Clay-bound Water Porosity Calculation Method Of Igneous Rocks Based On Conventional Logging Data

Recently, igneous reservoirs, as a new filed of oil-gas exploration, have caused extensive concern and high attention of scholars in oil domain. Compared with sand reservoirs, igneous reservoirs possesses more complex characteristic. In the area of Eastern Depression of Liaohe Basin, igneous rocks have a feature of common alteration that produces clay mineral.In the oil and gas exploration of igneous rocks, how to obtain parameters of igneous rocks accurately, such as water saturation, remains key and difficult points in evaluation of reservoirs logging. Clay-bound water porosity is important to the determination of water saturation, fluid category, oil and gas reserves, which is an major parameter for reservoirs assessment of igneous rocks. Complexity of oil-gas reservoirs of igneous rocks make the conventional logging method for clay-bound water porosity of sandstone unable to apply into igneous rocks directly. Utilizing the conventional logging method to calculate clay-bound water porosity of igneous rocks precisely have great significance for accurate assessment of igneous rocks reservoirs.Many scholars always devote themselves to research of clay-bound water porosity. Conventional logging methods, such as neutron-density cross plot method, acoustic-density cross plot method and resistivity method, are all used in sandstone. Because of complexity of igneous rocks, it is unable to adopt above mentioned methods to obtain clay-bound water porosity. For the new logging techniques, nuclear magnetic log is one of the best methods to obtain clay-bound water porosity, however it has a high cost that has restricted its application.In the area of Eastern Depression of Liaohe Basin, choosing Member 3 of Shahejie Formation as the objective layer and aiming at two kinds of lithology including basalt and trachyte in the oil and gas reservoirs of this layer, this paper researches a method to calculate clay-bound water porosity of igneous rocks.Nuclear magnetic log method is the best one for calculation of clay-bound water porosity at present, so this paper will regard the results from NML data as valid value. Based on lots information of core, debris lamina and x-rays diffraction of some clay mineral, this paper will determine the clay mineral category produced by alteration of basalt and trachyte. And according to the study of geothermy in the area of Eastern Depression of Liaohe Basin which was completed by predecessors, the formation temperature is determined. Further, shale content of different types is calculated by using the data of acoustic wave. Considering clay category, formation temperature and shale type comprehensively, and using the results of clay mineral absorbing bound water researched by predecessors, this paper constructs conventional logging data to obtain a computational formula of clay-bound water porosity of igneous rocks.Through real data processing, for trachyte and basalt, the accuracy of clay-bound water porosity calculated by this proposed method is almost the same as that obtained by nuclear magnetic log method which demonstrates the proposed method has high accuracy.