Identification of flow units using the gas flow experiments and static data in heterogeneous oolitic reservoirs of the Puguang gas field

Abstract

Identification of flow units in heterogeneous carbonate reservoirs is challengeable. The core wells, thin section, physical property measurements, and logging data from Feixianguan (Triassic) oolitic reservoirs of the Puguang gas field are studied in detail. Three pore types are identified: intergranular pore (Inter-P), intergranular and intragranular pore (Inter-Intra-P), and intragranular pore (Intra-P). There is a discrete correlation between porosity and permeability, but a relatively good linear relationship between Inter-P and Inter-Intra-P pore types. Combining the method with flow experiments, a new method for flow unit identification based on the flow experiments under simulated reservoir conditions is developed. The flow capability index (FCI) obtained from flow experiments can directly reflect the varieties of gas flow behavior in different reservoirs and can distinguish flow unit types. From the experiment results of 20 cylinder samples, similar FCI values are considered to be the same flow unit; meanwhile, the FCI, reservoir quality index (RQI), and permeability thresholds are obtained from related crossplots, thereby dividing four types of flow units and their thresholds. The RQI prediction formula is established by interpreting the measured physical property data and related logging data in Inter-P and Inter-Intra-P. The flow unit identification of coring well using predicted RQI and measured RQI is close to the observed results, especially in FU1 and FU3. This finds that the combination of the gas flow experiments and static data can effectively support flow unit identification and reservoir division in the Puguang gas field.