Abstract:

 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.

Key words: BZ25-1 oilfield, Shahejie Formation, lower porosity and permeability reservoir, classification and evaluation, testing verification