Study On Hydraulic Fracture Propagation Mechanism And Process Optimization Of Carbonate Reservoirs

The acid fracturing is applied wildly to simulate formation in vuggy carbonate reservoirs.But it does not figure out clearly the mechanism of fracture propagation while the fracture encountering the dissolved hole and there are less researches considering the influence of dissolved hole on fractures propagation.In order to study the laws of fracture propagation in vuggy carbonate reservoirs,numerical simulations are carried out by the seepage-stress-damage coupling equation based on the damage mechanics theory and the currency of the model is validated by the comparison with experimental results.Some factors influencing the fracture propagation such as dissolved holes,formation parameters and construction parameters are analyzed.The simulation results show that there are four fracture propagation forms after the fracture encountering dissolved hole,namely block,crossing over directly,crossing over after deflection and deflection.With the increase of permeability,the amount of fra-fliud loss raise and the net pressure in fracture is low relatively and the principle stress plays a leading role in fracture propagation.When the heterogeneous is strong,the developing fracture round dissolved hole.As the heterogeneous being weak,the propagation form of hydraulic fracture becomes more smooth and straight,and the upper and lower ends of hole model is more symmetric.The horizontal principal stress difference of formation control the tendency of fracture and the generation of branch fracture.It is easier to generate branch fracture under the condition of low horizontal principal stress.The increase of horizontal principal stress restricts the deflection of fracture,which makes main fracture propagation easier towards the direction of the maximum horizontal principal stress.The size of hole larger,the harder fracture crosses over hole.Increasing the displacement or prolong injection time can deal with this problem in theory.The hydraulic fracture in slender shape can easily generates branch fracture at both ends and turn round towards long side direction of dissolved hole while the wide and short hydraulic fracture makes it easy to generate energy storage space at the location of dissolved hole,which decreases the probability of branch fracture generation.Based on the data provided in the field,a dual-porosity/dual-permeability carbonate reservoir-fracturing model with natural fractures is established by using CMG.The effects of different fracture parameters and production systems on gas well productivity are studied.Based on this,the fracture parameters and production system are optimized,and further laboratory experiments are carried out to test the realization of ideal fracture conductivity.