Abstract
Hydraulic fracturing technology has become a key technology for the development of low-permeability/tight oil and gas reservoirs. The evaluation on the postfracturing effect is imperative to the formulation and implementation of the fracturing and development plan. Based on the characteristics of the flow in fracture network after a large-scale hydraulic fracturing, a numerical method for evaluating the effect of fracturing in vertical well was established. This study conducts postfracturing effect evaluations to block C Oilfield’s wells that underwent conventional fracturing and volumetric fracturing, respectively, proposes the definition of fracture network conductivity and its relationship with cumulative production, and analyzes the fracturing construction parameters. The results suggest that the conventional fracturing can only form a single fracture instead of a stimulated reservoir volume (SRV) region. However, the volumetric fracturing transformation can form a complex fracture network system and SRV region and meanwhile bring obvious increase in the production. The effective time lasts for a longer period, and the increase of average daily oil is 2.2 times more than that of conventional fracturing. Additionally, with the progress of the production, the SRV area within the core region of the volume transformation gradually decreased from 6664.84 m2 to 4414.45 m2; the SRV area of the outer region decreased from 7913.5 m2 to 5391.3 m2. As the progress develops, the equivalent permeability and the area of the fracture gradually decrease as the fracturing effect gradually weakens, and so does the conductivity of the network decreasing exponentially; a good correlation is observed between the conductivity of the fracture network, the cumulative production, and fracturing construction parameters, which can serve as the evaluation parameters for the fracturing effects and the basis for fracturing productivity prediction and provide a guidance for fracturing optimization design.
Highlights
As the technology of unconventional resource exploration and development advances, tight reservoirs and their production contribution have increased year by year and become a substantial part in China’s current and future crude oil reserves [1,2,3]
The development of tight reservoirs has become the key role in the progress of enhancing national energy source security and realizing energy selfsufficiency
The tight oil and gas reservoirs are characterized by low permeability, poor pore throat structure, and no natural production [4,5,6]
Summary
As the technology of unconventional resource exploration and development advances, tight reservoirs and their production contribution have increased year by year and become a substantial part in China’s current and future crude oil reserves [1,2,3]. Meyer and Bazan aimed at the formation of complex fracture network structures with high conductivity after volume fracturing in oil wells based on the material balance and momentum conservation equations; the discrete fracture network is proposed When using this model to calculate the fracture network parameters, it is necessary to combine the fracturing construction parameters and the in situ stress parameters, and the seepage field law of the well production stage after fracturing cannot be obtained [23]. In this paper, based on the mathematical model of numerical well testing, we used the hybrid meshing method with radial mesh and constrained PEBI mesh to evaluate the fracturing effect based on the production data. This method was applied to the vertical wells undergoing either conventional fracturing or volumetric fracturing in a block of the C Oilfield, China, and evaluated and compared their effects after fracturing
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