Dynamic Modeling of Invasion Damage and Impact on Production in Horizontal Wells

Abstract

Abstract We present a novel approach that combines dynamic reservoir simulations and special core tests to model the extent of invasive damage and its impact on flow-back during production. A radially adaptive 3D "micro" simulator is used to estimate the extent and impact of filtrate invasion on near-wellbore saturation and reservoir pressure.The lateral extent of the model is limited only to the invasive zone, and time-varying reservoir exposure is used to simulate the acts of drilling, tripping, completions and workovers. Extremely fine, core-scale grids are used to capture saturation and pressure in the invasion zone. Special core tests using a specially-designed core holder are conducted on the subject reservoir core.Test results are interpreted to obtain an estimate of end-point relative permeabilities at irreducible saturation, dynamic mud cake effect on filtrate loss, and impact of solids invasion on return permeability. Both overbalanced and underbalanced tests are conducted with different drilling fluids. The tests are used to describe the mud cake effect in the invasion model. The saturation and pressure profiles from this model are then used as initial conditions in a sector-scale simulator with near-wellbore fine-gridding to model flow-back effects.Absolute permeability damage is modeled using the core test results as an incremental and hyperbolically recovering effect during flow-back simulations. A near-wellbore fine grid overlay is used to capture the near wellbore effects from the micro-simulator results. Several sensitivities, including initial reservoir pressure, degree of overbalance (during drilling) and drawdown (during production), heterogeneity, anisotropy, and mud cake effect are examined.Equivalent skin factors that vary with time and depth are developed to enable comparison with full-field simulations. A horizontal well example is used to illustrate the results of the study. Results illustrate stark and often under-appreciated effects of invasive damage on flow-back and therefore on production performance. The methods described in this work can be used in reservoir-specific studies to model formation damage and aid in the selection of mud types, drilling techniques and remediation methods required to improve performance. It is hoped that this work bridges the typically empirical damage characterization methods with dynamic reservoir simulations.