Residual opening of hydraulic fractures filled with compressible proppant

In hydraulic stimulations of oil and gas wells, injection of proppant (or small particles) is normally needed to avoid the closure of the created fractures under confining stresses. The residual openings of these fractures determine the efficiency and, in general, the success of the hydraulic stimulations. Despite the vast number of papers devoted to fluid driven fractures and hydraulic stimulation procedures, there has not been much research conducted on residual fracture profiles. This problem is characterised by a strong non-linearity and represents a challenge for numerical modelling. In this paper a simple semi-analytical method for calculating the residual openings of fractures partially filled with proppant is developed. It is based on the Distributed Dislocation Technique and Terzaghi's classical consolidation model. One of the results of simulations indicates that the proppant distribution and its mechanical properties have a significant influence on the residual fracture profiles. © 2013 Elsevier Ltd.Luiz Bortolan Neto, Andrei Kotouso

On the residual opening of hydraulic fractures

Hydraulic stimulation technologies are widely applied across resource and power generation industries to increase the productivity of oil/gas or hot water reservoirs. These technologies utilise pressurised water, which is applied inside the well to initiate and drive fractures as well as to open a network of existing natural fractures. To prevent the opened fractures from complete closure during production stage, small particles (proppants) are normally injected with the pressurised fluid. These particles are subjected to confining stresses when the fluid pressure is removed, which leads to a partial closure of the stimulated fractures. The residual fracture openings are the main outcome of such hydraulic stimulations as these openings significantly affect the permeability of the reservoirs and, subsequently, the well productivity. Past research was largely focused on the assessment of conditions and characteristics of fluid driven fractures as well as proppant placement techniques. Surprisingly, not much work was devoted to the assessment of the residual fracture profiles. In this work we develop a simplified non-linear mathematical model of residual closure of a plane crack filled with deformable particles and subjected to a remote compressive stress. It is demonstrated that the closure profile is significantly influenced by the distribution and compressibility of the particles, which are often ignored in the current evaluations of well productivity. © 2013 Springer Science+Business Media Dordrecht.Luiz Bortolan Neto, Andrei Kotouso

Residual opening of hydraulically stimulated fractures filled with granular particles

It is well-known that residual opening of hydraulically stimulated fractures significantly influences the production rate of a well. Despite the numerous studies carried out in the past, there still is a lack of simple mathematical models capable of foreseeing the residual opening of fractures filled with granular particles and subjected to a confining pressure. In this paper a mathematical model based on the Distributed Dislocation Technique was developed and implemented to predict the height of the residual opening of a single crack filled with granular particles after releasing the stimulated hydraulic pressure. The mechanical response of the proppant (granular particles) to the applied pressure in this work was simulated by Terzaghi's classical consolidation model. Two limiting cases were investigated in detail in order to demonstrate the model behaviour and validate the computational technique. The developed model can be further utilised to predict the increase of the production rate during hydraulic fracture stimulations and investigate other important phenomena influencing well productivity, such as, for example, secondary cracking of the fractured media. © 2012 Elsevier B.V.Luiz Bortolan Neto, Andrei Kotouso

On the residual opening of cracks with rough faces stimulted by shear slip

The hydraulic stimulation of fractures has been widely employed worldwide for increasing the productivity of hydrocarbon reservoirs. Many exciting potential applications of this technique, specifically for geothermal reservoirs and coal seam gas (CSG) industries stipulate a strong need for new theoretical models and solutions capable to describe the residual fracture openings after hydraulic stimulations. In this paper a new mechanical model to predict the roughness induced fracture residual opening due to shear slip is developed. It is based on simplified and well established mechanical models of shear slip and contact law of rough surfaces. The solution procedure utilises the distributed dislocation technique, which reduces the governing system to a system of singular equations. The latter is solved using the standard Gauss-Chebyshev quadrature method.Luiz Bortolan Neto and Andrei Kotouso

The performance of hydraulic fractures partially filled with compressible proppant

Mechanical response of a proppant pack to confining stresses significantly influences the aperture of highly conductive artificial or natural fracture channels and, to some extent, determines the efficiency of hydraulic stimulations. This paper presents a simplified mathematical model of a crack partially filled with compressible proppant subject to remote compressive stress and a computational approach for evaluating the productivity rate of hydraulically stimulated wells. The conducted case studies confirm that the proppant pack distribution and compressibility have a significant impact on well productivity. Furthermore, it is suggested that under certain conditions, for example, relatively low confining stresses, the partially propped fractures can lead to higher well production rate than fractures fully filled with proppant. The benefit of reducing proppant pack compressibility for improving the performance of wells with partially propped fractures is also verified.L Bortolan Neto and A Khann

Conductivity and performance of hydraulic fractures partially filled with compressible proppant packs

Abstract not available.Luiz Bortolan Neto, Aditya Khanna, Andrei Kotouso

Elastic properties of porous media in the vicinity of the percolation limit

A new approach to calculation of the elastic bulk modulus of low consolidated porous media in the vicinity of the percolation limit under dry and saturated conditions is developed based on a physical consolidation model of rocks and the classical contact theory developed by H. Hertz in 1882. The derived analytical relationships for the elastic bulk modulus, which take into account the structural architecture of packing, are compared with theoretical predictions from popular micromechanic theories, Hashin-Shtrikman strict bounds as well as with experimental results available for low consolidated granular materials. The latter comparison demonstrates a good agreement under both dry and water saturated conditions. © 2011 Elsevier B.V.Luiz Bortolan Neto, Andrei Kotousov and Pavel Bedrikovetskyhttp://www.journals.elsevier.com/journal-of-petroleum-science-and-engineering

A new approach to evaluate the performance of partially propped hydraulic fractures

A new approach for evaluating the performance of hydraulic fractures that are partially packed with proppant (propping agent) particles is presented. The residual opening of the partially propped fracture is determined as a function of the initial fracture geometry, the propped length of the fracture, the compressive rock stresses, the elastic properties of the rock, and the compressibility of the proppant pack. A mathematical model for fluid flow towards the fracture is developed, which incorporates the effects of the residual opening profile of the fracture and the high conductivity of the unpropped fracture length. The residual opening profile of the fracture is calculated for a particular case where the propp ant pack is nearly rigid and there is no closure ofthe fracture faces due to the confining (compressive) stresses. A sensitivity study is performed to demonstrate the dependence of the well productivity index on the propped length of the fracture, the propp ant pack permeability, and the dimensionless fracture conductivity. The sensitivity study suggests that the residual opening of a fracture has a significant impact on production, and that partially propped fractures can be more productive than fully propped fractures. Application ofthis new approach can lead to economic benefits.L. Bortolan Neto, A. Khanna and A. Kotouso

On a rigid inclusion pressed between two elastic half spaces

Abstract not availableAndrei Kotousov, Luiz Bortolan Neto, Aditya Khann