渤海海域深层沙一段混积岩优质储层成因——以渤中13-A构造为例

Genesis of high-quality reservoirs with deeply mixed rocks in the Es_(1) in BZ13-A structure,Bohai Sea

渤海海域深层储层物性一般较差,油气产能较低,但在渤中13-A构造埋深大于4000 m的沙一段中钻遇了混积岩优质储层,并获得高产.为了揭示深层混积岩优质储层的成因,利用岩芯、铸体薄片、物性、碳氧同位素及流体包裹体等资料,对渤中13-A构造深层沙一段混积岩优质储层的发育特征和成因进行了研究,认为有利储层主要分布在盆内水下低隆起带、扇三角洲之上、混积滩中螺类等生屑大量发育的混积岩中.研究结果表明:研究区沙一段主要发育陆源碎屑岩(镜下百分比为42.9%)、含碳酸盐-陆源碎屑混积岩(镜下百分比为12.5%)、碳酸盐质-陆源碎屑混积岩(镜下百分比为12.5%)和含陆源碎屑-碳酸盐混积岩(镜下百分比为25.0%),见少量陆源碎屑质-碳酸盐混积岩(镜下百分比为5.4%)、碳酸盐岩(镜下百分比为1.8%).储层整体呈低孔、低渗的特点(孔隙度平均为12.7%,渗透率平均为42.1 mD),但混积岩中发育大量中-高孔、中-高渗的优质储层(孔隙度平均为24.3%,渗透率平均为252.3 mD).孔隙类型主要为生物体腔孔(镜下百分比为1.4%)和溶蚀孔(镜下百分比为4.1%),见少量的原生粒间孔(镜下百分比为0.2%).封闭—半封闭、咸化、浅水湖盆—局部低隆起—强波浪淘洗作用条件下形成的富含螺类化石的混积滩是形成优质储层的主要沉积条件,亦是深层混积岩优质储层发育的主因.螺云岩、(含)砂(质)或(含)砾(质)生屑云岩是优质储层发育的主要岩性因素.早期白云石化造成的强抗压实作用、中成岩期酸性流体对白云石胶结物的强烈溶蚀以及超压和油气的侵位是形成优质储层的主要成岩因素.

The physical properties of deep reservoirs in the Bohai Sea are generally poor.Oil and gas production capacity is low.However,high-quality mixed rock reservoirs were drilled in the first member of Shahejie formation(Es_(1))in the BZ13-A structure with a buried depth of more than 4000 m,and high productivity was obtained through oil and gas testing.In order to reveal the genesis of deep high-quality mixed rock reservoirs,using the core,cast flakes,physical properties,carbon and oxygen isotopes,and fluid inclusions,the development characteristics and genesis of the high-quality reservoirs in the Es_(1) of the BZ13-A structure were studied.It is believed that favorable reservoirs are mainly distributed in the mixed rocks with a large number of bioclastics such as underwater low uplift belts,fan deltas,and mixed beaches.The results show that the study area in Es_(1) mainly developed terrigenous clastic rocks(the percentage was 42.9%),carbonate-terrigenous clastic mixed rocks(the percentage was 12.5%),and carbonate-terrigenous clastic mixed rocks(the percentage was 12.5%)and terrigenous clastic-carbonate mixed rocks(the percentage was 25.0%).There was a small amount of terrigenous clastic-carbonate mixed rocks(the percentage was 5.4%)and carbonate rocks(the percentage was 1.8%).The reservoir as a whole is characterized by low porosity and low permeability(the average porosity was 12.7%,and the average permeability was 42.1 mD).However,a large number of high-quality reservoirs with medium-high porosity and medium-high permeability are developed in the mixed rock(the average porosity was 24.3%,and the average permeability was 252.3 mD).The pore types are mainly biological cavity pores(the percentage was 1.4%)and dissolution pores(the percentage under the microscope was 4.1%),and there is a small amount of primary intergranular pores(the percentage was 0.2%).Closed-semi-closed,salty,shallow lake basin-local low uplift zone-strong wave elutriation,formed under the conditions of mixed snail fossil-rich snail fossils,were the main depositional conditions for the formation of high-quality reservoirs.It was also the main reason for the development of high-quality reservoirs in deeply mixed rocks.Spiral dolomite,(including)sand(quality)or(including)gravel(quality)bioclastic dolomite were the main lithological factors for the development of high-quality reservoirs.The strong anti-compaction caused by early dolomitization,the strong dissolution of dolomite cements by acidic fluids in the middle diagenetic period,and the overpressure and oil and gas emplacement are the main diagenetic factors for the formation of high-quality reservoirs.