Formation-Damage and Well-Productivity Simulation

Abstract

In this paper, we describe a simulation model for computing the damage imposed on the formation during overbalanced drilling. The main parts modeled are filter-cake buildup under both static and dynamic conditions; fluid loss to the formation; transport of solids and polymers inside the formation, including effects of porelining retention and pore-throat plugging; and salinity effects on fines stability and clay swelling. The developed model can handle multicomponent water-based-mud systems at both the core scale (linear model) and the field scale (2D radial model). Among the computed results are fluid loss vs. time, internal damage distribution, and productivity calculations for both the entire well and individual sections.The simulation model works, in part, independently of fluidloss experiments (e.g., the model does not use fluid-leakoff coefficients but instead computes the filter-cake buildup and its flow resistance from properties ascribed to the individual components in the mud). Some of these properties can be measured directly, such as particle-size distribution of solids, effect of polymers on fluid viscosity, and formation permeability and porosity. Other properties, which must be determined by tuning the results of the numerical model against fluid-loss experiments, are still assumed to be rather case independent, and, once determined, they can be used in simulations at altered conditions as well as with different mud formulations. A detailed description of the filter-cake model is given in this paper.We present simulations of several static and dynamic fluidloss experiments. The particle-transport model is used to simulate a dilute particle-injection experiment taken from the literature. Finally, we demonstrate the model's applicability at the field scale and present computational results from an actual well drilled in the North Sea. These results are analyzed, and it is concluded that the potential effects of the mechanistic modeling approach used are (a) increased understanding of damage mechanisms, (b) improved design of experiments used in the selection process, and (c) better predictions at the well scale. This allows for a more-efficient and more-realistic prescreening of drilling fluids than traditional core-plug testing. September 2010 SPE Journal Simulation ModelThis section describes the various modules that constitute the newly developed simulation model. The two main parts of the Maximize program are (1) the filter-cake model handling filter-cake buildup and controlling flow into the formation and (2) the reservoir-flow model handling flow inside the formation. The fluids introduced to the formation contain a number of dissolved and dispersed components, which, in turn, may change the original flow properties of the formation through various chemical and physical processes. The retention of solids and polymer is split into a pore-throat-trapping model and a pore-lining-adsorption model. Brine interaction with the rock surface and clays is described by a multicomponent cation-exchange mod...

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