Identifying Formation Mineralogy Composition in Acid Fracturing From Distributed Temperature Measurements

Abstract

Summary The successful stimulation of carbonate formations by acid-fracturing operations depends on the ability to treat the entire pay zone. The acid dissolves carbonate rocks and creates conductive channels through which the reservoir's fluids flow. Heterogeneity in lithology causes acid to create a preferential path in the most-reactive zones. Temperature measurements by temperature logging or distributed temperature sensing (DTS) are commonly used to evaluate injection and production zones. The present research includes a modeling study from which the mineralogy in multilayer fractured formations can be identified by means of temperature measurements. Heat transfer is commonly coupled in acid-fracturing models to account for temperature effects on acid reactivity with carbonate minerals. Temperature profiles are usually evaluated during simulations of fracturing fluid injection, but seldom during fracture closure. Because most of the acid is spent during injection, many models assume that the remaining acid reacts proportionally along the fracture length. Because of this assumption, neither acid spending nor temperature is usually simulated during fracture closure. In this study, a fully integrated temperature model is developed in which both acid reaction and heat transfer are simulated while the fracture is closing. At each timestep, transient heat convection, conduction, and generation are calculated along the wellbore, reservoir, and fracture dimensions. Modeling temperature during this transient period provides a significant understanding of the near-wellbore fracture dissolution. During shut-in, cold fracturing fluids are heated mainly because of the heat flow from the formation to the fracture. Reactive reservoir sections that receive larger volumes of the cold treatment fluids usually require more time for the geothermal temperature to be restored. Because of this phenomenon, minerals distribution along the wellbore axial direction can be identified in acid fracturing. This information can be useful when designing acid-fracturing jobs in nearby wells or revisiting the same wellbore for further stimulation.