Fracability Evaluation Method and Influencing Factors of the Tight Sandstone Reservoir

Abstract

Fracability evaluation is the basis of reservoir fracturing and fracturing zone optimization. The tight sandstone reservoir is characterized by low porosity and low permeability, which requires hydraulic fracturing to improve industrial productivity. In this study, a systematic model was proposed for the fracability evaluation of tight sandstone reservoirs. The rock mechanics tests and sonic tests demonstrated that tight sandstone reservoir is characterized by high brittleness, high fracture toughness, and weak development of natural fractures. Numerical simulation was used to analyze the change of reservoir parameters during hydraulic fracturing and the influence of in situ stress on fracture propagation. The results showed that when the horizontal stress anisotropy coefficient is small, natural fractures may lead hydraulic fractures to change direction, and complex fracture networks are easily formed in the reservoir. The horizontal stress anisotropy coefficient ranges from 0.23 to 0.52, and it is easy to produce fracture networks in the reservoir. A new fracability evaluation model was established based on the analytic hierarchy process (AHP). The fracability of tight sandstone reservoir is characterized by the fracability index (FI) and is divided into three levels. Based on the model, this study carried out fracability evaluation and fracturing zone optimization in the study area, and the microseismic monitoring results verified the accuracy of the model.

Pore-Throat Structure and Fractal Characteristics of Tight Sandstones: A Case Study from the Chang 63 Sublayer, Southeast Ordos Basin

“…Fractal theory can quantitatively describe the complexity and heterogeneity of pore structure [9,10,[19][20][21][22][23]. The fractal dimension of the Chang 6 3 sublayer was calculated in this study, the results indicated that the larger fractal dimension, the more complex of porethroat structure, which was consistent with previous researches [24][25][26][27][28].…”

“…Experimental methods are conducted to evaluate the pore-throat structure, such as image observation methods represented by scanning electron microscopy (SEM) and casting thin sections (CTS), photoelectromagnetic radiation methods by nuclear magnetic resonance (NMR) and CT scanning, and fluid injection method by N 2 gas adsorption measurements and high-pressure mercury injection (HPMI) as well as constant-rate mercury injection (CRMI) [9][10][11][12][13][14][15][16]. Considering the complex pore-throat characteristics and strong heterogeneity caused by complicated deposition and diagenesis processes, it is hard to identify the microporethroat structure of tight sandstone reservoirs by a single method [5,[17][18][19][20][21][22][23][24][25][26]. For instance, although the image observation methods (SEM and CTS) can directly observe the geometry and the size of the pore-throat within sight, its visual field is too narrow to represent the whole sample [27].…”