Abstract:

Aiming at the poor understanding of structural styles and internal architectures of Mesozoic tight clastic fault-fracture bodies as well as ambiguous main controlling factors for high-yield hydrocarbon enrichment in the southern margin of Ordos basin, this paper conducts a detailed geological dissection of fault-fracture body reservoirs in major fault zones of the study area based on abundant core, field outcrop, laboratory testing, well-logging, seismic and production performance data. The geological definition and classification of fault-fracture bodies are clarified, the internal reservoir architecture model is established, and the main controlling factors for hydrocarbon enrichment are analyzed. The research shows that: 1) The fault-fracture body is a complex reservoir body composed of strike-slip faults, associated brittle fracture zones and fractured tight sandstone zones. It is characterized by widely developed medium-high-angle fractures with favorable porosity and permeability, serving as favorable sites for hydrocarbon accumulation. 2) Considering the differences in stress background for formation and structural styles, the fault-fracture bodies in the study area are divided into three types and five sub-types, among which the discrete type and translational type are dominant and relatively favorable for hydrocarbon accumulation. 3) Fault-fracture bodies develop multiple reservoir spaces, including fractures, broken cavities and dissolution pores. Tectono-diagenesis acts as the major reservoir-controlling mechanism. An identification criterion for internal structural units of fault-fracture bodies is established. 4) Fault properties, reservoir scale and local structures are the primary geological factors controlling hydrocarbon enrichment of fault-fracture bodies in the study area. Furthermore, combined geological conditions with production capacity data, a classified and graded evaluation of fault-fracture bodies is carried out to optimize favorable development targets.

Key words: fault-fracture body, strike-slip fault, geological model, enrichment pattern, Ordos basin