| Nowadays, most oilfields have entered highly water-bearing period and the conflicts between various factors of reservoir have been increasingly stood out as water flooding been applied. It is useful to analyze geological characteristics of reservoirs and the rule of oil-water movement through evaluating the effect of development by water injection, which can provide instructions for efficient and rational development of the reservoir.The upper Karamay formation oil reservoir in the8th zone of Karamay oilfield is fan delta deposit formed by alluvial fan and anastomosed stream, the average thickness of reservoir is218m and its stratigraphic position from top to bottom are sand layer Sin S2、S3、S4and S5. The sand layer S1and layers from S2to S5is fan delta-plain subfacies and fan delta-front subfacies respectively. The deposition thickness of layer S1、S2and S3is about100to120m, with an average porosity of15.5and average permeability of22mD, and the thickness of layer S4and S5is about80to100m, with an average porosity of13.9and average permeability of12mD. Therefore, the reservoir property is medium pore and low permeability reservoir. In addition, there are interlayers with thickness of about4to14m developed between the sand layers.Since the oil reservoir was developed in1982, it gone through four stages, including productivity construction stage (from1982to1984). high and steady yield stage (from1984to1988). depletion stage (from1989to1994) and comprehensive regulation stage to control production decline(from1995to now). From the later half of1995, there were about103oil wells and22water wells as adjustment wells been gradually drilled. With the implementation of adjustment program, the reservoir has been acquired a satisfactory development result—oil production is increasing obviously and water content declining to a certain degree. The monthly mass production was3.462×104t, monthly oil production was1.018×104t, monthly water injection was2.818×104t, annual injected gas-oil ratio was0.97, oil production rate was0.8%and the degree of reserve recovery was19.2%. The current formation pressure is21.3MPa, which is around84.5%of original pressure and the reservoir has come into the middle-high water cut exploitation.The reservoir has the following problems according to the production status of adjustment wells.(1) the injection imbalance is prominent;(2) there are some common problems, including high water content of some adjustment wells in start operation and low efficiency of oil recovery with water flooding;(3) failure to understand the rule of oil-water movement and distribution and potentiality of remaining oil lead to lack guidance for carrying out development technical policy of reservoir.In the paper, on the basis of the current situation of the reservoir, the information of adjustment wells, the results of reservoir geological research, genetic type and distribution pattern of sandstone, the numerical simulation was used to analyze contribution of remaining oil combining the precise reservoir geologic modeling, then modern reservoir engineering methods were used to evaluate the development effect of water flooding and adjustment wells and understand the rule of oil-water movement and reservoir potentiality. All research above can provide proper development program for reservoir and guidance for adjustment measures. There are four following parts of the content of the paper.1. Evaluation of waterflood development efficiency. In the paper, the development indexes were calculated such as water content, water consuming content, water storage rate, water drive index, growth rate of total injection volume, formation pressure and so on. Then the practical production data were marked on the theoretical curve chart plotted by the empirical equations to evaluate development efficiency of Block258and J53, understand the rule of oil-water movement correctly and designate the direction to the further waterflood development.2. Research on the stimulation treatment of oil wells and augmented injection of water wells. The optional simulation with described results mainly depended on fracturing, reverse flooding, re-perforation recommendation and other treatments. From1984to2006, simulation has been administered to the Block258and J53about465times and the efficiency was84.1%. The fracturing has become a quite effective well simulation technology and the output growth (1.01×105t) from it was38.9%of incremental oil. The physical and chemical injections have been carried out because that the target reservoir was a low ultra-low permeability reservoir with high shale content which can cause water e and velocity sensitivity. The cumulative injection was137×104m3.3. Evaluation of development efficiency of adjustment wells. In the start of adjustment, there was not a period of water free production and the water content of most wells is up to40%. The output of single-well was5-7t/d and depleted seriously. The contribution of adjustment wells to the production was upgrading. The adjustment production of the Block258and J53has once been taken up more than60%and80%of the total production since2009, which could prove that the adjustment wells had a positive effect on development efficiency. According to profile analysis, the layer S51"1and S52"2have excellent capacity of fluid production and fluid entry. In addition, the Lorentz curve proved that the fluid producing and fluid entry profile distributed uniformly and the interlayer conflict was small.4. Research on distribution rule of residual oil and its influence factors. The distribution patterns for vertical remaining oil are that the best-to-produce layers are S51-1、S51-2and S52-1and accumulated oil production rate is larger than the proportion of their reserves in all natural gas reserves; The distribution patterns for horizontal remaining oil are that the potential regions locate around the faults or interwell formation with weak waterflooding in belt and sporadically. The well field531and J531with rich remaining oil have more blocks with high abundance reserves and high oil saturation than well field258. And the distribution of remaining oil is determined by faults, well pattern, sand body and precipitation facie.5. Research on the liquid and oil production rates of well group. The design project of liquid withdrawal rate was researched according to the factors of zone position and development efficiency of well group and reservoir precipitation facie. The conclusion was drew that the proper liquid of Group8215were2.8%and8237were2.3%and the rates of Group8280were8%.6. Research on water intake per unit thickness of well group. In order to keep formation pressure, it is necessary to optimize water intake per unit thickness when liquid production rate being determined. The best injection-production ratio is1:1through injection-production project design, and the average water intake per day of injection wells in Group8215、8237and8280are10.9m3/d·m、8.9m3/d·m and9.4m3/d-m respectively. |
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