Sichuan Moxi Gas Field Dense Carbonate Reservoir Damage Mechanism

1/3 of the oil-gas fields is the carbonate rock oil gas-field in the world. Carbonate rock oil-gas reserves account for world 50% of total reserves. Oil-gas output accounts for 60% of total output. The content of clay minerals in carbonate rock reservoirs is usually lower than that in clastics, so it is generally thought that alkaline sensitivity of carbonate reservoirs is weak. Therefore people think it is no difference whether protecting carbonate rock reservoir or not, This has restrained the further research of the carbonate rock. Most carbonate reservoirs are rich in H₂S and CO₂, and clay minerals occur in carbonate reservoirs for a geological time under acid environments, the pH of drilling-in fluids contacted with reservoir is generally higher than 11, so the research of reservoir sensitivity damage is of particular importance.The distribution of tight carbonate rock reservoir is stable in Sichuan Moxi.The relation between gas and water is comparatively complicated. Carbonate rock reservoirs have a few natural fractures relatively and strong heterogeneity. A few salt limes exist in some carbonate rock areas. X-ray diffraction and SEM indicate that the main types of clay mineral is chlorite, kaolinite and illite. The damage of carbonate gas reservoir is systematically described by lots of laboratory experiments based on T₂l and T₁j formations and by using core analysis and test measure in advance, from geology, reservoir sensitivity and capillary imbibition. Therefore this article presents new viewpoint, which deepens the research of damage mechanism and protect technology of carbonate gas reservoir.Laboratory findings indicate that the whole carbonate rock reservoir exists a curtain fluid sensitivity in Sichuan Moxi.Such as moderate to strong in velocity, salt and water sensitivity, strong alkali sensitivity. The experiment of capillary spontaneous imbibition shows that the higher block permeability, the faster the spontaneous imbibiton rate. Fracture core is faster than block core with the spontaneous imbibiton rate .As complicated interstitial space in carbonate formation, the stress sensitivity is investigated, which consist of block core, fracture core and acid fracture core by CMS-300.Laboratory findings indicate that the stress sensitivity is strongest in acid fracture rock, the stress sensitivity of fracture rock is stronger than block rock. With the gradual reducing of the stress, the permeability of core is unable to resume initial value.In order to simulate the reservoir damage of drill-in fluids with high pH,...