Water Quality for Water Injection Wells

Abstract

A multidisciplinary study has been carried out so as to characterize the permeability impairment due to suspended particles during water injection. The approach is based on extensive laboratory experiments reproducing the complete range of parameters met in the industry. Experiments were carried out at both constant flowrate and constant pressure gradient. They reproduce static filtration conditions, i.e. without a flow component tangential to the rock face such as can occur when there are open fractures. The analysis of experimental results has confirmed that injectivity damage can be separated into two successive processes. Internal permeability damage close to the entry face switches to the build-up of an external filter cake after the injection of a critical volume. This is true even when particles are very small as compared to the size of the pore throats. Analytical equations have been developed for each mechanism, as well as for the critical cumulative injection when the external cake starts to form. These equations require at most two parameters. The extensive range of experimental conditions in our laboratory study enables us to propose correlations for the values of these parameters from basic data (velocity, concentration, particle size). Introduction Many oil fields, if not the majority, are produced using water injection which plays the two roles of sweeping oil towards the production wells, and maintaining pressure and therefore productivity at the production well. The quality of water to be injected has a major impact on the economics of waterflooding. Surface water treatment most often involves chlorination, filtering and deoxygenation. It is expensive both in capital costs, particularly topside when offshore, as well as increased operating expenditure. This leads to a strong economic incentive to reduce water quality to the minimum required. On the other hand inadequate water quality can result in dramatic formation damage, failure to meet the water injection target, and sooner or later loss of the oil revenues which were anticipated from waterflooding. Thus water quality is a compromise which needs to be optimized. Optimizing water quality requires a reliable prediction of formation damage as a function of cumulative water injection, for the different water qualities that can result from different treatment facilities, and in particular different filtration criteria. The purpose of this study is to propose simple analytical equations predicting formation damage due to the injection of solid particles, and this should help to optimize the design of water injection facilities. Review of previous models. Formation damage during water injection due to the presence of particles has been the subject of numerous publications, and the recent papers published by Van Velzen and Leerlooijer1, and Pang and Sharma2 present excellent reviews of previous approaches due to Barkman and Davidson3, Eylander4, Rege and Fogler5, as well as Todd et al.6. Van Velzen and Leeriooijer1 carried out a large number of laboratory experiments and interpreted the permeability damage observed in terms of the continuous growth of internal damage. A mathematical description of this process was proposed, making use of Darcy's law, the material balance for the solids in suspension and in the internal filter cake, and a modified Iwasaki7 relationship for deep-bed filtration.

Online Quality Measurements of Total Suspended Solids for Offshore Reinjection: A Review Study

“…To ensure the quality of the IW fulfills certain criteria for the specific formation, operators must have confidence in the data generated from the measurement equipment. Action mislead by inaccurate measurements can cause more harm than not taking any action at all [28,42,53]. The main IW quality characteristics are described in the following subsections: Oil Content (Section 3.1), Total Suspended Solids (Section 3.2), Total Dissolved Solids (Section 3.3), Dissolved Gases (Section 3.4), and Bacterial Growth (Section 3.5).…”

“…Sufficient water quality provokes economic incentives to reduce water quality to a required minimum. Conversely, inadequate water quality can result in dramatic formation damage [25,28]. OPEX is necessary to be addressed to establish an economic basis of the IW quality.…”

“…If changes in the water quality are preferred, it will thus affect the OPEX. The cost of maintaining the desired IW quality must therefore be balanced against the accumulated production income as a result of changes in the oil recovery rate [25,28].…”