Study Of Hydrocarbon Inclusions In The Lianglitage Reservoir Of The 26-82 Wellblock Of Tazhong

The Tazhong 26-82 wellblock is located in the central and eastern area of No.I Tazhong slope break. It is the primary reservoir of condensate oil and gas in the Tangzhong area. The corresponding reservoir bed is Lianglitage Formation, especially sections 1 and 2, whereas the cap rocks are mudstone of Sangxiu Formation.For the reservoir of Langlitage Formation in the Tangzhong 26-82 wellblock, petrographic observations were carried out for the relevant hydrocarbon inclusions to classify the development periods for these inclusions. The homogenization temperature for the hydrocarbon inclusions, together with both homogenization and freezing temperatures for the coexisting aqueous inclusions, were determined to further characterize various periods for the formation of these hydrocarbon inclusions. Our results indicate the hydrocarbon inclusions in Ordovician reservoirs of Tazhong fall into four periods as described below. The hydrocarbon inclusions of periodⅠ(Ⅰ-OL) are black oil inclusions with no or darkish fluorescence, and primarily occur in the early calcite veins. The hydrocarbon inclusions of periodⅡ(Ⅱ-OL+OLG) are dominated by colorless to paleyellow oil inlusion which exhibit yellow to yellowish-white fluorescence of moderate intensity, and are mainly distributed within early calcite developed in holes or near sutures. Those of periodⅢ(Ⅲ-OLG+OG) are mainly colorless to palebrown oil-gas inclusions accompanied by a few gas inclusions of black color. They yield strong tinwhite to blue fluorescence, and primarily occur as monoliform or directionally in the healed fractures. Most of the hydrocarbon inclusions for periodⅣ(Ⅳ-OLG+OG+OA) are palebrown to brown oil-gas ones with strong yellow- to tan- colored fluorescence. There also exist small amounts of gas inclusions and brown yellow asphalt inclusions in half-open state. They seem to be mainly developed near tension cracks as monoliform or within half-filled calcite veins in groups.The biomarker compounds by GC/MS were further analyzed for the hydrocarbon inclusions of periodsⅡ,ⅢandⅣ. Our results demonstrate the biomarker compounds for the hydrocarbon inclusions of periodⅡresemble those of Middle to Upper Ordovician source rocks, whereas the oil in hydrocarbon inclusions of periodⅢ/Ⅳhave similar biomarker-characteristics to Cambrian to Lower Ordovician source rocks.In addition to the work above, the burial history for the reservoir and the spatial occurrence of source rocks were considered to define the corresponding formation time and source rocks for these four periods of the hydrocarbon inclusions from the Lianglitage Formation, respectively. The hydrocarbon inclusions of periodⅠmight form in the period of Late Cambrain to Early Hercynian and primarily derived from Cambrian source rocks. The source rocks for the hydrocarbon inclusions of periodⅡare likely to be Middle and Upper Oridivician, and the development timing seems to be in Late Hercynian. The hydrocarbon inclusions for periodⅢwere derived from Cambrian to Lower Ordovician source rocks. Although the hydrocarbon inclusions for periodsⅢandⅣboth developed in Himalayan, the hydrocarbon inclusions of periodⅣindicate an incomplete mixture between the high-maturity condense oil from Cambrian to Lower Ordovician and the normal oil from Upper Ordovician. This implies the oil formation represented by periodⅣmight be the continuation of those represented by periodⅢ. Therefore, the condensate oil and gas preserved in the Lianglitage Formation of Tazhong area was primarily accumulated in Himalayan and derived from Cambrian to Lower Ordovician source rocks.