| West 259 located in the southwest of the northern Shaanxi slopes of Ordos Basin, and its Chang 3 reservoir has been extensively exploited since 2008. Recently, it was found that the number of the wells with water increased year by year,and the average productivity of single well was low, together with the productivity of Oil well was quite different, and the situation of stable production was grim.Based on that, it is necessary to carry out research on the root cause of low productivity of single well, then Propose technical measures adapt to the study area. This is of great theoretical and practical significance to stable production. In this paper, comprehensive research of the reservior and analysis of its production were studied, on the basis of the geological characteristics such as the reservoir sedimentary, microfacies and petrophysical property etc. Furthermore, the next step to tap potential areas were confirmed through the comparison with actual oil production capacity.And then the main reason for low production of West 259 wells was analyzed, and the acid system and chemical remedial treatment experimental evaluation system was carried out, and the acid liquid and chemical solution plugging system was optimized, which provide a new technology means and methods to improve the acidizing and fracturing technology system. The main conclusion are as follows:1, The results indicate that the Chang 3 reservoir in West 259 is gray and brownish-gray sandstone, which is dominated by fine-grained and medium-grained structure. It is an ultra-low permeability reservoir with the characteristics of a fine-mesopore pore structure, poor porosity connectivity, and micro-cracks etc.2, It is concluded that the the main reasons leading to low productivity are reservoir pollution and the low utilization of water injection in the exploitation process, through the analysis of both the internal and external factors influencing the single well. The internal factors include sedimentation, reservoir properties, and fracture development, while the external factors include water injection of well group and injury by fluid into the well.3, Appropriate technical countermeasures was made according to the analysis of low productivity. These countermeasures include technology research such as measures to plugging, treatment to cracks with water, and Fine profile control, and together with on-site test, then achieved certain results:(1) The optimal site acid system formula is 12% HCl+2.5% HF+3.5% acetic acid+ 0.6% iron stabilizer+1.2% corrosion inhibitor +0.5% op-1 +0.5% pz-200+ 1% ethylene glycol butyl ether, which can improve the permeability of cores by 83%-106%.(2) The optimal chlorine dioxide composite plugging agent (which is chlorine dioxide +corrosion inhibitor+waterproof lock agent+composite clay stabilizer) can oxidative degradation of various polymer, Bacteria, asphaltene blockage, thereby expanding the flow channel. Thus can improve the rate of the core permeability by 60.49% on average.(3) The high-water area in the middle of West 259 was centralized management, by the combination of well blocking technology and water wells plugging. After the overall profile control, the daily oil production of single well increased from 1.2t/d to 1.6t/d and the natural decrement decreased from 15.1% to 6.0%.(4) The water absorption profile of the reservoir was improved, the degree of water drive was also improved, and maintainance of reservoir pressure was raised, after measures such as stratified water injection, single layer by injection, stratified oil etc. were taken.(5)To fill holes or seal water layers of the oil wells, which are of thick reservoir, and whose well logging data explain good nature, and to exploit the wells containing low water or no water, which can achieve the potential of mining single well reserves, both of the above two approach can effectively improve the level of remaining oil tapping. |
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