川西洛带气田沙溪庙组储层成岩作用与孔隙演化

DIAGENESIS AND POROSITY EVOLUTION OF SHAXIMIAO FORMATION IN LUODAI GAS FIELD OF THE WEST SICHUAN

通过薄片观察、鉴定可知,洛带气田中侏罗统沙溪庙组储层原生粒间孔普遍发育,次生孔隙类型多而复杂,成岩作用以及填隙物成分对孔隙度影响较大.经粘土矿物X衍射和扫描电镜分析,将成岩阶段划分为早成岩A期、B期和中成岩A期、B期4个期次.早成岩A期,压实作用和石英Ⅰ级次生加大使原生孔隙度迅速降低至10%～15%左右;早成岩B期,碳酸盐胶结物和硬石膏胶结物大量出现,孔隙度丧失至不足10%;到中成岩A期,由于强酸性水的存在,开始出现Ⅱ级石英加大边和自生高岭石沉淀;中成岩B期,溶蚀作用不断加强,对孔隙改善作用明显;整个中成岩阶段,孔隙不断的消长演化,孔隙度下降到4%～9%,并最终形成低孔低渗的致密性储层.

From the analysis of thin section,it shows widely growing primary porosity and complicate secondary porosity in Shaximiao Fm of Middle Jurassic,Luodai Gas Field of the West Sichuan.Diagenesis and interstitial matter have great influence on porosity.Based on the X ray diffraction of clay mineral and the scanning electron microscopic,the diagenetic stages here are classified as earlier diagenetic A,B and middle diagenetic A,B.In the earlier diagenetic A,the primary porosity decreased rapidly to 10%～15% because of compaction and quarts growth Ⅰ.And in the earlier diagenetic B,the porosity is evaluated to hit 10% because of arise of carbonate and muriacite cementations.Then quarts growth Ⅱ occurred in heavy acidulous water and authigenic kaolinite deposited in the middle diagenetic A.Until the middle diagenetic B,the porosity were improved by the enhancement of denudation.During the whole middle digenetic stage,the porosity descented to 4%～9% after constant decrease and increase.After a series of diagenetic stages,the reservoirs were densified to low porosity and low permeability ones.