压裂液基液粘度对压开地层的影响

针对大庆油田肇88-斜30井压裂施工失败的情况,进行了施工参数分析。同时室内通过调整基液粘度,完成了两次高压岩心驱替对比实验,观察到粘度为68.1 mPa·s的基液堵塞了1#岩心入口端面,岩心内的孔隙压力低,而21.6 mPa·s的基液在高压下通过了2#岩心孔隙,岩心内的孔隙压力提高。研究结果显示,粘度为68.4mPa·s的基液在现场施工时未能有效进入该井特低渗透储层的孔隙,以至不能提高地层孔隙压力到克服最小主应力和岩石的抗张强度之和是该储层未能实施加砂的根本原因。表明压裂液的优化还需要进一步评价基液在地层中的流动性,以发挥基液造缝的主要功能;也为其他特低渗透、超低渗透油藏压裂液配方的评价提供了经验教训。

Numerical Simulation of Land Subsidence at Tanggu District in Tianjin, China

Based on observed data from Tanggu District in Tianjin, a back-propagation neural network (BPNN) model was introduced to predict possible land subsidence due to exploitation of groundwater. According to model estimation under various hypothetical extraction scenarios, patterns of land subsidence at Tanggu District were studied and discussed.The predicted average background land subsidence rate of Tanggu is 9.47 mm/a.The significance of contribution of aquifers to land subsidence descends in order of units Ⅳ,Ⅲ,Ⅴ,Ⅱ.Land subsidence tends to deteriorate with the increase in total extraction rate.

Effects of gully terrain on stress field distribution and ground pressure behavior in shallow seam mining

This study proposes a novel approach to study stress field distribution and overlying ground pressure behavior in shallow seam mining in gully terrain.This approach combines numerical simulations and field tests based on the conditions of gully terrain in the Chuancao Gedan Mine.The effects of gully terrain on the in situ stress field of coal beds can be identified by the ratio of self-weight stress to vertical stress(η) at the location corresponding to the maximum vertical stress.Based on the function η =j(h),the effect of gully terrain on the stress field of overlying strata of the entire field can be characterized as a significantly affected area,moderately affected area,or non-affected area.Working face 6106 in the Chuancao Gedan Mine had a coal bed Jepth <80 m and was located in what was identified as a significantly affected area.Hence,mining may cause sliding of the gully slope and increased loading(including significant dynamic loading) on the roof strata.Field tests suggest that significant dynamic pressures were observed at the body and foot of the gully slope,and that dynamic loadings were observed upslope of the working face expansion,provided that the expanding direction of the working face is parallel to the gully.

Determining areas in an inclined coal seam floor prone to water-inrush by micro-seismic monitoring

The failure depth of the coal seam floor is one important consideration that must be kept in mind when mining is carried out above a confined aquifer.Determining the floor failure depth is the essential precondition for predicting the water-resisting ability of the floor.We have used a high-precision microseismic monitoring technique to overcome the limited amount of data available from field measurements. The failure depth of a coal seam floor,especially an inclined coal seam floor,may be more accurately estimated by monitoring the continuous,dynamic failure of the floor.The monitoring results indicate the failure depth of the coal seam floor near the workface conveyance roadway（the lower crossheading） is deeper and that the failure range is wider here compared to the coal seam floor near the return airway（the upper crossheading）.The results of micro-seismic monitoring show that the dangerous area for water-inrush from the coal seam floor may be identified.This provides an important field measurement that helps ensure safe and highly efficient mining of the inclined coal seam above the confined aquifer at the Taoyuan Coal Mine.

Strata-pressure behavior of double-unit mining method combining fully-mechanized and mechanized coal face

Based on the engineering background of double-unit face mining under complicated geological conditions and the lagging fully-mechanized face surpassing the fore mechanized face of double-unit face in Zhou Yuanshan coal mine, strata-pressure behavior in the process was analyzed based on FLAC3D and on-site measurement. The results show that the stress concentration factor of superposition abutment pressure and the alternate distance of double-unit face are meeting gauss function, the relationship between the depth of stress concentration point and alternate distance also meets gaussian function. When the alternate distance is larger than 24 m, the superimposition of pilot support pressure in the double-unit face is weak. When the alternate distance is more than 12-15 m, the changes of the roof subsidence coefficient and the depth of stress con- centration point are stabilized; when the alternate distance is 3-6 m, the fore working face end is in the greatest impact area of superposition abutment pressure, this area should be avoided in determining the reasonable alternate distance.

IMPACT COAL CUTTING AND TESTING

The paper analyses the stress characteristics in longwall face and its interaction with impact coal cutting, and puts forward the operation method for impact coal cotting. Similar material to the coal in particular mine was used to simulate the coal mass. Impact coal breaking test was performed on the test rig. The traveling pattern of the impact stress wave in coal and the dynamic response of impact parameters on coal property is analyzed.