Integrated analysis approach of water and solids for root cause of injectivity decline of water injection well – A case study

Abstract

Accurate sampling and analysis of injection and flow back water and solids are pivotal to identify the root causes of injectivity decline of water injection well. The present paper is focussed on case study of detailed characterization of injection and flowback water and solids using combination of techniques such as X-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy, inductively coupled plasma optical emission spectroscopy, ion chromatography and water isotope analyser in investigating the cause of injectivity decline. The present study emphasizes the effect of pressurized and non-pressurized water sampling on water analysis results, their scaling tendencies and correlation with compositions of solids encountered. Surface pressurized injection water sample pH result was found acidic with a higher dissolved iron and lower total suspended solids (TSS). Non-pressurized water samples showed comparatively higher pH due to release of CO2. Langelier saturation index (LSI) and ScaleSoftPitzer™ program SI of pressurized water sample showed lower scaling tendency than the non-pressurized water sample. Non-pressurized water samples contained significantly higher concentrations of TSS than the pressurized water sample indicated precipitation of salts in non-pressurized sample. Composition of TSS revealed presence of iron-based compounds, calcite and gypsum. Geochemical and water isotope analysis showed identical composition of injection and flowback water. XRD and XRF analysis of trapped solids revealed different forms of iron oxides and iron sulphides as major phase along with appreciable amount of calcite and quartz. XRF analysis also showed traces of Cr, Mo, and Ni in trapped solids indicated corrosion of tubing/pipes. Solid composition correlates with scaling tendency predicted by ScaleSoftPitzer™ program SI. Presence of iron in pressurized injection water and iron compounds in solids indicate iron-based scale/corrosion as key reason for reduction in injectivity of the well. Systematic sampling, accurate and integrated analysis of water and solids can help to find the dominant causes of injectivity decline and direct oilfield engineers at well site to take appropriate remedial and preventive action.