Modeling of Filtration Investigations Under Unstable Conditions of Injection of Water Into Hyperlow-Permeability Samples

Abstract

We report the results of modeling laboratory experiments for unstable fi ltration conditions. It has been shown that the form of pressure curves is infl uenced by the spurious volume coeffi cient, the length of the core sample, and the collectorpermeability. We have diagnosed by the log-log curves of the pressure and its logarithmic derivative the liquid fl ow conditions for early and later times of the nonstationary fi ltration experiment infl uencing the possibility of estimating the collector permeability. conditions already at distances of about 30 m from the well into the depth of the productive oil fi eld. In (2), the results are presented of the numerical simulation and estimation of the infl uence of a decrease in the effective permeability of the collector at nonlinear fi ltration in low-permeability fl ooded oil fi elds on the remnant oil stock distribution and the oil extraction factor. In the present paper, we have explored the possibility of determining the effective permeability as part of fi ltration investigations under unstable fi ltration conditions. The theory and approaches for working with data on the pressure change were developed and described well by many authors within the framework ofhydrodynamical investigations of wells (HDIW) under unstable fi ltration conditions (3-6). In the present work, these approaches for HDIW were also used to describe laboratory experiments performed under unstable fi ltration conditions. Important points in laboratory fi ltration works are designing of experiments, prevention of possible problems in interpreting obtained data, the infl uence of model parameters on the duration of the investigation and the necessary accuracy of the measuring equipment, and diagnostics of liquid fl ow conditions and boundary effects at early and later times by analyzing the pressure curves and the Bourdet logarithmic derivative (7). In the present paper, we propose a mathematical model that can be used for planning laboratory investigations of core samples under unstable fi ltration conditions and interpreting results. The model takes into account the infl uence of the spurious volume and the change in the collector properties in the skin zone and in the boundary effects of the core sample. 1. Infl uence of the Spurious Volume on the Flow Rate of the Injected Liquid. Thespurious volume is largely determined by the internal volume of metal pipes in the facility for liquid injection located before the inlet to the investigated sample model. In the initial period of the injection/termination processes, due to the infl uence of compression/expansion