致密砂岩有效厚度下限标准的确定——以鄂尔多斯盆地周长地区长7段为例

储层有效厚度下限标准对油气地质储量的计算至关重要,为了确定致密砂岩有效厚度下限的标准,选取鄂尔多斯盆地吴起油田周长地区长7段砂岩作为研究对象,基于岩心、测井、录井和试油资料,综合确定长7段致密砂岩储层的有效厚度下限标准。结果显示,长7段为特低孔特低渗致密砂岩储层;有效厚度下限标准为:岩性下限为细砂岩,含油级别下限为油迹级,物性下限值孔隙度Φ≥6.2%、渗透率K≥0.15×10^(-3)μm^(2),电性下限声波时差AC≥215.0μs/m、深感应电阻率RILD≥26.0Ω·m。参数值可为区域地质储量和储层评价提供依据,长7段砂岩储层条件有利,可作为致密砂岩油重点接替层位。

鄂尔多斯盆地周长地区长9油层组浊积岩及致密油勘探意义

对周长地区延长组长9油层组浊积岩进行研究,并通过油源条件、储层特征、储盖组合、排烃压力对其致密油勘探意义进行了探讨。研究发现,周长地区浊积岩岩性主要为长石砂岩,发育不完整鲍马序列及准同生变形构造。储层孔隙度平均为5.18%,渗透率平均为0.17m D,属致密储层。分析化验表明李家畔页岩为优质烃源岩,可为长9油层组致密油提供充足的油源,同时可作为有效区域盖层,浊积砂体与李家畔页岩构成良好储盖组合,具备一定致密油勘探潜力。长9烃源岩生烃增压产生的源储过剩压力差是原油向下运移的动力,应根据排烃压力与良好储盖组合相结合确定致密油勘探有利目标。

鄂尔多斯盆地周长地区长9浊积岩特征及致密油意义的研究

浊积砂体是鄂尔多斯盆地三叠系延长组重要的储集体,目前发现的深水浊积岩集中在长6、长7油层组,在长9油层组中尚无发现浊流沉积的具体报道。通过岩心观察结合分析化验资料对盆地吴起周长地区延长组长9砂岩进行了岩性、粒度分析、测井等多方面的研究,得出了长9油层组上部地层为深水浊流沉积,证实了长9沉积期盆地中部存在北物源的浊积岩。通过浊积岩的岩性、结构构造、垂向组合等特征的详细描述,将该段沉积划分为三角洲前缘滑塌浊积扇,进一步识别出内扇、中扇、外扇3个亚相及主水道、分支水道、水道间等3个微相。并从油源条件、圈闭及储层等角度分析了滑塌浊积扇的致密油成藏条件,明确了该地区长9浊积岩的致密油成藏条件及意义。

鄂尔多斯盆地周长区长7致密油储层特征及影响因素

周长区长7层是典型致密油层,分析清楚该层的储层特征,有利于储层评价和该区域致密油的勘探开发部署。通过利用薄片鉴定、岩心铸体薄片、岩心观察、扫描电镜和压汞实验等方法研究了长7储层岩石学特征,孔隙特征、孔隙结构、物性特征储层类型,并分析了对储层特征有主要影响的主控因素。结果表明,研究区长7层的岩石类型主要为细粒长石砂岩,胶结类型以孔隙式为主,孔隙结构为小孔细喉型,孔隙度范围为2.1%~15.0%,平均值为7.2%,渗透率分布范围为0.04~1.36 mD,平均值为0.31 mD,周长区长7储层属于特低孔特低渗储层。沉积相和成岩作用是储层发育的影响因素。

CO_2 flux and seasonal variability in the turbidity maximum zone and surrounding area in the Changjiang River estuary

The turbidity maximum zone(TMZ) is one of the most important regions in an estuary.However,the high concentration of suspended material makes it difficult to measure the partial pressure of CO_2(pCO_2) in these regions.Therefore,very little data is available on the pCO_2 levels in TMZs.To relatively accurately evaluate the CO_2 flux in an example estuary,we studied the TMZ and surrounding area in the Changjiang(Yangtze) River estuary.From seasonal cruises during February,August,November 2010,and May 2012,the pCO_2 in the TMZ and surrounding area was calculated from pH and total alkalinity(TA)measured in situ,from which the CO_2 flux was calculated.Overall,the TMZ and surrounding area acted as a source of atmosphere CO_2 in February and November,and as a sink in May and August.The average FCO_2was-9,-16,5,and 5 mmol/(m^2·d) in May,August,November,and February,respectively.The TMZ's role as a source or sink of atmosphere CO_2 was quite different to the outer estuary.In the TMZ and surrounding area,suspended matter,phytoplankton,and pH were the main factors controlling the FCO_2,but here the influence of temperature,salinity,and total alkalinity on the FCO_2 was weak.Organic carbon decomposition in suspended matter was the main reason for the region acting as a CO_2 source in winter,and phytoplankton production was the main reason the region was a CO_2 sink in summer.