Abstract

Techniques have been developed to investigate the impact of effective thickness on permeability interpretations by numerically modeling and simulating the pumpout flow pressure buildup dynamics obtained from a wireline formation testing (WFT) process. A high-resolution near-wellbore numerical model has been developed to simulate the WFT fluid sampling process together with transient pressures at a flowing probe. Subsequently, this newly developed model is validated analytically and then with the field data from the deepwater Gulf of Mexico, USA. Calculated pressure derivatives are used as a diagnosis tool to sensitize the impact of the effective thickness, which is defined as the maximum vertical thickness in the reservoir being sensed by the WFT device during a test within a given tool resolution. Subsequently, sensitivity analysis has been performed to examine the effect of permeability anisotropy, flow rate, gauge resolution, porosity, probe location, radial length of mud-filtrate invasion, and viscosity of mud filtrate on pressure transients and effective thickness of the tested formation. Pressure-transient measurements are found to be sensitive to permeability anisotropy, flow rate, porosity, radial extent of mud-filtrate invasion and mud- filtrate viscosity. In addition, effective thickness is found to be a strong function of permeability anisotropy, flow rate, porosity, gauge resolution, and probe location.

Introduction

Wireline formation testing (WFT) has gained increasing popularity in the oil and gas industry in the last two decades because of its economical and environmental benefits (Daungkaew et al., 2007; Elshahawi et al., 2008; Bertolini et al., 2009). In addition to fluid sampling, the WFT technique has been widely and successfully applied over decades to determine pressure gradient, fluid contact, and reservoir compartmentalization (Whittle et al., 2003). Recently, numerous attempts have been made to evaluate formation permeability and productivity by interpreting the pumpout transient data with the conventional pressure-transient analysis (PTA). Such an interpretation is based on the assumption of perforating the entire pay zone thickness, though it is suspected not to be the case in reality, especially in thick formations where a limited section can be sensed by a WFT probe (Al-Harbi et al., 2007). Therefore, it is of fundamental and practical importance to analyze and quantify the effective thickness to accurately interpret the WFT measurements.

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