Fractures in Tight Oil Reservoirs of the Early Jurassic Daanzhai Formation in Central Sichuan Basin, China

Wenya Lv
College of Geosciences, China University of Petroleum, Beijing, People’s Republic of China
[email protected]

The early Jurassic Daanzhai Formation in central Sichuan Basin, China, which develops shell-limestone, is a typical tight oil reservoir with an average porosity of 1%, and an average permeability less than 0.1mD.

As fractures are important reservoir space and major pathways of tight oil，this project is to study the types, controlling factors and development rules of fractures especially effective fractures of Daanzhai Formation. Based on 2136.0 m (7007.9 ft) of core from 36 wells, borehole image logs of 2 wells and outcrop studies of producing area, high-angle (60°-90°) tectonic fractures are the most abundant, while, oblique tectonic (30°-60°) fractures, low-angle (0°-30°) tectonic fractures and diagenetic fractures, such as near-horizontal bedding fractures and shell-boundary fractures, are also developed. There are four assemblages of tectonic fractures, namely, northeast-southwest, northwest-southeast, northnortheast-southsouthwest, and northwestwest-southeasteast in the tight oil reservoirs. Fracture development is influenced by brittle minerals, structure，thickness of layers and oriented shell arrangement .

As further study goes, this project will evaluate the contribution of fractures to the tight oil reservoir, make sure the time of fracture formation and predict the development rules of fractures especially effective fractures of Daanzhai Formation to make a better understanding of the accumulation and enrichment of tight oil and provide a geological basis for the exploration and development of tight oil reservoirs.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects