| Ordovician weathering crust in the Lower Paleozoic of Daniudi gas field is a major exploration strata of looking for reserve replacement zones. But So far there is no key breakthrough. Therefore, strengthening the research of reservoir characteristics has very important practical significance. Based on the carbonate sedimentology, reservoir geology and related theory, this paper study the reservoir characteristics on stratigraphy, karst growth and physical properties by comprehensive use of logging, core, casting thin sections. what’s more, classification standard of reservoir effective thickness was made. At last, the favourable distributions of main producing layer was forecasted.On the base of the predecessors’research, the strata of study area was divided by making full use of all information, and then described the stratigraphic characteristics by comparison with small layers in detail. The data shows the Ordovician Majiagou group of study area was tidal flat sedimentary environment, and with the help of logging curve and core, the sedimentary microfacies in study area are further divided.Karst rocks were the important symbol of the paleokarst. Using the interrelation between the breccia of karst rocks base on the classification scheme for karst breccia of Loucks(1999) and the identification and description of karst rocks in study area, karst rocks were divided into four kinds of lithofacies. Moreover, through the description of karst longitudinal development from single well and even inoue, the karst process in ma51-ma54of the study area has two phases. Through the collection of data and the drawing of related datum, we have a preliminary recovery to the tertiary geomorphology of paleokarst by using comprehensive method.Through core observation and data analysis for the casting thin sections, what can be reckoned is that reservoir space in the study area is mainly intercrystal pore, intercrystal dissolved pore, denudation vugs, cracks and micropore. The types of the reservoir pore space are porous type, corrosion pores type, fractured-porous-hole type and fractured type. According to the correlation analysis, the reservoir belongs to low porosity, low permeability reservoir, and physical property has a poor correlation with reservoir porosity and permeability in the study area.When comparing and analysis various parameters of gas reservoirs and dry layers, reservoir classification standard of Majiagou group which is offered by Changqing Oilfield was used, and classification standard of reservoir effective thickness was established. In this study, reservoir was divided into three classes, Ⅰ class for the good reservoir, the lithology is mainly fine grain or contain gypsum dolomite, through analysis to the well logs, the reservoir performances for the low natural gamma, low to medium electronic resistivity, gas production per day can be more than ten thousand cubic meters; The Ⅱ class for medium reservoir, reservoir lithology is mainly the dolomicrite, the logging responses is similar with the Ⅰ reservoir, gas production is between two thousand-ten thousand cubic meter; The Ⅲ class for the poor-non reservoir, the lithology of argillaceous dolomite or random breccia, the logging character are high natural gamma and high resistivity, and the gas production is under two thousand cubic meters. The distribution characteristics of effective thickness and average porosity in longitudinal and plane orientation were analyzed on the basis of the standard.Finally, favorable prediction for the main producing layer of study area by making good use of different parameters, as a result,the favorable area of ma51+2has435km2, the favorable area of ma54-1has443km2. |
PDF Full Text Request