Dynamics And Dynamic Coupling Mechanism Of Hydrocarbon Migration

Research on hydrocarbon migration is one of the most important fields in petroleum geology. But the theory based on the classic Darcy's law is difficult to characterize fluid migration in petroliferous basins at present especially in some rifted basin located in North China, in which hydrocarbon migrated under the background of weak tectonic activity. Research should be run to amend current theory on hydrocarbon migration- In this dissertation, theory of non-Darcy flow has been adopted to study the resistive force, migration agent and dynamic coupling mechanism of fluid migration in the Dong Ying depression. Research has been carried out in two ways including site test and numerical simulation. Some important achievements has been obtained, which wili enrich present theory of hydrocarbon migration.1. Present state on resistance and migration agent in hydrocarbon migration processCapiliary-pressure models and concepts have been used to evaluate filtrational resistance in porous media during fluid migration for many years. But the theory based on the classic Darcy's law is difficult to address some problems such as effects of thickness on cap formation sealing and characteristics of fluid migration under the background of weak tectonic activity during hydrocarbon generation process, which are as follows.(1) Existing problems in the research of (?)iltrationai resistance during fluid migration process:i. As mentioned above, capillary-pressure models and concepts have been regarded as the main filtrational resistance on the presupposition that the porous media are hydrophilic, losing sight of the oleophilic case.ii. Research on thickness sealing evaluation now has been restricted to some aspects such as continuity keeping, smear quality and so forth.iii. Non-Darcy flow has already been validated in low permeability media, while it hasn't been widely applied to the field of hydrocarbon migration research. Some work should be done to reappraise filtrational resistance in porous rock.(2) Existing problems in research of migration agent and dynamic coupling mechanism on fluid migrationi. Research of ground stress effects on hydrocarbon migration should be enhanced combined with solid-liquid coupling theory with 3D failure criterion.ii. The study on effects of microfracture activity on hydrocarbon migration has been restricted to laboratory experiments, lacking of site tests. Aditionally, some work using 3D failure criterion should also be carried out to determine the maximum pressure that the source rock could hold.iii. Hydraulic fracturing induced by seismicity has been regarded as the main way for hydrocarbon vertical migration only in view of notable production variety when earthquakes occur quantitative examination should be done to characterize hydrocarbon migration.iv. Effects of microfracrure activity and dilation on hydrocarbon migration have been studied on the assumption that the fault should be active, while little work has been done under the background of weak multiphase tectonic activity.2. Integrative and comparative study on filtrational resistance based on non-Darcy flow theoryNon-Darcy flow theory has been adopted to study hydrocarbon migration. And adsorbing resistance in connection with starting pressure gradient has been used as the most important filtrational resistance for hydrocarbon migration.(1) Comparative analysis on sorts of territorial resistance in hydrocarbon migration has been done in term of per 100m for each territorial cap formation of three territorial cap formations including Middle Shahejie3, Shahejiel and Ming Huazhen in the Dong Ying depression. It indicates that adsorbing resistance in each of the three territorial cap formations has values of 195MPa, 307 MPa, 12200MPa respectively, which is rather greater than capillary-pressure even on the assumption that the porous media are hydrophilic.(2) For the adsorbing resistance in connection with starting pressure gradient, it can be concluded that magnitude of adsorbing resistance is in direct proportion to migration distance. Consequently, for the cap formation, its sealing capacity is in direct proportion to thickness.3. Site test conducted on microfracrure activity induced under pressure charging conditionSite test has been conducted months in the Qing Nan sub-depression to monitor microfracrure activity under pressure charging condition. Five seismic stations have been installed around the water injection well to record seismic activity during the water injection process for 6 months. In the test, there are 5090 seismic events has been picked out manually from the recorded data, 274 failure events have been located. From which some conclusions could be concluded as follows:(1) The site test proves permeability enhancement caused by microfarcture activity under pressure charging condition.(2) Microfracrure activity had been monitored even at a lower rate of pressurization. The maximum rate of pressurization for each interval has been obtained with value of 53% for Shahejie3, 54% for Bottom Shahejie3 and 21% for Upper Shahejie3, respectively 48 percent of located failure events occurred during Upper Shahejie3 injection period, which could confirm stimulation of microfracture activity on hydrocarbon migration induced by point effect of preexist ing microfracture.4. Numerical simulation modeling of hydrocarbon migrationAccording to the requirement that research of crustai stress effects on hydrocarbon migration should combine with the solid-liquid coupling theory, a numerical simulation model of hydrocarbon migration has been proposed.5. Hydrocarbon migration under hydraulic fracturingNumerical simulation has been run to characterize hydrocarbon migration and accumulation using special hydraulic fracturing software, which indicates that more important hydrocarbon migration mechanism should work in the Dong Ying depression under the background of weak multiphase tectonic activity.6. Hydrocarbon migration in the Dong Ying depressionNumerical simulation has been run on the areal model and section model respectively to study hydrocarbon migration and accumulation in the Dong Ying depression using numerical simulation program described in the dissertation. Some important conclusions have been made out as follows:(1) Numerical simulation results indicate that corresponding to the main periods of hydrocarbon expulsion since 20Ma, although formations in the depression became more stabile in the mass, rocks in some main faults and secondary faults such as the segments of Bin Nan-Li Jin fault, eastern Central fault, Baminanhe fault, interjunction of the TG5 and Chen-Wang fault, convergent segment of Lin Pan fault in the Huimin depression reached to failure condition.(2) According to the numerical simulation result, hydrocarbon migration and accumulation in the Dong Ying depression has been studied with microfracture activity and dilation mechanism under the background of weak multiphase tectonic activity. The result indicates that hydrocarbon migration and accumulation in faults does not flow like that in hydraulic fracturing process, oil abundance in lower permeability reservoir will be lower than that in hydraulic fracturing process. and in this way, higher permcability in the fractured dilation zone of the fault will be kept in long duration, which would be propitious to oil reservoir in shallow layer. While there are still some disadvantageous respects for hydrocarbon to accumulation and conservation such as forming viscous crude or more geologic hazard during oil field exploitation.(3) Investigation on these fractured dilation zones of the fault zones mentioned above combined with exploratory development cases in the Shengli oil field shows that there are more geologic hazard during oil field exploitation, more viscous crude reservoir formed, or more higher recover ratio in the field around the belt which reaches to the failure condition mentioned above, which indicates that hydrocarbon migration and accumulation in microfracture activity and dilation mechanism under the background of weak multiphase tectonic activity might be another very important mechanism.7. Numerical research on the maximum pressure in source formation under pressure charging conditionNumerical simulation research has been run to obtain the maximum pressure in formation under pressure charging condition with the numerical simulation program for injection formations including Shahejie3 and Shaheje2 in the Qingnan sub-depression which has been taken as a region of interest. Simulation result shows that formation would reach the failure condition when fluid pressure in each interval approaches to the value of 0.85 times the minimum horizontal principal compressional stress in spite of the depth or lithologic character of the formation, which indicates that fluid pressure with value of 0.85 times the minimum horizontal principal compressional stress could be regarded as the maximum pressure in source formation under pressure charging condition.8. Modified modle of hydrocarbon migration and accumulationAccording to intergrated study on filtrational resistance in porous rock, site test conducted on microfracture activity induced under pressure charging condition in the Qinnan sub-depression, numerical simulation run in Dong Ying depression and Qinnan sub-depression respectively, a modified modle of hydrocarbon migration and accumulation style is suggested to characterize hydrocarbon migration under the background of weak multiphase tectonic activity.9. Achievements obtained(1) Non-Darcy flow theory has been adopted to study hydrocarbon migration. And adsorbing resistance in connection with starting pressure gradient has been counted as the most important filtrational resistance for hydrocarbon migration, which puts stress on thickness sealing.(2) Site test and numerical research under pressure charging condition indicate that permeability enhancement will be induced even at a lower pressure ratio, while fluid pressure with value of 0.85 times the minimum horizontal principal compressional stress could be regarded as the maximum pressure in source formation under pressure charging condition.(3) Numerical research combined with exploratory development cases in the Shengli oil field indicates that hydrocarbon migration and accumulation in microfracture activity and dilation mechanism under the background of weak multiphase tectonic activity might be another very important mechanism.