This paper considers methodology aspects for constructing one-dimensional (1D) geomechanical models and stability calculations for the case of viscoplastic behavior of rock under stress with a case study of the Vikulovskaya sandstone from the Em-Egovskoe Field in West Siberia.

The paper presents an algorithm for estimating the error of the 1D geomechanical model taking into account the measurement errors of the instruments and the correlation dependencies used. The sensitivity analysis of the resulting error to the quality of the source information was also performed. A confidence parameter has been introduced to assess the contribution of a measurement to the calculations. An approach is proposed for the transition from the convergence of correlation dependencies to the error of the correlation used. The application of this methodology allows at the initial stage to draw a conclusion about the quality of simulation results and take measures to increase the reliability of calculations.

The paper describes an approach to the analysis of the efficiency of water flooding in relation to the development of the oil rim. The ways of optimizing the existing water flooding strategy are shown based on the actual operation of the wells and the forecast based on the hydrodynamic model. The issues of monitoring and control are considered as well as monitoring the operation of injection wells with the aim of subsequent operational decision-making regarding their operating modes.

In the Timano-Pechora Region, the drilling of the 178 mm hole for the production casing in horizontal wells is often accompanied by challenges attributed to mud losses in thief zones. These challenges may not be overcome by application of conventional lost circulation materials (LCMs), often resulting in the abandonment of the parent wellbore and re-drilling of the section. A reactive multi-component system was proposed to the operator as an alternative solution to control mud losses while drilling this section and assist in reducing the well construction costs and duration. The multi-component reactive system has been developed as a combination with an oil-based fluid used to support reactions with water-based fluids in the well, regardless of the mud chemistry. When the oil-based composition contacts water-based fluids, it forms a coagulated, moldable substance that plugs off the mud loss channels in the near-wellbore zone. The substance does not ingress further into the matrix or fractures and, therefore, it does not provide any negative impact on the permeable zone of the reservoir. Prior to implementing the multi-component reactive system, the drilling of the 220.7 mm section used to be accompanied by mud losses as high as 100 m 3 /h. Two pilot operations utilizing this system demonstrated reduction of mud losses by 100%, thus allowing timely drilling of the 220.7 mm sections within the schedule. Furthermore, the 178 mm casing strings were run to TD with successful cementing, and without the need to sidetrack. The estimated time savings from application of the multi-component reactive system was 20% in comparison with the previously drilled four wells. The new technology helped the operator achieve success in preventing mud losses during well drilling, and removed the need for wellbore re-drilling. As the system may be pumped directly through the BHA, this provides additional time savings in not having to trip out of the hole. Based on the results of the pilot operations, this technology has demonstrated its advantages for solving lost circulation issues while drilling in target intervals. This paper addresses the application of the multi-component reactive system to resolve the lost circulation problem.

The complex interbedded heterogeneous reservoirs of the Severo-Komsomolskoye field are developed by horizontal wells in which, as part of the pilot project's scope, autonomous inflow control devices (AICD) are installed to prevent early coning and gas breakthroughs in long horizontal sections and reduce sand production, which is a problem aggravated by an extremely low mechanical strength of the terrigenous deposits occurring in the Pokur formation of the Cenomanian stage in this area. The zones produced through AICDs are separated by swell packers. The issue of AICD effectiveness is discussed in the publications by Solovyev (2019) , Shestov (2015) , Byakov (2019) and some others. One of the methods used for monitoring horizontal sections with AICDs is production logging (PLT). However, due to the complexity of logging objectives, the use of conventional logging techniques makes the PLT unfeasible, considering the costs of preparing and carrying out the downhole operations. This paper provides some case studies of the Through-Barrier Diagnostics application, including passive spectral acoustics (spectral acoustic logging) and thermohydrodynamic modelling for the purpose of effective estimation of reservoir flows behind the liner with AICDs installed and well integrity diagnostics. As a result of the performed diagnostics, the well completion strategy was updated and optimised according to the log interpretation results, and one well intervention involving a cement squeeze with a straddle-packer assembly was carried out.

Flow and injection profile monitoring in horizontal wells enhances the oil and gas field development efficiency, which is of particular importance when the target reservoirs have a complex geological structure, as is the case with oil-rim reservoirs located below a gas cap. The objective of this paper is to present the results of multi-well diagnostics carried out in order to estimate the flow and injection rates in Yarudey Field wells (Russia) and assess the downhole completion integrity status. When developing oil-rim reservoirs, flow and injection profiles need to be closely monitored so that gas and water breakthroughs along the length of thin beds and fractures could be promptly detected and appropriate remedial jobs planned. This task becomes more challenging in completions where multistage hydraulic fracturing was earlier performed, or the wells were cased with uncemented liners equipped with swell packers. To monitor the reservoir performance, advanced downhole diagnostics was performed in a group of wells in the field, where such reservoir-oriented techniques as passive acoustics and high-precision temperature logging were used. Application of the passive acoustic logging technique helped to identify reservoir flow zones and detect crossflows behind casing. The flow and injection rates were estimated through temperature simulations. Both these techniques were found to be useful, including those instances when the integrity of complex downhole completions was to be assessed. On the whole, the obtained results have proved the effectiveness of supplementing conventional production logging (PLT) with reservoir-oriented techniques.

Development of oil rims at oil-gas-condensate fields is accompanied by a high risk of gas coning which leads to well productivity losses followed by conversion of such wells to an idle stock. In order to increase the oil recovery factor of oil rims and to eliminate early gas breakthroughs, horizontal wells drilled in thin oil rims are equipped with autonomous inflow control system. The study describes the experience of AICD application for one of the largest fields in East Siberia with an oil rim and a large gas cap, where an integrated analysis of the AICD well performance was conducted for the first time in Russia. This analysis includes: choosing well-candidates, performing AICD lab testing, sector reservoir simulation, modeling of AICD effect, followed by the actual well performance analysis after running AICDs. All this became possible due to the well-organized cooperative work of the operator and the contractor. The wells included in this study were successfully put into production at lower GOR values compared to their surrounding wells

Modern technology of drilling and construction of horizontal wells allows for effective development of complex oil fields hard-to-recover oil reserves includes off low-permeability (less than 1-2 mD) and hyper-low-permeable (0.01-0.0001mD) fields. The latter in Russia include Bazhen, Domanic and Achimov fields. Their development provides for the mandatory completion of HW with Multiple-Fractured Horizontal Wells (MFHW). Experience in the development of layers of the specified type for Gazpromneft PJSC shows that the highest oil production rate is achieved if the MFHW system reveals not only the low-permeability rock matrix, but also captures the highly conductive (typically fractured) streaks — "strata-conveyors" (the latter may also be located in neighboring geological and stratigraphic differences). The difference in the permeability of such highly conductive layers and the hyper-low-permeable matrix of the host rocks can be very significant (up to 10 6 !). In addition to the positive aspects of the presence of highly conductive layers in the section associated with the achievement of high initial oil flow rates in new wells, in the process of further development, negative consequences may arise as a result of premature (even unpredictable) gas and water breakthroughs through narrow fractured layers. Is it possible to take into account the risks of loss of well productivity as a consequence of the pronounced geological heterogeneity of these fields, even if the scale of the impact of this heterogeneity is still difficult to assess by modern research methods? In this paper analyzes some of the results of core, logging, well testing and indicator studies with the allocation of characteristic features indicating the presence of local highly conductive fractured layers in the section of the oil the Bazhen-Abalak complex (BAC).

This paper presents the results of an integrated approach to the analysis of the geological structure and the subsequent of the productive Achimov deposits development: deposits X and Y located in Western Siberia. The main difficulties in the development of the Achimov deposits are associated with a high heterogeneity, a low degree of prediction of effective thicknesses, the difficulty of correctly calculating well flow rates, saturation behavior and, accordingly, water cut, and high production decline rates identified as a result of putting new wells into operation.

The staff of Belorusneft constantly invents, tests and adopts new technologies to develop hard-to-recover oil reserves in the fields of the Pripyat Trough. Conventional reserves are under fast-paced development in this region, while hard-to-recover reserves are not actively developed, although amounting up to 70% of total recoverable petroleum reserves. When targeted penetration of low-permeable intervals and creation of a system of branched deep drainage channels are required, we developed equipment and technology that allow creating a network of deep-penetrating flow channels. The channels run radially in relation to the wellbore with penetration depth of up to 100 m, which can significantly increase the formation fluid flow area toward the wellbore.

Lost circulation (LC) is commonly encountered in drilling and cementing operations and can significantly contribute to non-productive time (NPT). An operator in the Kyumbinskoe Field faced this challenge in a fractured production section of the formation, and conventional LC solutions had been ineffective at achieving strict regulatory top of cement (TOC) requirements and satisfactory cement bonding. This paper describes a tailored spacer fluid system engineered to effectively and efficiently prevent LC to meet the job requirements. The tailored spacer system includes additives that perform synergistically to help prevent LC in permeable and fractured formations and enables rheological hierarchy to facilitate effective mud displacement. The spacer was designed to meet operational parameters for cementing a production casing string in two stages through the use of a multi-stage tool and was subjected to thorough verification through lab testing and computer simulations to ensure job requirements could be met. The tailored spacer system was used in three trial jobs to assess its ability to minimize losses in a permeable and fractured formation with a history of LC with the ultimate goal to achieve planned TOC and improve cement bond quality as verified by Cement Bond Logs (CBL’s). Use of this tailored spacer system helped to minimize losses experienced on all three wells. CBL results were also significantly improved with an average of 70% of the cemented interval being classified as "good bond" on wells cemented without the tailored spacer system to 88% on the three wells where it was used. Barrier dependability with the new spacer system was improved through achieving strict regulatory requirements for TOC on two out of three wells and improved cement evaluation results, which is a critical requirement of well construction that allows for maximizing production over the life of the well.

Multilateral well completion technologies are becoming more common throughout the lifecycle of oil and gas fields due to increasing complexity of the reservoirs. Additional lateral drilling tends to increase the contact area with the formation and, as a result, the production rate of a well and allows avoiding the need of design, construction, and maintenance of the surface infrastructure and upper sections of a potential new well. ( Muslimov R.H., 2017 ) Various factors are considered while designing the well construction: starting from reservoir properties, thermobaric conditions, fluid composition, and up to the surface infrastructure. So, a Multilateral well might be a good solution under certain circumstances. ( Shenberger V.M., 2007 ) In Russia, the most popular Multilateral completion technology nowadays is level 1 according to TAML 1 international classification (with both lateral cased). The noteworthy strengths of the system include its reliability, simple deployment, and proven cost-effectiveness. However, its widespread use is hindered by such constraints as a fundamental limitation associated with the inability to perform following downhole operations (DHL 2 , HCT 3 , processing of BHZ 4 , etc.) in one of the boreholes, which directly affects the effective lifetime of such a well. Technologies TAML 2 and 3 are the next levels in the international classification describing the construction of a Multilateral well with an exit from previous casing (mainbore). ( Bellarby J., 2009 ) However, the TAML 2 system was not considered for this case due to the lack of mechanical integrity of the junction. The basic TAML 3 system requires both a longer well completion time and additional operations entailing associated risks. In view of the above, a further development of TAML 1 technology was considered as a solution: Multilateral well completion with TAML 3 junction installation in the open hole preserving its mechanical integrity, with the possibility of selective access to both laterals during following downhole operations without involving additional service equipment. 1 TAML - Technology Advancement for Multi-Laterals. This paper describes the field experience of TAML 3 system deployment in the open hole for the land project, which confirmed the effectiveness of an integrated approach and targeted solutions for further optimization of hydrocarbons production by the example of the Multilateral well construction.

The components of casing drilling technology are evolving and the application area is expanding. Drilling engineers today have more flexibility than ever before to redesign wells and can combine different technologies, materials and equipment to achieve new records in well construction efficiency. In recent years, PJSC Gazpromneft has been constantly using casing drilling technologies. The increasing complexity of geological conditions and the need to reduce well construction costs lead to more efficient solutions. The article presents the actual experience of using the following variations of the casing drilling technology: Non-directional drilling on 426mm casing together with 630mm thermal case at Yamburgskoye field Non-directional drilling on 324mm casing at the Vostochny Section of the Orenburg oil and gas condensate field (VUONGKM) Run in hole with rotation on 245mm casing at VUONGKM. Directional drilling with 245mm casing with a retrievable BHA at VUONGKF. The use of casing drilling technology has not in all the cases under consideration increased the efficiency of well construction, but at the same time the results obtained allow us to predict an additional increase in the efficiency of the application of these technological solutions. At the end of the article, a tree of casing drilling technologies was built and segments with development prospects were highlighted.

Several wells have been drilled recently by Arctic LNG 2 at the Salmanovskoye (Utrenneye) field. Horizontal drilling at this field is challenging because of an inclination angle up to 52° in the intermediate section, drilled with a 311.2 mm bit. Drilling of large (311.2 mm) intermediate sections with significant vertical offset is not common for this area. The production wellbore section was drilled at an angle of 86°. Solutions suggested for complex wellbore sections drilling, included the use of oil based mud. Multiple tests were conducted in order to select the best drilling fluids formulation and an action plan was developed to maintain stability of the wellbore and to optimize wellbore cleaning. Nevertheless, multiple issues were encountered during the first well drilling, which resulted in a significant extension of the construction period. Lessons learned during the first well were studied thoroughly and included into risk assessments made for drilling of subsequent wells. This contributed to the overall success of drilling these wells and to the significant reduction of their construction periods. Drilling practices and fluids properties were optimized as follows: The whole volume of mud was mixed as required for intermediate section drilling. Dedicated software was used for the continuous modeling of wellbore cleaning efficiency and drilling parameters were adjusted promptly in accordance with the modelling results. HPHT filtration rate was reduced to 2 ml/30 min in challenging wellbore sections. The decision tree was revised as required for the efficient response in case of lost circulation. Newly prepared OBM, combined with the developed and optimized action plan, contributed to the incident-free drilling of complex wells at the Salmanovskoye field. Located remotely, requirements for proper logistical solutions was vital for success. This is discussed in details below. With the success of these messures, it is expected that these practices will be implemented at two other fields on the Gydan peninsula and in other areas where traditional drilling practices may be ineffective due to challenging lithology, geological conditions and logistics and HSE risks

This paper provides the results of the application of integrated approach to drill the longest extended reach well which has ever been drilled in Odoptu-more field (North Dome) in Sakhalin. Although many extended reach drilling (ERD) wells have been already drilled by the operator in Odoptu-more field, extreme reach wells always require new solutions. Reaching remote reservoirs by applying standard well design of Odoptu-more field was not possible due to high standpipe pressure (SPP) and equivalent circulating density (ECD) in 8 ½-in production section. Engineering study resulted in partial upsize of a well design and change 9 5/8-in casing to liner followed by remaining challenges: 9 5/8-in liner could not be delivered to required depth due to string buckling. Several key technical solutions were implemented in the project thus allowing to deliver the longest well accident-free. Those solutions included well design modification allowing to drill 8 ½-in production section to reach remote reservoirs and 9 5/8-in liner delivery to the required depth using "mud over air" flotation technique for the first time in the project. Having applied integrated approach, the project team broke a new record in drilling the longest well at Odoptu-more field with total measured depth 8699m, ERD ratio 4.89 and Directional Difficulty Index (DDI) of 7.6 ( Alistair W. Oag 2000 ). Drilling extreme reach ERD well unlocked opportunities for the operator to reach and put into the production more distant offshore oil-bearing reservoirs from the land rig without changing existing pad facilities.

Massive implementation of multi-stage fracturing treatments increased demands in water. Huge number of oil fields haven't got access to the fresh water sources. This fact forces service companies to utilize high TDS water sources for hydraulic fracturing. Currently available solutions for preparation of crosslinked fluid based on high TDS water involve implementation of organometallic systems which are too expensive and operationally complicated. This paper describes approach for preparation of borate- based fluid utilising high TDS water. Thorough laboratory optimization of the fracturing fluid has been performed and novel approach for fracturing fluid composition has been involved to develop next generation of robust borate fracturing fluids being able to withstand high TDS of the water. Fluid was evaluated in terms of both stability and viscosity recovery after application of high shear stress. Optimized fluid formulation has been used during multi-stage fracturing treatment with 7 stages. High TDS water of Cenomanian formations was utilized as a water source. During treatments as high as 700 kgPA proppant concentration has been reached. During optimization novel approach involving implementation of low boron containing fluid with massive content of alkali was introduced. Low boron content is required for preventing syneresis in high ionic strength media caused by Debye-Huckel effect. High alkali concentration meantime required to keep fluid at high pH and avoid weakening of bonds between borates and polymer. Too high alkali concentration worsens viscosity recovery after high shear stress application and this fact dictates implementation of both immediate and delayed alkali compounds. Pre-job water treatment is also important. Addition of reagents being able to convert natural radical oxidizing aids in less damaging forms is imperative. During the treatment fluid was additionally tuned to reduce frictional losses in tubing by compensating effect of proppant on the rate of crosslinking components diffusion. And treatment design was modified to address increased efficiency of the fluid caused by filter-cake enhancement by delayed alkali. The study showed availability of approaches which allow to implement high TDS water sources for preparation of borate crosslinked fluids confirmed by successful field implementation. These practices can be widely used in industry for performing multi-stage fracturing treatments in areas with lack of fresh water sources and to shorten water preparation cycle time.

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.

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.

The Turonian siltstone is widely spread through the Siberian region in northern Russia. It is a laminated, heterogeneous and high-shale content formation with low permeability (1-3 mD) and low reservoir temperature (15 degC), with more than 300 trillion m3 of natural gas in place. Hydraulic fracturing is a necessity for economic and sustained development of the field in the described geological conditions. High montmorillonite contentand extremely low temperatures make the Turonian reservoir a true challenge for frac experts. A pilot stage of project development has been executed with horizontal drilling and multistage fracturing. A well has been constructed with 168-mm casing and 114-mm liner, with the liner separated into discrete segments with hydraulic packers. Each zone is equipped with filters integrated with the inflow control devices (ICD)plus frac portsenabling multistage frac jobs and subsequent controlled, solids-free production.Frac ports and ICDs are shifted using coiled tubing (CT) equipped with a downhole hydraulic key. Significant innovations were implemented for the frac fluid design in terms of a noveldiesel-based fluid breaker package.Additionallab investigation of proppant transport capacity has revealed some elastic properties of diesel-based fluid, that are not typical for crosslinked guar-borate water-based fluids. This provided the opportunity to significantly increase proppant concentration and frac design aggressiveness for the successful completion of a trial campaign.With the optimized fluid, the engineering team has achieved outstanding results in frac design, when large-sized proppant has been pumped at concentrations up to 1400 kg/m3 during multistage frac operations in horizontal wells.The combination of technologies led to rapid well cleanup with a quick transition to stable gas flow to sales. New achievements in well completion techniques andwater-free frac fluid optimization can be implemented when dealing with similar low-temperature reservoirs with high content of water-sensitive clays.

This study presents an approach based on machine learning to predict the lithology at the bit while drilling. This is necessary for (near) real-time adjustments of well path while providing reservoir characterization (reservoir rock, non-reservoir rock and tight rocks). The approach is based on an ensemble of decision trees and gradient boosting. Work on this project included analysis and preprocessing of the data, selection of features for training, creation of additional features to improve the quality of the model, comparison of machine learning algorithms to identify the most effective within the task, optimization of the hyperparameters. After that, the final model is built on a training dataset with desired outputs obtained from LWD formation evaluation and the quality of the algorithm is evaluated on a test dataset with the selected metrics. The computer program developed on the proposed approach receives drilling data as input and provides a reservoir characterization. High quality of the model is necessary for successful geosteering of horizontal wells due to the rapid detection of lithology changes in the reservoir and increasing the efficiency of well drilling by minimizing penetration through the non-reservoir rocks, which can further increase oil production. The proposed approach provides an accuracy of 80-90% for a number of oil fields.