Abstract
One of the key fundamental problems in using in jection wells to maintain the reservoir pressure for efficient roduction from oil and gas wells is the colmatation of the near-wellbore zone, which results in the permeability damage, and, hence, the decrease in the injectivity. In these cases one needs to increase the pumping pressure or introduce additional filtering systems on surface, which generally increases the cost of field development. For optimization of the flooding process, it is proposed to use a combined approach based on modeling of suspension filtration with account for colmatation of the near-wellbore zone and applying a cycling regime of injection.
A 1D three-continua model is proposed for suspension filtration to describe the permeability damage in the near-wellbore zone of injection wells in the fields of Western Siberia. Governing equations are derived using the multi-continua approach. The carrier phase, as well as the particles, which are being transported and deposited, are described as three distinct continua in terms of field variables. The application of the multi-continua approach allows one to reduce the number of free parameters of the model. The model takes into account the effects of sedimentation (trapping) of particles in the pores (colmatation), mobilization of particles at the velocities higher than a certain threshold value. The model has gone through a thorough validation campaign against significant amount of experimental data with contamination of porous samples by suspensions (core flooding experiments) and mobilization of pre-seeded particles in sand packs.
Experimental study of self-colmatation of cores produced from Vendian deposits in one of West Siberian oilfields during the injection of a particle-free fluid. It is found that at a fixed filtration rate, the permeability of rock cores decreases and levels off. An increase in filtration rate results in further decrease of the permeability. In order to reproduce the experimental data on self-colmatation, the three-continua model of filtration was modified to take into account two types of deposited particles: particles attached to pore walls, which are the source of migrating particles, and the particles plugging or bridging the pore throats, which reduce the permeability of the porous medium. The numerical simulations showed that the modified model allows to reproduce the self-colmatation of natural cores, the values of free parameters were found by tuning the model against theobtained experimental data.
We carried out the simulations of distributions of reduced permeablity, concentration of suspended particles and the concentration of trapped particles in pores in the nearwellbore zone at continuous and periodic water flooding. It is found that there are periodic regimes of water injection, in which the permeability of the rock is not damaged. The study will be continued after the generalization of suspension filtration model to describe colmatation of a rock both by external and internal fines as well as the calibration of the model against data of experiments carried out using on natural cores.
