TECTONIC FRACTURES IN TIGHT SANDSTONE RESERVOIRS OF THE UPPER CRETACEOUS QINGSHAOKOU FORMATION IN YAOYINGTAI AREA OF SOUTHERN SONGLIAO BASIN, CHINA

摘要

Fractures have an important influence on the development and capacity of Qingshankou Fm reservoir of Yaoyingtai oil field. With field outcrops, core observation, imaging logging etc., a systematic analysis of types, development characteristics, formation stages and influencing factors of fractures in this area was conducted by combining laboratory test. Most fractures developed in this area are tectonic and diagenetic ones, among which tectonic fractures, mainly consisting of high angle fractures with a dip angle of over 75 and vertical shearing fractures, are the primary fractures in the area with the features of small width (closed), large distance and small density. There are three formation stages of fractures in Qingshankou Fm reservoir of Yaoyingtai oil field, namely, diagenetic stage fractures, tectonic fractures and tectonic ones. The first one doesn't belong to tectonic fractures, for it's mostly filled with argillaccous or carbonaceous substances; the second one was formed in the tectonic movement of late deposit of Nen River Fm and it's mostly filled with calcites; the last one was formed in the structural inversion of late deposit of Mingshui Fm. Few fractures are filled with calcites with a bad overall filling degree. Factors such as rock property, stratum thickness and stratum structure determine the fracture development principally, Thin strata near the faults with dense lithology, fine grains and large content of rigid components are advantageous strata for fracture development.