Lower Property Limit and Controls on Deep EffectiveClastic Reservoirs of Paleogene in Chezhen Depression

Key words: 
• effective reservoir

Abstract: Based on the comprehensive application of properties, oil production test, and mercury injection data, the lower property limit of deep clastic reservoirs of Paleogene in Chezhen depression was determined by applying distribution function curve method, testing method, production test method, irreducible water saturation method, and the lowest effective pore throat radius method, and the influence factors were analyzed. On this basis, regarding the porosity and permeability difference as comparison parameters, the controlling actions of which sedimentation, formation pressure and diagenesis played on the deep effective reservoir were researched. The porosity lower limit and log depth are linear relationship, and the lower permeability limit and depth are exponential relationship. Deltaic front subaqueous distributary channel and mouth bar develop most effective reservoir, and porosity difference and permeability difference are well. while sublacustrine fan, nearshore subaqueous fan, fan delta and alluvial fan sandconglomerate develop less effective reservoir, and porosity difference and permeability difference are worse. The effective reservoir percentage content, porosity difference and permeability difference of middle and strong overpressure reservoirs are better than that of normal pressure and weak overpressure reservoirs. The effective reservoir percentage content, porosity difference and permeability difference of reservoirs on the middle diagenetic stage A1 are better than that of the reservoirs on the middle diagenetic stage A2 and B. In general, sedimentary facies is the main controlling factor on the development of deep effective reservoir, and the controlling action of overpressure on the deep effective reservoirs is stronger than diagenesis. The influence of diagenesis on the deep effective reservoirs is controlled by both sedimentary facies and overpressure. The reservoirs with high primary porosity and permeability protected by overpressure are dissolved easily to be good effective reservoirs.