Modelling Study Of Gas Migration And Accumulation Of Volcanic Rock

The Xujiaweizi Fault-Depression is a large and widespread depession accumulated with volcanic gas in SongLiao Basin. The main gas reservoir space in Xujiaweizi Fault-Depression is the volcanic rock body the first and third of K1 yc Formation. By far, the proved geological reserve that has been submitted is more than 2.4×1011m3, and display the great exploration potential for volcanic gas in deep formation of Xujiaweizi Fault-Depression. However, there are many problems in the study area, such as indetermination of the generation and expulsion timing of each gas resource rock, the ambiguous accumulation process and the forming-reservoir complexity of volcanic gas.The paper detailedly implement the four accumulation elements, that is the source rock, coming from the coal and mud rocks of K1 sh Formation and J3 h Formation; resvoir, which contains the first and third members of K1 yc Formation; cap rock, which is the first member of K1yc1 Formation and the first and second member of K1 d Formation, the first and second member of K1 q Formation, and the overlying strata; and carry out 1D, 2D and 3D basin modeling study of gas-bearing system of volcanic rock in the Xujiaweizi Fault-Depression. The conclutions are as follows: ① The character of the three-dimensional heat flow space-time field can be showed as below: the paleo-heat flow in Xushen7 well is lower, the value in Fangshen, Weishen and Chaoshen is higher, and it is higher in the uplifts than in the low-lying place. Moreover, paleo-heat flow is the higher, present heat flow is lower. ②The paper successfully implant the kenitic parameters into basin model, and successfully connect the mathematical model with the geologic model. ③ The deep volcanic rock in Xujiaweizi Fault-Depression developed vocanic weathered crust of certain thickness. The volcanic rock weathering crust mainly developed in structural high position and slope belt. The thickness of the dissolution belt and disintegration zone within volcanic weathering crust of Xujiaweizi Fault-Depression was about 100 metre, and consistent with the actual gas reservoir exploration position. ④Contrastively analysising the basin modeling result of four different migration arithmetics( FP, IP, Darcy, Hybird), we selected the compounded method(Hybird) as the most suitable method to gas migration and accumulation of volcanic rock. ⑤The results of 3D basion modeling turn out that: stratal uplifting and corroding can promote gas accumulate to form reservoir, as is the openning time of fault. ⑥2D and 3D basin modeling results revealed the process of gas migration and accumulaiton. That is, gas source rock from K1 sh Formation and J3 h Formation in the last phase of K1 yc Formation begin to generate gas, and has definite scale to generate gas in the last phase of K1 d formation, and the time from the last phase of K1 q Formation to the early sedimentary period of K1 qn Formation is the main accumulation and expulsion timing of volcanic gas.