Three-dimensional structural models, evolutions and petroleum geological significances of transtensional faults in the Ziyang area, central Sichuan Basin, SW China

Abstract

With drilling and seismic data of Transtensional (strike-slip) Fault System in the Ziyang area of the central Sichuan Basin, SW China plane-section integrated structural interpretation, 3-D fault framework model building, fault throw analyzing, and balanced profile restoration, it is pointed out that the transtensional fault system in the Ziyang 3-D seismic survey consists of the northeast-trending F_I19 and F_I20 fault zones dominated by extensional deformation, as well as 3 sets of northwest-trending en echelon normal faults experienced dextral shear deformation. Among them, the F_I19 and F_I20 fault zones cut through the Neoproterozoic to Lower Triassic Jialingjiang Formation, presenting a 3-D structure of an “S”-shaped ribbon. And before Permian and during the Early Triassic, the F_I19 and F_I20 fault zones underwent at least two periods of structural superimposition. Besides, the 3 sets of northwest-trending en echelon normal faults are composed of small normal faults arranged in pairs, with opposite dip directions and partially left-stepped arrangement. And before Permian, they had formed almost, restricting the eastward growth and propagation of the F_I19 fault zone. The F_I19 and F_I20 fault zones communicate multiple sets of source rocks and reservoirs from deep to shallow, and the timing of fault activity matches well with oil and gas generation peaks. If there were favorable Cambrian–Triassic sedimentary facies and reservoirs developing on the local anticlinal belts of both sides of the F_I19 and F_I20 fault zones, the major reservoirs in this area are expected to achieve breakthroughs in oil and gas exploration.