EXPERIMENTAL EVALUATION OF WATER SENSITIVITY IN POROUS MEDIA USING COMPUTERIZED TOMOGRAPHY SCANNING METHOD

During the design of an oilfield development plan, reservoir sensitivity must be considered since it will be related to the damage of formation and the change of field output. Traditionally, reservoir sensitivity is evaluated in laboratory by monitoring the change of core permeability through different types of flow experiments. This method can only reflect the macroscopic phenomena, such as pressure and production changes. However, some detailed information cannot be recognized well, like the positions in the core where the formation damage occurred or the microscopic mechanisms involved in that. In this paper, a new method is introduced in characterization and microscopic analysis of water sensitivity by the aid of computerized tomography (CT) scanning technology. Three formation core samples drilled from the same layer were used for waterflooding, gasflooding, and "designing waterflooding" experiments. Significant water sensitivity was implied by comparing the waterflooding with gasflooding experiment results. A "designing waterflooding" experiment with two new variables, virtual porosity and relative porosity, is proposed to investigate the details of water sensitivity. It can be deduced from the experimental results that the formation damage occurred only near the inlet end where the average porosity decreased by 10% to 15%. Porosity reduction of large pore area was relatively higher than that of small pore area by comparing the initial porosity histogram with the final virtual porosity histogram. Microscopic understanding of water sensitivity can be explained that new materials were produced by the reaction between brine and clay minerals, which led to a larger scale of porosity reduction and CT number reduction.