Directional Radial Drilling Increases Reservoir Coverage with Precise Wellbore Placement Resulting in a Significant Production Increase from a Thin Reservoir

In many oil and gas provinces not only in Russia, but throughout the world, carbonate strata make up a significant portion of the sedimentary cover, and large accumulations of hydrocarbons are associated with them. However, the purposeful study of them as reservoirs for hydrocarbons in our country practically began only in the post-war years. In the special petrography laboratory carbonate rocks composing various stratigraphic complexes of almost all oil and gas provinces of the Soviet Union were studied, and in particular, Paleozoic carbonate strata of the Timan-Pechora province, Ural-Volga region, Belarus, Kazakhstan, ancient Riphean-Cambrian formations of Yakutia and relatively young strata of the Late Cretaceous of the northeastern Ciscaucasia. Carbonates are widespread sedimentary rocks. A very significant part of them was formed in the conditions of vast shallow-water marine epicontinental basins. A large number of works are devoted to the study of such deposits. However, issues related to the conditions of formation of carbonate sediments and their postsedimentary changes cannot be considered resolved, as well as the classification of the rocks themselves. The analyzed field is the Osvanyurskoye one. It was discovered in 2007. The field is located in the north-east of the European part of the Russian Federation, 2 km from Usinsk in the Komi Republic. The field is a part of the Timano-Pechora oil and gas province and it is a mature field (fig. 1). The objective was a 2.5m thick layer of the Serpukhov horizon.

Enhancing Reservoir Stimulation and Productivity Through Reservoir Tunneling Technologies: A Review on Recent Development

The oil and gas industry has been developing various technologies to increase the productivity and recovery of hydrocarbons from conventional and unconventional reservoirs. Reservoir stimulation is an essential operation used to enhance production in many fields around the world. Hydraulic fracturing and acid treatments are the main stimulation methods. Reservoir tunneling concepts are used to drill branched channels in the formation from the main wellbore. With thousands of tunnels drilled to date, it is a viable technique that can improve the recovery of selected reservoirs. This paper reviews the recent developments in reservoir tunneling technologies and their current applications. These tunneling methods can be categorized mainly into water jetting, abrasive jetting, reactive jetting (acid), and needle and mechanical tunneling (radial drilling). The paper includes reviewing and analyzing these techniques based on documented literature results that include simulation studies, lab and yard experiments, field implementation, candidate selection, operational requirements, technology enhancements, advantages, limitations, and challenges of each technique. The paper provides a comprehensive summary of different tunneling techniques focusing on the operational practices, tunneling mechanisms, tunneling depth, and recent advancements available in the market. The most effective applications of the tunneling techniques are in stimulating low permeability, depleted and thin reservoirs, layers close to water zones, and bypassing near wellbore formation damage. The efficiency of creating tunnels is affected by many factors such as reservoir properties, nozzle, and fluid types, etc. The tunnel shape and trajectory are affected by reservoir geological properties. The combination of the tunneling with other stimulation techniques can result in more effective treatments, which enhance the methods of current stimulation. Reservoir tunneling technologies can pave the way to improve hydrocarbon recovery and enable access to unstimulated formations.

Improving Water Injectivity Through Lateral Radial Drilling into the Reservoir

Poor formation permeability and near well bore damage may limit water injectivity into the reservoir in a water injection project. This paper seeks to evaluate the effect of radial drilling technique on water injectivity and oil recovery in water flooding operation. Radial drilling technology utilizes hydraulic energy to create lateral perpendicular small holes through the casing into the reservoir. The holes may extend to 100 m (330 ft) into the reservoir to access fresh formations beyond the near wellbore, and damage zone. A black oil simulator (Eclipse 100) was used to modeling a lateral radial drill from the borehole into the reservoir, and that of a conventional perforation of the wellbore respectively. A simulation study was carried out using various presumed radial drill configurations in determining injectivity index, displacement efficiencies, recovery factor and water cut of the process. The determined results were further compared with that of the conventional perforation process case respectively. The results show a significant improvement in water injectivity in radial drill case with the increasing length and number of radials as compared to the conventional wellbore perforation case. The determined Recovery factor shows a progressive increase with increase in the numbers of radials drilled, irrespective of the radial length. However, it was observed that, the more the number and length of the radials drilled in to the reservoir, the higher the water cut from producer wells. Radial Drilling Technology, therefore, has a promising potential to improving water injectivity into the reservoir and thereby optimizing oil recovery in a water flooding operation.

An Analytical Model for Fracture Initiation of Radial Drilling-Fracturing in Shale Formations

Radial drilling-fracturing, the combination of radial drilling and hydraulic fracturing, can guide fractures toward the target area and effectively enhance the recovery of the low permeable reservoir. In this paper, based on the stress superposition principle, we establish an analytical model to predict fracture initiation pressure (FIP) and the shale failure mode for radial drilling-fracturing applied in shale formations. In contrast with the former studies, this model can additionally consider the failure from shale beddings and is more applicable in the shale reservoir. The model classifies the shale failure into three modes and, respectively, gives the criterion for each failure mode. Then, a series of sensitivity analyses is conducted by examining effects of various parameters. By analyzing the variation characteristic of the initiation pressures required for three failure modes, the main conclusions are as follows. Firstly, matrix failure and shear failure along bedding tend to take place when the azimuth of radial borehole is moderate. Small and large azimuths are favorable for the occurrence of tensile failure along bedding. Secondly, a high ratio of horizontal in situ stress predisposes shale to generate matrix failure, and bedding tensile failure and bedding shear failure are apt to occur when the ratio of horizontal in situ stress is low. Thirdly, with the increasing intersection angle of the radial borehole wall and bedding plane, the failure mode apt to occur changes from bedding tensile failure to bedding shear failure and then to matrix failure. Fourthly, shale prefers to yield bedding shear failure under a small Biot coefficient and generate the other two failure modes when Biot coefficient is large. Fifthly, permeability coefficient virtually has no influence on the failure mode of shale. The research clarifies the fracture initiation characteristics of radial drilling-fracturing in shale formations and provides a reference for the field application of radial drilling-fracturing.

Fracture Initiation Mechanisms of Multibranched Radial-Drilling Fracturing

Compared with conventional hydraulic fracturing, radial-drilling fracturing presents remarkable advantages and can effectively develop low-permeability reservoirs. The radial borehole can reduce formation fracture pressure and guide the fracture initiation and propagation. Due to the large radial borehole azimuth or the strong anisotropy of the reservoir, the single radial borehole may not efficiently guide the fracture propagation. The researchers proposed multibranched radial-drilling fracturing. However, the research on fracture initiation of multibranched radial-drilling fracturing is inadequate. Radial boreholes usually need certain dip angles to avoid penetrating the interlayer, but the effect of dip angle on the stress field has never been considered before. In this paper, an analytical model for predicting stress distribution around the main wellbore with multiradial boreholes of arbitrary dip angle, azimuth angle, and phase angle is established for the first time, taking full account of the influences of in situ stress, internal pressure, and fracture fluid infiltration on the stress field. The model is utilized to calculate the fracture initiation pressure (FIP) and point out the specific fracture initiation location (FIL). The influences of azimuth angle, dip angle, phase angle, depth difference, and the stress profile radius on fracture initiation pressure, fracture initiation location, and maximum tensile stress distribution are investigated, and a series of sensitivity analyses are carried out. The results show that the areas between the radial boreholes and closer to the walls of radial boreholes are more prone to tensile failure, which provides a theoretical basis for radial boreholes guiding fracture initiation. The reduction of phase angle and depth difference enhances the interference between radial wells, which is conductive to the formation of hydraulic fracture networks between them. As the dip angle increases, the stress becomes increasingly concentrated, and the preferential rock tensile failure becomes increasingly easy. The farther the stress profile is from the main wellbore axis, the smaller it will be influenced by the main wellbore. When the distance exceeds 2R, the maximum tensile stress distribution on the profile remains constant. The research enriches the fracture initiation mechanism of multibranched radial-drilling fracturing and provides guidance for optimizing radial borehole layout parameters of hydraulic fracturing directed by multiradial boreholes.

Controlled deep perforation by radial drilling of channels with the "Perfobur" technical system to intensify the reservoir inflow

The paper presents a technology for controlled deep penetrating perforation using the Perfobur technical system to intensify inflow by drilling radial channels 69 mm in diameter, up to 25 metres in length. This technology was first applied to a carbonate reservoir in the Bashkirian tier, characterised by high heterogeneity and close proximity of bedrock water. An adjacent well, close to the acid fracture well, with identical reservoir properties, was selected. Well "A" was acid fractured and well "B" was drilled using Perfobur technology with two directional channels, each 14 metres in length. In well "B", after drilling the channels, hydrochloric acid solution was injected through a special hydromonitor nozzle at two points. A total of 48 m3 of acid was injected into the "B" well. Comparing the results of well "B" with the well where the hydrofracturing was performed allow speaking about high efficiency of the controlled radial drilling technology. The ability to predict the channel trajectory, knowledge of its actual trajectory in combination with acid treatment of the reservoir using hydromonitor nozzle at a considerable distance from the reservoir allows achieving a significant increase in oil flow rate with lower water cut of the produced oil.

Reservoir Stimulation Technique Combines Radial Drilling Technology With Acid Jetting

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202661, “Combination of Radial Drilling Technology With Acid Jetting: New Approach in Carbonate Reservoir Stimulation,” by Ayrat Bashirov, Ilya Lyagov, and Ilya Galas, Perfobur, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed. The complete paper describes an approach to stimulate carbonate formations with bedding water or a gas cap. The technique is a combination of acid jetting and a radial drilling technology that uses mechanical radial drilling with a slim mud motor. The primary advantages of the technology include controlled trajectory and the possibility of re-entry into channels. The novelty of the technology is in its ability to deploy acids in the rock far away from the wellbore through the mechanically drilled holes with known depths and azimuths. Reservoir Description The mature field is in central Russia in the Republic of Bashkortostan. The field contains both sandstone and carbonate reservoirs. Oil depth is from 780 to 1830 m. Six reservoirs are in development. This study concentrates on projects in a carbonate formation that is a substage of the early Pennsylvanian Period. This formation is highly heterogeneous with closely underlying water. Permeability of the reservoir is approximately 43 md; reservoir pressure is 1,000 psi, and oil density is 0.891 g/cm3. Two adjacent well candidates with identical reservoir properties were selected for the study, with a distance between wells of approximately 136 m. Net oil thickness in Well A is 4.4 m and 3 m in Well B. Mechanical Radial Drilling Technology The technology described by the authors uses mechanical radial drilling with a slim mud motor. The technology allows the drilling of a network of radial channels up to 15 m long with up to four channels of different trajectories on one level. The technical system features a modular construction for ease of assembly at the wellhead area and increased operational efficiency. The main elements of the technical system include the following: - Pipe pusher connected at the top with an overflow valve module and, at the bottom, with a guiding device connected by means of a hydraulic pusher - Flexible pipe assembly with a small (nonstandard) sectional mud motor - Drilling bit (milling cutter for window cutting) - Special whipstock and an anchor module with an orienting funnel connected from below to the pipe frame

Application of Machine Learning Algorithms to Predict the Effectiveness of Radial Jet Drilling Technology in Various Geological Conditions

This study presents a methodological approach to forecasting the efficiency of radial drilling technology under various geological and physical conditions. The approach is based upon the integration of mathematical statistical methods and building machine learning models to forecast the liquid production rate increment, as well as to forecast technological indexes using a hydrodynamic model. This paper reviewed the global practice of radial drilling and well intervention efficiency modeling. The efficiency of the technology in question was analyzed on the oil deposits of the Perm Territory. Mathematical statistical methods were used to determine the geological and technological parameters of the efficient technology use. Based on the determined parameters, machine learning models were built, allowing us to forecast the oil and liquid production rate. A script was developed to integrate machine learning methods into a hydrodynamic simulator. When the method was tested, the deviations in the difference between the actual and the forecast cumulative oil production did not exceed 10%, which proves the reliability of the method. At the same time, the hydrodynamic model allows for taking into account the mutual influence of oil wells, the dynamics of water cut, and reservoir pressure.