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This paper focuses on a new test method and theoretical model for measuring and evaluating the reopening pressure during hot dry rock hydraulic fracturing. Firstly, rock blocks of four lithologies were collected from the hot dry rock strata. Hydraulic fracturing tests at high temperatures in real-time were conducted using drilled cubic specimens and drilled cubic specimens with a pre-crack. Breakdown pressure, reopening pressure, and fracture toughness were measured, respectively. In addition, Brazilian splitting tests at high temperatures in real-time were performed using Brazilian disc specimens to measure tensile strength. Secondly, an empirical equation for evaluating the reopening pressure during hot dry rock secondary fracturing was developed based on fracture mechanics and hydraulic fracturing theory. Third, the values calculated by the new equation, considering breakdown pressure, fracture toughness, and tensile strength, were compared to the values determined by the classical equation and to measurement results. It was found that the new equation predicted closer reopening pressure to the measurement results, regardless of the lithology of the hot dry rock. Moreover, with increasing temperature in the specimens, the error between the value calculated by the new equation and the measurement value remained low. In contrast, the difference between the classical equation predictions and the measurement results was widened. In addition, the reopening pressure was positively correlated with tensile strength and fracture toughness. Variations in lithology and temperature affected tensile strength and fracture toughness, which then changed the hot dry rock reopening pressure.
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Objective To evaluate the feasibility and therapeutic efficacy of real-time virtual navigation system (RVS) combined with contrast-enhanced ultrasonography (CEUS) for hepatocellular carcinoma undetectable by conventional ultrasound and CEUS.Methods A total of 213 patients with 265 lesions (undetectable on conventional ultrasound but detectable by other imaging examinations) were enrolled in this study.CEUS was performed,and lesions which were detected with CEUS were given CEUS guided radio-frequency ablation (RFA) (CEUS group).RVS combined with CEUS was performed to locate the rest lesions and guide RFA (RVS + CEUS group).Diagnostic value and therapeutic efficacy of RVS + CEUS were assessed.Results In 256 lesions,174 (65.7％) could be detected with CEUS,and among the rest 91 lesions,82 (90.1％) lesions could be detected by RVS combined with CEUS.The technique effectiveness rate of RVS + CEUS was significantly higher than that of CEUS (x2 =18.85,P ＜0.0001).Complete ablation rate after one month in RVS+ CEUS group was 9t.5％ (75/82),which was significantly higher than that in CEUS group [86.2％ (150/174),P ＜0.05].Local progression in one year in CEUS group and RVS + CEUS group were 13.4％ and 10.9％,respectively.Conclusions RVS combined with CEUS is feasible for hepatocellular carcinoma undetectable by conventional ultrasonography and CEUS,and the therapeutic efficacy of RVS + CEUS guided RFA is satisfactory.
