Fine characterization of large composite channel sandbody architecture and its control on remaining oil distribution: A case study of alkaline-surfactant-polymer (ASP) flooding test area in Xingshugang oilfield, China

Abstract

Lateral accretion deposit, the most critical element in channel sandbody architecture, significantly affect the distribution of remaining oil in the middle and late development phases of oilfields. However, the lateral accretion deposits in a composite channel sandbody are extremely thin and small, complicating the identification through log data. In this regard, the fine characterization of sandbody architecture is an effective alternative, which can further guide the evaluation of the remaining oil distribution in composite channels. In this paper, illustrated by an example of the alkaline-surfactant-polymer (ASP) flooding test area of Xing 12 block in Daqing oil field, China, a fine characterization method of the sandbody architecture of large composite channel was proposed. Integrated with the production data, the influence of the lateral accretion deposits of the sandbody on the direction and uniformity of waterflooding was analyzed, and the distribution pattern of the remaining oil controlled by sandbody architecture was discussed. The results show that, although the sandbodies in the large composite channel seem to have characteristics of connectivity and efficiency as a whole, the sandbody is only an apparent connecting body in reality. Due to the complicated contact relationship of the various architectural elements at all levels and stages, and the existence of low permeability barriers, for instance, thin lateral accretion beds and abandoned channel, the sandbodies of the large composite channel are not completely connected. The fifth and third level of architectural interfaces in the sandbody architecture of large composite channels control the frame of non-permeable lateral accretion deposits. Blocked by these lateral accretion deposits, the thickness of watered out reservoirs decreases along the lateral accretion direction, in which the bottom of the point bar is watered out severely. Hence the remaining oil is mainly distributed in the middle and upper parts of the composite channels, the inter-channel sands where the production and injection wells are imperfect, as well as the edge of channels. Under the control of the sandbody architecture of large composite channels, three types of remaining oil were determined: remaining oil blocked by lateral accretion units, remaining oil blocked by abandoned channel and remaining oil located at the edge of the channel with poor petrophysical properties.