Abstract:

Pu-1 oil layer of the Upper Cretaceous in the third northern development district of Daqing Oilfield, can be divided into three 4th order and eight 5th order high-resolution sequences, in terms of lacustrine flooding surface. Correlation of these stratigraphic units based on densely-spaced borehole data provides a high resolution correctable stratigraphic framework for the study of the architecture of the reservoir sandbodies. Most of the major reservoir sandbodies are composite sandbodies formed by amalgamation or superimposition of single sandbodies, and include the incised valley-distributary channel, distributary channel superimposed subaqueous distributary channel, distributary channel superimposed delta front mouth bar, crevasse channel superimposed crevasse delta or marginal sand bar composite sandbodies. The complex of the facies architecture of the sandbodies determines the reservoir inhomogeneity of the oil layer. Within the high-resolution sequence stratigraphy framework, three composite sandstone belts have been classified, and their depositional architectures had a significant influence on the remaining oil distribution. The main fluvial channel composite belts are of high porosity, permeability and connectivity, with remaining oil mainly formed by the inhomogeneity of the upper intrabed and obstruct layer. The marginal fluvial channel-mouth bar belts are characteristic of complex amalgamation of sandbodies with more inter obstructs, and the remaining oil are commonly formed by inhomogeneity of the sandbodies with poor permeability and dispreaded areas in development. This is the important facies zone for prediction of remaining oil in the oil field. The marginal sandy bar-crevasse and flooding interbeded fine belt are characterized by limited sandstones and poor permeability, with remaining oil often formed by deficient borehole network or poor connectivity.

Key words: high-resolution sequence framework, composite sandbody architecture, remaining oil distribution, Pu-1 oil layer, Daqing Oilfield