Study on the genesis and controlling role of deep and dense volcanic reservoirs

As conventional oil and gas production declines, global exploration and development efforts have shifted towards unconventional oil and gas resources, with tight volcanic reservoirs emerging as a primary focus. The tuffaceous rocks of the Dehui Fault Depression in the Songliao Basin, characterized by fine-grained volcanic ash deposits, have undergone diagenetic modifications, resulting in low porosity and low permeability with complex pore structures. Identifying the main controlling factors of high-quality reservoir formation and understanding the mechanisms behind secondary pore formation are critical areas of research that require urgent attention.

The study provides several key insights: (1) It identifies the main types of diagenetic processes in the reservoir and establishes a diagenetic evolution sequence. The formation of high-quality reservoirs is primarily controlled by "dual phases" (lithofacies and depositional facies), which includes both pore preservation and enhancement. Acidic dissolution is identified as the primary cause of secondary pore development, with the mechanism of acidic dissolution and its three necessary conditions being discussed; (2) An innovative technique combining large-view stitching and human-computer interaction for thin-section identification images has been developed. This technique establishes a face porosity-porosity model, accurately quantifying the impact of various diagenetic processes on reservoir physical property and identifying the main factors controlling these properties. A porosity evolution history map is created using a combination of back-stripping inversion and computer image analysis techniques. Simultaneously combining chemical kinetics models and fluid inclusion identification to determine the reservoir formation period, clarifying the reservoir-diagenesis coupling characteristics; (3) Methods for distinguishing volcanic eruption periods and identifying lithofacies are established, revealing the main lithologies and depositional characteristics of different eruption periods. The advantageous lithofacies, periods and their distribution characteristics are ultimately determined

Figure: Attached Figure Large Visual Field Splicing and Quantitative Characterization of the Dissolution of Huoshiling Formation in Dehui Fault Depression