Predicting Multiple Thermal Fractures in Horizontal Injection Wells; Coupling of a Wellbore and a Reservoir Simulator

Abstract

Abstract Injection well performance over the long term is often critically dependent upon how the well has been operated during its commissioning period. Whether the well is ultimately to be a seawater (or fresh water) injector or to be used for produced water re-injection, it may be beneficial to commission the well with a different water, probably at a different temperature, since this can have a marked effect upon the initiation of thermal fractures (more precisely these are usually in fact hydraulic fractures that have been initiated at reduced fracture gradients due to near wellbore reservoir cooling). In long horizontal injectors it is likely that several separate thermal fractures may be generated, and their creation needs to be controlled and managed to ensure optimum well performance. To generate a procedure for the well commissioning requires us to be able to predict bottom hole injection temperature, rate and pressure variation along the horizontal (or highly deviated) section and couple this into a reservoir fracture model. Achieving this using separate models soon becomes impractical, requiring too may iterations between coupled problems. This paper presents an overview of how an existing commercially available transient wellbore model has been coupled to a special purpose reservoir simulator, and how this has been applied to the modelling of multiple thermal fractures in horizontal injection wells. The paper also reports how the wellbore simulator has been modified to allow the prediction of depth dependent bottom hole temperatures. The paper will also comment on the application of this new coupled model to intervention work in production wells.