Production evolution patterns and development stage division of waterflooding oilfields

The continuous growth of recoverable reserves in a waterflooding oilfield has a significant impact on the patterns of production evolution. A new production evolution model is established by improving the Weng Cycle model. With the new model, the statistical correspondence between the production decline stage and the reserve-production imbalance is clarified,and the correlation of water cut with the recovery percent of recoverable reserves is discussed, providing quantitative basis of reservoir engineering for dividing development stages of oilfield and defining mature oilfields. According to the statistics of oilfields in eastern China, the time point corresponding to the reserve-production balance coefficient dropping to less than 1dramatically is well correlated the beginning point of production decline, thus the time when the reserve-production balance coefficient drops dramatically can be taken as the initiation point of production decline stage. The research results show that the water cut and the recovery percent of recoverable reserves have a good statistical match in the high water cut stage, and it is more rational to take both the start point of production decline stage and the water cut of 90%(or the recovery percent of recoverable reserves of 80%) as the critical criteria for defining a mature oilfield. Five production evolution patterns can be summarized as follows: growth–peak plateau–stepped decline, growth–stepped stabilizing–stepped decline, growth–stepped stabilizing–rapid decline, growth–peak plateau–rapid decline, and growth–continuous decline.

社会保障制度化规范化条件下的政府选择

针对我国目前社会保障制度存在的问题，政府应选准三大着力点对其进行完善，即搭建一个平台——城乡兼容的社会保障制度：构筑两大板块——社会统筹和个人账户整体结合下的分块征管；树立三层体系——中央、地方和个人收支责任的划分。在保持现有制度微观主体利益不变的情况下，实现社会保障政府管理的规范化和制度的广覆盖与可持续性。

超高层建筑结构健康监测现场实施状况验收方法

以在建的某超高层(WHGC)为平台,设计了一套集成的健康监测系统对主塔楼在施工阶段和使用阶段的施工环境、结构荷载和响应进行连续实时监测。从项目简介、系统设计介绍了WHGC监测系统的总体概况,并分析了WHGC现场实施监测的难点。强调建立超高层建筑结构健康监测现场实施状况验收标准的重要性,并提出了超高层健康监测实施状况验收方法。

Stress sensitivity of coal reservoir and its impact on coalbed methane production in the southern Qinshui Basin, north China

Stress sensitivity has significant negative effects on the permeability and production of coalbed methane(CBM)reservoirs.To effectively minimize these negative effects,the degree of stress sensitivity during the CBM production process should be carefully studied.In this work,the curvature of the stress-sensitivity curve was adopted to explore the degree of stress sensitivity,dividing the stress-sensitivity curve and the drainage process into five stress stages:sharp decrease,rapid decrease,low-speed decrease,slower decrease and harmless with four critical stress points—transition,sensitivity,relief and harmless.The actual stages were determined by the initial permeability,stress-sensitivity coefficient and difference between the reservoir pressure and desorption pressure.The four critical stress points did not completely exist in the stress-sensitivity curve.With an increase in the initial permeability of coal,the number of existing critical stresses increases,leading to different gas-water drainage strategies for CBM wells.For reservoirs with a certain stress-sensitivity coefficient,the permeability at the sensitive stress point was successively greater than that at the transition,relief and the harmless stresses.When the stress-sensitivity coefficient is different,the stage is different at the beginning of drainage,and with an increase in the stress-sensitivity coefficient,the decrease rate of the permeability increases.Therefore,the stress-sensitivity coefficient determines the ability to maintain stable CBM production.For well-fractured CBM reservoirs,with a high stress-sensitivity coefficient,permeability damage mainly occurs when the reservoir pressure is less than the relief stress;therefore,the depressurization rate should be slow.For CBM reservoirs with fewer natural fractures,the reverse applies,and the depressurization rate can be much faster.The higher the difference between the reservoir and desorption pressures,the higher the effective stress and permeability damage after desorption,resulting in a much longer drainage time and many difficulties for the desorption of coalbed methane.The findings of this study can help better understand and minimize the negative effects of stress sensitivity during the CBM production process.