PWRI-Induced Injectivity Decline: New Insights On In-Depth Particle Deposition Mechanisms

Abstract

Injectivity decline during PWRI originates not only from filter-cake build-up, but also from in-depth deposition of oil droplets or solid particles. Physical modelling of particle deposition mechanisms in porous media is thus of key interest for optimizing PWRI operations. The present work brings new insights on oil droplets and solid particle deposition mechanisms in porous media. The experimental conditions were selected such as the ratio between pores and particle sizes is sufficiently large to ensure in-depth propagation. The parameters are: the nature of the particles injected and a Peclet number calculated on the size of the collector grains (Peg), that encompasses in a non-dimensional form the impact of both flow rate and particle size. The results are analysed in the frame of the "colloidal approach". For oil droplets and solid particles, the deposition efficiency (h) shows a transition from a behaviour in which h varies as a power-law of Peg, with exponent values -2/3 (Diffusion Limited Deposition, DLD) to -1 (Reaction Limited Deposition, RLD), characteristic of convection-diffusion regime, to a behaviour characterized by an increase of h versus Peg, characteristic of hydrodynamic deposition regime. In the case of oil droplets (not or slightly charged), the transition occurs at a critical Peg value,, corresponding to a diffusion layer thickness around the collector grain equal to the droplets diameter. In the case of electro-sterically stabilized solid particles, the transition takes place at for small particles and at for larger particles. Introduction As the environmental regulations for water discharge are becoming more and more severe, the re-injection of produced water (PWRI) is now recognized as an important issue with respect to environmental protection and profitability. In many mature zones, PWRI is becoming economically attractive. It enables reducing processing costs of the produced water prior to disposal and allows handling the ever larger volumes of produced water without increasing environmental risks associated with water discharges. PWRI can also be used for waterflooding or pressure maintenance in the initial stage of production. Therefore, most of the produced water has to be re-injected either in a suitable formation for disposal or in the producing formation for IOR purposes. However, great uncertainties still remain about the consequences of PWRI and the actual injectivity behaviour. If injectivity decline is severe, sustainable injection rate for prolonged period will become impossible, jeopardizing the whole re-injection operation. It was recognized, from field observations that:with produced water, plugging is important and injectivity is lower than expected. The solids and oil do not behave separately;with matrix PWRI, a continuous loss of injectivity is obtained, even in high permeability formation (soft rock) [1];successful PWRI is likely to require fracturing [1–4]. Thus, injectivity performance is increasingly viewed as being dictated by a dynamic coupling between fracture growth and plugging of fracture faces. This general scheme raises additional challenges related to the issues of fracture containment, sweep efficiency and conformance, especially in soft rock formations. Simulation of produced water re-injection under fracturing conditions is therefore necessary to optimize the injectivity behavior and to establish a production water re-injection strategy [5–7]. However, up to now, development of models with reliable prediction ability suffers from the lack of a clear insight in the actual physics of the damage process. Understanding the damaging mechanisms when injecting water containing solid particles and oil droplets, and evaluating the impact of such damage on injector performance are thus important research needs.

The Colloidal Approach. A Promising Route for Asphaltene Deposition Modelling

“…This colloidal approach has been used successfully to model the deposition kinetics of different kind of colloid such as solid particles [16] and emulsion droplets [17]. This approach has been recently [15,18] experimentally validated through a systematic and thorough experimental investigation of the asphaltene deposition kinetics using different systems and under different experimental conditions.…”

A simulation investigation of performance of polymer injection in hydraulically fractured heterogeneous reservoirs

“…Injection under fracturing condition is a useful action that initiates polymer flood above formation parting pressure (FPP), which creates induced fractures contributing to injectivity increment. Calculations of injectivity for both below and above FFP were studied by Prasad Saripalli et al (1999) and Rousseau et al (2007).…”