Application Of Laser Induced Breakdown Spectroscopy To Identify Lithology In Petroleum Exploration

Cuttings logging is one of the important means to identify formation lithology in petroleum exploration. In recent years, the development and application of drilling technology has made cuttings' sample very small, while the method of traditional debris description based on human eyes has become difficult to identify lithology. So it is important and significative to apply new method, such as element analysis technology, for detecting cuttings and high precision identification of rock lithology in the field of petroleum exploration.Laser induced breakdown spectroscopy(LIBS) has been developed fast and started application in recent years, which can be used to analyze element through detecting the plasma emission spectrum generated by pulsed laser. Compared with traditional optical spectrum analyser methods, it has advantages of detecting nearly all elements, short analysis cycle and simple pretreatment of sample.Using independent laser-induced breakdown spectroscopy(LIBS) system, rock samples are inspected qualitatively and quantitatively. Factors influencing spectral signal, such as pulse energy, acquisition time delay, distance between sample surface and focus of convergent lens, precombustion and average number are researched through contrast experiments. The best analysis conditions of rock are determined: pulse energy is 50 mJ, acquisition time delay is 2 ?s, the distance between sample surface and focus is 2mm, without precombustion, and the analysis result is integral average of 20 different points of sample's surface.Characteristic lines of 7 elements used for lithology identification are determined, and rocks of different lithology are analyzed and compared. Calibration curves of Mg, Na, K, Si are generated by using national standard series of rock samples, and all the linearly dependent coefficients are greater than 0.9. Element content of rock sample is analyzed quantitatively by external standard method, and its lithology is identified accurately by plate method, whose accuracy rate is better than 90.7%. The study indicates that LIBS can effectively achieve the high precision identification of rock lithology in petroleum exploration industry.