Standards Development

Scope

This document specifies the terms and definitions, principles and methods, apparatus and materials, sample requirements and preparation, testing, calculation of shale linear swelling ratio, precision, and requirements and procedures for reporting when the linear swelling ratio of shale in water-based fluids is determined using a dilatometer.

This document is applicable to the testing of rock samples delivered to the laboratory. The collection and preparation of rock samples are not covered by this document.

This document is applicable to the assessment of wellbore collapse, permeability impairment and other risks caused by shale swelling after interaction with downhole working fluids, as well as to the guidance of liquid system and formulation optimization.

Purpose

Shale gas is an important clean energy source, Countries such as China, the United States and Canada have already achieved large-scale, cost-effective shale-gas development. The combination of horizontal wells and volumetric fracturing is the core technology for shale gas development. After contact with external fluids (drilling or fracturing fluids), shale undergoes hydrationinduced swelling. This can cause wellbore instability during drilling, induce hydration-related cracking during stimulation, and reduce formation permeability during production. The determination of linear swelling ratio of shale provides the most direct means of quantifying hydration-induced swelling of shale. The results can be used to evaluate the impact of hydration on shale strength and permeability, predict stress from swelling-induced cracking, and optimize drilling and completion parameters as well as working liquid systems, thus ensuring efficient shale gas development.

Since 2000, with the large-scale and cost-effective development of shale gas in North America, the testing and evaluation of shale swelling has been gradually applied in shale gas development, including drilling fluid performance optimization, fracturing fluid system selection and fracture conductivity evaluation. In response to the characteristics of shale reservoirs, experts and scholars worldwide have conducted research on shale swelling testing technologies and have published a large number of research results. They unanimously recognize that laboratory determination of shale linear swelling ratio is the most effective method. The test results have been widely applied in shale gas blocks in China, the United States, Canada, Australia and Norway, facilitating the efficient development of shale gas. Globally, the determination of the shale linear swelling ratio is well established, supported by extensive expertise and broad market demand, forming a solid foundation for developing an international standard.

China has conducted extensive research on test methods for shale linear swelling ratio in recent years. A dilatometer method for determining liquid-absorption swelling of core plugs has been developed to address the long test cycle of real cores. This method has been validated through inter-laboratory comparisons involving enterprises and higher education institutions including CNPC, Sinopec, CNOOC, Shell, Southwest Petroleum University, and China University of Petroleum (Beijing). The results confirmed the method’s effectiveness and data accuracy. It has been issued as the Chinese industry standard NB/T 14022-2017, Water sensitivity evaluation of shale.

The researchers and enterprises holding the technology intend to share this technical solution with international peers to support the development of an international standard (IS). The method has been applied in more than 630 wells in key shale gas production areas in southern Sichuan and Chongqing Fuling (China) by June 2025. It supports working-fluid optimization, prevents wellbore instability, improves fracturing performance, and sustains stable shale gas production, achieving efficient shale gas development.

The shale gas resources of the United States, Canada, France, Saudi Arabia, the United Kingdom, Australia and other countries have the same needs, and relevant experts have shown great interest in this testing method. There is now a demand, a technical foundation and an expert base to form an international working group and to develop a globally unified International standard for the determination of the linear swelling ratio of shale. At present, the upstream natural gas sector lacks a unified International Standard for the experimental determination of the linear swelling ratio of shale. In international collaboration, this has led to significant differences in understanding shale swelling among shale gas production companies in different countries, which is not conducive to the joint preparation of shale gas development plans. A unified method for determining the shale linear swelling ratio would allow sharing and mutual recognition of experimental data, facilitate the implementation of international collaboration projects, and contribute to achieving the goal of efficient global shale gas development. Therefore, the above-mentioned experimental determination method of shale linear swelling ratio will be developed into the International Standard Natural gas upstream area — Determination of linear swelling ratio of shale under the action of fluid using dilatometer to establish a standardized test method, standardize experiment process and ensure the reliability and comparability of results. It will support oil and gas companies, drilling service providers, drilling fluid suppliers, research institutions, and other stakeholders in optimizing engineering decisions, reducing operational risks, and improving development efficiency.