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ABSTRACT: Sand production experiments were carried out under true-triaxial stress conditions. The experiments were conducted on 100ร100ร100 mm3 cubes of synthetically made samples. The samples were prepared based on an established procedure developed in the laboratory to produce samples with identical physico-mechanical properties and representing weakly consolidated sandstone. Using a true-triaxial stress cell (TTSC), the samples were subjected to 3D boundary stresses and radial fluid flow from the boundaries. The fluid flows through the sample uniformly and discharges from a hole drilled at the center of the sample. The experiment setup and procedure are explained in detail in this paper. The experiments were performed under three different states of stress to study the effect of the intermediate principal stress (in this study, the minimum lateral stress) on the development of the failure zone. The dimension (i.e. width and depth) of the failure zone developed around the borehole were investigated at the end of the experiments. 1. INTRODUCTION Laboratory experiments on sand formation stability were initially carried out to study the effect of arching on stability of cavities in unconsolidated sands [1]. It has been shown that if the stresses around a perforation tunnel exceed the formation strength, sanding may occur [5]. Also, the effect of stresses and flow rate has been investigated by other researchers on sand production in consolidated sandstones [5 - 11]. The majority of these studies have been conducted on cylindrical samples with a hole drilled at center, and is subjected to axial and lateral (i.e. radial) mechanical loads. Pressure draw-down may be simulated by applying fluid pressure at the outer boundary of sample and producing from the borehole. In this arrangement it is not practically possible to conduct test under real stress conditions (i.e. with three independent far-field stress magnitudes applied to the sample).
- North America > United States > Texas (0.30)
- Oceania > Australia > Victoria (0.28)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.64)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.56)
ABSTRACT: Laboratory experiments of sand production conducted under true-triaxial stress conditions were simulated numerically using ABAQUS program. The experiments were performed in a true-triaxial stress cell on 100ร100ร100 mm3 cubes of synthetic sandstones. Two and three dimensional numerical analyses were conducted to investigate the impact of the magnitude of far-field intermediated principal stress and pore pressure on the failure in the vicinity of a borehole. Different stress boundary conditions were modeled for this purpose. The results provide a better understanding on how the stress anisotropy may have an impact on borehole failure and sand production mechanism. The simulation was used as a tool to optimize and plan the future tests conducted in the laboratory on cube samples. 1. INTRODUCTION A borehole drilled or perforated in a formation composed of unconsolidated sands prone to sanding problems during its production life. Sand production may occur in consolidated sandstones if the stresses induced around the borehole wall exceed the formation strength. In the context of geomechanics, the magnitude of stresses induced around a single borehole is a function of three principal far-field stresses; usually a vertical and two horizontal stresses, and pore pressure. Several theoretical models have been developed to use these stresses to predict sand production in a borehole [1, 2, 3, 4]. In addition, the extent of the failure zone developed in the vicinity of the borehole wall is a function of these stresses. The dimension (i.e. volume) of the failure zone is directly proportional to the volumetric rate of sand production. The effect of these stresses on failure dimension can be investigated either by experimental or theoretical approaches. The common practice to simulate sanding in laboratories is to conduct thick walled cylinder (TWC) experiments on hallow cylindrical shaped sample [3, 5, 6, 7].
- Oceania > Australia (0.68)
- North America > United States > Texas (0.29)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.45)
A Hydraulic Specific Energy Performance Indicator For Coiled Tube Turbodrilling
Mokaramian, A. (Department of Petroleum Engineering, Curtin University, and Deep Exploration Technologies Cooperative Research Centre (DET CRC)) | Rasouli, V. (Department of Petroleum Engineering, Curtin University, and Deep Exploration Technologies Cooperative Research Centre (DET CRC)) | Cavanough, G. (CSIRO, Queensland Centre for Advanced Technologies (QCAT), and Deep Exploration Technologies Cooperative Research centre (DET CRC))
ABSTRACT: Efficient drilling of hard rocks in mineral exploration requires a comprehensive knowledge of the energy spent at the bit. The use of mechanical pecific energy (MSE) proposed in the past for drilling performance studies does not consider the impact of fluid hydraulics and therefore the concept of Drilling Specific Energy (DSE) was later developed to apply the hydraulics parameters into the drilling performance optimization. With respect to the purpo e of mineral exploration, coiled tube (CT) Turboclrilling ha be n propos d r c nlly for d ep hard rocks mineral exploration applications, with everal advantag s over conventional drilling method. oiled tube (CT) is a continuous pipe and con equently a downhole motor i needed to provid rotation and mechanical power to the bit. UD . is to be u ed a a drilling performance indicator when downhole motor are part of the bottom hole as embly (BRA) it hould be modified in such a way that it include motor pecification in the calculation. In this paper, a methodology is presented for performance optimization in CT Turbodrilling with re pect to pecific energy perfonnance model. As a r ult, a hydraulic sp cific nergy performance indicator i d fin d for CT Turbodrilling in hard rocks mineral exploration. 1. INTRODUCTION In mjneral exploration, the main purpose of drilling is to acquire large number of samples to test them in the lab and obtain information about the vertical and lateral distribution of the geological formations, the structural regime, ore and its grade. This would detern1ine if the site is feasible for fhrther investigations and studies. With this in mind, perhaps obtaining core samples over whole overburden is not always essential and having cuttings of small sizes could be used for the analyses needed during the exploration phase.
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.95)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.68)
Abstract: The rock mass, by nature, includes fractures at different scales, which in-fluence the hydro-mechanical behavior of formation. In many engineering applications the formation is porous, for example, tunneling in sandstone layers or production from a sandstone reservoir. The fluid flow in a fractured porous formation would be partly through the formation but the major flow path is the fracture. This, however, depends on different parameters including the formation permeability and more importantly the applied stresses. In this paper, 2D fluid flow simulations are performed using FLU-ENT on a simple lab scale porous formation which includes one fracture plane. One phase flow with water in a laminar regime was assumed for the analysis. The simula-tions were conducted for fractures with different surface roughness and also for-mations with different permeabilities. Also, the fracture aperture was changed to in-vestigate the corresponding effect of applied normal stresses to the fracture plane on permeability. The results indicate how the contribution of fracture in fluid flow reduc-es at smaller apertures and also larger fracture surface roughness. In general, similar results were observed for larger formation permeabilities. 1 INTRODUCTION It is well established that formation permeability is a function of the in-situ stresses (Zhang et al., 1999; Bai et al., 1999; Somerton et al. 1975). Through several laboratory and field tests, empirical correlations have been proposed to estimate formation per-meability in relation to the in-situ stresses (Zhang et al., 1999). The importance of fracture properties and fluid flow changes with respect to different overburden pres-sures and stress-state conditions have also been reported (Vance, 2005). In this study X-ray CT scan was used to estimate fracture height distribution for fluid flow studies within the fracture plane and also investigate the fluid transfer mechanism between fracture and matrix.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.74)
Abstract: Hydromechanical behaviour of sheared rock fractures is complex as it high-ly depends on the evolution of surface roughness after the degradation of asperities. A new fracture shear cell (FSC) which is able to conduct tests under large normal and shear loads was used in this study to investigate the effects of fracture surface rough-ness on asperity contact degradation and micro-cracking of the intact sample. Frac-tures with synthetic and real-rock geometries were built in mortar specimens and sub-jected to shear tests at different normal stresses. Specimens were also tested in two cycles in such a way that the second cycle was repeated at the same level of normal stress after cleaning the produced debris in the first cycle. Damaged regions were marked and it was observed that the significant damage occurs through the steepest asperities of the fracture surface. The analyses enable investigation of roughness evo-lution and asperity degradation during the fractures shearing. The results showed that by increasing the normal stress, asperity degradation sig-nificantly increases and this will affect the fracture shearing mechanisms. The results also indicated that shear strength is reduced in the second cycle due to a reduced roughness after the first shearing cycle. 1 INTRODUCTION The shear behaviour of rock fractures can be experimented in the laboratory using a direct shear apparatus. Different direct shear test devices have been developed to study the effects of surface roughness on shear strength. These devices are mainly different in terms of their loading capacity and loading condition, i.e. under constant normal load (CNL) or constant normal stiffness (CNS). In CNL the normal load is main-tained constantly during the shearing process (Barla et al., 2009; Hans and Boulon, 2003; Huang et al., 2002; Indraratna and Haque, 2000; Jafari et al., 2003; Jiang et al., 2004; Yang and Chiang, 2000).