Research On Fracture Development And Brittleness Index Of Chang 8 Reservoir In Xiasiwan Area

The development of fractures has an important influence on the formation and enrichment of tight sandstone oil and gas.Predecessors have done more qualitative research on tight sandstone reservoir fractures,but less quantitative research,which leads to unclear understanding of their development and distribution rules.This paper takes the tight sandstone reservoir of the Chang 8 member of Yanchang Formation in Xiasiwan area of Yanchang Oilfield as an example to carry out research on the characteristics of fracture development,quantitative interpretation of fracture logging,main controlling factors of fracture development and its control on oil and gas,etc.It is expected to provide guidance for the development of tight sandstone oil and gas in the Ordos Basin.Using outcrop observation,logging and core data,qualitatively and quantitatively explain the fracture development of Chang 8 reservoir in this area,and calculate the brittleness index of Chang 8 reservoir in this area to discuss its fracture,brittleness index and oil and gas productivity Summarize the main controlling factors of fracture development in Chang 8 reservoir in this area.The study concluded that:(1)The fracture development of Chang8 reservoir in Xiasiwan area is controlled by many factors,mainly including tectonic movement,basement fault,lithology and strata thickness.The tectonic fractures at the high part and the two wings of the local structures during the period of fracture formation are more developed.Lithology and thickness have obvious control effect on fracture development density,the larger the strata thickness and the stronger the rock power,the smaller the fracture development density,but the larger the scale.The NEE and EW direction basement fault as well as the extrusion movement direction of indo-china and Yanshanian structures have control effect on the distribution and tectonic style of fractures.(2)Based on the existing conventional logging data,a study on the brittleness index distribution of Chang8 strata was carried out.It is concluded that the brittleness index is closely related to the sandstone content with a positive correlation trend,that is,when the sandstone content is high,the brittleness index is large,vice versa,and the plane distribution features are also consistent with the main course of the river.(3)It is considered that there is a certain correlation between brittleness index and productivity,that is,when brittleness index increases,the daily liquid output increases to a certain extent.The correlation between fracture development degree and productivity is not strong.In the range of daily liquid output at 0-5m3 per day,with the increase of fracture porosity,the productivity increases.