Study on composite fracture-network acid fracturing technology for tight carbonate reservoirs and its field application: a case study on Mawu₅ carbonate reservoir of Lower Paleozoic in Daniudi Gasfield

In Daniudi gasfield, the Mawu₅carbonate reservoir of Lower Paleozoic is a low-porosity and low-permeability tight reservoir with low reservoir abundance and developed natural fractures.When conventional acid fracturing is applied in this reservoir, the stimulated volume is limited.The production after the commissioning of horizontal well declines fast and production stabilization is of high difficulty.To solve these problems, rock brittleness index characteristics of Mawu₅ carbonate reservoir of Lower Paleozoic in Daniudi gasfield were analyzed.Composite fracture-network acid fracturing technology was studied.The design concept of "create fracture by using large-displacement prepad fluid + perform large-scale acid fracturing of fracture network by using gelled acid + keep fracture conductivity by using post proppant" was adopted.Hydraulic sand fracturing was combined with gelled acid fracturing.Lineargel prepad fluid system, gelled acid system and composite proppant system were selected for composite fracture-network acid fracturing.And the construction parameters of composite fracture-network acid fracturing were optimized, including discharge capacity, operationalliquid dosage and proppant volume.This technology was actually applied to Mawu₅ tight carbonate reservoir of Lower Paleozoic in Daniudi gasfield.And it is better applicable to this reservoir and its stimulation effect is remarkable.This technology is of great significance to the large-scale productivity construction of Lower Paleozoic gas reservoirs in Daniudi gasfield.