四川盆地威远—资阳地区筇竹寺组页岩气富集规律及勘探开发潜力

Enrichment law and resource potential of shale gas of Qiongzhusi Formation in Weiyuan-Ziyang areas, Sichuan Basin

作为我国南方海相页岩气勘探的主要层系之一,筇竹寺组尚未实现规模商业化开发,其页岩气富集规律和勘探开发前景亟需进一步深化认识和总结提炼。四川盆地威远—资阳地区是筇竹寺组页岩气重要的勘探区,以14口页岩气及常规钻井资料为基础,阐明了研究区页岩展布特征,分析了页岩气的成藏条件和富集模式,指出了筇竹寺组页岩气下步勘探方向。取得4项主要成果:(1)初步明确了威远—资阳及周边地区地层划分标准,指出该区域主要发育4套页岩气分布的有利层段,厚度为20~50 m,并从威远到资阳方向呈增厚趋势;(2)重点对研究区内W7井的含气性和孔隙度特征进行了分析,指出页岩含气量、孔隙度和储层压力从威远到资阳方向呈增大趋势;(3)建立了威远—资阳地区页岩气富集模式,明确裂陷槽内(GS17井周边)储层厚度大、孔隙发育、压力高、底板条件好,是页岩气富集的有利区,指出储层超压和孔隙发育是筇竹寺组页岩气富集的关键;(4)明确研究区内5 000 m以浅有利区主要分布于威远—资阳地区的裂陷槽内,资源量为3.5×10^(12)m^(3),但页岩储层成熟度高、孔隙度偏低、埋深较大和地应力条件尚未明确给该套层系能否取得高产突破和经济开发带来了不确定性。

Qiongzhusi Formation is one of the main shale gas exploration strata in China,which has great resource potential. At present,it has not yet realized large-scale commercial development,and its exploration and development prospects need to be further confirmed. Based on the data of 14 shale gas wells and conventional wells,this paper analyzes shale gas accumulation conditions,establishes the shale gas enrichment model,and points out the next exploration direction in Sichuan Basin. The main conclusions are as follows:(1)The stratigraphic division criteria of Weiyuan-Ziyang and its surrounding areas are preliminarily defined. It is pointed out that four sets of favorable shale gas layers are mainly developed in this area,with a single layer thickness of 20-50 m,and the thickness tends to increase from Weiyuan to Ziyang.(2)Combined with conventional drilling data,it is pointed out that shale gas content,porosity and reservoir pressure are increasing from Weiyuan to Ziyang.(3)The shale gas enrichment model in Weiyuan-Ziyang areas is established. It is clear that the reservoir in the rift trough(around Well GS17)is a favorable area for shale gas enrichment with large thickness,well-developed pores,high pressure and good floor conditions. It is pointed out that overpressure and pore development are the key factors for shale gas enrichment in Qiongzhusi Formation.(4)It is clear that the favorable areas(burial depth < 5 000 m)in the work area are mainly distributed in the rift trough of Weiyuan-Ziyang areas,and the resource amount is 3.5 trillion cubic meters. However,the high maturity,low porosity,large burial depth and unclear in-situ stress conditions of shale reservoir,bring uncertainty to the high-yield breakthrough and economic development of Qiongzhusi Formation.