Research On Dynamic Mechanism Of Hydrocarbon Expulsion From Carbonate Source Rocks In Northern Tarim And Its Surrounding Areas

Tabei and its adjacent Shunbei area are the key areas of exploration and development in Tarim area in recent years.Previous studies on carbonate source rocks in Tabei area have proved that carbonate source rocks contribute to oil and gas accumulation in the study area.However,due to the lack of quantitative research on the generation and expulsion of oil and gas from carbonate source rocks in the study area,the contribution of carbonate source rocks in Tabei and its adjacent areas to oil and gas resources is not evaluated enough.Hydrocarbon expulsion can occur only after the source rocks meet the various residual requirements of self adsorption,water-soluble,oil-soluble and liquid forms.The actual residual hydrocarbon amount of source rock calculated by pyrolysis data is different from the residual hydrocarbon amount of source rock hydrocarbon expulsion threshold simulated by mathematical model,so as to judge the effectiveness of carbonate source rock in the target horizon.Using the corresponding logging curve characteristics of the identified effective source rocks,the logging comprehensive evaluation index is established to identify the effective carbonate source rocks.On the basis of single well identification,the well connection profile and plane contour map are established to analyze the distribution characteristics of the effective source rocks.The thickness of carbonate source rock in the South and southeast of Tuole uplift is more than 20m,and the thickness of effective source rock in the South and southeast of Tuole uplift is not thinner than 200m.The principle of material conservation shows that the total amount of elements in organic parent material before and after transformation should be consistent.According to the phenomenon that the total amount of elements remains unchanged,combined with the geological and geochemical characteristics,a mathematical calculation model is established.Combined with the distribution characteristics of effective source rocks,the hydrocarbon generation of middle and Upper Ordovician carbonate source rocks in the study area is calculated.The results show that the source rocks generate gaseous hydrocarbons 116.0889×10¹²m³,liquid hydrocarbon 549.0057×10⁸t.Based on the characteristics of hydrocarbon expulsion threshold residual hydrocarbon amount of source rock simulated by theoretical model,combined with the distribution of effective source rock,the residual hydrocarbon amount of source rock is simulated and calculated.Based on the simulation analysis of hydrocarbon generation characteristics and residual hydrocarbon characteristics,the hydrocarbon expulsion characteristics of source rocks are analyzed.The simulation results show that the amount of residual gas in the study area is 3.5083×10¹²m³,residual liquid hydrocarbon 11.582×10⁸t,gas discharge 112.5806×10¹²m³,liquid hydrocarbon quantity 537.4237×10⁸t.Combined with the oil and gas migration and accumulation coefficient in the study area,the gas resources available for accumulation formed by the middle and Upper Ordovician carbonate source rocks are7161×10⁸m³,oil resource 20.225×10⁸t.According to the theoretical calculation models of different hydrocarbon expulsion forces,the correlation between calculation forces and oil and gas displacement can be simulated,and the relative contribution of different forces can be determined.According to the magnitude and relative contribution of hydrocarbon expulsion force,the amount of fluid discharged and the phase state of oil and gas in different depth ranges,the fluid expulsion process under the hydrocarbon expulsion force of carbonate source rocks in the study area can be divided into four stages:（1）compaction and fluid expulsion stage;（2）Compaction,dehydration of clay minerals and molecular diffusion,a small amount of hydrocarbon expulsion stage;（3）Multi dynamic multiphase hydrocarbon expulsion stage;（4）Capillary force,product compatibilization force and thermal expansion force discharge free gas stage.