Exploration for Oil and Gas With the IP Method—The Anomaly Model
Nie Xinwu, Zhou Anchang, Yang Guanding, Zhang Saizhen, Jian Ai, Zhang Shuchun, 1989. "Exploration for Oil and Gas With the IP Method—The Anomaly Model", An Overview of Exploration Geophysics in China — 1988, Zhao Jingxiang, Wang Yanjun, Fu Xuexin, Stanley H. Ward
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Results of experimental prospecting for oil and gas using the induced polarization method (IP) over more than 20 reservoirs in China are presented. Some field tests and theoretical calculations for assessing the effects of well casing and pipeline on IP anomalies due to oil and gas are made. Pipelines and well casings can not give rise to strong IP anomalies, which might be confused with those due to oil and gas, if survey grids are carefully arranged. Still, care is needed in data interpretation when well casings or pipelines exist in survey areas. Items discussed are the effectiveness of the method, characteristics of the anomalies, the effects of overburden, the depth of detection, and the typical model over reservoirs. Over the great majority of the reservoirs studied, distinct IP anomalies are observed. The reservoirs covered with thick Quaternary formations are characterized by a low resistivity, whereas those covered with thin Quaternary formations or—Mesozoic formations—are characterized by high resistivity; additionally, apparent resistivity responses differ from place to place. Under favorable conditions, reservoirs with a depth of 3000 m or more can be detected with IP.
Pseudosections over the studied reservoirs in east and northwest China are similar. The part of the pseudosections with a small electrode spacing exhibits a high central resistivity and medium high chargeability surrounded by low values of resistivity and chargeability; whereas the part of pseudosections with a large electrode spacing exhibits a central low resistivity and a high chargeability. Many experimental investigations of prospecting for oil and gas using the induced polarization (IP) method have been carried out in north China, east China, Sichuan, and Xinjiang since 982 and optimistic results have been obtained.