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Model to Predict Tight-gas Sands Previous HitPorosityNext Hit of West Depression in Liaohe Basin, China

Abstract

The Eocene–Oligocene Es3 member of Shahejie formation in our study area is a feldspathic, debris-rich and tight gas Previous HitsandstoneNext Hit Previous HitreservoirNext Hit (Previous HitporosityNext Hit 2.4–10.4%, permeability 0.09 −0.38 md), a consequence of depositional attributes (grain composition, size and sorting) acted upon by diagenesis (significant mechanical and chemical compaction, precipitation of carbonate cements and authigenic clays, and deep-burial cementation by quartz) throughout the time. Considering these impacts, a comprehensive Previous HitporosityNext Hit prediction model is developed based on the correlation between sedimentary facies and diagenesis. The result could also provide for the exploration of other tight gas Previous HitreservoirNext Hit. Based on the analyses of sedimentology and petrography data of 80 cored wells, the study investigated the distribution and influences of Previous HitporosityNext Hit, established a model by the following steps: (1) Diagenesis index (ID) was established integrating with temperature, Ro, quartz overgrowth, I/S and depth and its relationship with Previous HitsandstoneNext Hit Previous HitporosityNext Hit was determined to build the exponential Previous HitporosityNext Hit model. (2) Sedimentary facies index (IF), which was higher in the advantageous sedimentary facies, was calculated by the distribution of porosities in different sedimentary facie during each diagenetic stage. (3) The ultimate Previous HitporosityNext Hit model based on the relationship between the exponential Previous HitporosityNext Hit model and sedimentary facies (IF) was developed since the Previous HitporosityNext Hit was the cumulative effects of sedimentary facies and diagenesis. This improved model can also restructure the evolving history of the Previous HitreservoirNext Hit aside from Previous HitpredictingNext Hit present Previous HitporosityNext Hit. The improved model was applied to 16 wells from slope to sag throughout the field. A comparison of predicted and measured porosities showed and 1.84% average absolute error with the pore-filling of 16%. This indicates the model may be used elsewhere to predict porosities. The results show that: Previous HitporosityNext Hit decreased sharply by compaction during the early diagenetic stage; secondary Previous HitporosityNext Hit developed in the middle diagenetic stage A1-A2; the Previous HitreservoirNext Hit became tighter with the continuous compaction alongside with quartz and carbonate cement. The Previous HitreservoirTop in the middle diagenetic stage A1 can be described as conventional and stage A2 unconventional.