潞安矿区山西组3^#煤储层低压特征及控制因素研究

A research on low reservoir pressure of coal 3^# of Shanxi Formation in Luan mining area, Qinshui Basin

煤储层压力是影响煤层气开发地质条件评价和钻完井、增产改造技术工艺设计以及排采制度制定的重要参数,获得可靠的煤储层压力参数并认识其区域分布规律,对于指导煤层气高效开发至关重要。以沁水盆地中南段潞安矿区山西组3^#煤层为对象,分析发现前期煤储层压力数值可靠性不足,改进并应用大时长关井注入压降套管试井方法,完成了潞安矿区34口煤层气井的储层参数测试和压力特征的系统研究。结果表明：（1）大时长关井压降套管试井是潞安低渗透低压储层矿区获得可靠储层压力参数的先进技术和方法;（2）山西组3^#煤层为低压和超低压储层,在800m埋深以浅,平均储层压力梯度为4.2kPa/m,这远低于本世纪初期关于潞安矿区储层压力（6～7kPa/m）的水平;（3）3^#煤层的低压特征与煤层埋深和底板高程线性相关,其区域性分布规律的控制性地质因素是地下水流场和辛安泉域的地面排泄;（4）潞安矿区3^#煤层的低压和超低压储层的保护性增产改造技术工艺亟待开发,这包括压裂液体系,压裂泵注程序、压裂后返排,及时排采施工,以及排采制度的设计和实施;（5）潞安矿区山西组3^#煤层低压—超低压现象的发现对重新认识沁水盆地煤储层压力规律具有重要启发和借鉴。

Pressure is one of the most important parameters for characterizing coal reservoirs and for evaluating coalbed methane （CBM）production potential, and for designing the well drilling, well completion, stimulation and production.Reliable pressure data and the distribution of a CBM play are critical for CBM exploitation.Based on the pressure data obtained through injection falloff test （IFOT）in open-hole wells completed in 1990＇s,it was found that the pressure was over evaluated for coal 3^# of Lower Permian Shanxi Formation.In this study, an advanced pressure test methodology was newly developed with cased holes and extending shut-in time.Though application of this new method from 2010 to 2013,34 data wells have been tested in Luan mining area,Qinshui Basin,China.It was found that： （1）The newly developed method is an advanced technology for obtaining reliable reservoir pressure in low permeability and low pressure CBM play.（2）The reservoir pressure gradient of coal 3^# in average is 4.2kPa/m in the study area,characterizing a low to ultra low pressure reservoir.Ultra low pressure gradient was found in Changcun （2.6kPa/m）, Gaohe （3. 3kPa/m） and Yuwu coalmines （3. TkPa/m）, and low pressure gradient was obtained in Wuyang （4.TkPa/m） ,Licun （5.2kPa/m）and Gucheng （5.4kPa/m）.These values are significantly lower than those of previously collected data from open holes in the study area Yuwu coal mine.（3）The low reservoir pressure is related to the Xin＇an Spring Group,located on the eastern edge of the Qinshui Basin,which discharges reservoir groundwater to the surface hydrological system. （4）For increasing CBM production in such low to ultra low pressure reservoir in Luan mining area,reservoir protect fluid system and optimizing stim- ulation technologies should be developed in the near future.