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Ji, D. G. (China University of Petroleum) | Zhang, S. C. (China University of Petroleum) | Zou, Y. S. (China University of Petroleum) | Ma, X. F. (China University of Petroleum) | Zhang, Z. P. (China University of Petroleum) | Zhang, X. H. (China University of Petroleum) | Song, H. X. (China University of Petroleum)
ABSTRACT: The mechanical parameters in complex lithological reservoirs, such as the development degree of natural fractures and fracability, exhibit considerable differences, which result in an unclear fracture propagation mechanism that poses difficulties to fracturing treatment design. A fracability evaluation model that is suitable for different lithological reservoirs was established through a case study of Tamulangou Formation in Hailar Basin, China, and on the basis of rock mechanics test results, brittleness, fracture toughness, horizontal stress difference, and natural fracture development degree. Then, the effect of pumping rate and fluid viscosity on the propagation of multiple fractures was studied using the true tri-axial fracturing simulation experimental system, and the geometry of fracture initiation was observed through the distribution of tracers. Results showed that (1) Tuff had moderate fracability (0.35≤FT≤0.65) and was sensitive to pumping rate and fluid viscosity. (2) Siltstone had moderate fracability (0.40≤FS≤0.68) and was sensitive to changes in pumping rate and fluid viscosity. (3) Breccia had poor fracability (FB<0.45) and was not sensitive to changes in pumping rate and fluid viscosity. The findings of this study can provide guidance for the fracturing treatment design of complex lithological reservoirs. 1. Introduction Complex lithological reservoirs have the characteristics of large lithology differences, complex structures, significant anisotropy of reservoir physical properties, and uneven development of natural fractures. The physical and mechanical heterogeneities of complex lithological reservoirs mean that different lithological rocks exhibit dissimilar fracability [1-4]. As the reservoir fracability vary with lithological layers or regions, hydraulic fracture propagation behaviors may be different from conventional reservoirs, tight shale and sandstone reservoirs [5-9]. At present, the existing fracability evaluation models are mainly applied to conventional sandstone and shale reservoirs, which may not suitable for complex lithological reservoirs [10-11]. Therefore, it is necessary to establish a fracability evaluation model for complex lithological reservoirs, and study the hydraulic fracture propagation mechanism of different lithological reservoirs, so as to provide guidance for the fracturing treatment design of lithological reservoirs .
Xu, Kaijun (Department of Geophysics, China University of Petroleum (EastChina), Qingdao, Shandong, China) | Li, Yaoguo (Center for Gravity, Electrical, and Magnetic Studies, Colorado School of Mines, Golden, CO, USA)
ABSTRACT We present a method to constrain magnetic inversions by magnetotelluric (MT) sounding data at sparse locations for the purpose of imaging volcanic units in the gas exploration. Magnetic data are a cost-efficient means to map volcanic units but lack the necessary depth information. MT data can provide the required depth information. Integrating MT with 3D magnetic amplitude inversion therefore leads to better recovered effective susceptibility. We have found that the magnetic amplitude inversion with the structural constraint from the 1D blocky inversions at even a small number of MT stations can dramatically improve the inverted effective susceptibility model and help better image the distribution of the volcanics. We demonstrate the approach using a case study from Dayangshu Basin in China. Presentation Date: Monday, September 16, 2019 Session Start Time: 1:50 PM Presentation Time: 2:15 PM Location: Poster Station 1 Presentation Type: Poster
Abstract This paper consideres how the initial hydraulic fractures and the oil and gas wells production/injection impact on initial stress field, and forms the stress field prediction software. Applied the software in Xinzhan Oilfield, 5 layers of 4 wells which might be reorient were selected from 19 layers of 7 wells. In the treatment of these wells, tiltmeter was used to monitor how the fractures propagation. After refracturing, the production histories of the wells were matched. The results show that the reorientation occurred in the refracturing of experiment wells, and so the validation of the software was verified. Introduction Reorientation refracturing is that some measures are taken in refracturing process to make the refracturing reorientation. At present, more and more fields and wells need to be refractured. Refracturing has two ways: 1.fractures spreading along original fracture azimuth, 2. fractures spreading along a new azimuth different from original azimuth, reorientation refracturing belongs to the latter. As we know, fractures always spread along the azimuth vertical to the minimum principal stress, so the stress field after the first hydraulic fracturing determines the fractures breakdown and spreading. The research on change trend of stress field could direct the refracturing, predict fractures azimuth and decide the best refracturing opportunity.1–2 The theory of the stress field prediction No matter what refracturing reorientation induced by principal stress reorientation or that induced by shear stress change making fractures spread along shear plane, the original stress field change is the basic dominating factor. The existence of the first hydraulic fractures and the production of wells, the anisotropy of reservoir, the fractures and injection or production of neighboring wells cause the change of original stress field, and may make the stress reorientation. In these factors, the existence of the first hydraulic fracture and the production of wells are the most important ones.3 The physical models (Fig. 1) are used to describe stress induced by the existence of the first hydraulic fracturing:4 a plate with a 2 a long linear fracture, the fracture has the same thickness with the plate, and the tension on the fracture is - P. The principal stress and shear stress in x, y, z direction induced by the first hydraulic fractures can be described by the following formulas: