| Author's Name: WANG Ke, ZHANG Ronghu, LI Baogang, WANG Junpeng, SONG Binghui,
ZENG Qinglu, ZHANG Zhiyuan, HUANG Qingxuan |
| The characterization and geological modeling are of great significance to exploration and development of
fractured tight sandstone gas reservoir. Taking the Dabei-12 gas reservoir in Kuqa Depression of Tarim Basin as an
example, the types and occurrence, influence factors and formation sequence of structural fractures were characterized
based on core, rock thin section, imaging logging and other data. Then, the small scale and large scale fracture model of
the Dabei-12 gas reservoir were established by stochastic and deterministic fracture modeling method respectively, and a
total fracture model was established by superimposition of the two models. The results show that: (1) The Dabei-12 gas
reservoir, an anticlinal gas reservoir which formed under the background of NS tectonic compression due to the
Yanshanian movement and Himalayan movement, is located in the Bozi-Dabei area of Kelasu structural belt, Kuqa
Depression. The target layer of the Dabei-12 gas reservoir is the tight sandstone of Lower Cretaceous Bashijiqike
Formation. The macroscopic fractures in the Dabei-12 gas reservoir are mainly vertical or with high dip angle, and
shearing and tensile fractures are both developed to some extent. The microscopic fractures can also connect matrix pores
and therefore enhance the connectivity of reservoir. (2) Under the geological background of Dabei-12 gas reservoir, the
development extent of structural fractures is related to average thickness of single layer in condition of same lithology, and
distance to fault and lithology in condition of same or similar thickness of single layer. Taking fine sandstone in the
Dabei-12 gas reservoir as an example, the density of structural fractures in fine sandstone decreases with the increase of
thickness of single layer, and so does the decreasing amplitude. In condition of similar thickness of single layer, the
density of structural fractures shows good negative correlation with the distance to faults. As to different lithology in the
same condition, the fine sandstone has the highest density of structural fractures, the coarse sandstone and medium
sandstone take the second place, while siltstone and finer lithology have low density. (3) There are 3 periods of structural
fractures in the Dabei-12 gas reservoir, which are the Late Yanshanian period (Late Cretaceous-Paleogene), the Middle
Himalayan period (Neogene Kangcun period), and the Late Himalayan period (Neogene Kuqa period-Quaternary)
respectively. The second and third period fractures formed at the Middle and Late Himalayan periods are the critical factor
of efficient accumulation of natural gas. (4) The hinge of an anticlinal reservoir has structural fractures with low density
but high aperture and permeability, and therefore has always high production. The wings of a faulted-anticlinal reservoir
have structural fractures with high density but low aperture and permeability, and fracturing measures should be taken to
improve production. This study can provide data foundation for the establishment of fracture property equivalent model
and gas reservoir numerical simulation, and then serve for the development of gas reservoir. |
