Fine characterization and favorable area prediction of Changxing Formation reef-shoal reservoir in the central Sichuan Basin, China

Abstract

The Changxing Formation in the central Sichuan Basin developed on a central isolated gentle-slope platform, where multiple rows of high-energy reef-shoal bodies occur. In some local areas, dolomitized reservoirs are well developed, indicating significant exploration potential. However, strong reservoir heterogeneity and the pronounced characteristic of “one reef, one reservoir” have resulted in challenges such as unclear delineation of internal reservoir boundaries and ambiguous seismic response characteristics. Therefore, further refined delineation of reef-shoal body boundaries are required. Based on geological and logging data, the petrological and seismic response characteristics of reef-shoal reservoirs in the Changxing Formation were first clarified. Combined with the results of forward modeling, a seismic identification model for reef-shoal reservoirs was then established. Subsequently, by integrating paleogeomorphic restoration, seismic attribute analysis, and related techniques, a method for delineating internal boundaries—namely, the Three-Determination Method—was proposed. Finally, through the combined application of seismic inversion, seismic facies analysis, and related techniques, the vertical and lateral distribution characteristics of reef-shoal reservoirs were defined. The results indicate that, vertically, reef-shoal reservoirs in the study area are mainly developed in the Chang 1 Member and the middle-upper part of the Chang 2 Member, with thicknesses ranging from 10 to 60 m. Laterally, they are primarily distributed along the platform margin and at local paleogeomorphic highs within the platform, and the characteristic of “one reef, one reservoir” is evident. Reef-shoal bodies in the platform-margin zone, characterized by clear seismic response patterns and relatively large individual extents, still exhibit considerable exploration potential.