Application of Effective Permeability Calculation Method Based on Time-Dependent Inversion of Resistivity While Drilling in Tight Formations in the East China Sea

The study explores a method to estimate effective permeability in tight formations of the East China Sea using time-dependent inversion of resistivity while drilling. Permeability is a critical parameter in reservoir management, influencing decisions on well completion and oilfield development. Traditional methods of obtaining permeability, such as formation testing, are costly and complex, often providing average permeability over small sample sizes that may not represent the entire reservoir accurately. This research leverages the dynamic data from multi-depth resistivity logging, which captures the invasion process of drilling fluid into the formation over time. By correlating these resistivity changes with permeability, the study proposes a time-shift resistivity inversion technique to construct dynamic profiles of the reservoir, of which the data processing flow has been shown in Figure 1. This method addresses inconsistencies that arise when calculating formation hydrocarbon saturation using resistivity data collected at different times, thereby providing a more reliable estimation of effective permeability. The proposed method involves a joint inversion of resistivity profiles obtained at various times during drilling. By incorporating parameters such as drilling fluid soak time, fluid viscosity, and changes in saturation and invasion depth, the method calculates relative permeability characteristics using Darcy's law. A least-squares fit is applied to these parameters to derive a functional relationship between saturation and relative permeability, allowing the construction of continuous effective permeability curves and permeability damage ratios. These curves are crucial for evaluating reservoir contamination and guiding formation testing and production forecasting. The study verified the feasibility and effectiveness of the method through field applications on a specific well in the East China Sea, comparing the estimated effective permeability with calibrated flow rates from formation tests. The results demonstrated that the calculated permeability was consistent with observed data, validating the dynamic approach and making it a valuable tool for reservoir evaluation, especially in complex and tight formations like those in the East China Sea. Overall, this method represents a significant leap from static to dynamic reservoir evaluation technology, contributing to energy conservation and efficiency enhancement in oil and gas exploration and development. By providing a more comprehensive understanding of reservoir permeability through dynamic resistivity measurements, this approach offers a cost-effective alternative to traditional methods, ultimately supporting better reservoir management.