Evaluation of Multilateral Wells Efficiency in the Fields of Vankorsky Cluster in Different Geological Environments

Summary The purpose of the work is to assess the efficiency of difficult wells having different geometries (sidetrack/multilateral wells) under similar subsurface conditions. The work includes the following: formation of principles for selecting analogues to evaluate efficiency; selecting well sections in reservoirs of continental and marine genesis, comparing porosity and permeability; comparing productivity factors of producing horizontal section at the start of operation; evaluating the oil production decline rate and growth in cumulative oil production; and presentation of promising trends of multilateral well technology development. In order to evaluate the multilateral well efficiency as compared to the other types of completion, principles of site selection are developed based on close position of wells and similar porosity and permeability, energy condition of reservoir and development settings. The following stages were included in evaluation of site efficiency: 1) selection of sites for comparison in accordance with similar porosity and permeability; 2) comparison of well completion technologies and energy conditions of reservoir in the area of sites; 3) estimation of productivity factor and oil rates at the start of well operation; 4) analysis of oil production decline rate and cumulative oil production. In accordance with well commissioning data, the trend of productivity factor growth from the producing horizontal section is observed for horizontal holes; at the same time, based upon the trend lines, there is a limit of productivity factor growth because of draining the same volume of reserves. For the areas with representative operational statistics, the sites were broken down in accordance with continental (2 sites) and marine (4 sites) genesis; 5 more sites in the Vankorsky field were assigned to a separate block because of the lower energy conditions in multilateral wells compared to sidetracks (reservoir pressure by 15% lower on average). As a result of the assessment, efficiency of multilateral wells with respect to sidetracks was proved; the average increment of cumulative oil production per well for 6 months amounted to 5 thousand tons compared to sidetracks (+14%), while the predicted effect for 20 years makes 63.2 thousand tons (+75%). The best results in multilateral wells are obtained in reservoirs of continental genesis having better reservoir quality.