Study Investigates Formation Damage Induced by Water Reinjection in Unconsolidated Sands
Authors: Carpenter Chris 
Published: January 2019

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 189513, “An Experimental Investigation of Formation Damage Induced by Produced-Water Reinjection in Unconsolidated Sands,” by Jalel Ochi and Rezki Oughanem, Total, prepared for the 2018 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 7–9 February. The paper has not been peer reviewed.

In recent years, many studies have focused on investigating formation damage caused by produced-water reinjection (PWRI). Nevertheless, many questions about this subject remain unanswered, particularly with respect to the occurrence of this phenomenon in unconsolidated sands. This paper describes a coreflooding program performed with sandpacks at different permeabilities, water qualities, and injection conditions.

Introduction

The authors performed a complete experimental laboratory study using suspensions containing solid particles, mono-sized oil droplets, or both. Several coreflooding experiments using highly permeable sandpacks were performed over a long duration, during which significant volumes, sometimes reaching 100 L, have been injected. Also, permeability evolution has been monitored along three sections of each sandpack in order to better understand the dynamic of associated formation damage.

A schematic of the experimental setup used to carry out the coreflooding experiments is shown in Fig. 1. The suspensions containing solid particles or oil droplets were previously prepared in a 70-L reservoir tank. The tank is made from glass to facilitate suspension stirring and to prevent the aggregation of solid particles within it. The tank’s volume allows an injection over days and nights without interruption. The injection of suspension is ensured by a pump equipped with two low-diameter section pistons to ensure a proper injection of suspension without sedimentation of solid particles.

Experimental Results

Injection of Emulsions With Only Oil Droplets. In investigating the permeability decline generated by the injection of an emulsion with 100 mg/L of oil and 2-µm mean droplet size, the authors found that the formation damage generated by the deposition of oil droplets took place over the entire length of the sandpack. Also, results showed that oil deposition took place first at the entry section, followed by the second and third sections. The oil-deposition dynamic suggests the propagation as a front. Indeed, the oil droplets deposit along the first section until the permeability decline reaches a minimum. Once the permeability decline is stabilized within the first section, the same phenomenon is reproduced successively in the second and then third sections.

These results indicate that the permeability reduction of sandpacks depends on the droplet size rather than on oil concentration even if the kinetics of the permeability decline depend on the oil concentration. For the same mean droplet size of 2 µm, the permeability decreases more slowly for an emulsion of 50 than for 200 mg/L, for example. However, whatever the oil concentration, the final permeability decline stabilizes at the same level of approximately 74% of the virgin permeability (26% of permeability loss).