section; decrease in uncontrolled leakoff of fracturing fluid; decrease in fracture height subject to adjacent water- and gas-saturated interlayers. To date, a number of technologies have been successfully adapted and applied at the facilities of Komi and NAO fields. Integrated approach in the selection of hydraulic fracturing technology modifications subject to current issues in field development and specifics of carbonate facilities structure, have enabled maintaining consistent efficiency of the method given the deteriorating structure of candidate well stock, as well as expanding the technology application range. The trends for expanding the scope of laboratory research have been proposed, including determination of stress intensity factor - fracture resistance and Biot’s poroelastic parameter, research of dynamics of leakage rate of various fracturing fluids depending on reservoir properties of core samples at given gradients, determination of dependency of dynamic transfer of proppants on rheological properties of fracturing fluids and their flow velocity for various fracture model openings.
| |
Abstract
Currently, attaining the maximum possible and economically feasible oil recovery factor is the priority task in engineering the development of hydrocarbon deposits. Deterioration in the structure of remaining oil reserves and the demand to bring hard-to-recover reserves to development have stimulated the search for new effective technological solutions in engineering. To date, there is a gradual transfer (replacement) of the technology of drilling vertical and directional wells (including horizontal and multilateral wells) and application of equipment for simultaneous multiple operation of wells in standard diameter to small diameter. More than 385 horizontal wells have been drilled at the Perm Krai fields, of which 3.4% (13 wells) have small diameter. The analysis of well operation shows that the efficiency of horizontal wells in a number of cases is significantly lower than the potential efficiency and is deteriorating economic indicators of the facility development, thus resulting in the decrease in the asset value. The low efficiency of horizontal wells may essentially result from the insufficient comprehension of geological and physical conditions for their operation. The accumulated practice in drilling horizontal wells in the reservoirs with heavy compartmentalization, low values of net effective oil-saturated thicknesses and deteriorated hydrodynamic connectivity to aqufier has proved their low success, as the dynamics of yield decline to the average flow rates is being observed for directional wells. In this connection, selecting the well structure and its orientation in specific geological and physical conditions is of pressing concern.
| |
Abstract
The development of hydrocarbon deposits involves inflow of formation waters into wells over time. The increase in produced water volumes affects adversely economic performance of field development and entails a range of other harmful effects, including equipment corrosion. The corrosion of downhole equipment causes the maximum economic damage, since well accidents require costly repair operations. Therefore, the prevention of equipment corrosion is a crucial task. The key properties and composition of formation waters are considered. The influence of Cl-, SO4-2, HCO3- anions contained in formation water on kinetics of corrosion processes at the metal (electrode) / water (electrolyte) interface is analysed from open literature sources. Furthermore, the research data on the influence of presence of dissolved acid gases (H2S and CO2) on the mechanism and rate of corrosion process are presented. The impact of hydrogen index on corrosion rate is reviewed. The content of various salts in formation water determines the complexity of corrosion processes that take place under actual operation conditions. The presence of aggressive media in some cases accelerates corrosion, yet sometimes slows it down, which also affects the efficiency of inhibitor protection. Based on laboratory data, the effectiveness of corrosion inhibitors in formation waters with different compositions and properties has been assessed. As it has been established, the presence of a mixture of aggressive components - chloride ions and hydrogen sulfide - in formation water results in the inhibition of hydrogen-sulfide corrosion, while the rate of chloride corrosion process also declines. The presence of ions of dissolved salts and acid gases in formation water increases the efficiency of corrosion inhibitors due to strong passive films formed on the surface of steel equipment.
| |