Drill-in fluids are generally water-based muds containing a viscosifier, a fluid loss reducer, salts and sized calcium carbonate particles. Formation damage mechanisms induced by the use of water based mud formulations (WBM) have been extensively studied and correspond to different phenomena such as water trapping, polymer adsorption and retention, and particle plugging. In this paper, a detailed study was carried out on the behaviour of scleroglucan based formulations generally proposed for high temperature zone and/or high permeability reservoirs. In addition, a classical xanthan based mud was prepared and the performances of xanthan and scleroglucan containing formulations were compared. This work covers not only the effect of the fluid composition, including the presence or not of drilled solids but also the filtration conditions such as shear rate and temperature. Filtration curves obtained under static conditions can be related to the rheological behaviour and thermal stability of the biopolymer used as a viscosifier. These curves are not related to the solid content of the mud. Under dynamic conditions, the filtration curve strongly depends on the aggregation tendency of the scleroglucan sample.

Mud filtrates have been characterized by multi angle laser light scattering coupled with size exclusion chromatography (SEC/MALLS). Characterization of the composition of the filtrate as well as the determination of the polymer molecular weight distribution, is very important to understand the formation damage tests performed on high permeability cores under downhole saturation conditions. Also, both the cake permeability and structure obtained by cryo SEM helped to understand the damage mechanisms observed with such formulations.

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