Transient Pressure Behavior of Volume Fracturing Horizontal Wells in Fractured Stress-Sensitive Tight Oil Reservoirs

Abstract

Tight oil reservoirs tend to contain more natural fractures, and the presence of natural fractures leads to a greater stress sensitivity in tight oil reservoirs. It is a very challenging task to model the seepage in the volume fracturing horizontal wells considering the stress-sensitive effects. Based on the Laplace transform, Perturbation transform and Stefest numerical inversion, this paper establishes a horizontal well seepage model for volume fracturing in fractured stress-sensitive tight oil reservoirs. This model allows us to analyze and study the effect of stress sensitivity, fracture interference, dual media and complex fracture network on seepage flow in tight oil reservoirs. We apply the model to delineate the seepage stages of volume fracturing horizontal wells, it can be divided into seven seepage stages I wellbore storage flow, II surface flow stage, III transition flow, IV natural fracture system proposed radial flow, V interporosity flow, VI system proposed radial flow and VII stress-sensitive flow stage. Wellbore storage coefficient mainly affects the flow in the wellbore storage stage. The larger the wellbore storage coefficient is, the longer the duration of wellbore storage flow will be. The higher the skin coefficient is, the greater the pressure drop is. The storage capacity ratio has a greater influence on the flow before the occurrence of channeling flow, and the “groove” depth on the derivative curve of dimensionless pressure drop becomes shallower with the increase in storage capacity ratio. The higher the channeling coefficient is, the earlier the channeling occurs from the matrix system to the natural fracture system and the more leftwing the “groove” position is.

A Volume Fracturing Percolation Model for Tight Reservoir Vertical Wells

“…Although scholars have conducted extensive research on the seepage law of volume fracturing, there is relatively little research on multistage volume fracturing in vertical wells [25][26][27][28]. Currently, most of the seepage models for tight oil reservoirs with volume fracturing in vertical wells are radial composite models, and the assumption that the reconstruction area is a cylinder does not match the results of on-site microseismic monitoring [29][30][31][32]. Therefore, the establishment of a seven-area seepage model for volume fracturing of tight oil reservoirs is of great significance.…”