An Experimental Investigation of Formation Damage Induced by PWRI in Unconsolidated Sands

Abstract

Formation damage is still a controversial subject within the industry especially when it takes place during Produced Water Re-Injection (PWRI). However, there is a consensus that formation damage results from a complex interaction between water quality, petro-physical and rock mechanical properties of the reservoir as well as the well architecture and completion. A lot of experimental work has been made in these last decades to understand and quantify the main mechanisms, parameters governing formation damage due to PWRI and the literature in this domain is plentiful. Nevertheless, a lot of questions are left unanswered particularly when it is a question of unconsolidated sands. This paper describes a core-flooding program performed with sand packs at different permeabilities, variable water qualities and injection conditions. Experiments were performed by injecting well-characterized system that contains either solid particles, mono-sized oil droplets or both of them at various sizes and proportions. It was shown that for mixture of solid and oil particles, the damage approach based on flow of solid suspensions alone doesn't apply and solid particles-oil droplets interaction is to be considered. This paper also details the role of each of the produced water components, their interaction and deposition within the core as well as the subsequent damage they induce. More generally, answer to some practical questions would be provided like: Do solid particles act by their size or concentration? Is oil in water content a key factor? How and where solids and oil deposit? Is there a critical concentration of solid particles and/or oil allowing injecting always in matrix regime and avoid fracturing unconsolidated reservoirs which often lie at shallow depths and in which fracturing can induce cap rock integrity and injection confinement issues? Would it be possible to control formation damage by controlling the injection conditions (flow rate, water salinity, etc…)? The answers provided here would give practical rules to help in adequately designing and optimizing PWRI projects.

Experimental investigation of plugging and fracturing mechanisms in unconsolidated sand reservoirs under injection of water containing suspended fine particles

“…To better understand the difference of the critical fracturing pressure, it is interesting to analyze the effect of the filter cake on the critical pressure required for fracturing. Similarly to our results, other works (Farajzadeh, 2004;Wong and Mettananda, 2010;Feia et al, 2015;Ochi and Oughanem, 2018) have shown that, during the plugging process, only the deposition of particles at the first layer (filter cake) affects the overall permeability decline of the specimen (equivalent to the increase of the inlet pressure measured at the entrance of the specimen) whereas the pressures measured at different positions within the specimen do not exhibit any significant change as illustrated in Fig. 22.…”

“…On the contrary, when plotting the results in terms of pressure versus injected volume, it is observed that a higher concentration results in a faster increase of the injection pressure, and consequently, a faster plugging rate. Similar results were also obtained by Ochi and Oughanem (2018). Following Feia et al (2015), this could be explained by the fact that, at a relatively low injection rate, when injecting at a lower particles concentration, the particles have time to settle on the sand grains with little reentrainment, thus less deposited particles are needed to plug the medium.…”

“…The re-injection in the matrix regime (i.e., the injection pressure is lower than the horizontal in-situ stress) of treated produced water through the injection well into reservoirs leads to the clogging of the medium and consequently, loss of injectivity, due to filtration of these impurities at the reservoir inlet (Sharma et al, 1997;Li and Wong, 2008;Feia et al, 2015). An experimental study conducted by Ochi and Oughanem (2018) showed that the level of plugging damage is mainly controlled by deposition of the suspended particles compared to that contributed by the deposition of oil droplets. Formation damage due to suspended particles has been extensively studied through experiments (Todd et al, 1990;Feia et al, 2015) and modeling approaches (van Oort et al, 1993;Shutong and Sharma, 1997;Zhou et al, 2018).…”