| At present, the proportion that low permeability oil reserves which have been developed in China accounts for total producing reserves is getting larger and larger. With the further development of oil field, injection water or edge-bottom water of parts of blocks creates the fingering or coning appearance along the high permeability, large pores and micro cracks by reason of flat contridiction and intrabed contridiction. This phenomenon results in earlier water breakthrough and faster water content ascending velocity, which leads to the production decline and oil recovery rate reducton. With the extension time of oil field development, this increasingly prominent contridiction has become one of the main influencing factors of stable production. As an effective means to solve flat contradition and intrabed contradition, profile control and water shutoff technology in low permeability oilfield is getting more and more important.Water shutoff technology in oilfield has been put into application for over50years. Profile control of injection well has been developed on the basis of water shutoff technology. Its development experienced5stages:first stage-exploration and research; second stage-oil well water plugging and mechanical water plugging; third stage-profile control of injection well; fourth stage-overall profile control water plugging of oilfield blocks; fifth stage-profile control of depth reservoir. Deep profile control and displacement technology of weak gel has been developed in recent years as a new technology in EOR, which is used for water injection wells in deep processing in order to improve the development effect of water flooding in well group. This technology uses polymer of which concentration is close to polymer flooding and add to a little delay crosslinker to make it slowly generate weak gel in formation. On one hand, weak gel has the plugging effect. On the other hand, as the crosslinking intensity is not very high, weak gel can slowly move to the deep part of formation in the preferential path by the push of subsequent injection water and then generates the effect like polymer flooding. This dynamic sweep effect is much better than the fixed gel sweep effect, which can enlarge the swept volume and improve oil displacement efficiency on a lager extent.Gaoji Oilfield is located in Chenqiao-Jinbei Township, Jinhu County, Jiangsu Province. Its structure position is located in the middle part of west slope in Jinhu depression. It is a layered structure reservoir locally affected by physical property and lithology. Gao7block is one of the main block in Gaoji Oilfield. Its main oil-bearing series are E1f22、Eif23. The E1f22limestone reservoir can’t be developed separately because of its oil reserves being less than the other reserves. Thus, the oil-bearing series-E1f22、E1f23are a set of development layer system. The oil-bearing area is1.7km2and geological reserves is157×10t. The geological reserves of E1f2limestone reservoir is33×104t. The geological reserves of E1f23sandstone reservoir is124.0×104t. The effective thickness of Eif22and E1f23reservoir is respectively4.1m and7.9m. They are the middle-shallow layer、middle bearing、and low-middle deliverability small integral-type assembling fault block reservoir. The fault block has been put into producing test since1996and has been put into waterflood development since1997.By June2013,19oil wells of Gao7block of Jiangsu Oilfield are open, composite water cut is73.8%, yearly oil production is1.03059*×104t, oil recovery rate of geological reserves is0.66%, degree of reserve recovery geological reserves is22.57%.11water injection wells are open, average daily water-injection rate is25.2m3/d, yearly water-injection rate is7.8073×104m3, monthly injected gas/oil ratio is1.31, cumulative injected gas/oil ratio is1.02, injection and production roughly achieved a balance, injector producer ratio is1:1.72. The heterogeneity of Gao7fault block is longitudinally and planely serious. And it’s entry profileis poor. Injection water formed dominant flow paths along the high capacity channel and high permeability zone, which led to the rapid water-cut asending.This paper analyses the Gao7block reservoir of Jiangsu Oilfield and its development features. Combine the indoor core water-plugging experiment, weak gel, which is made from HPAM、crosslinker and auxiliary is respectively injected into single and parallel core with high、middle and low permeability. Then test the plugging effect and get the start-up pressure gradients and entry profile after being plugged. Use CMG reservoir simulator to invert the experimentation and give reasonable static and dynamic parameters to numerical simulation model according to the experimental data. Then set well spacing pattern, which is nearly similar to the physical experiment, and reasonable time step. And use simulated physical modeling experimentation by the corresponding constant pressure and liquid of producer bottom, injection pressure and entry profile of numerical simulation are matched by changing the adsorptive capacity and participant resistant coefficient.Uniflow mathematical model is established to optimize profile control agent injection rate and injection pressure. Assume that wellhead pressure of injectivity profile modification well is reasonably controlled and profile control agent only flows into the high permeability zone (profile control layer) in the injection process. Assume that low permeability zone (non-profile control layer) is not contaminated and the performance parameters(concentration、viscosity、density ect.) of profile control agent are constent. The layer is horizontal homogeneous thickness and ignore the elastic effect of liquid and rock stratum. In combination with profile control agent physical simulation flooding experiment, A uniflow profile modification agent optimization mathematical model is established. In the implementation process of profile control, reasonable injection pressure can ensure the profile control agent flow into the profile target zone as much as possible and then prevent target zones from being contaminated. Thus, the goal of stabilizing oil and controlling water can achieved. In the process of injecting profile control agent, the pressure of the injection system is balanced at any time. Thus, pressure equation of uniflow profile control construction can be established according to the pressure balance theory and filtration theory. |
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