Preliminary Studies on the Proppant Embedment in Baltic Basin Shale Rock

Abstract

Proppant embedment is a serious issue that reduces fracture width and conductivity. The paper presents the results of experiments on embedment phenomena on a shale rock from the region of the Baltic Basin, which is regarded as an unconventional gas deposit. A novel laboratory imaging procedure was implemented to the proppant embedment visualization. The tests were performed for conditions corresponding to the average reservoir conditions occurring in the studied deposit formation. The parameters characterizing damage of the surface of the fracture faces by the grains of proppant material, after the application of axial compressive stress to two shale core samples with proppant placed in between, are presented. The tests were carried out for rock samples pre-saturated with fracturing fluid. The obtained results of relatively low total effective penetration depth of proppant grains into the walls of the fracture (0.293 mm), and high effective width of fracture with proppant material after hydraulic fracturing (87.9%), indicate the proper selection of proppant and fracturing fluid for the properties of the rock and the reservoir conditions. The results of the experiments present a range of embedment parameters, that have not been widely described before. The test procedure presented in the article is a good method for assessing the vulnerability of a deposit rock to embedment phenomenon.

Hydraulic Fracturing in Enhanced Geothermal Systems—Field, Tectonic and Rock Mechanics Conditions—A Review

“…In the reservoir, v determines rocks' ability to fail under stress [22]. In formations of low v, the embedment phenomenon rises, which leads to a decrease in the conductivity of the fracture (e.g., [23][24][25]). Both E and v parameters allow determining susceptibility for fracking, defined by the brittleness index [22,[26][27][28][29][30].…”

“…Nevertheless, the extensive experience was gained in hydraulic and chemical stimulation operations, based on fracturing in unconventional deposits and matrix acidizing [15,89]. Research works were also carried out in the field of the design, environmental impact and performance of energized fluids for fracturing [90]; the embedment phenomena [24,25]; and the dynamic elastic parameters of the various types of rocks [27,30]. Their results may be useful in the implementation of a prospective Polish HDR geothermal collector program.…”

A Viscoplasticity Model for Shale Creep Behavior and Its Application on Fracture Closure and Conductivity

“…As an important source of natural gas, shale has attracted increasing attention [2], and pores and natural micro-fractures of shale are the main reservoir space of shale gas. However, shale has extremely low porosity and permeability [3], usually ranging from millidarcy to nanodarcy, and must be fractured to create complex artificial fracture networks to form effective productivity. The key to hydraulic fracturing is determining whether a fracture with high conductivity can be formed.…”

“…Comparison of axial creep strain with time-two viscoplastic models. Units: 𝜂 is in MPa 3 •h; 𝜏 and time are in hours [12].…”

Carbonate Rock Chemical Consolidation Methods: Advancement and Applications

“…The conductivity of created fractures is maintained by the injection of a so-called proppant (solid material, usually sand) or, more naturally, by asperities, which result from the reaction between an acid (usually HCl) and reservoir rock . The extraction of hydrocarbons results in increased stresses on the fracture surface, which, combined with the elevated temperatures, causes gradual plastic deformation of the reservoir rock (rock creeping). , Creeping, in turn, leads to reduction of the fracture width (conductivity reduction), presented in terms of a failure of asperities and embedment (indentation) of proppant into formation rock. − Researches have shown that the mechanical characteristics of the reservoir rock (hardness, Young’s modulus), fracture surface roughness, proppant properties (type, size, concentration), and acid properties (type, reaction time) are critical factors that affect the decline of the fracture conductivity. − ,− Moreover, Aljawad et al validated through modeling the carbonate formation that hardening of the fracture surface improves sustenance of its conductivity and the well’s productivity . On the basis of this, strengthening carbonate reservoir rocks can mitigate the effect of the above-mentioned problems and provide long-term sustenance of the fracture conductivity in carbonate formations. , However, practical application records of chemical rock strengthening techniques in carbonate reservoirs, including hydraulic/acid fracturing operations, are still absent.…”