渤中25-1油田沙河街组低孔低渗储层特征及分类评价

Characteristics and Classification and Evaluation of Low Porosity and Permeability Reservoir in Shahejie Formation of BZ25-1 Oilfield

渤中25-1油田位于渤海南部海域,其主力油层为古近系沙河街组,总体上属于低孔低渗储层。通过薄片、扫描电镜、X衍射分析和测井解释等手段,对沙河街组砂岩储层的岩石学特征、沉积特征、物性和孔隙结构特征进行了分析研究。沙河街组沙三段为较深水湖泊环境下的浊积扇沉积,沙二段为扇三角洲沉积;岩性主要为岩屑长石砂岩,储层孔隙类型为混合孔隙、次生孔隙和原生孔隙,由于沙三段溶蚀孔隙发育较沙二段少,沙三段物性较沙二段差。结合储层试油结果,提出了低孔低渗储层宏观成因、微观孔隙结构和综合评价3种分类方案,总体上把储层分为好、中和差3类,对应产能分别为大于80 m3/d、介于10~100 m3/d之间、小于10 m3/d和微量或无产能。经过该油田沙河街组5口井、15个储层段的测试验证,储层宏观成因分类评价结果与实际试油结果符合率达到86.67%,微观孔隙结构分类和综合分类评价结果与实际试油结果基本吻合。

BZ25-1 oilfield is located at southern Bohai Bay.The Shahejie Formation which is the main reservoir is a typical lower porosity and permeability reservoir.For the purpose of studying the petrological characteristics,sedimentary characteristics,physical properties and pore structures of the reservoir,a large numbers of thin sections,scanning electron microscopes,X-ray diffraction analysis and well logging data were analyzed.The sedimentary characteristics of Shahejie Member Ⅲ is of turbidite fan deposition of deep-water lake environment,while Shahejie Member Ⅱ is of fan delta deposits.Debris-feldspar sandstone is the main lithology of this area.The pore types in the reservoir are as follows： mixed pore,secondary pore and primary pore.For the dissolved pore in Shahejie Member Ⅲ is less than that in Shahejie Member Ⅱ,the physical properties of Shahejie Member Ⅲ are worse than those of Shahejie Member Ⅱ.With the oil testing verification of reservoir,three types of classification and evaluation of lower porosity and permeability reservoir which are the macro-causes,microscopic pore structure parameter and comprehensive methods are put forward.Generally the reservoir is subdivided into three categories as follows： good,medium and poor reservoirs,and their corresponding productivity are more than 80 m3/d,between 10 and 100 m3/d,less than 10 m3/d and micro amounts or no productivity,respectively.After the testing verification of 15 reservoirs of the Shahejie Formation in 5 wells of the oilfield,the coincidence rate of the result of macro-causes classification and evaluation and the testing result is 86.67%,and the result of microscopic pore structure parameter classification and evaluation basically tallies with the testing result.