Tarim Basin Keping Bachu Area Of ​​cambrian - Ordovician Carbonate Reservoir Research

Tarim basin is the biggest oil & gas-bearing one in China, which has huge resourcepotential. Cambrian and Ordivician are the main source rock formation and reservoir.The researching time of this paper is Cambrian and Ordivician. It is based on thesample of carbonatite in the middle and the North-West Tarim Basin and mainly throughthree ways: microfacies identify, the stable carbon and oxygen isotope test, sedimentaryfacies to research the carbonatite reservoir.First, in the middle Tarim Basin, through the thin slice of four well such as zhong 1,zhong 12, zhong 13,zhong 4, it shows the phenomenon that limestones are alternated bydolomite in the biology body cavity and in the sature. It is more available for holding oilbecause the dolomite's crystals are often the macrocrystalline and medium-crystalline. Fromthe Lower Ordovician to the Cambrian, it shows the rule that limestones are transited intodolomite. We also think that the porosity will increase when the dolomite is more than 50%and the dolomite reservoir is better than the limestone. Meanwhile in the Keping and Bachuarea, carbonanite karsts are more developed in the high frequency bed succession cycle.The karsts grow along the bed succession and approve that the bed succession is the mainterm of controlling the karsts.Second, the method of stable carbon and oxygen isotope is proved to available todistinguish the diagenetic environmenthas. In the middle Tarim Basin, the dolomite rocksshow that the number boundary of δ¹³C is -1.80‰ and the δ¹⁸O is -6.60‰. Thedolomite rocks of Lower Ordovician are mainly built up in surface-evaporation-marinediagenetic environmenthas;The dolomite rocks of Cambrian are mainly built up in burieddiagenetic environmenthas. There is much data tested from 45 carbonate samples ofCambrian and Ordovician period taken in the Keping and Bachu area in the tarim basin. Theresearch result indicates that the δ¹³C values shift towards obviously higher positivevalues in marine diagenetic environment. While in buried diagenetic environment, the δ¹³C values shift towards relatively higher negative values. From the Z value which wascalculated usingδ¹³C and δ¹⁸O, we can see that meteoric diagenetic environment has littleaffect on the carbonate environment. In the sequence stratum, theδ¹³C values showgradually increase with the stratum sediment. ⁸⁷Sr/⁸⁶Sr shows that the geographicenvironment is lower than the average sea level.Last, precipitation facie is the important key to the diagenetic process of dolomite inthe Middle Tarim Basin. With the time-lapse, the diagenetic evolutions of dolomite displaythe rule from the west to the east: penecontemporaneous dolomitization, refluxdolomitization, admixing water dolomitization. There is always different in porosity andpermeability for different dolomite origin. We common think that juvenile origin dolomiteand penecontemporaneous dolomite do not available for the reservoir. However, recirculateand admixing water and buried dolomitization is more available for the reservoir.