| The regular development technique of thin interbed low permeability marginal reservoir faces high risk and low economic effect problems. So far in the worldwide there are successful cases of this type reservoir been exploited by unconventional techniques such as horizontal well and gas injection. The F4-V reservoir of M oilfield is a classical thin interbed low permeability marginal unit, the reserves producing degree is relative low. The oil field is located at Illizi basin with abundant nature gas resource. So two enriched gas injection technique has been employed twice in the medium and high permeability eard of F4main productive unit and positive achievement have been obtained. In this paper, for the purpose of enhancing oil recovery and studying the development pattern of gas injection, the gas injection technique for F4-V reservoir has been researched and the main results and achievement are presented as follow:(1)The reservoir characteristic of F4-V reservoir has been studied and the suitability of gas injection has been analyzed. F4-V reservoir is a classical thin interbed low permeability marginal unit with good physical property. the reserves producing degree is relatively low. So the gas injection technique is suitable.(2)The feasibility research and pilot experiment achievement of miscible flooding have been analyzed. In F4reservoir, en-riched gas flooding achieved positive results including the forecast and implementation. The OOIP recover was enhanced4.87%-11.79%. In the meantime, the influence of well pattern perfection and injection method on displacementefficiency have been analyzed.(3)Based on the PVT experiment, the fluid phase behavior has been fitted. By virtue of slim tube experiment and phase simulation, the miscible mechanism has been studied and the MMC has been determined. Under the reservoir condition, the LPG amount in knee point method was39.4%. which was3.5%higher than94%method and1%higher than phase behavior simulation method. The cost of enriched gas is high so the EMC gas (economical miscible component) is suggested to utilize as gas injection medium.(4)The gas injection technique for thin interbed low permeability marginal reservoir has been systematically analyzed in several ways such as injection timing, injection method, flooding pattern. Then the flooding parameters, reasonable advises and parameters are given. The research results show:the variation of producing gas density is able to reflect the enriched gas displacement efficiency and quantitatively character the relation of injection amount and residue oil in swept area. Then three new and efficient gas injection method (EWAG, EGAG and EWGAG) are provided. Under the reservoir condition, the MMCs of EMC method and long slim inflected point method are close, so based on the fact of missing long slime tube experiment data, the MMC has been replaced by EMC with conceptual model.(5)The history matching of water flooding shows:the recovery degree of F4-V reservoir is only6.34%. So the V1and V2bed with high reserves abundance were chosen to arrange well pattern and process the gas injection development reservoir engineering project. The simulation results presented:gas injection (EMCenriched gas) achieved excellent development results, the cumulative producing oil amount is338.0620×104m3. In control area, the ROIP recovery is as high as49.57%, the reclaimed proportion of LPG is7.97%. Cumulative net cash flow is good. The results showed that this gas injection method is an effective method to develop the interbed low permeability marginal reservoir. |
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