Modelling of Both Near-Wellbore Damage and Natural Cleanup of Horizontal Wells Drilled With a Water-Based Mud

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPrediction of formation damage that occurs in horizontal wells, often open hole completed, is a critical point for optimising an oil field development. The economic impact of near wellbore induced drilling-damage and cleanup efficiency has led to make significant progress in both experimental and numerical studies in order to assess the wellbore flow properties during oil production.There is a fundamental difference between water-based and oil-based mud invasions. In an oil-bearing formation, the displacement of the oil in place with an oil-based mud (OBM) filtrate is a miscible displacement process, while the displacement with a water-based mud (WBM) filtrate is a twophase flow process (imbibition), generating high wetting phase saturations in the invaded zone. Then, during oil back flow, a portion of the wetting phase is trapped, leading to residual wetting phase saturations greater than the initial ones. Even in the absence of chemical interactions between filtrate and fluids in place, this induces an adverse water/oil relative permeability effect, which is an additional permeability impairment. In a previous paper, a methodology combining both experimental and numerical approach was presented to evaluate the natural cleanup of horizontal wells drilled with an oil-based mud (OBM). This paper presents an extension of the methodology for simulating both i) near wellbore invasion and permeability damage generated with a water-based mud (WBM), and ii) natural cleanup during oil back flow when the well is put under production. This paper describes a numerical approach to model the formation damage with WBM and predict well performance for natural clean up when the well is subject to a pressure drawdown. The kinetics of mud filtrate invasion, the filter cake properties and the filtrate/oil relative permeability curves in imbibition and drainage, together with damaged and return permeabilities are obtained from specific mud damage laboratory tests. Using these data, the mud filtrate invasion during the drilling phase is simulated, leading to a cone-type invasion depth along the horizontal well. This approach has allowed us to study the impact of various parameters related to fluids or cake properties, drilling conditions and natural cleanup process on the well performance.

Near-Wellbore Formation Damage Effects On Well Performance - A Comparison Between Underbalanced And Overbalanced Drilling

“…Wellbore radius is 0.108 m. Both UBD and OBD are considered in simulations under different drilling conditions: Case 1: OBD, the overbalanced pressure is 15 bars (drilling pressure at 335 bars) for a drilling period of 2 days. To simulate well productivity with OBD, it is necessary to put cake properties in the model 7 . Permeability reduction in the zone occupied by internal cake measured from laboratory are presented in Figure 1.…”

“…Modelling of well performance in OBD has already been presented 7,8 . Both internal and external cakes are considered in the model, and filtrate invasion is calculated using a two-phase flow equation.…”

Formation-Damage and Well-Productivity Simulation

“…Further improvement of the filter-cake model was presented by Dewan and Chenevert (2001), who demonstrated the derived model's capability to reproduce complex laboratory experiments with sequential changes in dynamic shear rate and overbalance pressure. Others also have investigated filtrate invasion by numerical simulations [e.g., Ding et al (2002), Wu et al (2004), and Suryanarayana et al (2007)]. …”

“…The properties from which the cake's porosity and permeability are computed are ascribed to the individual components. In Ding et al (2002) and Suryanarayana et al (2007), the damage in invaded zones is simulated on the basis of experimental return permeability and an assumed damage profile. We make no such assumptions but model the flow and retention of both particles and polymers inside the formation and compute the permeability reduction from the amount of trapped material.…”

High-Resolution Near-Wellbore Modeling and Its Applications in Formation Testing

“…Though attempts have been made to increase the resolution around the wellbore by using local grid refinement, no wellbore or tool factors have been rigorously considered. More recently, Ding et al 6 have developed and used a numerical simulator to study both near well formation damage and the natural cleanup of a horizontal well with water-based mud. Bøe et al 7 addressed the coupling issue of near-wellbore, high-precision simulation while accounting for global field behavior.…”