Characteristics Of Deep Fluid In Ordovician Carbonate Reservoir In Central Tarim Basin

The Ordovician carbonate under the tarim basin has great potential in exploration,while the generation, migration and accumulation of hydrocarbon are closely relatedto the fluid evolution and its influence on the formation. Therefore it is crucial tounderstand the diagenesis and fluid evolution to support the exploration anddevelopment of hydrocarbon in central tarim basin. A lot of researches have beendone on lithology, lithofacies, sedimentary characteristics and regional correlation ofOrdovician carbonate formation based on stratigraphy. It is believed by mostresearchers that the fluid which affects Ordovician carbonate formation originatedfrom magmatic hydrothermal, which formed and evolved associated with themagmatic incident at tarim basin in late Permian.Currently the concept of deep fluid or hydrothermal fluid is still confusing. Propertiesof specific fluid types and the distribution of fluids are not well known. In this paper,concrete analysis is carried out with respect to fluid in central tarim basin according tomineralogy and geochemistry of the filling matter in the pores and the holes,including the analysis of REE characteristics, analysis of carbon and oxygen stableisotopic, analysis of strontium isotope and the studies on fluid inclusion.Result shows that for the fluid which leads to magmatic hydrothermal is characterizedby thermal fragmentation or thermal fading in lithology and special mineralassociation in mineralogy. Compared with surrounding carbonate, the characteristicsof the magmatic hydrothermal fluid crystal substance are as follows: a higher87Sr/86Sr ratio, more tend to negative isotope of13C and18O, a positive anomaly ofδEu, a lower w(Th)/w(U) ratio, higher homogenization temperature of fluid inclusionsand lower salinity. Development of barite and porphyritic gypsum, rich in87Sr, thevalue of34S in pyrite fillings on both sides of calcite is between15‰to30‰, higherw(Th)/w(U) ratio and high values of δCe, higher fluid inclusions homogenizationtemperature(＞120℃), and high salinity is the important characteristics of deep hotbrine crystallization. While the formation fluid show a similarity with surroundingcarbonate in geochemical characteristics.The reformation of carbonate reservoir from the fluids of different origins are not the same. Magmatic hydrothermal fluid isusually acidic and they alter the upper carbonate reservoirs through fluoritization,hydrothermal fluid dolomitization and hydrothermal fluid corrosion.On the other hand,the magmatic hydrothermal can lead to local precipitation of calcite. Deep hot brineoccurred TSR when it met hydrocarbon, TSR often takes the positive role to thecarbonate reservoir. The main effect of formation water is filling holes and cracks.