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Nowadays, volcanic reservoirs show great development potential. However, the stimulation mechanism of volcanic reservoir is yet unclear. In this article, hydraulic fracturing, acid fracturing, and proppant-carrying acid fracturing of volcanic rock were analyzed by the laboratory tests. The average acid etching and proppant-embedded depths were assessed. The effect of different proppant sizes and acid types on fracture conductivity was studied. The results indicate that acid fracturing is failed to produce high-conductivity fractures. Large-sized proppants had larger embedded depths. For the hydraulic fracturing, the average depth of the 30/50 mesh proppant (5 kg/m2, 60 MPa) embedded in the volcanic rock is 33 μm, and the conductivity is 45.27 D·cm, which is 1.5 times that of the 40/70 mesh proppant. Embedded depth of proppant in the proppant-carrying acid fracturing (347 μm) was ten times larger than that in hydraulic fracturing (33 μm), but in terms of conductivity, hydraulic fracturing is only 20% better than proppant-carrying acid fracturing. This study is helpful to elucidate the mechanism of different stimulation methods and provide scientific means for the efficient development of volcanic reservoirs. In this article, experimental study is made on the stimulation mode of volcanic reservoir. There are few studies on volcanic. This study is helpful to elucidate the mechanism of different stimulation methods and provide scientific means for the efficient development of volcanic reservoirs. Based on the three-dimensional (3D) surface data of the rock, the average acid etching depth and the average embedding depth of proppant are accurately calculated by a new method. The experimental results can provide a good basis for the selection of volcanic reservoir stimulation. The embedded depth and etching depth have an intuitive image display. [ABSTRACT FROM AUTHOR]

Stimulation of oil and gas volcanic reservoirs is quite topical, while particular stimulation mechanisms of various fracturing technologies applied to volcanic rocks need to be clarified. This paper explores volcanic rock sample fracture surfaces' morphology, the acid etching depth, and/or proppant embedment depth under propped, acid etching, and propped-etching. The conductivity is an important evaluation index for the effect of stimulation treatment such as fracturing and acid fracturing, therefore, fracture conductivity under different conditions, such as proppant size and concentration, acid concentration and activity, the separate or joint application of acids and proppant, was evaluated with the samples from Permian igneous in the Sichuan Basin, China. The results indicate that the reaction between acid and rocks is hindered by the complexity and heterogeneity of mineral distribution, forming discrete dissolution holes in local areas instead of flow channels. The maximum embedding depth was 67 μm without acid etching, while those obtained after gelling and cross-linking acid etching were increased by 2.3–3.2 times, reaching 178 and 227 μm, respectively. The etching depth of the samples with the acid can reach 1000 μm. By the effect on conductivity, the increasing order was as follows: acid etching fracture, propped-etching fracture, and propped fracture, while there was a slight difference in conductivities of propped and propped-etching fractures. Therefore, hydraulic fracturing with proppant provides the volcanic reservoir's most effective stimulation. Acid-carrying-proppant fracturing would also be a lucrative stimulation technology if natural fractures are developed and contain acid-dissolved minerals. Acid fracturing failed to form the main fracture with high conductivity, and therefore is not recommended. This study is considered instrumental in clarifying the mechanism of different stimulation methods and substantiating the most efficient development of volcanic reservoirs. The research results can provide a reference for the optimization of stimulation method and the design of treatment parameters of volcanic reservoir. • The morphology, etching, and embedment depth of volcanic rocks were tested. • Fracture conductivity under different experimental conditions was evaluated. • The stimulation mechanism of different stimulation methods is clarified based on the experiment results. • Hydraulic fracturing is considered the most effective technique for the volcanic reservoir. [ABSTRACT FROM AUTHOR]

The urgent need to address climate change, driven by the increasing concentrations of greenhouse gases, has made it imperative for the world to focus on enhancing carbon emission mitigation and carbon utilization. Consequently, carbon-negative technologies have garnered significant attention, such as Carbon Capture, Utilization, and Storage (CCUS). In order to achieve the circular utilization of carbon and improve the economic viability of conventional carbon-negative technologies, this paper proposes the innovative concept of Carbon Capture, Circular Utilization, and Sequestration (CCCUS). This multifunctional carbon-negative technology couples underground biomethanation of carbon dioxide and hydrogen-rich industrial by-product gases with geothermal energy production. CCCUS also offers several additional functions, such as renewable natural gas storage, natural gas displacement, and carbon dioxide geological sequestration. Furthermore, a preliminary assessment of the techno-economic feasibility of CCCUS is undertaken. A numerical case study, conducted using the XGS gas storage in the Sichuan Basin, China, unveiled that over a 425-day period, the conversion ratio of carbon dioxide to methane in the working gas can achieve 98.9%. Moreover, the net present value (NPV) of CCCUS over a 30-year period is estimated to be approximately 4.67 × 108 CNY under the base scenario. These findings, along with field monitoring and laboratory experiments, preliminarily present evidence supporting the potential techno-economic feasibility of CCCUS. This paper offers a fresh perspective on the development of the circular carbon economy. [ABSTRACT FROM AUTHOR]