The paper considers borehole wall stability in a junction zone of coaxial wells where a borehole of bigger diameter connects with a smaller one. To determine the shapes and character of rock destruction, 3D poroelastic modeling of the stressed state of the rock around the coaxial junction with account for mudcake formation was performed. The geomechanical model considers the anisotropy of the medium’s deformation properties that are characteristic for the coastal-marine reservoirs of Western Siberia. The rock failure is estimated based on the Mohr-Coulomb criterion with account for tensile destruction condition. The paper considers cases of vertical and inclined junctions of a well drilled at a depth of 2 km in sandstone productive pay with known poroelastic anisotropic properties. The stress and pore pressure analysis has been performed for a mud pressure drop range from 1 to 70 atm and coaxial junctions with different combinations of borehole diameters. The safe mud pressure window has been determined for vertical and inclined junctions. It has been found that the rock failure pattern for junction of bigger diameters is, in general, similar to that for smaller diameters with some insignificant differences in the destruction areas shapes. It has also been demonstrated that in vertical junctions, the bottom holes of smaller diameter are more stable to reduced drilling-mud pressure than the mainboreholes, while in the inclined junction it is the mainwellbore that is more stable to increased drilling-mud pressure than the bottom hole.

The paper describes the use of new generation of inflow chemical tracer application at Salym Petroleum Development Upper-Salym oilfield as a part of Smart Field project. This kind of well surveying using indicators that allow the evaluation of the inflow composition for each hydraulic fracturing port in horizontal wells remotely, without any additional risky and costly downhole activities. The new inflow chemical tracer technology is based on the use of nano-particle quantum dots, which give a level of high accuracy in quantitative analysis of fluid inflow. Markers, which are micromillimeter in size, are inserted into the polymer coating of the proppant. The technology involves the injection of marked polymer-coated proppant in the process of MHF (multi-stage hydraulic fracturing). Once the MHF is done, and the well is producing, the fluid samples are taken at surface and tested in a laboratory using machine learning software. Once the obtained data is interpreted, a flow profile of oil and water can be generated for each frac stage. One of the main advantages of marker technologies is that they provide data over a long period of time, with a significant reduction in operating cost. It opens the door for new opportunities in terms of more accurate reservoir characterization and better hydrocarbon recovery. The key element of the technology is the use of specialized intelligent machine-learning software based on Random Forest algorithm to produce production flow profile. The described methodology was used during the multi-stage hydraulic fracturing operation on oil wells 8105 and 8064 of Upper-Salym field. The volume of proppant injection at each stage was 20 tons, out of which 15 tons were of marked proppant containing a unique code for each stage. As soon as marked proppant has a contact with well fluid markers are emitted into fluid and sampling at the wellhead can be done any time when information required. The results of samples analysis are reports with graph showing quantitative distribution of water and oil production of each fracturing interval. The new generation of inflow markers allows for continuous production, surveillance and quantitative analysis of oil and water phase from each fracturing stage. This enables better decision making to optimize the production and make better decisions for water conformance interventions. This surveillance method does not require complex and risky well interventions or production shutdowns, making it substantially more cost effective than the existing conventional methods. Optimization of oil production, remote monitoring for risks minimization, reduction of operating costs - all these are the results of the introduction of Smart Fields technology systems in the Salym group of oilfields.

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