Quantitative Prediction of Natural Fractures in Shale Oil Reservoirs

Abstract

Natural fractures are the key factors controlling the enrichment of shale oil. It is of great significance to clarify the distribution of natural fractures to guide the selection of sweet spots for shale oil. Taking the Qing-1 Member shale oil reservoir in the northern Songliao Basin, China as an example, a new method considering the factors affecting fracture distribution was proposed to quantitatively predict the structural fractures. And the effect of natural fractures on shale oil enrichment was discussed. Firstly, the types and characteristics of fractures in shale oil reservoirs are characterized by using core and outcrop data. Combined with the experimental analysis, the influences of fault, mechanical stratigraphy, mineral composition and content, TOC, and overpressure on fracture intensity were clarified. Then, the number and density of fractures are quantitatively predicted according to the power-law distribution of fault length. Next, geomechanical simulation and fracture prediction were carried out on the model which was established with comprehensive consideration of the influencing factors of fracture distribution. Finally, the fracture distribution is evaluated comprehensively based on above prediction. The prediction results in this work are consistent with the core measurements.

Study on Well Logging Technology for the Comprehensive Evaluation of the “Seven Properties” of Shale Oil Reservoirs—An Example of Shale Oil in the Lucaogou Formation in the Jimsar Sag, Junggar Basin

“…The prediction technology of the in-situ stress direction is relatively mature at present and mainly includes the borehole caving method and the drilling-induced fracture and prediction method based on fast shear waves (Zhao et al, 2005;Lei et al, 2007;Ding et al, 2009;Su et al, 2017). The principles of these methods have been introduced in detail in the relevant literature and are not repeated in this article (Zeng et al, 2010;Zeng et al, 2013;Gong et al, 2019;Gong et al, 2021a;Gong et al, 2021b). In this study, three methods were used to estimate the direction of the in-situ stress.…”

Prediction of Fracture Opening Pressure in a Reservoir Based on Finite Element Numerical Simulation: A Case Study of the Second Member of the Lower Triassic Jialingjiang Formation in Puguang Area, Sichuan Basin, China

“…Since the three-dimensional numerical simulation of the stress field can more realistically reflect the subsurface morphology, the three-dimensional finite element numerical simulation method has been widely applied in China to evaluate the differences in vertical stress caused by the weight of the overlying strata. However, when applying this method, researchers generally simulate the entire formation as a homogeneous body (Tan et al, 1997;Shen et al, 2004;Li et al, 2007;Su and Li, 2009;Sang et al, 2010;Tian et al, 2011;Zhan et al, 2011;Dai et al, 2013;Zeng et al, 2013;Meng et al, 2014;Zu et al, 2014;Hu and Li, 2015;Wang et al, 2015;Gong et al, 2021a), ignoring the heterogeneity of the layer due to the variations in sedimentary facies and lithology. Yet, strong heterogeneity can lead to redistribution of the in-situ stress magnitude and abrupt changes in the in-situ stress direction across the layer (Zeng et al, 2010;Zu et al, 2014;Gong et al, 2019;Gong et al, 2021b), thereby directly affecting the exploitation effect of the reservoir (Gao et al, 2000;Su and Li, 2009;Zeng et al, 2013;Li et al, 2019;Gong et al, 2021a;Gong et al, 2021b).…”

“…However, when applying this method, researchers generally simulate the entire formation as a homogeneous body (Tan et al, 1997;Shen et al, 2004;Li et al, 2007;Su and Li, 2009;Sang et al, 2010;Tian et al, 2011;Zhan et al, 2011;Dai et al, 2013;Zeng et al, 2013;Meng et al, 2014;Zu et al, 2014;Hu and Li, 2015;Wang et al, 2015;Gong et al, 2021a), ignoring the heterogeneity of the layer due to the variations in sedimentary facies and lithology. Yet, strong heterogeneity can lead to redistribution of the in-situ stress magnitude and abrupt changes in the in-situ stress direction across the layer (Zeng et al, 2010;Zu et al, 2014;Gong et al, 2019;Gong et al, 2021b), thereby directly affecting the exploitation effect of the reservoir (Gao et al, 2000;Su and Li, 2009;Zeng et al, 2013;Li et al, 2019;Gong et al, 2021a;Gong et al, 2021b). This study attempted to establish a three-dimensional, heterogeneous present-day in-situ stress model for the Jia 2 member in Puguang area based on the tectonic framework, distribution of the rock mechanical parameters, and present-day in-situ stress state calculated from logging data, which can provide an essential basis for well pattern deployment and wellbore-instability prevention during drilling.…”

Natural Fractures in Low-Permeability Sandstone Reservoirs in the LD-A HPHT Gas Field, Yinggehai Basin: Implications for Hydrocarbon Exploration and Development

“…Quantitative characterization methods of multiscale natural fractures based on outcrops, cores, thin sections, SEM, and CT were established (Fall et al, 2015;Zeng et al, 2022). Natural fractures were identified and evaluated using logging and drilling data with production performance data (Ezati et al, 2018;Fernández-Ibáez et al, 2018;Stockmeyer et al, 2018), and methods including the curvature method, geomechanical simulation, and geophysical methods have been proposed (Olson et al, 2009;Yin et al, 2016;Hooker et al, 2018;Gong et al, 2021). Additionally, the fracture effectiveness and influencing factors are investigated to analyze the effects of fractures on fluid flow (Alghalandis et al, 2015).…”