Water Occurrence Characteristics of Gas Shale Based on 2D NMR Technology

Abstract

Determination of water occurrence in gas shale reservoirs is vital for understanding the gas storage and migration behavior. Clay, kerogen, and shale samples with different water contents were analyzed based on the 2D NMR technology to decipher the characteristic of water occurrence in different shale compositions. By establishing a new classification method of water in shale, the water absorption characteristics of shale during hydraulic fracturing and the law of water mobilization in shale reservoirs during development are quantitatively analyzed. The results suggest that the water in shale can be classified as mobile water and immobile water, with the boundary T1 = 0.1 ms. The mobile water can be further divided into clay bound water, capillary bound water, and free water by the T1–T2 map. Most of the water in shale is clay bound water, which is also the most important object in the study of fracturing fluid retention. The influence of free water and clay bound water on the gas–water two-phase flow of shale is greater. Accurate analysis of different types of water in shale can clarify their different effects on methane occurrence and migration. This study overcomes the shortcomings of inaccurate quantitative analysis of water in shale by traditional methods and provides help for the analysis of fracturing fluid retention law and the development effect of gas wells.