The Mechanism Study And Field Application Effect Evaluation Of The Enrich-gas Miscible Flooding In Zarzaitine Oilfield

The Zarzaitine oilfield in Algeria ILLIZI basin has been exploited over50years. The F4top layer which is the main layer has already been shut down because the high water cut and high degree of reserve recovery. But remaining geological reserves still accounts for17%of the total reserves of oil field, which have great potential for the exploitation. The polymer chemical flooding can’t be implemented as the result of the ground facilities, natural environment and local policies. Meanwhile more than80ten thousand Cubic meters nature gas has been lighted. So the miscible flooding mechanism research and application effect assessment has been evolved. The research includes the reservoir characteristics and the choice of pilot site, miscible flooding mechanism, physical model experiment research, and simulation research and field application effect evaluation. The main knowledge obtained as follows:1) From the reservoir characteristics, with the history and current situation of the reservoir, the residual oil distribution has been researched; according to the screening criterion of the miscible flooding with enrich gas, the suitability to hydrocarbon injection has been investigated and the two pilot test areas which are typical in terms of geology trait has been selected.2) Much literature reviewed, the phase behavior during the injection has been summarized and the mechanism of the gas injection has been realized; different kinds of miscible displacement has been analyzed for the pros and cons and finally the method to simulate the phase behavior of the multi-contacted miscible flooding has been given.3) The approach to minimum miscible pressure and the minimum miscible composition has been in retrospect and induced; the long slim tube tests, the experiment of oil expansion and viscosity reduction and the long core displacement tests have been conducted.4) The fluid phase behavior in the pilot test areas has been fitted and the long tube tests has been simulated, the simulation software has been applied to study the enrich gas contact with the crude oil in the front and the rear of the injected gas; the simulation results show the enrich gas with the minimum miscible enrichment can not miscible with the crude oil physically; the error that the enrich gas with the minimum miscible enrichment miscible or not, of the long tube tests and the simulation is about13-17%.5) The small well spacing well group has been introduced to evaluate the pilot test of the enrich gas for miscible flooding; the well spacing has been optimized as per the grey incidence decision model and the injected amount, slug size, injected method and the injected layers has been optimized with the simulation software and at last the proposal scheme for the pilot test has been provided.6) The injection and production performance of the pilot test have been analyzed with the simulation method, etc. Gas channeling was distinctly in the first WAG cycle of the area IV and the’impulse’was markedly in the well group of the area IA. However, the oil and water production rate increased and decreased obviously respectively in both test areas. 7) Three methods, miscible condition, phase behavior simulation and the change pattern of the production’s physical property are used to determine the miscibility; the result shows that the enrich gas miscible with crude oil. The variation of the oil saturation distribution in the test areas has been analyzed; the statistic of the production index in the test areas has been done; the displacement effect of the pilot test areas has been appraised. The result shows that the pilot test in the field was successful. However, the enrich gas overflowed obviously because of the well pattern’s defective.All above, the reservoir characteristics, the selection of the pilot test area, the mechanism of the miscible flooding, the physical modeling and the numerical simulation of the enrich gas miscible displacement and the appraisement of the field tests are supplied to provide a green, low carbon, sustainable tertiary oil recovery technology for the Zarzaitine oilfield. Meanwhile, an integer package of techniques from the mechanism of the miscible to the evaluation of the gas injection has been established. Lastly, this paper can also be a technique mirror for the enhance oil recovery after water flooding of the oil reservoir with medium to high permeability, high water cut and high oil recovery.