Analysis of flow distribution in fractured-cavernous carbonate reservoir basing on tracer tests and isotope survey

Abstract

© 2019, International Multidisciplinary Scientific Geoconference. All rights reserved. The article describes the results of implementation tracer studies at one of the complex fractured-cavernous carbonate reservoir in the Republic of Tatarstan. Water injection in one well leaded to the water cut rise in one producer well then neighbor wells are insignificantly reacting on the pressure maintenance. On one hand low efficiency of water flooding in carbonates can be caused by hydrophobic properties of minerals like calcite and by heterogeneity of the void space including presence of fractures and caverns on another hand. As optimization of water injection process is needed in the object of study, the definition of actual distribution of filtration flows, reservoir properties and connectivities is of a great importance. In such conditions, the different tracer tests have shown an efficiency in terms of obtaining up-to-date information about reservoir under development. The solution of fluorescein indicator was injected into one well, followed by sampling in surrounding production wells. Then an analysis of indicator concentration in liquid produced by the wells in study area was performed. To detect fluorescent indicators in the wells, unique equipment was used allowing significant reduction of sample processing and detection time. The isotope survey results were added to the complex interpretation of tracer test. The data obtained includes the ratio of oxygen isotopes (O18/O16) and deuterium-to-hydrogen isotope ratio in water produced by the wells of study area. It was shown that the producer well with absence of tracer in liquid produced can be characterized by different isotope ratios and consequently produces water from another formation, than other wells. Thus, the velocities of fluid injected were obtained as well as different ways of flow propagation are identified. The reservoir is found to be complicated by presence of dislocated zones of high fracturing.