Abstract
The heterogeneity of the rock fabric is a significant factor influencing the initiation and propagation of a hydraulic fracture (HF). This paper presents a laboratory study of HF created in six shale-like core samples provided by RITEK LLC collected from the same well, but at different depths. For each tested sample, we determined the breakdown pressure, the HF growth rate, and the expansion of the sample at the moment when the HF reaches the sample surface. Correlations were established between the HF parameters and the geomechanical characteristics of the studied samples, and deviations from the general relationships were explained by the influence of the rock matrix. The analysis of the moment tensor inversion of radiated acoustic emission (AE) signals allows us to separate AE signals with a dominant shear component from the signals with a significant tensile component. The direction of microcrack opening was determined, which is in good agreement with the results of the post-test X-ray CT analysis of the created HF. Thus, it has been shown that a combination of several independent laboratory techniques allows one to reliably determine the parameters that can be used for verification of hydraulic fracturing models.
Highlights
In the last decade, unconventional oil and gas resources have become increasingly promising sources of hydrocarbons due to the approaching depletion of available conventional oil and gas deposits
This paper presents a laboratory study of hydraulic fracture (HF) created in six shale-like core samples provided by RITEK LLC collected from the same well, but at different depths
According to [14], the entire volume of fluid injected into the specimen can be divided into two components: (1) the volume of fluid linearly increasing with pressure, associated with the elastic expansion of the elements of the hydraulic system, the compressibility of the fluid, and of the rock, and (2) a part of the fluid volume that nonlinearly increases with pressure, associated with other processes, including the filling of cracks and pores during the propagation of a hydraulic fracture
Summary
Unconventional oil and gas resources have become increasingly promising sources of hydrocarbons due to the approaching depletion of available conventional oil and gas deposits. Hydraulic fracturing is one of the most effective ways to stimulate shale oil and gas production. Hydraulic fracturing in the field does not always turn out to be as effective as predicted by the model. This is because some factors cannot be quantified, such as horizontal bedding, natural fractures, and the presence of inclusions, which may play an essential role in fracture propagation, and are often overlooked when considering fracture geometry [3,4,5]. It is necessary to take into account that the oil production process from unconventional reservoirs is very difficult and expensive, and increasing the efficiency of applied technologies such as hydraulic fracturing will help to reduce expenses for oil companies [6]. The majority of works on hydraulic fracturing techniques have been focused on various ways to make the process more effective, as mentioned below
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