In China the researchers successfully applied high precision computer models to evaluate geologically complex, but high-potential methane reserves in coal beds – one of the most important fossil materials in the key field of Zhengzhuang in Quinshui basin. Producing methane from coal beds becomes more and more of strategic importance for China – the country striving for assuring its energy security simultaneously complying with its environmental commitments.
Simulation was performed by the research teams from the Northern China Science and Technology University (NCST) and China University of Geosciences in Beijing (CUG) on the commission of Petro China Huabei Oilfield, the company producing mineral reserves in this region. The objective for the scientists was to evaluate the size and parameters of methane reserves in coal beds in layer No. 3 of Shanxi Permian formation — the main production target.
Detailed 3D geological model of the layer was created for this purpose, and the scientists integrated circa 100 km² of seismic data, information about 973 wells, archive data about producing gas and water at 27 wells between 2010 and 2017, as well as geophysical exploration data (electric, acoustic, rock density data, etc.). The resulting geological model allowed not only for reconstructing the inner structure of coal layers assessing the cleavage and coal lithotypes, but also for calculating the rock stress fields for accurate identification of the most fit for hydrofracturing zones.
The next stage was the numeric simulation of the production processes, when dewatering, gas release and water drain were modelled. This allowed for analyzing the dynamic behavior of the deposits and calculating the size of residual resources.
Based on the simulation results, the field area was divided into three categories of zones depending on the quality of the deposits: zones with the highest potential, mid-potential zones and zones with low feasibility. The overwhelming majority of the first category zones turned out to be concentrated in the South-Western part of Zhengzhuang block. The residual gas content in such zones reaches 33.5 m³ per ton of coal. To compare: the level above 20 m³/t is believed to be feasible for typical developments in China. The permeability of such zones, i.e., the ability of rock to give off gas, reaches 1 millidarcy (mD), and the porosity is from 8 to 12%. These values are a sign of high productivity at minimal stimulation costs.
The results of the efforts by Chinese scientists became a bright example of integration between digital geological models and engineering practice at mature fields with technical complexity. This vector may become an important element of the carbon transformation strategy both for China itself and for other countries facing depletion of their hydrocarbons reserves and striving for balancing their energy security and environmental commitments.
