The concept of stimulated reservoir volume (SRV) has conquered the whole oil and gas industry after it was firstly put forward by Fisher et al. in 2004. This concept was used to provide a visual display of hydraulic fracturing performance based on the monitored microseismic data, and had played very important roles in evaluating the stimulation effectiveness, while at the same time, accompanied with numerous queries and criticisms.
In this paper, we firstly carried out large-scale rock block experiments (the rock block size is 1m×1m×1m) under the in-situ stress condition to simulate the whole process of hydraulic fracturing, and during the period, we use acoustic emission (AE) monitoring method to obtain the fracture propagation events. Via the indoor experiment, we want to show the corresponding relationship between SRV events (obtained via AE monitoring) and artificial fracture propagation (obtained via fluorescence irradiate of cut rocks after experiment). Secondly, we carried out series of numerical reservoir simulation, fracture propagation simulation and well testing analysis to history match the experimental data and field production data, aiming to reveal the applicability of SRV concept in tight or shale reservoirs.
Results showed that fracture propagation is a competition controlled by stresses and rock fabric. The propagation of the hydraulic fracture is generally perpendicular to the minimum principal stress while is locally controlled by the rock fabric. Rock fabric will directly affect the fracture propagation including the bedding development, the interface bonding strength, the bedding fracture toughness and the bedding longitudinal stress difference. A large amount of acoustic emission events were obtained on rock sample's horizontal bedding position, not only along the vertical artificial cracks, and this may result in low correlation of the actual SRV events with the later well production. After the experiments, we cut the large rock block into three small parts and fluorescence irradiated, we found that the main fracture propagation has crossed some rock beddings, while still controlled by the bedding, and finally expanded along the bedding.
SRV events obtained in beddings or other discontinuous surfaces have less contribution to well production, and totally believe in SRV concept or SRV clouds may be a misleading to the evaluation of well performance.