Characteristic Analysis of Tight Oil Reservoir Combined with Fracturing Fluid Damage Experiment - A Case from Chang-7 Formation in Ordos Basin

Abstract

Fracture is the main method of tight oil reservoir development. It transforms reservoir and brings on reservoir damage. Taking the Chang-7 formation in Ordos Basin as an Example, combined with physical properties, the casting thin sections, scanning electron microscope, X-ray diffraction (XRD), speed mercury penetration, CT and sensitivity test experiment analyse the characteristics of the tight oil reservoir and fracturing fluid damage relations. Chang-7 formation belongs to typical tight oil reservoir, filler content as high as 15%, easy to transport and expansion clay (illite and illite/smectite formation) is large; pores & throats are micro-nanometer level, the narrow and medium-sized reservoir throats occupy a larger proportion, pores connectivity are poor, throats are narrow. Chang-7 formation belongs to medium weak velocity sensitive (core permeability damage rate is between 0.33 to 0.48), strong water sensitivity (core permeability damage rate is between 0.14 to 0.28), easy water locked reservoir. Clay stabilizing agent, expansion agent and cleanup agent is added in the fracturing fluid formula, to reduce fracturing fluid damage; Fracturing fluid into the well critical salinity is higher than 10000 mg/L can prevent salt sensitivity damage; Fracturing fluid residue diameter between 2.25 to 8.39 μm. There are filter cake damage, sedimentary, adsorption jams and bridging in tight reservoir, with low damage fracturing fluid is the main way to reduce the residual damage.