On the selection of suitable operate durations for injection tests in low permeability reservoirs

Abstract

The article discusses the aspects of conducting and analyzing the results of hydrodynamic studies of wells (well test) at steady-state injection modes conducted in injection wells in order to assess reservoir pressure and injectivity. The main goal of this work is to determine the necessary duration of injection modes at which reservoir pressure will be determined at the maximum research radius. In view of the considerable duration of the study, in low-permeability reservoirs, the work of the environment wells is taken into account, which, in the process of well research, should have a minimal impact on the results of data interpretation. To this end, we simulated the dynamics of pressure changes for this type of well test for various parameters of the reservoir and the duration of injection modes, taking into account the influence of the work of the surrounding production wells. To solve this problem, we used a numerical model of fluid filtration in an element of a nine-point development system in a low-permeable reservoir. The production and injection of fluid is carried out in wells with main technogenic fractures of hydraulic fracturing. During the simulation, the filtration parameters of the “fracture-formation” system and the duration of the well operating modes were varied, and synthetic data on the change in pressure in the wells were reproduced. Pressure and flow rates at the well operating modes were analyzed by plotting the indicator diagram (ID). Estimates of the extrapolated pressure from the ID graphs were compared with the pressures in the numerical model, in particular, the pressure on the supply circuit and on the study radius. It is shown that for low-permeability formations when studying injection wells using the steady-state injection method, it is necessary to take into account the research radius, which depends on the permeability of the formation and the duration of the injection regimes. Also, the research radius must be taken into account when constructing isobar maps along with the reservoir pressure value.