New technological progress in the development of Sinian large carbonate gas reservoirs in central Sichuan Basin

The gas reservoir of Sinian Dengying Formation in the central Sichuan Basin is a large-sized old deep karst weathering crust type carbonate gas reservoir, and it is overall characterized by low porosity, low permeability, developed small-scale fractures and vugs, and strong reservoir heterogeneity, which bring a series of challenges to its development in terms of reservoir characterization, well deployment and benefit development. Taking the Dengying Formation gas reservoir in the Anyue gas field as the research object, this paper further understands the reservoir development characteristics and formation mechanisms by means of geology-engineering integrated technological research. In addition, a new model of gas reservoir development is proposed, and the key technologies for efficient gas reservoir development are developed. And the following research results are obtained. First, the Dengying Formation reservoir is mainly of karst genesis, and presents the development characteristic of differential control of superimposed karst on reservoirs. Second, karst reservoir has strong heterogeneity, which can be characterized precisely by means of the dissolution facies genesis controlling reservoirs. Third, the new development model of superposition of single well index to demonstrate the scale of gas reservoir is suitable for the Dengying Formation gas reservoir. Fourth, the dual-interface karst paleogeomorphology restoration and quantitative characterization method is innovatively developed to guide the area selection on the plane, which increases the proportion of class Ⅰ and Ⅱ wells from 40% in the evaluation period to 100% in the construction period. Fifth, the small-scale fracture and vug identification and characterization technology is established to guide the drilling trajectory design, which increases the proportion of gas wells with tested production rate of one million cubic meters from 41.6% in the evaluation period to 60% in the construction period. Sixth, the staged acid fracturing technology is improved. As a result, high-quality reservoirs are produced efficiently, low-quality reservoirs are liberated, and the reservoir permeability is increased from 0.62 mD to 6.77 mD after acid fracturing. In conclusion, during the 14th Five-Year Plan period, these development technologies support the transformation from the efficient development of the fourth Member of Dengying Formation in the marginal platform belt to the long-term stable production and multi-layer benefit development within the platform in the Anyue gas field and from single-well high yield to block high yield and to large-scale gas productivity construction in the Penglai gas bearing area, which will provide powerful support for PetroChina Southwest Oil & Gasfield Company to achieve the production target of 500×108 m3 by the end of the 14th Five-Year Plan period. © 2024 Natural Gas Industry Journal Agency. All rights reserved.