沁水盆地南部郑庄区块15号煤与3号煤储层物性及产气差异研究

Reservoir properties and gas production difference between No.15 coal and No.3 coal in Zhengzhuang Block,southern Qinshui Basin

随着煤层气勘探开发的深入,同一区域不同层系开发差异逐步呈现,深化储层认识对开发策略的制定显得尤为重要,以沁水盆地南部郑庄区块为例,以往重点关注主力层3号煤资源,根据区块增产需求,需要逐步多层系开采。本研究重点剖析15号煤层气资源,采取与开发较为成熟的3号煤层气资源对比分析的方法,得出储层差异和分区差异,并推测其成因机制,指导针对性开发策略的制定。通过钻井岩心描述及镜下观察,结合分析化验、地震勘探、测井及生产等资料,对比研究了郑庄区块15号煤层与3号煤层在煤厚、物性和含气性等方面的差异。结果表明:与3号煤层相比,15号煤层厚度较薄,且平面分布不稳定,存在局部分叉现象;总体上,15号煤层含气量与3号煤层相当,一般为10~29 m^(3)/t,但在区块内部呈现出具有一定规律的分区差异;15号煤层的吸附时间较3号煤层明显缩短,表明其较为有利的开发潜力。研究认为,沉积环境差异和构造影响程度不同是导致两套煤储层物性和含气性差异的主要原因,太原组障壁海相沉积环境水体变化大导致15号煤层沉积厚度平面变化大,强还原沉积环境造成15号煤层镜质组分含量较高;相比于3号煤层,局部地段太原组15号煤层受基底构造、断层、褶皱等地质构造影响更为明显。根据煤储层参数特征,将15号煤有利区划分为三类,指出开发“甜点区”;试采结果表明,I类区15号煤层套管压裂水平井日产气量突破10000 m^(3),3号、15号煤层直井合采较单采3号煤层产量翻番;Ⅱ类区15号煤层套管压裂水平井获得高产,为区域增产、规模扩建起到技术支撑作用。

With the in-depth exploration and development of coalbed methane(CBM),the development differences between different strata in the same region are gradually emerging.Deepening the understanding of reservoir is crucial to formulate development strategies.Taking the Zhengzhuang Block in the southern Qinshui Basin as an example,in the past,the focus was on the main No.3 coal resources.With the stimulation demand in this block,the CBM needs to be gradually recovered in multiple layers.In this paper,the CBM resource of No.15 coal is analyzed.Comparative analysis with well developed No.3 CBM resources is carried to probe into the cause of reservoir differences and regional differences.Furthermore,the genesis mechanism is speculated to guide the formulation of targeted development strategies.Based on the description of drilling cores and observation under microscope,combined with the indoor test,seismic exploration,logging and production data,the differences in coal thickness,physical properties and gas-bearing properties between the No.15 and the No.3 coal seams in Zhengzhuang Block are investigated.The results show that compared with the No.3 coal,No.15 coal is thinner and the plane distribution is unstable with local bifurcation phenomenon.In general,the gas content of No.15 coal is equivalent to that of No.3 coal,ranging from 10 m^(3)/t to 29 m^(3)/t,although there are regular regional differences within the block.The adsorption time of No.15 coal is significantly shorter than that of No.3 coal,indicating its favorable development potential.The distinction in sedimentary environment and tectonic influence are the main reasons for the difference in petrophysical properties and gas-bearing properties between the two seams.Specifically,because of the barrier coast sedimentary of Taiyuan Formation,the water turbulence and strong reducing environment lead to a varying coal thickness in plane and a higher vitrinite content of the No.15 coal.Tectonically,compared with the No.3 coal,partial No.15 coal is more obviously affected by geological structures such as basement structure,faults and folds.According to the characteristics of coal reservoir parameters,the favorable area of No.15coal is divided into three categories,and the“sweet spot”is identified.Pilot production suggests that the daily production of casing fractured horizontal wells in No.15 coal in category I area exceeds 10000 m^(3)and the production of vertical wells in No.3 and No.15 coal seams has doubled than that of single-mining No.3 coal seam.In categoryⅡarea the output of casing fractured horizontal well developing No.15 coal achieves high yield.This research provides technical supports for regional production increase and scale expansion.