Abstract
Near-wellbore properties can be modified by invaded components of drilling muds or other technological fluids during drilling, completion, and workover operations. At different penetration depths, mud-component invasion creates multizone structures in the vicinity of the wellbore. These structures include external mudcake (mud solid components deposited at the sandface), internal mudcake (which is formed by mud components invaded into the reservoir formation), and mud-filtrate invaded zones. We suggest a model which is able to reproduce the dynamics of near-wellbore zone properties due to the invasion and removal of mud components. The model includes external mud cake buildup and lift-off processes, dynamics of internal mud cake, invasion of the mud filtrate. A new technique is suggested for estimating empirical parameters of both external and internal mudcakes by combining laboratory mud filtration experiments with core samples and a profile of invaded mud components reconstructed by X-ray microCT, image processing of a cleaved sample, and ultrasonic wave scanning.
Examples of reconstructed profiles of invaded mud components (solid particles and bentonite clay) as well as the procedure of determining internal mudcake parameters are discussed. A sensitivity study of the characteristics of mud invasion and early production stage is carried out to the properties of reservoir, external and internal mud cake and perforation length. The effects of fines migration and wettability alterations on dynamics of early production stage are simulated. It is shown that modification of properties of near-wellbore zone can significantly increase the final skin-factor and even kill the productivity of some formation layers that is especially applicable to the open-hole completion.
