| Our country contains abundance oil and gas resource in carbonate reservoir reaches 58.3billion tons, which is an important domain for reserves growth.Acid stimulation has become the indispensable important method for carbonate reservoir high-efficient development. Acid leakoff is always a key issues which restricting the high-efficient development of carbonate reservoir.At present, the foreign methods to study the acid leakoff is conbining the physical modeling and numerical simulationand our country is concentrated on the numerical simulation which is baesd on the experimental ourcome of aboard research results that don’t combine with the reservoir characteristics of our country. which leads to the selection of leak off control measure lack pertinence. In view of the above problems, we has conducted systematic study of acid leakoff mechanism and leakoff control technology, and made the following findings:(l)Taking the reservoir charactreistics as key points, and study the leakoff characteristics of porous carbonate at the conditions of different permeability, lithology, acid system, temperature, injection pressure, and combined with microanalysis to reveal the leakoff mechanism of different types of porous carbonate.(2)Focusing on the fracture filling degree through CT and SEM test. We has studied the leakoff characteristics of full-filling fracture, partly-filling fracture and non-filling fracture, and specifying the leakoff laws of different types of fractures.(3)Basing on the theory of micelle formation and taking use of molecule simulation calculation to study the viscosifying mechanism from the angle of thermodynamics.(4)Through dynamic light scattering experiment and Laser particle analyzer analysis study the change law of micelle size with the influence of external factors. And study the change of microstructure of micelle through Cryo-TEM.(5)A fiber diversion experimental setup has assembled. Through systematic experimental study, the critical parameters of fiber plugging capacity have established which can be used to reveal the plugging mechanism of fiber diversion.Through the systematic study of acid leakoff mechanism and leakoff control of fracture carbonate reservoir, conclude the following understandings:(1)For high permeability reservoirs, the leakoff volume and rate is determined by chemical leakoff, and chemical leakoff further promote physical leakoff. For complex lithology carbonate reservoir acid chemical leakoff is determined by the random distribution of reactive mineral, leakoff volume is mainly determined by physical leakoff. While for tight carbonate reservoir the leakoff volume is determined by physical leakoff.(2)The leakoff characteristics of full-filling fracture rock is similar to porous rock, the leakoff volume is determined by physical leakoff. For partly filling fracture rock, the leakoff rate is determined by chemical leakoff. For non filling fracturing rock acid leakoff rate is determined by the creation of high conductivity channel.(3) Basing on molecule association theory and thermodynamic theory, revealing the viscosify mechanism of VES self-diversion acid is stimulating by change of surfactant molecule charge, electron screening by anti-ion and hydrogen bond association.(4) Through dynamic light scattering experiment, Laser particle analyzer analysis and Cryo-TEM test study the impact extent of factor, and found that electron screening by anti-ion is the mainly factor for the change of acid viscosity.(5)Through experimental study of fiber diversion tests revealing the triple plugging mechanism of enhanced fiber diversion system, which including fiber cake mechanical plugging,fiber and carrier fluid mixture and pure carrier fluid chemical plugging. This can be used to optimize treatment parameter and fiber diversion system. |
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