| The fracture-cavity carbonate reservoirs are low-porosity,low-permeable and dense in matrix.Beside that,the karst caves are the main oil and gas reservoirs.Therefore,the key to their development is to communicate as many karst caves as possible through artificial fractures to increase production.In the process of communicating the reservoirs of karst caves,controlling the fracturing fractures to initiate and expand again after connecting the karst caves is the key to improving the transformation effect.However,the lack of research on the mechanical mechanism of the re-cracking of carbonate karst caves has led to unclear factors and laws affecting the re-cracking of fracturing fractures,and unclear control methods and methods.Therefore,this paper deduces and establishes the fracture initiation mechanical model and the mathematical criterion for judging whether it can be reinitiated in response to the problem of carbonate karst cave reinitiation.On the basis of theoretical research,a simulation experiment study on the re-cracking of carbonate karst caves was carried out.Finally,based on the established mechanical model and the summary of experimental influence rules,the on-site fracture-cavity carbonate reservoir fractures were optimized and designed.It guarantees that the fracturing cracks can start again in the karst cave.The main innovations of this article are as follows::(1)A mechanical model and criterion for reinitiation of fracture-caves for carbonate karst caves are established.The model based on the edge folding method under stress constraints to conduct regular research on different types of reservoir caves,and established a mechanical equivalent model of carbonate cave shape.Based on the regularized cave shape,a single-crack communication karst mechanical model is established.The model is based on linear elastic fracture mechanics and fluid mechanics.It considers the joint effect of karst caves connected by single fractures by in-situ stress,internal pressure of karst caves and fracturing fluid injection pressure,and calculates the stress distribution around the karst caves during fracturing.Combined with the rock failure conditions,a criterion for establishing cracks was established(2)Based on the established mathematical model,through the combination of karst cave re-cracking simulation and karst cave fracturing experiment,clarified the influencing factors and laws of fracturing fracture re-cracking in carbonate karst cave are.Firstly,the artificial carbonate rock fracturing experiment with karst caves was used to experimentally study the karst cave initiation conditions with different displacements,viscosities,karst cave sizes,and in-situ stress conditions,and the karst cave initiation morphology was clarified.Combined with the simulation study on the cracking mechanical model of karst cave,the influence of the difference of the geological parameters and fracturing parameters of fracture-cavity carbonate rock on the karst cave initiation,initiation time and initiation pressure are evaluated. |
PDF Full Text Request