蒸汽吞吐后期近井地带储层的变化及其对油田开发效果的影响

Reservoir characteristics in the near region of thermal recovery wells and their effects on development of oilfield in the later period of steam stimulation

针对蒸汽吞吐超过5～6个周期之后稠油油藏开发效果明显变差的问题,以距原开发井仅13m的侧钻取心井为依据,研究了近井地带储层性质变化规律及其对开发效果的影响。结果表明:在开发后期,近井地带储层及流体性质变化较大,颗粒溶蚀破碎现象严重,超大管状孔发育;油层动用程度高,含油饱和度接近甚至低于实验室确定的残余油饱和度;存在不可逆的沥青积淀现象。近井地带储层性质的一系列变化是造成钻井液漏失、固井质量差、油层污染严重并最终导致加密调整井开发效果不佳的主要原因,近井地带存水量的增加降低了吞吐后期的热效率;高渗透性大孔道使蒸汽在储层中发生窜流;原油中的硫化物在高温蒸汽作用下所发生的脱硫反应使热采稠油管柱严重腐蚀。虽然近井地带储层性质的一系列变化会对开发效果造成不利影响,但是孔隙结构的改善及亲水性的增强对于提高采收率也具有一定的积极作用。

A sidetracked core hole with 13 meters away from original well in the pay zone was investigated. The changes of heavy oil reservoir property and their effects on production performances after five to six cycles of steam stimulation were analyzed. The result showed that in the later period of oilfield development, the characteristics of reservoir and fluid in the near region of thermal recovery well changed obviously. Rock grains were corroded seriously, and big pores were enhanced. The high-permeability wormhole appeared, and volume of clay decreased. Oil saturation was close to and lowers than the remaining oil saturation determined by water flooding test in laboratory. Bitumen was deposited in pores and could not be reversed. All changes have brought a series of problems in the process of steam stimulation development, such as sanding, leakage and loss of drilling fluid, poor quality of well cementing, casing failing, electrical anisotropy, steam channeling and low steam heat efficiency. Those factors affected the development effectiveness of infill wells and adjusting wells. Otherwise, wettability of reservoirs and improvement of pore structure would enhance heavy-oil recovery.