Research On Fluid Inclusions Of Ordovician Carbonate Rocks Reservoir, In Tahe Oilfield

Tahe region showed significant oil and gas, the Ordovician is the most important production layer of Tahe Oilfield, and has good prospects for oil and gas exploration. This paper studied the characteristics of fluid inclusions, different types of diagenesis and their relation with reservoir, based on technical methods of fluid inclusions and a lot of information and previous results, in Tahe Oilfield. Results showed that :(1)Through a large number of microscopic observation, we identified Tahe Oilfield fluid inclusion characteristics of the lithofacies and reservoir. Fluid inclusions with disparity size and diverse shape, can be broadly divided into H2O inclusions, inclusions of organic matter, organic matter-H2O inclusions in three categories. In addition to liquid water and liquid water inclusions inclusion,here are still single- facies hydrocarbon inclusions and two- facies hydrocarbon inclusions; Tahe region mainly has liquid water and two- facies fluid hydrocarbons inclusions; In the early stage,calcite mainly has pure liquid inclusions, in the late , while consisting mainly of gas-liquid inclusion of organic matter and the two- facies water inclusions .(2)Homogenization temperature and salinity of brine inclusions, were systematicly determined in Tahe Oilfield through the host mineral occurrence, the study area is divided into six types of fluid inclusions to discuss: Calcite veins, quartz veins, karst cavity in calcite (including megacrysts calcite), cavernous dolomite, cement and crystal dolomite. Then, the selection of the S65, S67, S88 wells in the verticality and horizontality, were detailly studied.(3) After homogenization temperature testing, Tahe Oilfield is filled by calcite of five different periods in the seam and cavity: the first phase (homogenization temperature of 50~70℃), is liquid water inclusions, in syngenetic stage. the second Phase (homogenization temperature of 75~100℃), is pure liquid water inclusions, occasional inclusions of organic matter, in shallow burial condition; the third Phase (homogenization temperature of 110 ~ 125℃), gas-liquid waterinclusions and two-facies liquid water inclusions, middle-deep bury; the fourth phase(homogenization temperature of 130~160℃), a large number of hydrocarbon inclusions and gas-liquid Water inclusions, deep bury;the fifth Phase(homogenization temperature of the more than 170℃) , Hydrothermal fluids. Then, we respectively compares homogenization temperature of the calcite of the cavity, quartz veins, and crystal dolomite and cavernous dolomite with temperature stage of calcite vein.(4) the homogenization temperature of brine inclusions mainly converge between 50~160℃in Tahe Oilfield. The calcite in seam cavity and hole has low, middle and high salinity in three stages; quartz vein, crystale dolomite and cavernous dolomite are of low temperature-high salinity stype.Through the relationship points between homogenization temperature and salinity,density of the liquid was obtained, and it proved the conclusion of high temperature-low salinity-lowdensity, medium temperature-medium salinity-medium density, low temperature-high salinity-high density.(5) the formation time of calcite in cavity and hole is classified as the contemporaneous stage, early diagenetic stage, medium diagenetic stage, lately diagenetic stage stage and lately hypergene diagenesis (because of the Ordovician experience of polychronic exposure) in five stages; in the Tahe Oilfield.The cement and low temperature quartz vein can be considered as being connected with atmospheric fresh water and the and shallow–medium burial condition;The dolomite sample materials are located in Penglai dam group, away from the unconformity surface, so,it can be connected with midium-deep, deep bury;Five fluid is filling the five holes of the middle period of Caledonian and early phase of Hercynian. At the same time, Tahe oilfield has experienced five major diagenetic environment:normal shallow diagenetic environment, the atmospheric freshwater diagenetic environment On the surface, early shallow burial diagenetic environment, upliftedly exposed surface atmospheric freshwater diagenetic environment, shallow-deep burial diagenetic environment in five diagenetic environment.(6)According to the fluid temperature,this paper explained Oilfield polychronic cement and polychronic filling in the Ordovician,in the Tahe oilfield; the existence high-temperature fluid inclusions, proved the existence of hydrothermal fluid in the study area; the existence of low-temperature fluid inclusions well explaned the phenomenon of polychronic karstification; according to oil and gas inclusions with Brine inclusions,it judged the maturity of oil and gas; according to the temperature of fluid inclusion of oil and gas,it obtained the filling time of oil and gas , it is concluded that natural gas filling occurred in the late Hercynian, Indosinian-Yanshanian, early and mid-term Himalayan, the late Himalayan, and main accumulation period occurred in the late Hercynian.