Research on Remaining Oil Distribution and Further Development Methods for Different Kinds of Oil Layers in Daqing Oilfield at High Water-cut Stage

Abstract

Abstract Daqing oilfield is multi-layered sandstone oilfield with serious heterogeneity1. After more than 40 years flooding, the oilfield has entered the high water-cut stage when the water flooding and polymer flooding are coexisting. After multi infill drilling and multi adjustments, different kinds of oil layers have been swept with certain degree, and the remaining oil distributes highly scattered2,3. Three types of oil reservoirs can be divided according to their properties and their grown conditions. Due to the difference in reservoir properties and development strategy, the potential and problems exited for various oil reservoirs are not the same. In Class I oil reservoir, the contradiction is mainly caused by the coexistence of remaining oil, which is resulted by heterogeneity in oil layers, and inefficient water circulation; In Class II oil reservoir, the main contradiction is caused by the coexistence of water flooding and polymer flooding both in vertical and areal; In Class III oil reservoir, two main contradictions are incomplete production-injection structure caused by discontinuous sand body development in areal and interlayer interference caused by too many oil layers in vertical. In view of the main contradictions and problems in different oil reservoirs, and with the consideration of current production technology, the relevant further development measures for different oil reservoirs are determined, and the field application results are fairly good. New methods and techniques to improve the swept volume and displacement efficiency in different oil reservoirs at super high water cut stage are also discussed in this paper. Remaining Oil Distribution Characteristics for Various Oil Reservoirs From the north to the south in Daqing oilfield there developed braid river sand body, meandering stream sand body, distributary channel sand body, sheet sand body inner delta front, sheet sand body outer delta front and other kinds of sand body of river-delta sedimentation types. The oil reservoirs can be divided into 3 types based on their properties and grown conditions. Class I Oil Reservoir This kind of oil reservoir mainly consists of 3 types of sand body: braid river sand body, meandering stream sand body and distributary channel sand body, and they are developed in the north part of the fields in general. The effective thickness of individual layer is generally above 3m. The channel sand body distributes stably with large width, high connectivity and high permeability. Braid River Sand Body. This type of sand body distributes continuously with large areal extent in plane, and there are few pinching areas or abandoned channels inside the sand body. Due to the poor areal and intrastratal heterogeneity and the improved injection/ production relationship under basic well pattern, almost all the well points have been watered-out. For example, in central Saertu development area, the sand body in layer PI23 of Well G1129-J 25 is 4.5m thick with the effective thickness of 4.1m. This layer is 600m from the injector, and the swept thickness has reached 98.8% with the displacement efficiency of 58.6% after 27 years water injection. The remaining oil in this type of oil layers mainly distributes in the medium-poor swept intervals. Meandering River Sand body. In areal, the meandering river migrates and reforms again and again, so, wide compound meandering river sand body is formed with the means of lateral erosion and lateral deposition. Many pinching areas, interstream sand bodies and abandoned channels grow inside the meandering river and at the edge part, therefore, the lateral connectivity in the upper part of the meandering river sand body becomes poor. This type of sand body is 3–5m thick, and most are positive rhythm overlapped in vertical.