In-Situ Determination of Displacement Efficiency and Oil and Water Relative Permeability Curves through Integrated Well Test Study at Exploration-to-Pilot Stage of the Oilfield Development Project

摘要

Relative permeabilities are very important for reservoir engineering, because these parameters highly influence waterflooding efficiency, oil/liquid production forecast and therefore economics of an asset. Evaluation of multiphase flow parameters from core data suffers from small REV and pointwise level of averaging. It distorts the actual flow conditions at the reservoir level, and their history matching from production data requires long history of waterflooding. The technological complexity of new oil reservoirs development rises the problem of determining the displacement effeciency (Edisp) and relative permeability functions (RP) in the downhole conditions for reliable evaluation of investment attractiveness of the asset and creating sound development of the project. This paper summarizes the experience and interpretation of two-phase well testing using OGRI RAS technology. Integrated well testing to determine Edisp and RP (for oil-water system) is based on the creation of two-phase (oil and water) multidirectional flows and repeatable recordings of pulsed neutron logging (PNL) to monitor changes in water saturation near wellbore. For reliable geophysical interpretation it is necessary to monitor changes in the water phase salinity in contact with formation water, injectied water and technological solutions. Integrated interpretation of such testing procedure is based on the numerical solution of direct and inverse problems in the two-dimensional, two-phase (oil-water), two (oil + water) or three (oil + water + salt) component statement. The experience of conducting and interpreting such tests for oil fields at the exploration stage and pilot projects in conditions of autonomy and arctic climate is delivered in the paper. Accumulated experience allowed us to justify the optimal design of the testing process, well preparation and the well testing procedure itself. Special schemes of downhole and wellhead equipment setup are devised for solving all the research problems without lifting operations. Original technical solutions for well completion and continuous pumping of water-based agent in arctic climate, with large permafrost interval and very low formation injectivity were also developed. Complex technique of joint geophysical and flow measurements interpretation in the course of well testing is substantiated. The effective numerical algorithms and software for solving inverse problems to identify oil and water RP at reservoir conditions in two-dimensional, two-phase (oil-water), two (oil + water) or three (oil + water + salt) component model were also proposed and validated. Significant effect of technological fluids penetration into the formation during well completion and tripping on reservoir water salinity in the near wellbore area is revealed, Simplified method of accounting for and controlling salinity changes during interaction between reservoir, injected and residual technological water phases is proposed. For the object tested, effective estimates of displacement efficiency and RP curves are obtained. These parameters substantially correct core data and provide more reliable prediction of water flooding system efficiency and assessment of the investment attractiveness of the asset.