孔隙型致密砂岩气藏产能控制因素

Controls on the productivity in porous tight sandstone gas reservoirs

为了探究天然裂缝欠发育致密砂岩气藏的产能主控因素,以四川盆地北部元坝地区上三叠统须家河组二段和川中东峰场地区须家河组五段气藏为研究对象,分析了二者的地质特征、钻井工艺和储层改造技术,明确了孔隙型致密砂岩气藏天然气产能主控因素。研究结果表明:①古、今构造高部位是油气运聚成藏的指向区,天然气富集程度较高,气井高产概率较大,而构造低部位气井生产效果较差;②储层物性越好,成藏过程中天然气富集程度越高,且生产过程中天然气流动能力较强,故优质储层发育段越厚,气井产量越高;③裂缝欠发育致密砂岩气藏需通过储层改造才能获产,加大改造规模对优质储层发育的钻井增产效果明显;④由于致密砂岩储层局部发育,水平井能够钻遇更多的优质储层,故较直井而言,提产效果明显;⑤由于钻井液中的重晶石会对物性差—中等的储层造成污染,进而影响产量,故致密砂岩气藏钻井过程中需加强储层保护。结论认为:①孔隙型致密砂岩气藏产能主要受古、今构造位置,优质储层发育程度,储层改造规模和井型等因素控制;②优质烃源岩发育区、正向构造区和相对优质储层发育区的叠合部位可优先考虑部署井位。

In this study,two suites of gas reservoirs in Sichuan Basin were taken as objectives to identify controls on the productivity in tight sandstone reservoirs with underdeveloped natural fractures,including the Upper Xujiahe 2 Member in Yuanba area of northern basin and Xujiahe 5 Member in Dongfengchang area in central basin.Their geological characteristics,drilling techniques and fracturing stimulation were discussed to ascertain the productivity controls.Results show that(i)vastly enriched in natural gas,both ancient and current structural highs with a great possibility in big output are available for hydrocarbon migration and accumulation.While there exists a poor effect in structural lows;(ii)the better the reservoirs'physical properties,the higher the enrichment in the reservoir-forming process,and the stronger the flowing rate in the production process,also implying the thicker the developed reservoirs with high quality,the higher the output;(iii)it is essential to perform the stimulation in such reservoirs with underdeveloped fractures.Especially,to expand fracturing scale may create an obvious stimulation effect in the developed quality reservoirs;(iv)not all of tight sandstone reservoirs are developed everywhere,creating more quality ones encountered in horizontal wells.So,an evidently incremental production can be attained in vertical wells;and(v)reservoir protection shall be stressed because some reservoirs with poor to moderate physical properties are contaminated by barite in drilling fluid to further condition the output.In conclusion,for the porous tight sandstone gas reservoirs,the productivity is mainly influenced by ancient and current structural highs,growth of quality reservoirs,stimulation scale and well types.What's more,the priority for well deployment shall be set in some superimposed zones developed with quality source rocks,positive structures and comparatively quality reservoirs.