Reasearch Of Cementing Qulity Evaluation Based On The Distributed Fiber-optic Sensor

Oil is the strategic resource for a country, usually produced underground forthousands of metres, how to efficiently exploit oil is a profound subject. The oil’srecovery processes underground are all completed in the casing. And cement is placedoutside the casing in order to improve the strength of casing, namely for cementing.Therefore, how to effectively reduce the influence of layer stress on casing and cementlayer, especially in the maturing field exploited for the second or third times, and howto improve the service life of the casing with the effects of corrosion and cyclic stresshave become a key technology of oil extractio. The research shows that the bettercementation degree of casing with cement layer, the ability for casing to resist corrosionand cyclic stress is stronger. At present there is no good way to evaluate casingcementing quality and cementation effect during the oil recovery phase. And once thecasing is damaged, exploit can not be continued, which will birng huge loss.To solve the problem that cementing quality is unable to realize real-timemonitoring during oil recovery process, this article comes out a new way. Thedistributed optical fiber strain sensor with temperature compensation is arranged outsidethe casing. After cementing the sensor is fixed into the space between casing andcement layer. The demodulation system conducts real time data acquisition on ground.And through comparing the theory with experiment data for the analysis of cementcracking and spalling, evaluating and predicting for the well cementing quality and thecasing residual life during the whole production process, the improved method forcementing of the same type well is provided, which will direct the following production.The main research contents are as follows:The first, through analyzing the related parameters influencing the cementingquality, the initial solidification of cement, cement cracking and cement spalling arechosen as the main monitoring indexes to evaluate cementing quality. Taking thedistributed strain sensor with temperature compensation as the main sensitive element,distributed monitoring system has been built. Through the calculating of thecircumferential stress transferring, and study on the mechanism of the optical loss, anoptimization scheme about enhancing sensor sensitivity and reducing optical loss couldbe concluded.The second, analyzing the coupling relationship between technical indexeseffecting cementing quality and the parameters of optical fiber sensor. According totheoretical analysis and finite element calculation of cement cracking and cementspalling, theoretical calculation model based on elastic mechanics and fatigue life modelbased on fracture mechanics are put forword, which will be the basis of cementing quality monitoring.The third, buliding the indoor monitoring system to evaluate cementing quality.Through arranging defects, simulating the cementing process and cementing monitoringindex’s change with the variation of underground stress, response of optical fiber sensorcould be concluded. The experiment research is based on the real-time strain monitoringevaluating method of cementing quality and result.