bluuebunny/crossref_metadata_2025 huggingface dataset:
Borehole Failures and Stress Regime Identification Challenges in Fractured Carbonates of Boca De Jaruco Field
Authors: Zhekenov Temirlan , Norkina Anna' , Petrashov Oleg , Chettykbayeva Kamilla , Mylnikov Danila , Petrakov Yuriy , Sobolev Alexey
Published: September 2020

This article is continuation of geomechanical estimations for wellbore stability and horizontal wells drilling optimization to M formation of the Boca de Jaruco oilfield, Republic of Cuba. Following the completion of the first part of the work presented in the article SPE-196897-RU, the first horizontal wells were successfully drilled. In the first part of the work, the stress-state analysis and horizontal in-situ stresses directions were analyzed using pressure behavior during steam injections, cross-dipole acoustics, as well as data from oriented caliper from vertical wells. As a result, according to the recommendations, an additional study in the deviated sections of the wells, including core sampling and micro-imager logging were conducted. Presence of wellbore failures at the inclined sections allowed to use the method of inverse in-situ stress modeling based on image logs interpretation. The main result of the work were the determination of the stress state and horizontal stresses direction, as well as classification of the failures detected using the image log into groups. Moreover, the genesis of breakouts which had deviation from each other different that 180° were evaluated.
Selection of Optimal Developing Strategy for A Group of Prospects in Terms of Geological Uncertainties and Infrastructure Constraints
Authors: Legkokonets Vladislav Aleksandrovich , Vasilenko Alexey Aleksandrovich , Khasanov Mars Magnavievich
Published: September 2020

The aim of this work is to create a tool that can help in making difficult investment decisions about the sequence and commissioning periods of new hydrocarbons fields, maximizing expected monetary value and considering infrastructure constraints across a group of assets in terms geological uncertainties.

The approach is to use probabilistic calculations and the modern portfolio theory, adapted to the conditions of the sphere of petroleum exploration and production. The goal of optimization is finding a strategy for new assets development that would have the maximum profit with minimal economic or technological risk. Measures of spread of a random variable (a.g. NPV) around its expected value are used to measure an economic risk. Also, we propose a method of technological risk assessment, reflecting the probability of hydrocarbon production in the required range. To obtain a probability distribution of the objective function according to uncertainties in input data the stochastic Monte-Carlo simulation and "Latin hypercube" technique were used. Due to high dimensionality of the problem, heuristic optimization methods have been used to solve the optimization task.

A proxy model, based on the change in recoverable reserves volumes, starting production rates and decline rates of hydrocarbon production for newly drilled wells is proposed in this paper. The model combined with the calculation of economic measures. The combination of simulation models with an optimization algorithm allows to analyze a set of mathematical equations, containing a number of decision variables (e.g., years of commissioning periods and/or the paces of drilling wells) and to determine their optimum values, leading to a solution with the desired ratios of the expected economic effect and risk value. As a result, the numerical experiment revealed that application of the portfolio optimization methods allows to find new non-obvious solutions. The result of portfolio analysis is not a final product of project works, but, however, may be a basis for explanation of optimal development scenarios for a group of assets and can help in finding non-obvious, but more effective investment and project decisions.

A comparison of four heuristic algorithms in the single-criterion optimization problem was conducted. Conclusions about the effectiveness of the algorithms in terms of time and the fitness function values were made. The developed model and methods were used in task of searching the optimal development strategy for a group of real hydrocarbons fields.
Practical Application of the Geosteering Difficulty Index.
Authors: Kudashov Kirill Valerievich , Filimonov Victor Petrovich , Golovchenko Mikhail Anatolievich , Rahimov Timur Rinatovich
Published: September 2020

The development of drilling technologies, the constant increase in the complexity of the geological conditions in the drilling areas, the need to involve hard-to-recover reserves in the development, and economic aspects have stimulated the development of horizontal drilling in the Russian Federation. Horizontal drilling volumes have increased several times over the past ten years. There are also changes in the design and completion of horizontal wells (multi-laterals for example), increasing the variety of geology of the target layers, the variability of the LWD. Therefore, taking into account the high volume of horizontal drilling in Rosneft, it is became necessary to systematize and classify wells by degree of complexity for geosteering in order to more effectively develop resources and improve the efficiency of geosteering of horizontal wells.

This article will describe an approach to calculating the new parameter "Geosteering Difficulty Index" (GDI), which characterizes a horizontal well, and classify wells by geosteering complexity. Examples of optimization of used resources and services based on the presented classification are given, which, as a result, reduce costs and increase the economic efficiency of drilling horizontal wells.

The drilling complexity index DDI (Drilling Difficulty Index) usually uses in international practice. The higher the DDI for a well, the more complex the design of the well, the more complex the technologies needed for drilling this well, the higher the qualification of personnel, etc. (Filimonov et al 2012). Similarly, we introduce a new industry indicator-the geosteering complexity index. It will take into account the geological features of the drilling area and may be used to rank wells by complexity for geosteering.
Gas Cap Injection as an Associated Gas Utilisation Method. Experience of Novoportovskoye Field
Authors: Janan Bogdan Sultan , Koryakin Fyodor Andreevich , Sherstoboev Evgenii Andreevich , Isakov Kirill Dmitrievich , Virt Vitaliy Igorevich , Kashapov Denis Zabirovich
Published: September 2020

This work describes the technological solutions that were used in the development of the Novoportovskoye field - a large oil and gas condensate field in the Yamalo-Nenets Autonomous Okrug. In particular, optimization of the associated gas utilization strategy is considered by organizing the reservoir pressure maintenance. The decisions were based on 3D mathematical calculations, analytical estimates, analysis of field information and reservoir simulation.

The paper presents the results of calculations performed to determine the specific efficiency of gas injection at productive formation. Additionally, weight coefficients of gas injection were calculated for gas well sites to identify the best injection zones. The paper provides the estimation of the current effect of the continuous two-year gas injection. The formation response to the gas injection into the gas cap was estimated by the usage of pressure-observation wells data, data from wells equipped with fiber-optic monitoring systems and by performing retrospective simulation.

The calculations made it possible to achieve complete utilization of associated petroleum gas and significantly increase the oil recovery factor.
Enhancement of Condensate Recovery of Fractured Well by Accumulated Condensate Vaporization at HPHT Reservoir Conditions
Authors: Solovev Daniil Yurievich , Eliseev Petr Ilich
Published: September 2020

On the example of a gas condensate reservoir of field in Western Siberia with HPHT conditions, high condensate content and low permeability, the problem of reducing well productivity during operation are considered. Restoring of the near wellbore area permeability methods, reduced due to the buildup of retrograde condensate are studied. The effectiveness of previously performed acid treatments and solvent injection has been considered in order to increase the productivity of such wells. The analysis of the ambiguity and variable success of such events is carried out.

An unconventional, but promising method of the condensate saturation reducing in the near wellbore areaof wells with multi-stage fracturing is proposed. These wells operate Achimov deposits with HPHT. This method consists of creating special thermobaric conditions in the near wellbore area, which allow to vaporize the largest part of the hydrocarbon condensate accumulated around the borehole. A condensate-saturated gas is extracted from the well to the surface. A search was held for simple, available and inexpensive technologies aimed at increasing both pressure and temperature in the wellbore and near-wellbore region.

Based on the results of calculations performed on digital wells models in OLGA software, the thermobaric conditions created at the bottom due to the thermobarochemical effects are determined. The measures effectiveness of the retrograde condensate evaporation in the near wellbore areaand restoration of well productivity have been evaluated.
Method for Solving Problems of Gas Production from Turonian Reservoirs
Authors: Bakulin Alexandrovich Denis , Zobov Mikhailovich Pavel , Cheremisin Nikolayevich Aleksey , Khlebnikov Nikolayevich Vadim
Published: September 2020

It is shown that hydrophilic (inhibitor) and hydrophobic (hydrophobizing) compositions are able to increase the permeability of the bottom-hole zone of the clay Turonian formation and prevent the formation (and, if necessary, destroy) gas hydrates in the bottom-hole zone of the formation. Hydrophilic and hydrophobic compositions contain solvents (methanol or petroleum ether) that are easily removed by the gas flow, and active non-volatile components (ABR or magnesium chloride) that remain in the formation. The use of "active substance + volatile solvent" compositions allows to have a long-term effect on the reservoir Bottom-hole formation zone (BHFZ) and easily remove liquids from the gas formation by gas flow.

The use of hydrophobic compositions and fluids is promising in the production of oil and gas from clay reservoirs (Cenomanian, Turon, Senon, Bazhenov and Tyumen formations, etc.).
Study of Polymer Flooding at Pore Scale by Digital Core Analysis for East-Messoyakhskoe Oil Field
Authors: Yakimchuk Ivan , Evseev Nikolay , Korobkov Dmitry , Ridzel Olga , Pletneva Vera , Yaryshev Mikhail , Ilyasov Ilnur , Glushchenko Nikolay , Orlov Alexander
Published: September 2020

This work demonstrates the results of polymer flooding simulation at pore-scale level using digital rock analysis by means of the density functional method for representative core samples from the PK1-3 formation of the East-Messoyakhskoe oil field. Obtained results made it possible to estimate the key factors impacting the polymer solution efficiency and to determine the relative permeability curves and displacement efficiency at pore level. This allows to conduct a sensitivity analysis and provides recommendations for further development of the field.

In the study, an increase in the displacement coefficient due to polymer flooding is observed in a wide range with a maximum of about 26% with respect to the baseline scenario of the water displacement. Furthermore, a decrease in the ratio of the viscosities of oil and displacement agent from 100/1 to approximately 3/1 led to a switch of the dominant physical mechanisms, from viscosity instability to velocity stripping.
Some Possibilities of Fluid Typization in Core Samples at Rig Site Applying Nuclear Magnetic Resonance
Authors: Belousova Natalia , Murzakaev Vladislav , Alexandrov Artem , Skirda Vladimir , Doroginitsky Michael
Published: September 2020

Resume

In the framework of the contract with the Ministry of Education 2010-2012, TNG-Group andKazan Federal University developed a mobile YaMR-Kern unit to acquire information on filtration-capacitive properties of full-sized freshly drilled and extracted core samples, to estimate porosity, to determine free and bound fluids, permeability, residual water saturation, to assess the nature of saturation by analyzing the two-dimensional distribution of relaxation times and diffusion coefficient directly at the wellsite without preliminary core preparation for studies. Efficiency of the unit was tested on more than 1600 m of full-sized core samples taken from sediments of various ages and saturated with oils of various viscosity grades.

The core study directly at the wellsite, that is, immediately after its extraction to the surface, allows not to lose the very first information about the studied object as soon as possible, since the study of the core drying process showed that during the first hours the core loses up to a third of fluid-saturated porosity, and 20 days later dries out almost completely. Scanning the NMR properties of the core is carried out with high detail, every 1-2 cm, and does not involve any preparatory work, that is, the core does not break down and can later be used for laboratory studies of both full-sized core and standard samples. Such information is extremely important at the stage of exploratory drilling on poorly studied survey targets, as well as in the study of a thin-layered section of wells.
Quantitative Analysis of Whole Core Photos for Continental Oilfield of Western Siberia
Authors: Abashkin Vladimir Viktorovich , Seleznev Ilya Alexandrovich , Chertova Anastasia Alexandrovna , Istomin Sergey Borisovich , Romanov Dmitry Vladimirovich , Samokhvalov Andrey Fedorovich
Published: September 2020

The paper considers methods for automatic description of lithotypes as well as modeling of reservoir properties based on analysis of whole core photographs. The specific nature of the considered approach is the solution of applied problems based on relatively small training data sets using machine learning techniques. Also, one should highlight that the results of lithotype classification and reservoir properties modeling can be obtained in a form of high-resolution curves, which resolution is restricted by the quality of the core images. Additionally, during analysis of core photos several sets of curves are derived, which also could be used at different stages of analysis and interpretation of geological and geophysical data. Also, the considered approach could be useful for development of high-quality training data sets for neural network models.
Some Rules to Optimize Process of Planning Geomechanics Core Testing Program
Authors: Zinovyev Alexey Alexeevich , Korelskiy Evgeny Pavlovich , Chettykbayeva Kamilla Nusupbekovna , Petrakov Yuriy Anatolyevich , Sobolev Alexey Evgenyevich
Published: September 2020

In this paper, some features of conducting experiments on core samples to determine mechanical properties were established. Detailed description for such type of testing is poorly described in regulatory documents (Russian State Standard, ASTM).

Problem of specific test methods selection in accordance to task before the geomechanical modeling is considered. For the most issues, a series of experiments to build a failure envelope is required. Details of sample preparation for compression tests are regarded. In particular, the advantages and disadvantages of different methods for preserving in-situ core saturations are discussed: the collection of an isolated core with subsequent conservation or the preparatory work with the extraction, drying and saturation of samples.

While conducting multi-stage compression tests for building Mohr circles, chose of the right moment to stop the loading stage has a significant effect to prevent destruction of the sample in the early stages. This paper demonstrated that for specimens characterized by a shear failure type, it is recommended to focus on the plot "axial stress - volumetric strain". In particular, the inflection point of the curve, that is the moment of reaching the maximum value of volumetric deformation could be selected as a criterion for the loading stage termination.

For samples with high porosity, a complete testing cycle to build the Mohr circles and the entire failure curve is given.
Methods for Studying Two-Phase Flows in Porous Media: Numerical Simulation and Experiments on Microfluidics Chips
Authors: Khayrullin Marsel Mansurovich , Zakirov Timur Rustamovich , Grishin Pavel Andreevich , Shilov Evgeny Dmitrievich , Bukatin Anton
Published: September 2020

In this paper, experimental and computational approaches are used to study multiphase flows. In the first method, filtration experiments are carried out using microfluidics technology. Microfluidic chips were made from polydimethylsiloxane using soft lithography. To give the desired surface properties, the inner walls of the channels were treated with a hydrophobic or hydrophilic coating. Injection of liquids was carried out using a syringe pump at a constant flow rate. To measure the pressure difference at the inlet and outlet of the microchip, we used the method of measuring changes in gas volume. For numerical modeling, the most modern model of the Boltzmann lattice equations, adapted for two-phase flows of incompressible immiscible liquids, is used. The effects that occur at the phase boundary are described using the color field gradient model. Experimental studies have shown the possibility of studying the processes of liquid displacement from the microchannel system in a microfluidic chip simulating a porous medium. The dynamics of the displacement of liquids (water and oil) from a system of microchannels with different hydrodynamic drag cardinally depends on the angle of wettability of its walls. In the case of microchannels with hydrophilic walls, a complete displacement of oil by water occurs almost simultaneously from both channels. When water is displaced by oil from channels with a hydrophilic and hydrophobic coating, it is required to create an increased flow rate of the displacing liquid through microchannels. In this case, at the junction of the microchannels, before leaving the chip, emulsion droplets of "water in oil" will form. In the case of oil displacement by water from microchannels with a hydrophobic coating, complete removal of oil from the channel with high resistance did not occur. This is due to the fact that the viscosity of the oil is 30 times higher than the viscosity of water. The paper shows a successful comparison of the results of numerical modeling and experimental research in a two-phase flow in a pore doublet. Demonstrated examples of the developed program code are shown: the formation of emulsions at high flow rates, the motion of a drop under the influence of mass force; flow in digital microtomographic image; displacement of viscous oil from the pore medium.
Method of Integrated Seismic and Geological Support for Drilling Horizontal Wells
Authors: Samoylenko Ivan Yuryevich , Tarasov Artem Evgenievich , Belousova Natalia Alexandrovna
Published: September 2020

Currently, one of the most widely used methods of extracting hard-to-recover oil reserves in Russia is drilling horizontal wells. Support for drilling horizontal boreholes is based on a 2D geonavigation section using LWD and MWD data, without taking into account 3D seismic data.

In the conditions of development of deposits with hard-to-recover reserves, which have a large number of disjunctive violations and geological uncertainties, there is a need for operational use of 2D and 3D seismic data as a method of increasing the efficiency of geonavigation.

Specialists of the Department of geological support for drilling Of the branch of LLC LUKOIL-Engineering" VolgogradNIPImorneft " in Volgograd have developed a method for using seismic data in the operational mode in the process of geonavigation. The method was tested on the example of drilling and drilled wells and the analysis of the obtained material was carried out, the efficiency of using this method was determined.
Application of the Theory of Clamped Water in the Justification of Water-Oil Contact for the Purpose of Calculating Hydrocarbon Reserves on the Example of Famen Organic Deposits of the Vostochno-Lambeshorskoye Field
Authors: Dorofeev Nikita Vladimirovich , Ananyeva Evgeniya Vladimirovna , Khromova Inga Yurievna , Saetgaraev Almir Damirovich , Sheykina Angelina Fyodorovna , Garifullin Ilfat Ilsurovich , Kuzmicheva Anastasiya Vladimirovna
Published: September 2020

The article describes the theory of "clamped" water to justify the position of the oil-water contact of the reservoir, exposes in detail the experience of applying this theory on the example of an oil reservoir in Famennian organic deposits of the Vostochno-Lambeyshorskoye field of the Komi Republic.

During the field development, geologists have encountered a problem of different oil-water levels established in different parts of the structure, which is determined by well data with a high degree of confidence.

The analysis of reservoir pressure data shows, that the separation of the reservoir into tectonically shielded blocks with different levels of water-oil contact is impossible.

According to the results of seismic facies modeling and sequence stratigraphy, there were not identified any significant channels that could separate the reservoir by area.

The solution to the problem of substantiating the oil-water contact was found by applying the theory of "clamped" water. The idea of this theory is that during the migration of hydrocarbons into the trap, controlled by lithology and faults, there remain the so-called hydrodynamically isolated "pockets" (hereinafter referred to as "pockets") in which the formation water is sealed with oil and the oil-water contact is fixed at the level of the structure bend. The article describes the mechanism for the formation of such "pockets".

In the issue, a new conceptual model of the Famennian reservoir of the Vostochno-Lambeyshorskoye field was created as a layer-uplifted deposit, controlled by lithology, with different horizontal oil-water levels. The oil-water level is gradually increasing from north to south, along the path of hydrocarbon migration from the source rock to the reservoir. Oil-water levels are controlled by structural inflections defined on the maps of the reservoir bottom.
Method of Multivariate Seismic Tomography Based on Stochastic Analysis of Input Data Reliability
Authors: Anisimov Ruslan Gurievich , Finikov Dmitry Borisovich , Silaenkov Oleg Aleksandrovich
Published: September 2020

Seismic tomography is one of the main tools for obtaining a depth velocity model. Its result largely determines the estimated geometry of oil and gas reservoir. Tomography is a deterministic procedure and does not provide an opportunity to assess the reliability of the results. However, in fact these results directly affect the subsequent economic decisions. For this reason, the aim of the current work is to develop a method of multivariate tomography which allows to determine the reliability of the results. The paper considers several factors of multivariance. Factor of input data quality is generally considered and stochastic averages tool is proposed for estimating input data reliability. Typically, input data estimation involves calculating supergathers. Usage of equivalent weights for supergathers accumulation means that all gathers have an equivalent quality but in practice this is far from the truth due to various regular noises. Replacing weights by random ones is equivalent to filtering with random kernel. These means assigning a random confidence levels to input gathers. This allows to generate many realizations of the input data for inverse problem. Also incorporation of tomography smoothness parameters variation to inverse problem is proposed. Such approach differs from traditional ones where these parameters are set by a specialist based on purely personal ideas. All together this allows to generate many realizations of depth velocity model and estimate its reliability. The proposed method of multivariate tomography doesn't use the known statistical distributions of the input data errors, thus, it is the most general and realistic. Its result can be utilized in the assessment of economic risks.
Development of Hazard Assessment Matrix for Wells as an Industrial Safety Assurance Method When Designing Oil and Gas Well Construction
Authors: Shirieva Nadezhda Sergeevna , Shiriev Artur Kamilevich , Tlyasheva Rezeda Rafisovna , Kafisov Fanil Shamilievich
Published: September 2020

The article considers statistical data on accident rate in oil production: types of accidents, accident distribution over constituents of the Russian Federation, number of fatalities, incident distribution over constituents of the Russian Federation. Causes initiating fire and explosion hazardous situations on a drill site are studied.

Executed analysis of statistical data clearly demonstrates that accident rate and fatal injuries in the industry still remain at high level, therefore necessity to develop scientifically validated methods for assessment of well hazards from various condition is relevant. In its turn, it will enable to promptly provide preventive measures aimed at assurance of the required industrial safety level.

As drill sites belong to hazardous industrial facilities (HIF), when managing industrial safety, at construction design stage, it is necessary to carry out accident risk analysis in order to identify hazards and undesired events.

According to the analysis of problem statistics, criteria that influence on occurrence probability of problems initiating fire and explosion hazardous situations, as well as the factors, on which severity of accident consequences depend, are determined.

As a result of the work executed a method for calculation of quantitative risk assessment indices that considers well construction conditions is proposed on the basis of the developed well hazard level matrix. The proposed approach can be applied to forecast risk level for any territory when using initial data on accident rate of the specific field or group of fields.
Automated Geosteering While Drilling Using Machine Learning. Case Studies
Authors: Denisenko Ivan Denisenko , Kuvaev Igor Andreevich , Uvarov Igor Borisovich , Kushmantzev Oleg Evgenievich , Toporov Artem Igorevich
Published: September 2020

Today's oil & gas industry faces a number of different challenges. Drilling activities are ramping up due to an increase in hydrocarbon demand combined with a reduction of easy-to-recover reserves. Horizontal drilling is growing and has become an integral part of field development. The geology is becoming more and more complex requiring drilling through dense layers targeting thin-layered reservoirs with lateral changes and anisotropy. In recent years, companies have been looking at the ways of optimizing drilling costs by increasing efficiency and process automation. This has been a driver for many companies to stay profitable and efficient in the market.

One of the areas of interest for process automation has been a geosteering. Geosteering is the real-time adjustment well trajectory while drilling to maximize effective footage in the target zone. In this paper, innovative new approaches to automation of the geosteering process will be discussed. This approach has been successfully tested and deployed in several leading O&G companies.

The main objective of automated geosteering is to optimize horizontal well placement while freeing up time operational geologists had spent doing routine work in order to focus on complex and more intense tasks as well as the reduction of operational errors related to human factors. This paper will provide details on several automated geosteering algorithms. They have been tested successfully on large numbers of wells. The results of automated geosteering were as close as 90% to the manual interpretations done by geologists. When the results diverged, the geologists often "agreed" with the interpretation proposed by the algorithm.
TIV-Anisotropy in Geomechanical Modeling for Planning of Hydraulic Fracturing at the Kharampurskoye Field
Authors: Pavlyukov Nikolay , Pavlov Valeriy , Samoilov Mikhail , Prokhorov Alexey , Korolev Aleksandr , Yagudin Radik , Kamionko Maria , Aleksandrov Aleksandr , Savchuk Danil
Published: September 2020

The choice of the optimal trajectory of horizontal and directional wells, the placement of frac-ports for multistage hydraulic fracturing, taking into account prepared input data (using geological and geomechanical modeling with the rock properties anisotropy), provide optimization of hydraulic fracturing operations and field development. Formation T contains more than 3 trillion m3 of gas, and is already an object of close attention of the largest oil and gas companies. The unique character of the object is due to the high reservoir compartmentalization of the collector and low permeability. Therefore, the main development strategy for the reservoir is to drill low-angle and horizontal wells, followed by multistage hydraulic fracturing. The main goal of multistage hydraulic fracturing is to join productive intervals and at the same time avoid undesirable fracture breaks into neighboring layers. To achieve this goal, several tasks were solved: creation of a petrophysical and geological basis for geomechanical modeling, creation 1D and 3D geomechanical models taking into account the rock properties anisotropy due to the high layering of the reservoir, and preparing input data for hydraulic fracturing design.

For the qualitative creation of the geomechanical model at the observation wells of the field, an expanded complex of special well logging studies has been performed, borehole measurements of reservoir pressure and minimum horizontal stress have been carried out according to the results of stress tests, core sampling and research to determine petrophysical and mechanical properties. The analysis of the obtained information revealed the features of the stress state along the section and reservoir area, which were taken into account in the design of hydraulic fracturing. Geomechanical modeling was carried out in a uniform work procedure, which made it possible to unify the result, improve the quality of calculations and forecast parameters for horizontal wells.
Experience with 6/10 and 10/14 Mesh Size on Mid-Permeable Reservoirs
Authors: Chaplygin Dmitry , Khamadaliev Damir , Chernyshev Alexey
Published: September 2020

One of the engineering tasks of hydraulic fracturing design is the correct selection of the propping agent. Ceramic proppant, which is used in most fields in Western Siberia, makes a proppant pack that is several times more permeable than the formation (sometimes even 1000 times). However, the gelling agent used for treatment, depending on the size of the proppant, reduces the permeability of the proppant pack from 2 to 5 times. However, workover operations after hydraulic fracturing and during production period has a significant colmatage effect on the near-wellbore zone and can significantly reduce the productivity of the well.

A common practice in the fields of Western Siberia is to prop a fracture at the near-wellbore zone with a proppant of mesh size 12/18. Despite a small difference in the calculated skin factor, the analysis of operations at the Salym group of oilfields shows a significant change in the production decline rate on wells with 16/20 and 12/18 mesh size propping agents.

Engineering group of the Salym group of oilfields conducted trials on hydraulic fracturing treatments with a mesh size 10/14 and, after successful results, 6/10 proppant. The treatment results, lessons learned and the analysis of production of these wells is the scope of this work.
Practical Experience of Unconventionals’ Multistage Fracturing in Belarus
Authors: Mironenko Kirill Viktorovich , Drabkin Andrew Valerjevich , Shakulja Maksim Ivanovich , Serebrennikov Anton Valerjevich
Published: September 2020

Nowadays, the vast majority of the oil fields of the Republic of Belarus are at the last stage of development. In this connection, the goal of Belarusian oil industry is to search, to explore and to develop ultra-low permeable tight fractured carbonate rocks. Commercial production of such resources is only possible with the use of advanced stimulation methods, such as hydraulic fracturing / multi-stage hydraulic fracturing.

Taking into account the features of tight carbonate rocks, the use of conventional hydraulic fracturing technologies cannot provide optimal results, and therefore, selection of more advanced approaches to hydraulic fracturing is necessary. Selection and optimization of technologies based on theoretical research is not possible, instead it requires practical implementation, and according to our experience, flexibility in decision making.

This article presents the experience of unconventional reservoir development in the Republic of Belarus from 2014 to 2020. We briefly described the main technologies used and how these technologies evolved depending on the resulting operational and economic effect. The technology of repeated multi-stage hydraulic fracturing in an unconventional reservoir is described; the possibility of producing from previously untapped reservoir zones within the horizontal wellbore by creating additional flow channels (hydraulic fractures) was confirmed.
Logging, Well Testing and Microseismic Fracture Geometry Investigations: Mistakes, Lessons Learnt and Challenges
Authors: Salishchev Mikhail Vsevolodovich , Shirnen Alexander Alexandrovich , Khamadaliev Damir Mudarisovich , Chaplygin Dmitry Alexandrovich
Published: September 2020

As the number of stages of hydraulic fracturing along the horizontal wellbore increases, the cost of fracturing starts to exceed the cost of drilling the well. Therefore, the issue of costs optimization for hydraulic fracturing in general become highly important problem.

In this regard, for optimization calculations, it is necessary to operate with such important geometric characteristics of fracture as half-length and height of the fracture, which can be determined by logging, well-testing and micro-seismic studies.

This paper analyzes all types of studies to determine the geometric characteristics of the fracture, except its width. Logging surveys, which have been carried out on vertical and inclined wells, allow to determine with some degree of accuracy the height of the fracture, provided that the conditions of applicability of these surveys considering well azimuth and inclined angle in the zone of fracturing & logging.

Among the logging methods that have been applied to that kind of problem, the highest priority in terms of the reliability of the results obtained is given. Well testing allow us to determine the effective half-length of a fracture, but with some limitations. Micro-seismic studies allow comprehensively and in three-dimensional view to determine the configuration of a fracture in a orientational well or a system of fractures in a horizontal borehole to a certain degree of accuracy.
Acidizing Combined with Heat Generating System in Low-Temperature Dolomitized Wax Damaged Carbonates
Authors: Folomeev Aleksey Evgenyevich , Magadiev Azat Failievich , Khatmullin Arslan Rustemovich , Taipov Ildar Azatovich , Vakhrushev Sergey Aleksandrovich , Galiev Timur Railevich , Mukhametov Flyus Khanifovich
Published: September 2020

The article demonstrates the results of experimental and field studies of the thermal foam-acid treatment technology with the use of water solutions of heat and gas generating system. The potential temperature of the heat-generating reaction upon mixing of agents was estimated in laboratory conditions and the physical and chemical properties of acid solutions were determined. A series of filtration experiments was conducted on treating dolomitized core samples with a basic hydrochloric acid solution.The constant of the rate of reaction between the basic acid solution and dolomitized carbonate rock was determined based on the experiment results.

The article provides a brief analytical overview of world experience of the thermochemical treatment of the bottomhole area. The technology selected for the tests called thermo-foam-acid and implies the step-by-step injection of water heat and gas generating solutions with an addition of surfactants and an initiator into the bottomhole area. The heat-generating reaction is accompanied by the generation of a large amount of heat, gases and hot foamed acid. Heating melts high molecular weight oil compounds, washes oil sheen from rock surface and increases the speed of its dissolution with hydrochloric acid. This foam acts as a diverter for the next portion of active acid and prevents undesired stimulation of high-permeability interlayers and fractures. Surfactants in the acid solution increase its ability to penetrate pores and microfractures. The physical modeling of a thermal foam-acid treatment has been performed.

Arlanskoe (Kashirskian-Podolskian deposits) and Nadezhdinskoe (Famennian stage) fields where carbonate formations are characterized by high and increased oil viscosity, low reservoir temperature, fractured and dolomitized reservoirs were selected as a site to perform field tests. Well operation at these formations is complicated by the precipitation of asphaltenes, resins and paraffins in the bottomhole area.

Solution injection parameters were recorded during treatments based on this technology. The technological efficiency of this treatment was confirmed based on bottomhole pressure and temperature changes during injection operations. Technology efficiency was analyzed and the well flow rate was monitored based on the field test results.

The main stages of this work are shown in Figure 1.Figure. 1Project stages
Advanced Pressure Monitoring Technique – New Horizons of Workover in Russia
Authors: Borisenko Alexey , Parkhonyuk Sergey , Zotov Kirill , Korkin Roman , Kiselev Nikita Vladimirovich , Laptev Artem , Rapeyko Vitaly Tadeushevich
Published: September 2020

In the case of many workover operations associated with fluid loss inside the well or multistage refracturing, one of the most significant uncertainties is the fluid entry point. Starting from uneven depletion of the horizontal part of the well, not knowing the fluid entry point may lead to ineffective well restimulation and absence of any positive effect. In this paper new technique will be reviewed for several locations across Russia.

Implementation of high-frequency pressure monitoring (HFPM) method and based on it, Well Watcher Stim technology, allows locating downhole events caused during well workover and refracturing without interruption of the well stimulation operations. The high frequency pressure monitoring technology is based on automatic processing of wellbore pressure oscillations recorded at the wellhead. The wellbore completion elements such as hydraulic fractures, casing diameter changes or wellbore restrictions serve as effective reflectors for the tube waves. In this paper, we will demonstrate an integrated approach to the utilization of high-frequency pressure monitoring technique, which has served as an engineering tool for fluid entry point validation in the projects all across Russia. The project validated the intrinsic benefits of the new approach in solving uncertainties about the fluid entry point.

The Well Wacther Stim technology requires minimum changes in operational procedures, is easy and safe to install and provides real-time answers that allow the frac engineer to take decisions on location and optimize the re-fracturing process

Selected stimulation approach enables the horizontal well refracturing operation to be concluded within 2-3 days, minimizing well intervention operations and reducing the overall costs and risks of the restimulation. The selected workover approach demonstrates reliable technique for fluid loss extensional control in well workover.

One of the opportunities which is became available with high-frequency monitoring is analyze of conditions of well construction and downhole equipment. That was practically confirmed at a well with completion for multi-stage fracturing. Suspicion about damage of casing or sliding sleeves and corrosion of isolation packers was verified and localized. Further application of Well Watcher Stim made possible to decrease leakages by conventional reservoir dynamic fracture diversion technology and provide multi-stage fracturing with constant control of identified zones.

This paper presents case studies of the technology that was used widely in Russia in the recent years proving reliability of high-frequency pressure monitoring technique. It will provide meaningful insight for the petroleum engineer who will look after solving uncertainties during well workover operations and refracturing.
Support Vector Regression for Petroleum Reservoir Production Forecast Considering Geostatistical Realizations
Authors: Da Silva Luciana Maria , Avansi Guilherme Daniel , Schiozer Denis José
Published: September 2020

Decision analysis related to petroleum field development and management phases with complex models can be time-consuming, especially in highly heterogeneous fields. Probabilistic approaches require a large number of simulation runs to cover all possible solutions, and this can be slow. In this study, we present a methodology to include high-dimensional spatial attributes (geostatistical realizations) in proxy modeling, based on support vector regression (SVR), for building risk curves with decreased run time. The proposed workflow accomplished the following: definition of uncertain inputs, such as porosity and horizontal and vertical permeabilities; selection of outputs from the simulator (cumulative oil, water and gas productions) to be mimicked by the proxies; sample inputs to generate scenarios for training and proxy building; and consistency check to evaluate if the proxy model is reliable to mimic simulator output. We then used proxy models to generate risk curves at the final forecast period (7,305 days) as an application. Using the SVR with high-dimension inputs, we show that the proxy was able to provide reliable results with 300 scenarios, which represent 35% less computational effort compared with using only a reservoir numerical simulator. As a result, we can use this proxy to perform a risk analysis with a high level of accuracy [mean absolute percentage error (MAPE) lower than 0.5%] to predict the production curves. In conclusion, we can use the SVR proxy model technique as an alternative to a reservoir simulator when spatial uncertainty attributes (geostatistical realization) are present.
Rate-Transient Analysis of a Constant-Bottomhole-Pressure Multihorizontal Well Pad with a Semianalytical Single-Phase Method
Authors: Chu Hongyang , Liao Xinwei , Chen Zhiming , John Lee W. John
Published: September 2020

Because of readily available production data, rate-transient analysis (RTA) is an important method to predict productivity and reserves, and for reservoir and completion characterization in unconventional reservoirs. In addition, multihorizontal well pads are a common development method for unconventional reservoirs. Close well spacing between multifractured horizontal wells (MFHWs) in the multiwell pads makes interference from adjacent MFHWs especially significant. For RTA of production data from multihorizontal well pads, the influence of adjacent MFHWs cannot be ignored. In this work, we propose a semianalytic RTA model for the multihorizontal well pad with arbitrary multiple MFHW properties and starting-production times. Combining Laplace transformation and finite-difference analysis, we obtained a general solution of a multiwell mathematical model to use in RTA. Our model is applicable to cases of multiple MFHWs with different bottomhole pressures (BHPs), varying hydraulic-fracture properties, and different starting-production times. In the solutions, we observe bilinear flow, linear flow, transition flow, and multi-MFHW flow. Rate-normalized pressure (RNP) and its derivative are also affected by multi-MFHW flow. Two case studies revealed that the negative effect of interwell interference on the parent-well productivity is closely related to the pressure distribution caused by the production of child wells.
Utility of the optical quality analysis system for decision-making in Nd: YAG laser posterior capsulotomy in patients with light posterior capsule opacity
Authors: Lu Bo , Zhu Weijie , Fan Yu , Shi Dong , Ma Liwei
Published: September 2020

Background: A prospective cohort study was performed to evaluate whether the Optical Quality Analysis System (OQAS) can serve as a valuable additional indicator for appropriate posterior capsulotomy referral. Methods: One hundred and five eyes from 96 patients undergoing capsulotomy were divided into precapsulotomy logMAR CDVA ≤ 0.1 group and logMAR CDVA > 0.1 group. CDVA， and the Visual Function 14 index (VF-14) score were estimated before and one month after capsulotomy. The objective scattering index (OSI) value was measured by using the OQAS. Posterior capsule opacification (PCO) severity was assessed with Evaluation of PCO 2000 (EPCO 2000) software. Results：In logMAR CDVA > 0.1 group, the correlations of OSI, logMAR CDVA, EPCO score and VF-14 score were very strong preoperatively. In logMAR CDVA ≤ 0.1 group, preoperatively, OSI was correlated with logMAR CDVA (r = 0.451), EPCO score (r = 0.789), and VF-14 score (r = 0.852). LogMAR CDVA has weak correlation with VF-14 score (r = -0.384) and EPCO score (r = 0.566). VF-14 score was correlated with EPCO score (r = -0.669). In the logMAR CDVA ≤ 0.1 group, there was no significant difference in logMAR CDVA between precapsulotomy and postcapsulotomy (P > 0.05). In the two groups, all the other optical quality parameters were significantly improved after capsulotomy (P < 0.05). In logMAR CDVA > 0.1 group, the area under the curve of the ROC of the OSI was 0.996 (P = 0.000). In logMAR CDVA ≤ 0.1 group, the area under the curve of the ROC of the OSI was 0.943 (P = 0.000).Conclusions：The OSI was useful for evaluating of PCO and prediction of beneficial capsulotomy. Especially for patients with slight PCO and better visual acuity, OSI is more valuable than CDVA and completely objective examination. Trial registration: The study protocol was registered at the Chinese Clinical Trial Registry. Register: ChiCTR1800018842 (Registered Date: October 13th, 2018).
SARFIMA model prediction for infectious diseases: application to hemorrhagic fever with renal syndrome and comparing with SARIMA
Authors: Qi Chang , Zhang Dandan , Zhu Yuchen , Liu Lili , Li Chunyu , Wang Zhiqiang , Li Xiujun
Published: September 2020

Background

The early warning model of infectious diseases plays a key role in prevention and control. Our study aims to using seasonal autoregressive fractionally integrated moving average (SARFIMA) model to predict the incidence of hemorrhagic fever with renal syndrome (HFRS) and comparing with seasonal autoregressive integrated moving average (SARIMA) model to evaluate its prediction effect.

Methods

Data on notified HFRS cases in Weifang city, Shandong Province were collected from the Disease Reporting Information System of the Shandong Center for Disease Control and Prevention between January 1, 2005 and December 31, 2018. The SARFIMA model considering both the short memory and long memory was performed to fit and predict the HFRS series. Besides, we compared accuracy of fit and prediction between SARFIMA and SARIMA which was used widely in infectious diseases.

Results

Model assessments indicated that the SARFIMA model has better goodness of fit (SARFIMA(1, 0.11, 2)(1, 0, 1) 12 : Akaike information criterion (AIC): -631.31; SARIMA(1, 0, 2)(1, 1, 1) 12 : AIC: -227.32) and better predictive ability than the SARIMA model (SARFIMA: root mean square error (RMSE): 0.058; SARIMA: RMSE: 0.090).

Conclusions

The SARFIMA model produces superior forecast performance than the SARIMA model for HFRS. Hence, the SARFIMA model may help to improve the forecast of monthly HFRS incidence based on a long-range dataset.