Ordovician Carbonate Reservoir Evaluation In Salt Covered Area Of Tahe Oilfeild

The location of interest regoin is in the south of Tahe oilfield where it is covered with salt layers. Between 2002 and 2003, there were many wells deployed here such as S105, S106 and so on. All of these wells proved that Ordovician carbonate is more prospecting. Now, three reservoirs are confirmed: Yingshan, Yijianfang and Lianglitage formations, but there are little knowledge on them and many difficulties in the producing process. With the exploration and development going in depth, the number of oil well is decreasing while the number of water well is increasing.In order to broaden discovery and increase reserves, this paper has done some analysis work based on drill core, physical property, well logging, seismic data and well testing. Beginning with study on reservoir category, laying emphasis on seismic properties prediction and conventional and image logging analysis, using the method of step marks, distribution of carbonate reservoir can be cleared. Combining reservoir physical properties and well testing data, hydrocarbon favorable area is pointed out.Due to all kinds of diagenesis such as compaction, pressolution and so on, porosity space is mostly fractures and caves. According to its array mode in space, three reservoir types are recognized as cave-fracture or fracture-cave, fracture and fracture-fissure reservoirs. On application of seismic and well logging method, different response models are built up based on different type reservoir. (1) Through extracting various parameters such as amplitude rate, fine coherence, phase rate, amplitude absolute value and average instant frequency, seismic response model is built up: palaeostructure and strong moniliform reflection, strong amplitude rate, low frequency, strong phase rate and low coherence. (2) Logging response model of effective reservoir is also established: decreasing on deep to shallow resistivity log and positive separation, increasing on neutron porosity log, increasing on acoustic log, decreasing on density log and increasing on caliper log. In FMI, fractures often look like dark sine curve while caves often like black gravel with disperse state.Reservoirs with good physical properties mainly extend in warp direction near salt wedge out, and develop more favorable in the west part than the east part. Well testing data shows that hydrocarbon favorable area is consistent with reservoir. Fields such as S116-S117-S106-3, S111, S108, T904-S107 and S112 are more profitable.