Using Thickness of Adsorption Water Film to Determine Lower Limits of Physical Parameters of Unconventional Gas Reservoir—Taking Turpan-Hami Basin as an Example
Using Thickness of Adsorption Water Film to Determine Lower Limits of Physical Parameters of Unconventional Gas Reservoir—Taking Turpan-Hami Basin as an Example
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DOI：
10.1166/jnn.2017.14495
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发表时间：
2017-09
影响因子：
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通讯作者：
Jijun Li;Weiming Wang;Shuangfang Lu;Xuan Chen;Tanguang Fan;Jie Li;Weichao Tian
中科院分区：
文献类型：
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作者：
Jijun Li;Weiming Wang;Shuangfang Lu;Xuan Chen;Tanguang Fan;Jie Li;Weichao Tian
Rapid advancement of exploration and production technologies for oil and gas has made the commercial development of unconventional oil and gas possible during the last decade. The lower limits of porosity for valid gas charge in one of the unconventional gas types—tight sandstone—have also been greatly reduced because of these technology advancements. Unlike conventional gas reservoirs whose lower limits of porosity do not necessarily mean the reservoirs reach the standards of commercial development, the lower limits of tight sandstone simply indicate the formations are qualified as recoverable with available technologies. Therefore, determination of lower limits is the key to assessment of tight gas formations. This article introduced a concept of water film to determine the lowest values of porosity a tight gas formation based on constant-rate mercury injection tests and analyses of low-temperature nitrogen absorption inside pore throats of nanometers in radius. The study shows that on the surface of tight sand particles, there are layers of strong bound water, weak bound water, and free water from center to the outside. The strong bound water and weak bound water are absorbed upon the surface of the sand particles and form a sheet of absorbed water film with a thickness of nanometers. The minimum throat radius for valid gas charge is equal to the thickness of water film under the same pressure and temperature. Based on force balance analysis, we established a relationship between water film thickness and throat radius, and then calculated the minimum throat radius for valid gas charge. When the throat radius is smaller than water film thickness, valid gas charge is not possible. Only when radius of pore throats is larger than the film thickness, can they can be valid gas charge pathways. Neglecting the gravitational force, the absorbed water film is balanced under three forces: the hydrostatic pressure, opposing separation pressure, and capillary pressure. Using the relationship of water film thickness with porosity, specific surface area, and bound water saturation, the value of minimum throat radius for valid gas charge can be converted to the minimum porosity of economically qualified formations. Finally, such lower limits determined using the water film thickness were verified to be in good agreement with the conventional gas-bearing determination method.
