Phenomenological Model of Nonlinear Dynamics and Deterministic Chaotic Gas Migration in Bentonite: Experimental Evidence and Diagnostic Parameters

Understanding gas migration in compacted clay materials, e.g., bentonite and claystone, is important for the design and performance assessment of an engineered barrier system of a radioactive waste repository system, as well as many practical applications. Existing field and laboratory data on gas migration processes in low-permeability clay materials demonstrate the complexity of flow and transport processes, including various types of instabilities, caused by nonlinear dynamics of coupled processes of liquid–gas exchange, dilation, fracturing, fracture healing, etc., which cannot be described by classical models of fluid dynamics in porous media. We here show that the complexity of gas migration processes can be explained using a phenomenological concept of nonlinear dynamics and deterministic chaos theory. To do so, we analyzed gas pressure and gas influx (i.e., input) and outflux (i.e., output), recorded during the gas injection experiment in the compact Mx80-D bentonite sample, and calculated a set of the diagnostic parameters of nonlinear dynamics and chaos, such a global embedding dimension, a correlation dimension, an information dimension, and a spectrum of Lyapunov exponents, as well as plotted 2D and 3D pseudo-phase-space strange attractors, based on the univariate influx and outflux time series data. These results indicate the presence of phenomena of low-dimensional deterministic chaotic behavior of gas migration in bentonite. In particular, during the onset of gas influx in the bentonite core, before the breakthrough, the development of gas flow pathways is characterized by the process of chaotic gas diffusion. After the breakthrough, with inlet-to-outlet movement of gas, the prevailing process is chaotic advection. During the final phase of the experiment, with no influx to the sample, the relaxation pattern of gas outflux is resumed back to a process of chaotic diffusion. The types of data analysis and a proposed phenomenological model can be used to establish the basic principles of experimental data-gathering, modeling predictions, and a research design.

A gas migration law study of a large-scale 3D physical similarity simulation with an adaptive Kalman filter algorithm

Purpose In this study, a physical similarity simulation plays a significant role in the study of crack evolution and the gas migration mechanism. A sensor is deployed inside a comparable artificial rock formation to assure the accuracy of the experiment results. During the building of the simulated rock formation, a huge volume of acidic gas is released, causing numerous sensor measurement mistakes. Additionally, the gas concentration estimation approach is subject to uncertainty because of the complex rock formation environment. As a result, the purpose of this study is to introduce an adaptive Kalman filter approach to reduce observation noise, increase the accuracy of the gas concentration estimation model and, finally, determine the gas migration law. Design/methodology/approach First, based on the process of gas floatation-diffusion and seepage, the gas migration model is established according to Fick’s second law, and a simplified modeling method using diffusion flux instead of gas concentration is presented. Second, an adaptive Kalman filter algorithm is introduced to establish a gas concentration estimation model, taking into account the model uncertainty and the unknown measurement noise. Finally, according to a large-scale physical similarity simulation platform, a thorough experiment about gas migration is carried out to extract gas concentration variation data with certain ventilation techniques and to create a gas chart of the time-changing trend. Findings This approach is used to determine the changing process of gas distribution for a certain ventilation mode. The results match the rock fissure distribution condition derived from the microseismic monitoring data, proving the effectiveness of the approach. Originality/value For the first time in large-scale three-dimensional physical similarity simulations, the adaptive Kalman filter data processing method based on the inverse Wishart probability density function is used to solve the problem of an inaccurate process and measurement noise, laying the groundwork for studying the gas migration law and determining the gas migration mechanism.

Deep Penetration Resin Systems Overcome Annular Gas Migration: Case History

Well Integrity is a critical compliance requirement during oil and gas operations. Abandonment procedures must ensure that all hydrocarbon sources are properly isolated and effective barriers are placed. This paper describes the use of resin systems to isolate annular gas migration identified during the Obiwan – 1 well abandonment in Colombia. The main challenge was to select and design fluid systems capable to fill tight spaces and isolate the annular channel. Resin systems are high-strength, elastic polymers which act as dependable barriers to isolate fluid flow. They can be designed as a solid-free, pure liquid or may contain solids (cement with a formulated percent of resin). Solid-free formulations are ideal for remedial operations, such as isolating annular gas. Acoustic logging enabled identification of the influx zones. Annular isolation was achieved by executing two cementing remedial operations using the bradenhead squeeze technique. A tailored resin system was selected to deliver the proper barrier addressing the influx zones after injectivity tests were performed in each interval. For the first intervention a solids-free resin system was used, and for the second one a resin-cement composite system was applied. During cementing remedial operations, it was determined that the resin systems were able to achieve deep penetration into the channels more readily and form a seal. The correct system was selected for each case, and during execution, the required volume was injected to intersect and properly isolate the annular gas channel. As a result, the tailored resin systems isolated the gas channel eliminating annular pressure and gas migration to surface. In addition, a post remedial operation acoustic log indicated that the influx zones were successfully isolated. Well abandonment was accomplished according to country regulatory requirements and delivered dependable barriers both annular and interior pipe sections. Use of resin to repair channels of this type exhibited a higher success rate and improved reliability in comparison to conventional particulate-laden fluids, which helps to decrease costs for additional remedial treatments.