Source Rock Evaluation In Cambrian Of The Northwestern Tarim Basin

The main structures in the northwest of Tarim basin are Kalpin uplift, Patruluplift, Makit slope and Awat fault depression. This region is both in the Tarim basinand South Tianshan mountain intracontinental structure and the geology condition iscomplex. It has huge potential for producting petroleum. Though much explorationhas conducted in this region, the evaluation of Cambrian hydrocarbon source rock isstill uncomprehensive, such as the spatial distribution, the geochemical characteristicsand the evolution history. Our study aimed at the comprehensive evaluation ofCambrian hydrocarbon source rock in northwest Tarim basin, discussing therelationship between growth of high-quality hydrocarbon source rock andsedimentary facies, calculating the petroleum resources quantity of the key area, andguiding the exploration in the future.The hydrocarbon source rocks in northwest Tarim basin include argillaceous rockand carbonate rock. The argillaceous rock mainly distribute in Kalpin uplift and Patruluplift. Kalpin uplift argillaceous source rock mainly located in Yuertus formation,lower Cambrian. Represented by Xiorbrag section, the thickness of high abundancehydrocarbon source rock is about6-8m. on the whole, the thickness of argillaceoussource rock decreases from the north Patrul uplift to around., and the thickest part isabout40m. Carbonate source rock widely distributed in northwest Tarim basin, thethickness decreases from Patrul to Awat fault depression and Makit slope,the thickestpart is about200m.Combined the research achievement of eighth five-year plan, ninth five-year planand thrice resource evaluation and practical geochemical characteristics of the studyregion, we consider that organic carbon bottom is about0.5%, separately in highmaturity region, the maturity reduce to0.4%. Northwest Tarim basin hydrocarbonsource rocks are medium or fine, and the potential is huge. The main type of organicmatter is type I or type II. The hydrocarbon source rocks are moderate or post mature.In one word, the hydrocarbon source rocks in northwest Tarin basin are characterizedby well organic matter abundance, valuable organic matter, and high maturity, and considerated as the high-quality hydrocarbon source rock in Tarim basin.The development of high quality hydrocarbon source rock is closely related tothe sedimentary facies. Argillaceous source rock always develops in low energyenvironment such as shelf facies, restricted platform facies and basin facies.Carbonate source rock always develops in high energy environment such as evaporateplateau facies, slope facies and tidal flat facies. The sedimentary facies are mostlyplateau facies in Patrul, shelf facies and basin facies in Kalpin, shallow sea shelffacies in Makit and Awat. It conforms to the distribution of argillaceous source rockand carbonate source rock.By means of simulation analysis of thermal evolution history, the fastigium ofgenerating and exhausting hydrocarbon is from late Caledonian to middle Hercynian.It’s mainly liquid hydrocarbon reservoir forming. In late Caledonian, the organicmatter was high maturity, and generated humid gas and condensate oil. In lateHemalaya, the hydrocarbon source rocks are all high or post mature. It’s in dry gasstage so far.Applying the volumetric method to calculate the quantity of resources, thequantity of resources for oil is7.245×108t, and2.602×108t for gas. The total amount is9.847×108t. Calculating the resources quantity by area, there are7.993×108t oil and3.915×108t gas in Makit, the total amount is11.908×108t. The whole resourcesquantity is21.755×108t in Patrul and Makit. Comparing the resources structure, weconsider that oil is dominate, and the potential of Patrul and Makit is great, suggestingthat explorating as the main areas.