Research and Application of Logging Evaluation Method for Lower Limit of'Dynamic'Physical Property of Tight Gas Reservoir

摘要

Different from conventional gas reservoirs,it is difficult to determine the lower limit of effective reservoir for tight sandstone gas reservoirs,because of the influence of Hydrocarbon expulsion power of source rocks on the location and enrichment of natural gas,the strong heterogeneity of tight sandstone,poor connectivity of sandstone and inconsistency of gas-water interface,etc.We have carried out the study on the lower limit of effective reservoir in tight sandstone,on the basis of using abnormal formation pressure to estimate hydrocarbon expulsion power of source rocks,using logging data calibrated by rock physics experiments to evaluate migration resistance and testing results to determine reservoir validity.We put forward the viewpoint of"dynamic"lower limit of effective reservoir.That is,the lower limit of physical properties of tight sandstone is variable by difference value of hydrocarbon expulsion power and migration resistance.The lower limit of effective reservoir with strong hydrocarbon expulsion power is low,whereas the lower limit of effective reservoir with weak hydrocarbon expulsion power is high.On this basis,the"dynamic"lower limit evaluation method of tight sandstone gas is established with parameters,such as abnormal pressure(hydrocarbon expulsion power),breakthrough pressure(hydrocarbon expulsion resistance)and displacement pressure(migration resistance)of source rock.This method can be accurately used to evaluate the tight sandstone gas reservoirs,especially tight sandstone reservoirs near the lower limit of effective reservoirs.It can emancipate tight sandstone gas reservoirs near strong hydrocarbon expulsion power source rocks,which poor reservoir physical properties,therefore,the utilization ratio of tight gas reserves can be improved.This method has achieved a good practical application effect in Ordos and Sichuan basins.