Fracture propagation mechanism in artificial reservoir of deep hot dry rock, Matouying and its applications

doi:10.13745/j.esf.sf.2024.7.21

Abstract

Abstract:

Hot dry rock (HDR) has the advantages of clean, stable, renewable and power generation potential. The construction of fracture network and artificial thermal reservoir through hydraulic fracturing are the key technology to the efficient development of HDR energy. Traditional oil & gas fracturing mechanics are almost unable to induce tensile failure in deep HDR, therefore fracture network initiation and propagation are the key to the construction of artificial reservoirs. The reservoir construction mainly includes tensile fracture initiation near the wellbore, artificial fracture propagation and rock matrix destablization, and natural fracture displacement and dilatation. In this paper, taking the hydraulic fracturing of deep HDR in Matouying as an example, considering the geological characteristics and fracture network expansion mechanism, the temperature resistance, shear resistance and gel breaking performance of the artificial reservoir are evaluated. Low-viscosity slick water with a resistance reduction rate of 74% was selected as the main fracturing fluid, and variable-viscosity slick water with a viscosity of 40 mPa·s after shear stabilization was selected as the sand-slurry fluid for temporary plugging and diverting. Optimized into five pumping stages and 15 units, alternating between three stimulation methods including acid injection, hydraulic-shearing and sand slurry, the total of 15000 m³ fracturing fluids were pumped into reservoir to expand fracture network. Degradable plugging agents with different particle sizes, 200 mesh, 2 mm and 5 mm, were selected to promote uniform expansion of fractures, and 40/70 medium-density, high-strength proppant was optimized to strengthen the support of high conductivity. Post-fracturing evaluation and microseismic monitoring confirmed that a 1004.03×10⁴ m³ artificial heat reservoir was constructed between underground well groups, which contained 18 typical interconnected fractures and the fracture model was “tension-shear”. The plugging agent carried by the high viscosity slick water with low pumping rate promoted the continuous opening of new fractures at the far end, increasing the area of fracture network without inducing earthquakes. The success of this hydraulic fracturing practice validated the use of multifluid mini fracturing testing, multistage step-by-step main fracturing, and multiplan plugging fracturing in the construction of artificial reservoirs. This engineering approach provides a valuable reference for HDR hydraulic fracturing.

Key words: hot dry rock, hydraulic fracturing, artificial thermal reservoir, fracturing propagation, Matouying

CLC Number:

P624
P314

QI Xiaofei, XIAO Yong, SHANGGUAN Shuantong, SU Ye, WANG Hongke, LI Yingying, HU Zhixing. Fracture propagation mechanism in artificial reservoir of deep hot dry rock, Matouying and its applications[J]. Earth Science Frontiers, 2024, 31(6): 224-234.

Figures/Tables 16

Fig.1 Simplified geological map of the Matouying prospecting area

Fig.2 XRMI image log of the target section

Fig.3 Macroscopic failure characteristics of triaxial testing of deep hot dry granite in Matouying

Fig.4 Fracture propagation in artificial thermal reservoir constructed by hydraulic fracturing in deep hot dry rock

Fig.5 Stress status and instability envelope of HDR after long-term fracturing

Fig.6 Hydro-shearing displacement and dilation of natural fractures in HDR

Fig.7 Resistance performance of low-viscosity slick water

Fig.8 Temperature and shear resistance rheological diagram

Fig.9 Effect of sticky and smooth water breaking

Fig.10 Fracture network after 15000 m3 fluid injection

Fig.11 Degradable particle plugging agent

Fig.12 3D model of multistage fracture network in artificial thermal reservoir in well M-1

Fig.13 Pumping pressure changes with opening of new fractures after plugging agent injection

Fig.14 Microseismic event before (left) and after (right) injection of plugging agent

Fig.15 Microseismic event during hydraulic fracturing in M-1

Fig.16 Fracture surfaces generated from typical microseismic events

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