Key seismic survey technologies for deep complex geological structures: A case study of the northern section of the Longmenshan Fault Fold Belt in the Sichuan Basin

Abstract

The northern Sichuan Basin, spreading in the northern section of the Longmenshan Fault Fold Belt, is characterized by dramatic fluctuations in the surface landforms, development of abdominal faults, and low-quality seismic data, resulting in difficulties in clarifying relevant structures. The key target formation, the Mid-Permian Qixia Fm, is deeply buried with thin reservoirs and high heterogeneity, which brings great challenges to seismic prediction. Under such circumstances, researches have been conducted jointly in terms of seismic data acquisition, processing and interpretation, and finally some relevant seismic survey technologies were developed suitable for surface/underground complex structures. Through surface structural surveys, dynamic deep-well lithologic identification, single-point detector deployment and process optimization, acquisition parameters can be excited. In addition, by using an observation system with high-coverage, wide-azimuth and huge-displacement, quality of acquired seismic data can be enhanced dramatically. Seismic imaging technologies for complex structures have been developed to enhance the quality of images for deep formations. These technologies are dominated by microscopic logging-constrained tomography static correction, high-resolution processing with fidelity and amplitude preservation and all-around PSDM in an angular domain. By using high-resolution gravity, magnetic and electric data, details related to geological structures and faults can be identified. In combination with fine seismic data interpretation, structural details and fault features can be verified effectively. Based on forward modeling and fine seismic calibration of reservoirs in individual wells, suitable attributes can be identified for predictions related to the distribution of reservoirs. By using all these auxiliary technologies, a large-scale structural–lithologic composite trap with a total area of 1223 km2 has been discovered in the NW Sichuan Basin. The Shuangyushi–Jiangyou area as a whole distributes on structural highs. In the areas to the south of Shuangyushi, the Qixia Fm dolomite reservoirs of platform margins are continuously developed. In conclusion, these auxiliary technologies can effectively allow trap identification and thin reservoir prediction in complex structures in the study area. In addition to clarifying the exploration orientation and providing a necessarily technical supports for well development, these technologies help to accelerate the construction of demonstration projects for the exploration and development of deep marine carbonate formations. Keywords: Sichuan Basin, Longmenshan Fault Fold Belt, Mid-Permian, Surface/underground complex structure, Thin reservoir formation, 3D seismic data acquisition, Seismic imaging, Reservoir prediction