Geological Reservoir Analysis On Yanchang Formation In JIYUAN Area, Ordos Basin

The Chang 4+5 oil bed groups of Yanchang Formation in JIYUAN area, Ordos Basin has beneficial potential of oil . There are both similarities and differences existed among chang 4+5 and the upper Chang 3, the lower Chang 6 oil bed groups. In general, it is similar in pore assemblage type, the stage division and the type of diagenesis, but there are great differences existed in rock types, clastic granularity, the type of infillings, and the influence of reservoir, because the reservoir located in different deposition belts and the different degree of diagenesis.In this area, structural traps have fewly been discovered, the sedimentary facies has been changed comparatively and vertically, the reservoir distribution in space becomes more complicated with strong reservoir heterogeneity. As a whole, the reservoir in this area is the extra lower porosity and permeability reservoir developed widely. This makes the study of the area more difficulty.The sand reservoir clastic fragment, the characteristics of infillings, digenesis and the structure and evolution of pores have been studied by means of many techniques including of microscope, EMS, high pressure mercury intrusion and thin section. Reservoir heterogeneity has been studied by the way of mathematical statistics, mainly focused on reservoir property, especially on the analysis and evaluation of permeability heterogeneity. Then, the evaluation of pore space and reservoir types have been evaluated by using the method of geomathematics, and these results provide a few theoretical supports in further petroleum exploration and choice of favorable exploration targets.It is showed that: a) reservoir rock types are mainly as feldspar sand and clastic feldspar sand, b) pore types are mainly intergranular pores and second dissolution pores; c)pore structures are mostly the type of middle class of discharge pressure and throat and the type of high class of discharge pressure and thin throat; d)The reservoir types are mainly as â…¢ and â…£ type, e)The distributary sand bodies in the submerged delta frontier are the most favorable face belt for reservoir development.