Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (1): 28-40.doi: 10.11743/ogg20210103

• Petroleum Geology • Previous Articles     Next Articles

Evaluation of gas content in shale

Jinchuan Zhang1,2(), Shugen Liu3, Xiaoliang Wei1,2,4, Xuan Tang1,2, Yang Liu1,2   

  1. 1. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. Key Laboratory of Strategic Evaluation of Shale Gas Resources, Ministry of Natural Resources, Beijing 100083;China
    3. Xihua University, Chengdu, Sichuan 610039, China
    4. Research Institute of Exploration and Development of Shengli Oilfield Company, SINOPEC, Dongying, Shandong 257022, China
  • Received:2020-08-17 Online:2021-02-28 Published:2021-02-07

Abstract:

The evaluation of gas content as the core of shale gas resource assessment has drawn great attention.Gas accumulation and enrichment in shale is a dynamic geological process that results in a complex occurrence of gas: free gas coexisting with adsorbed gas and their shifting proportions.The accumulation mechanism of shale gas is quite different from that of coalbed methane.Shale gas of direct or indirect origins can have quite different forming conditions and gas-bearing characteristics.The vertical variation characteristics of gas-content-related indicator curves can provide more information on sedimentation, gas content and reservoir preservation.There are, in essence, six kinds of shale gas content evaluation methods, falling into three credibility gradients.The field desorption method, among others, is the major one.According to the method, the lost gas amount of a core sample is physically meaningful only when it is the result of a linear or polynomial regressions of the gas amount desorbed from the sample before restored to its original ambient temperature (formation temperature) during evaluation.The gas content in shale is controlled by the shale's gas generation capacity and gas content.The lost gas, desorbed gas and residual gas are internally related to adsorbed gas and free gas respectively.The adsorbed gas content and total gas content of shale are important evaluation parameters for shale gas content.The ratio of free/adsorbed gas content in shale is an ideal indicator of gas occurrence and recoverability.Assessment targets with both high total gas content and high free/adsorbed gas ratio can be considered as promising.It is recommended to combine these parameters in shale gas evaluation to obtain more accurate results.Machine Learning and big data analysis are also proven to be useful in improving data processing efficiency of shale gas evaluation, indicating intelligent evaluation being one of the important evolving directions of shale gas content evaluation.

Key words: Machine Learning, big data, intelligent evaluation, gas bearing structure, field desorption, evaluation method, gas content, shale

CLC Number: