Activity characteristics of Langshan Branch Fault in Jartai Structural Belt, Hetao Basin and its control on hydrocarbon accumulation

Abstract

Langshan Branch Fault is the dominant fault controlling Jartai Structural Belt in Hetao Basin and the hydrocarbon accumulation of many high-capacity oil-gas wells has close evolutional relationship with the formation of the fault. The geometric characteristics and motion characteristics of Langshan Branch Fault were analyzed based on 3D seismic data and well-drilling data. According to the changes in fault displacement, and occurrence of the fault, Langshan Branch Fault was divided into three sections: north section, middle section and south section. Based on reverse fault theory, the inversion types and stages of the fault were made clear. A model was established with the method of formation tendency. and the drilling well sound wave time-difference point-control correction method was adopted to calculate the original thickness of the stratum of the hanging wall and the footwall and recover the ancient fault displacement of the fault, 6 different calculation methods were summarized for three kinds of growth faults including the normal fault, the reverse fault and the negative inversion to quantify and calculate the activity rate of each fault section in different depositional stages. The quantitative evaluation of the activity characteristics of the faults at north section, middle section and south section was carried out. Based on the comparison of the balanced cross-sections and analysis of the activity rate, it was deemed that Langshan Branch Fault experienced four evolution stages. There were three "isolated" faults with different trends and strikes in the early stage of development. In the depositional stage of the Lisangou Formation in the Early Cretaceous, the sectionalized thrusting existed and the north section and the middle section of the fault were flexibly connected. In the depositional stage of Guyang Formation, all thrust faults in the sections were reversed into the normal faults. It was strongly extended from the Paleogene to the Neogene, and the northern section and the middle section of the fault were hard-connected as a whole fault. From Late Neogene to the Quaternary, the fault underwent the local strike-slip twist, and these three sections of the fault were formally linked into the present connected fault. The activity of this fault in different historical stages obviously controlled the development of the sedimentary system of both the hanging wall and the footwall, the formation and evolution of traps, and the migration and accumulation of oil and gas.

Keywords

• langshan branch fault
• geometry
• negative inversion
• fault activity rate
• sectionalized evolution
• hydrocarbon accumulation