Fine Evaluation of Coal Measure Gas in Huhehu Depression in Hailar Basin of China

The Huhehu Depression in the Hailar Basin represents an important target for coal measure gas exploration in the northeastern part of China. This paper systematically conducted fine evaluation of coal measure gas resources through integrated geological-geochemical analysis, reservoir micro-characterization, and volumetric method for grading resource volume calculation. The study shows that: (1) The Huhehu Depression has thick layers of hydrogen-rich coal rock in the second member of the Nantun Formation, which belongs to water-rich swamp deposits, characterized by high organic matter abundance and hydrogen index, with continuous planar distribution and coal-bearing throughout the depression. (2) Coalbed reservoirs mainly develop organic matter interparticle pores and organic-matrix pores, accompanied by macro-pores-fracture systems. These reservoirs demonstrate high porosity and strong heterogeneity. (3) The first member of the Damoguaihe Formation, which is above the second member of the Nantun Formation, has thick mudstone with wide distribution, good continuity, and excellent sealing performance. And the underlying mudstone of the first member of the Nantun Formation can form a local advantageous sealing unit, which has the conditions for the formation of medium to large-sized coal measure gas fields. This paper has finely evaluated the coal measure gas resource to be 1.5395 × 1012 m3 by the volume method, of which the second member of the Nantun Formation accounts for 94%. Meanwhile, the eastern trough zone and eastern steep slope zone are identified as favorable areas for coal measure gas exploration in the Huhehu Depression.