Study On Pore Structure Characterization Of Carbonate Reaction Flow Based On CT

In recent years,our country has discovered some large and ultra-large scale oil and gas reservoirs with carbonate rock in the Sichuan basin and Tarim basin.With complex formation structure,the pore space in carbonate reservoir will undergo change during various geochemical processes(such as acidification of reservoir and carbon dioxide geological storage).And the evolution of pore structure caused by dissolution and deposition will in turn significantly change the physical properties of rocks and the transport characteristics of fluids in them.At present,there are many related researches on the acidification of carbonate rocks at the macro-scale.The description of the reaction mechanism inside carbonate rocks and the characterization of pore structure changes are insufficient.Existing models don’t effectively characterize the acid corrosion of heterogeneous minerals.The objective law of the heterogeneous reaction between rocks and acid has not been fully explained.In this thesis,focusing on the effect of acid etching reaction on carbonate rocks,we used computed tomography(CT)to study the effect of reactive flow on carbonate rocks at micro-scale.CT technology was used to obtain a three-dimensional digital core model before and after the carbonate rock was dissolved,and the image was processed to quantitatively study the change of pore structure and flow capacity.Finally,the relationship between permeability and pore structure parameters was obtained,and the dynamic quantitative analysis of pore structure and dissolution channel was performed.In this thesis,it is found that the difference in the morphological characteristics of pore structure has a great impact on the dissolution pattern of the rock.4 rock samples with different pore structure types(homogeneous pore type,heterogeneous pore type,fracture type,bio-shell type)were selected to carry out the core flow experiments.Rock sample with homogeneous pore structure was dissolved uniformly,and the acid only widened the original pore structure without forming new dissolution channels;multiple branched worm holes were formed at the inlet end for heterogeneous pore-type samples,but with the continuous injection of acid,a main flow channel was finally generated;for fractured samples,the acid only flowed along the fracture which was continuously extended;due to the heterogeneity of bio-shell sample,the single channel was grown by dissolution.The geometrically and topologically equivalent pore network models were extracted from the digital cores before and after dissolution for above 4samples,the changes of pore structure parameters at different dissolution stages were analyzed,and the permeability of different samples were simulated.Finally,the permeability and multiple pore structure parameters estimated from pore network model were fitted to obtain a quantitative expression of the relationship between pore structure parameters and permeability,and the fitting indexes are all above 0.91.The effects of acid-rock reaction on the change of pore structure and flow capacity investigated in this thesis have a value of field application for acidification of oil and gas reservoirs and geological storage of carbon dioxide.