A New Method for Improving the RQD Determination of Rock Core in Borehole

Azimian, Abdolazim

doi:10.1007/s00603-015-0789-8

Cited by 37 publications

(26 citation statements)

References 17 publications

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“…Meanwhile, Palmstrom confirmed in 1996 that the WJD value is similar to the volume joint number J v , which is used for RQD calculations, as detailed in rows 2 and 3 of Table 1 [39]. In 2006, Shirouyeh Araghi introduced a new method for calculating borehole RQD (MRQD) [38], which was based on the number of joints, karst, fracture zones, cavities, and strongly weathered rock formations, as shown in row 4 of Table 1. In another related study, Li et al proposed a definition of corrected RQD (RQD c ) [40], which is believed to be not only dependent on the cumulative lengths of unbroken pieces but also controlled by the number of unbroken pieces, as illustrated in row 5 of Table 1.…”

Section: Rqd =mentioning

confidence: 99%

“…In another related study, Li et al proposed a definition of corrected RQD (RQD c ) [40], which is believed to be not only dependent on the cumulative lengths of unbroken pieces but also controlled by the number of unbroken pieces, as illustrated in row 5 of Table 1. In 2015, Azimian proposed a rock structure evaluation method using RQD I values, as shown in row 6 of Table 1 [38]. The RQD I mainly considers the joint-core angles and the core fractures.…”

Section: Rqd =mentioning

confidence: 99%

“…where L is the travel or run length and L i is the length of ith unbroken piece; f N ð Þ is the function of the total number of unbroken pieces; f N ð Þ = N a , where a is the material parameter Azimian [38] RQD I = 100 − f i + CW + Fr + Cr + K total core run length × 100 f i is the rating factor obtained from Table 2; CW is the length of the core washed segment; Fr is the length of the fragmented segment (with spacing of 15-50 cm); Cr is the length of the crushed segment (with spacing of <15 mm); K is the length of the karstic segment (karstic zone including vuggy, cavity, core loss, and other karstic phenomena) Table 2: Angle intervals and ratings of the factor for each interval [38].…”

Section: Case Applicationmentioning

confidence: 99%

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A New Evaluation Method for the Fracability of a Shale Reservoir Based on the Structural Properties

Sui

Gao

2019

Geofluids

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The fracability of shale reservoirs is one of the key indicators used for evaluating whether or not the shale can be used as a “sweet spot zone.” It has been determined that the structural properties of rock have important influences on the evaluation of the fracability of reservoirs. In the current study, five rock quality designation (RQD) calculation methods were compared and analyzed for the purpose of selecting an RQDI for characterizing rock structures. Focused on the lack of structural factors included in the previous fracability evaluation methods, a new model for fracability evaluation based on the combination of the brittleness index, structural index, and fracture toughness was constructed using a linear elastic fracture theory. The model showed that good fracability not only included higher brittleness but also required less energy to produce cracks. Meanwhile, good fracability also required more discontinuous structural planes. In the current study, a formation with a higher fracability index was considered to be a fractureable interval and a formation with a lower fracability index was a fracture barrier. Finally, the reservoir fracability index was modeled using the Xike 2 well in the north of Guizhou Province as a case study. Subsequently, a fracability logging evaluation method based on the fracability index model was determined, which will potentially provide a new technical tool for future fracturing optimization processes.

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Section: Rqd =mentioning

confidence: 99%

Section: Rqd =mentioning

confidence: 99%

Section: Case Applicationmentioning

confidence: 99%

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A New Evaluation Method for the Fracability of a Shale Reservoir Based on the Structural Properties

Sui

Gao

2019

Geofluids

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“…To reduce the side effects to disc a core and that of core breakage during the drilling process, the improved methods of RQD determination are developed. Such improvements are based on incorporating more factors like angle between joint and borehole (Azimian 2016) or fracture index (Şen 2014) into RQD calculation. The utilization of new technologies, e.g.…”

Section: Initial Random Variables Of Rockmentioning

confidence: 99%

Global Sensitivity Analysis for Transformation of Hoek-Brown Failure Criterion for Rock Mass

Štefaňák

Kala

Miča

et al. 2018

Journal of Civil Engineering and Management

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A variety of engineering activities require reliable evaluation of rock strength. For instance, the stability of rock slopes depends on structural geology of rock massif in which the slope is excavated. Hoek-Brown (HB) failure criterion applied in rock design practice introduces factors based on the properties of jointed rock. The non-linear finite element safety calculation is conveniently used for calculation safety the factor of slope stability. The Mohr-Coulomb (MC) failure (strength) criterion for soil is widely applied in geotechnical design. Therefore, the appropriate transformation from HB to the equivalent MC, employing angle of shearing resistance φ and cohesion c, is necessary. This article studies the effect of jointed rock massif properties on the transformed MC parameters by using Sobol’s global sensitivity analysis (SSA) and HB transformation equations. Statistical parameters needed for the evaluation of sensitivity analysis are processed using classical statistical methods upon the emulation of Latin Hypercube Sampling simulation methods. Developed and adapted by authors techniques are illustrated by processing real rock investigation data from survey of the trachyte massif located in the Czech Republic. The first and higher order effects of random inputs are identified using SSA. It is illustrated that the effects of inputs on the MC parameters varies significantly depending on the discontinuity distribution and height of the slope.

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“…e RQD index is influenced by different parameters which mainly include joint orientation, joint spacing, fracture frequency, and joint roughness [31]. Although predecessors have conducted extensive research on the limitations of the traditional method to calculate the generalized RQD, how the development of the discontinuities in rock mass will affect the characteristics of the generalized RQD remains unclear.…”

Section: Introductionmentioning

confidence: 99%

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

Sha

Gao

et al. 2021

Advances in Civil Engineering

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Rock quality designation (RQD) is widely adopted as a fundamental tool in characterizing rock masses since it was devised in 1964. Since the conventional RQD calculation is limited due to its dependence on the selected threshold, previous research introduced generalized RQD to adequately reflect the anisotropy and scale effect of RQD. However, the influence of the joint development inside rock mass on generalized RQD remains unclear. The objective of this work is to investigate characteristics of the generalized RQD in view of different development degrees of discontinuities in rock mass, including spacing (density) and trace length. Three-dimensional fracture network modelling is employed to simulate the actual rock mass of open-pit iron mine in China. Virtual scanlines are set to obtain RQD values in different directions. The results primarily show that the generalized RQD should be introduced to calculate the RQD with different thresholds to fully reflect the anisotropy of rock mass. The optimal threshold can be obtained based on an anisotropic coefficient, which is defined by (RQDmax-RQDmin). It is also indicated that the fracture spacing has a great influence on both the anisotropy of RQD and the selection of the optimal threshold. The optimal threshold of the generalized RQD increases with the increase in the fracture spacing. In addition, the scale effect of RQD in different models is discussed by changing the length of the scanlines. The longer the scanlines we set, the more stable RQD value can be obtained in the model. It is recommended to fit much longer scanline to get realistic RQD in heavily fractured rock mass.

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A New Method for Improving the RQD Determination of Rock Core in Borehole

Cited by 37 publications

References 17 publications

A New Evaluation Method for the Fracability of a Shale Reservoir Based on the Structural Properties

A New Evaluation Method for the Fracability of a Shale Reservoir Based on the Structural Properties

Global Sensitivity Analysis for Transformation of Hoek-Brown Failure Criterion for Rock Mass

Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development

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