应力垂向分带对储层的控制作用——以库车前陆冲断带为例

Effect of stress vertical zoning on reservoirs: An example from Kuqa foreland thrust belt

岩层的褶皱弯曲通常会引起层内部各质点的相对差异变位,这为研究挤压构造区应力对储层的控制作用提供了可能。通过对库车前陆冲断带深部区构造高部位某钻井的三轴应力计算,划分应力中和面,分析不同应力性质段的储层响应特征及成因,并探索应力垂向分带性的油气勘探意义。研究结果表明:①库车前陆冲断带地应力的垂向分带对储层影响明显,张性应力段受拉张应力影响,储层发育高角度—近直立天然构造裂缝,天然裂缝具有开度大、延伸长、密度小、充填性低等特征,储层普遍发育原生粒间孔、粒间溶孔、粒内溶孔,物性好,对产量贡献大;②挤压应力段受挤压应力影响,发育多期低角度交织网状裂缝,天然裂缝具有开度小、延伸短、密度大、充填性高等特征,储层孔隙发育较差,主要是一些粒内与粒间微孔隙,物性较差,对产量贡献低;③应力垂向分带性划分可为后期开发井的钻探节约钻井成本,提高钻探效益,并能对新的勘探圈闭进行钻前地质储量评估,指导天然气勘探。应力垂向分带性对前陆冲断带的油气勘探具有重要经济意义。

Fold bend occurring in strata usually lead to relatively differential displacement of particles within these strata,making it possible to study an effect of stress in compressed zones on reservoirs.Triaxial stress of one well drilled at a certain structural high, Kuqa foreland thrust belt,was calculated.Then,stress neutralization plane was classified,and both characteristics and genesis of reservoir response were analyzed for many sections with different stress property.Finally,the significance of stress vertical zoning to oil and gas exploration was explored.Results show that (1) in Kuqa foreland thrust belt,the vertical zoning of in-situ stress has an obvious influence on reservoirs.One tensional-stress section is affected by tensile stress,and high-angle to near-vertical natural fractures characterized by large opening,long extension,and low density and filling are developed.And primary intergranular pores,and intergranular and intragranular dissolution pores are also generally developed,so these reservoirs with better physical property make great contribution to production;(2) in compressive stress zones,low-angle fracture network of multiple stages is developed.Natural fractures are featured by small opening,short extension,and high density and filling.Pores are poorly developed with intragranular and intergranular micropores as the soul,so these reservoirs with poor physical property make less contribution to production;and (3) to classify the stress vertical zoning is conducive to not only saving drilling cost but also improving drilling benefit for some development wells in the late stage,and it also can be used to evaluate pre-drilling geological reserves in newly explored traps,and further guide gas exploration.It’s deemed that this zoning is economically of great significance to oil and gas exploration in foreland thrust belts.