New Types Of Remaining Oil In Complex Reservoir Of The Old Oilfield

Taking the narrow and thin sandstone reservoir of pu I oil group in Putaohua and Aobaota oilfield as a case,with the data of seismic, geology, well logging, well test and early production test, the paper deeply studied the controlling function of the reservoir type, the low-grade fault, reservoir architecture and the channeling path on the remaining oil under the theory and method of reservoir geology, described the law of the distribution of remaining oil on four scales: reservoir, layer, single sand body, and internal layer, finally revealed new area of remaining oil in the narrow and thin sandstone reservoirs and proposed the corresponding potential exploitation measures.The paper achieved some innovational scientific payoffs. Main achievements of the study are summarized as following:(1) According to the classification scheme of the narrow and thin sandstone reservoir, the paper carried out the reservoir architecture study. The sand body was analyzed from both vertical and horizontal aspect to identify the channel boundary, with the six class structural surface,such as muddy intercalation, calcareous intercalation in the vertical; based on the form of logs and the changes of the thickness of sandbody in the adjacent wells in the horizontal, thus the single sand body was recognized in the composite channels. The architectures of the single channel of the Putaohua and Aobaota oilfield are mainly four kinds: isolated monogene sand body, butt jointed monogene sand body, cutting piled monogene sand body and superposed monogene sand body, among them, the butt jointed is common in the narrow and thin sand body reservoir.(2) On the basis of the reservoir architecture study, a 3D geological model was set up. Through numerical simulation, combining with the oil saturation distribution, the paper discussed the influence of the architecture, especially the intercalated layer, and the flow barrier in the jointed place on the exploitation and the remaining oil distribution. The butt jointed monogene sand body has a rich remaining oil accumulation. (3) Following the rule "degree of association to decide direction, monitoring data to decide layer, dynamic analysis to decide time", the channeling paths can be identified under the condition of commingled water injection and oil extraction. Degree of association can block out the development direction of the channeling paths; based on the high accuracy injection and production data can identify the layer of the channeling paths; the dynamic data can be used to judge the time the channel paths formed. The study of the cored well shows that the development of channeling paths in the narrow and thin sandstone reservoir can hinder the formation of remaining oil.(4) With the low-grade faults interpreted by the high-resolution 3D seismic data, the faults were assemblaged based on the changes of the plane distribution of the breakpoints, the fault character, dip direction, fault displacement, breakpoint location and regional of stress. The paper studied how the characteristics of the low-grade fault, the genesis and the fault lateral sealing control the remaining oil distribution. The study shows that the low-grade fault, under the limitation of its scale and sealing property, can play better on barring oil migrating with the coordination of micro-relief structure and sand body. The remaining oil caused by the fault cut is mainly five kinds, and the enriched area distributed near the fault joint.(5) Through the quantitative research on the reservoir type from the development point of view, a set of evaluation system suiting for reservoir classification and producing reserves in middle and late development stage was established. Using the reservoir engineering method, combined with the development reality, the evaluation was carried out, which provided more effective evidence to dispose the well pattern arrangement and exploit the remaining oil.(6) Making full use of the data of cored well, monitoring data and numerical simulation results, the paper described the law of the distribution of remaining oil from four different levels: reservoir, layer, single sand body and internal layer. The study indicates that the remaining reserve of reservoir size is still concentrated in the first and second type reservoir, both structural reservoirs. To different trap genesis, the abundance of remaining oil is structural reservoir> structural - lithologic reservoir> lithologic reservoir. Also, the abundance reduces as the structural location becomes lower. The formation of remaining reserve of oil layer size is affected by the plane and interplayer heterogeneity, including sedimentary face, reservoir property, the plane connectivity of the sand body, micro-relief structure, fault and inter zone interferences, etc.(7) Based on the research of the reservoir architecture analysis, the identification of channeling paths, numerical simulation, study of the low-grade fault and comprehensive evaluation of the reservoir, a frontier of remaining oil distribution is proposed: firstly, the remaining oil caused by the sand body architecture with improper injection patterns; secondly, the remaining oil hindered by the channeling paths; thirdly, the remaining oil controlled intergratedly by the low-grade fault, micro-relief structure and sand body.(8)The strategies of potential tapping have been proposed according to the formation and distribution characteristics of remaining oil, and some of which succeeded with better effects. This research is of great significance not only in the peripheral oilfields in Daqing but also in other similar oilfields.