Northeastern Sichuan Cracks Loss Of Carbonate Reservoir Damage Mechanism And Protection Of Technology Research,

There are almost 300×10~4km~2 carbonate rocks distribution area in China, oil and gas pool from the Proterozoic Era to the Cainozoic Era stratum also. It is huge on potential in oil and gas's exploration and exploitation. The carbonate reservoir is easy to be damaged, because of numerous fractures, complex pressure systems, multi-formation, and dropout or filtration. And what is worse is that the formation damage is a important reason of the low production rate of carbonate rocks reservoir oil and gas in our country. Therefore, it is essential to study on the mechanism of fractured and leaked carbonate reservoir formation damage and find out effective ways which can improve the fruitage in oil and gas of exploration and exploitation.The research, which is based on Leikoupo, Jialingjiang, Feixianguan and Changxing group of Si Chuan basin northeast carbonate reservoir, show that there are many potential factors of formation damage in cluding intensive aeolotropism, numerous fractures, the dolomite, the calcite, the feldspar, the micrite quartz , the kaolinite, the illite, the chlorite, the gypsum, the asphaltene, and mount of hydrogen sulfide. It also show that the gypsum, the hydrogen sulfide and the asphaltene interact with each other.the new assessment method of fractures stress-sensitivity, been showed in drilling and well completion's opinion, which has been used for evaluating the reservoir stress sensitivity. Experiment results indicate that stress-sensitivity of block core is weak or middle, stress-sensitivity of cores with single nature fracture is middle, that of cores with single artificial fracture is strong, and the stress-sensitivity of cores with two artificial fractures is the strongest, Meanwhile, the fractures are opened much easier than them be closed. The mechanism of reservoir stress-sensitivity and the influence factors are also analysesed.It is thought that there are three main reasons leading to the circulation loss of drilling-in fluids, by studied the circulation loss mechanism and characteristic of reservoir. One is that lay formation is many and pressure systems is complex. when high density drilling-in fluids was applied on high-pressured reservoir, it will causes the low-pressure reservoir leakage, which means that the strength of filter cake in low pressure section is too weak to pressurization; Two is that there are too many fractures, and the seals off the ability of drilling-in fluids is not strong; Three is that hydrogen sulfide become hydrosulfuric acid, when they contact with each other, hydrosulfuric acid acidified fractures of nearby the wellbore and causes the fractures broaden.Formation damage caused by dropout or filtration of drilling-in fluids is serious. The carbonate reservoir are lack of clay minerals, but they are still sensitive to fluids. The attitude and microstructure of clay minerals is more important factor of formation damage contrary...