Depositional Characteristics of Sandstone and Conglomerate Reservoirs of Fan Delta and Relationship to Reservoirs' Physical Properties ——Taking the Fourth Member of Shahejie Formation, Luojia Oilfield, Zhanhua Depression for An Example

Based on the sedimentology and reservoir geology, combined with drilling, logging and analytical data, depositional characteristics of sandstone and conglomerate bodies' reservoirs for the fourth member of the Shahejie Formation in the Luojia oilfield are studied in detail. The rusults show unacceptability of some previous cognition. As to depositional environment of fan deposits, the conception of fan delta is better than the nearshore subaqueous fan and the subaqueous alluvial fan. According to the characteristics of sandstone and conglomerate bodies, the fan-deltas can be subdivided into three subfacies and five microfacies. It is elaborated that physical properties of reservoirs are effected by lithological properties, sedimentary microfacies and other factors. The porosity and permeability of reservoirs of sandstone and conglomerate bodies is improved by dissolution of feldspar and carbonate rock-fragments. However, it would be decreased awfully with increase of fine matrix and carbonate contents. A style of parabola is shown in the relationship of the mean grain size with the porosity and permeability of the reservoirs which is greatly different from sandstone reservoirs. The oil-bearing properties of the packsand and the pebbled gritstone with parallel bedding and homogeneous bedding is better than glutinite with wavy bedding and graded bedding. Among all microfacies classified, the best reservoir is developed in subaqueous distributary channels.