The Advances and Challenges of the Ediacaran Fractured Reservoir Development in the Central Sichuan Basin, China

Abstract

The largest Precambrian gasfield in China has been found in the central Sichuan Basin. It has been assumed as an Ediacaran (Sinian) mound–shoal, microfacies-controlled, dolomite reservoir. However, the extremely low porosity–permeability and heterogeneous reservoir cannot establish high production by conventional development technology in the deep subsurface. For this contribution, we carried out development tests on the fractured reservoir by seismic reservoir description and horizontal well drilling. New advances have been made in recent years: (1) the prestack time and depth migration processing provides better seismic data for strike-slip fault identification; (2) seismic planar strike-slip structures (e.g., en échelon/oblique faults) and lithofacies offset together with sectional vertical fault reflection and flower structure are favorable for strike–slip fault identification; (3) in addition to coherence, maximum likelihood and steerable pyramid attributes can be used to identify small strike-slip faults and for fault mapping; (4) fusion attributes of seismic illumination and structural tensor were used to find fractured reservoir along fault damage zone; (5) horizontal wells were carried out across the strike-slip fault damage zone and penetrated fractured reservoir with high production. Subsequently, a large strike-slip fault system has been found throughout the central intracratonic basin, and the “sweet spot” of the fractured reservoir along the strike-slip fault damage zone is widely developed to be a new favorable domain for high-production development. There is still a big challenge in seismic and horizontal well technology for the economical exploitation of the deep fractured reservoirs. This practice provides new insight in the deep tight matrix reservoir development.

An Overview of the Differential Carbonate Reservoir Characteristic and Exploitation Challenge in the Tarim Basin (NW China)

“…Unfortunately, there are still many tight carbonate reservoirs (porosity less than 8%, permeability less than 1 mD) in deep pre-Mesozoic carbonate rocks [6][7][8][9]. In this context, karstic and fractured reservoirs with a much higher secondary porosity in tight carbonates have attracted much attention in deep reservoir exploitation [10,11]. The geological characterization and seismic description of the secondary high porosity-permeability reservoirs have been used to optimize target and enhance oil/gas recovery in the deep tight carbonates [10][11][12][13][14][15].…”

“…In this context, karstic and fractured reservoirs with a much higher secondary porosity in tight carbonates have attracted much attention in deep reservoir exploitation [10,11]. The geological characterization and seismic description of the secondary high porosity-permeability reservoirs have been used to optimize target and enhance oil/gas recovery in the deep tight carbonates [10][11][12][13][14][15]. Whereas the secondary reservoirs of the ultra-deep pre-Mesozoic carbonates generally show varied reservoir features with strong heterogeneity, which resulted in a fundamental challenge in reservoir description of the deep reservoirs.…”

Seismic Description of Deep Strike-Slip Fault Damage Zone by Steerable Pyramid Method in the Sichuan Basin, China

“…The fracture network develops well along the fault damage zone and affects the fault zone's mechanical and petrophysical properties [1][2][3][4]. The fracture can greatly enhance the reservoir permeability and porosity and is of great importance in the deep (>4500 m) tight matrix reservoirs [5][6][7][8][9]. In the deep subsurface, seismic attributes (such as coherence, amplitude, variance, curvature, etc.)…”

“…play an important role in describing the fault damage zone and its fractured reservoirs [10][11][12][13][14][15][16]. Recently, seismic process methods, such as maximum likelihood, structural tensor, and illumination have been used to image the deep fault damage zone and fractured reservoirs [8,9,17]. These methods could describe the envelope of the fault damage zone and the intensely fractured reservoirs in the deep subsurface.…”

“…These methods could describe the envelope of the fault damage zone and the intensely fractured reservoirs in the deep subsurface. However, seismic characterization of the small fracture network is still a big challenge [8,9], which constrains the understanding of the "sweet spot" of the fractured reservoir and oil/gas exploitation in the deep subsurface.…”