Fractured Dolomite Reservoirs Acid Pressure Filtration Mechanism And Applied Research

Low permeability and herterogenous dolomite reservoir is one of the vital cartonate-rock reservoirs. Acid fracturing technology is becoming a key technology of petroleum exploration,development and increase reserves and stabilize production for this reservoir.low permeability and herterogenous dolomite reservoir is chariterisized with low permeability in matrix, the natural fracture and developed cavity, storng heterogeneity . so, the fracture and cavity system is the main medium of the oil/gas storage and penetration. Wormhole is formed inevitabiy during the process of high pumping rate acid fracturing treatment, which results in serious acid leak-off and short acid penetration distance. Thus this directly leade to a bad effect on the carbonate stimulation, and even brings the treatment into failure. Generally, the main reasons for the failure are the unclearness of acid leak-off mechanisms and the inaccurate calculation of the acid leak-off in the naturally fractured carbonates.So, the acid leak-off mechanism and the design of the controlling the leak-off method have been the concerned for the stimulation technician, and it plays a significant role in improving the acid fracturing effects.Based on the long core parallel plate acid-rock reaction model and the acid dynamic leak-off experiment, we have developed a set of acid leak-off physical model for different geologic condition and have developed a set of acid leak-off experiment,which is to analysis the initiation and propagation mechanisms of wormhole and the acid leak-off mechanisms during the process of the acid fracturing.acid leak-off mathematical model was built up bymodeling the wormhole as a cylinder and numerically solving the mass balance equation that describes acid transport by convertion and duffusion.baded on that and considered the acid fracturing model is developed.for fractured heingt and the variational pressure,the acid fracturing model is developed .for fractrured herterogenousdolomite reservoir,on the other hand,we have developed a suit of Viscoelastic surfactant fluid loss acid system by a number of organic synthesis experiment and a series of comprehensive ecaluation experiment for this acid system.It's illustrated in this paper sa following:1, The acid leak-off in the acid fracturing treatment falls into three parts:1)the leak-off in matrix,2)the leak-off on the wormhole wall and 3)the increase of wormhole volume.this paper presents an acid fracturing mathematic model,including wormhole leak-off.2, The acid wormhole leak-off volume is concerned with the pumping rate,the acid viscosity,the acid concentration,acid injection time and the formation physical property.The acid wormhole leak-off can be decreased effectively and the available acid penetration diatance is improved by optimixing the interest treatment parameter and adopting thecorresponding procedure treatment.3, Based on the three-dimensional model of fracture extension and the model of acid flowing and resction with rock, a acid fracturing design procedure,considering the acid wormhole leak-off,has been programmea with the Visual Basic 6.0 software to guiding the acid fracturing treatment in the carbonate reaervoir,and the model in this paper is modified and improved during the application on the field.4, the effect of acid fracrueing is not good by using the conventional polymet acid system,so we can adding the ciscoelastic surfactant into the acidixing fluids to low fluid loss...