Porosity Evolution in Clastic Reservoir with Geological Time

The matching relationship between porosity evolution history of the deep(>3500m) buried clastic reservoir and hydrocarbon expulsion history of source rocks is the key control on hydrocarbon accumulation. Especially, as the deep buried clastic reservoir experienced complex diagenesis reform with time, the evolution of porosity is complicated, so recovering the reservoir porosity during the geological time is of great difficulty. Taking the middle-deep buried Paleogene clastic reservoir in Dongying Sag in East China as the example, we esabilished the evolution process of reservoir porosity and established the research method of reservoir porosity evolution during the geological time constrained by diagenesis sequence-the inversion and back stripping methods with 7 steps. Step 1: Establish reservoir diagenesis sequence and diagenesis environment evolution histories. Step 2: Determine the occurrence time of each diagenesis in geological time and the reservoir's corresponding buried depth. Step 3: Establish normal compaction charts about different types of rocks. Step 4: Created the functional relationship between plane porosity of casting thin sections and reservoir porosity. Step 5: Calculate and obtain the positive or negative contribution value of various secondary porosities and authigenic minerals to reservoir porosity with casting thin sections. Then carry out the porosity's inversion and back stripping under constraint of diagenesis evolution sequence. Step 6: Calibrate the results of step 5 through mechanical compaction and thermal compaction. Reconstruct reservoir's real porosity during the geological time. Step 7: Establish the evolution curve of porosity-geological time (ancient buried depth). This method can resolve the current difficulties, such as the occurrence time of diagenesis, the relationship between plane porosity and porosity and the amount of porosity loss caused by compaction during each diagenesis stage. Thus we are able to make the observed porosity closer to the real porosity in geological time. The combination between reservoir porosity evolution history obtained with this method and hydrocarbon generation and expulsion history of source rocks can provide practical guidance for the prediction of hydrocarbon enrichment areas in the middle-deep buried clastic reservoir.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California