In order to evaluate the physical and chemical properties of polymer surfactants and analyze their oil displacement mechanisms, three types of poly-surfactant used in the Daqing oil field were chosen to be researched, and the oil displacement effects were studied using poly-surfactants of different viscosity, dehydrating rate, and core permeability. The main purpose is to determine the reasonable range of different characteristic indexes of polymeric surfactant flooding. The oil displacement effect of 15 cores was analyzed, and the effects of viscosity, the dehydrating rate of emulsion, and permeability on EOR (Enhanced Oil Recovery) were analyzed. The oil displacement mechanisms of polymeric surfactants were researched using a photolithographic glass core. This paper explores the mechanism underlying production enhancement as an EOR target, while simultaneously conducting laboratory tests to assess the physical and chemical properties of polymeric surfactants. The poly-surfactant agents exhibit a notable increase in viscosity, with the optimal displacement effect observed at a core effective permeability exceeding 400 mD, resulting in a potential EOR of 15% or higher. Moreover, at a viscosity ranging between 40 and 70 mPa·s, the total EOR can reach 73%, with the peak efficiency occurring at a viscosity of 60 mPa·s. The water loss rate of the emulsion, ranging between 30% and 70%, achieves optimal performance at 50%. The poly-surfactants’ higher viscosity extends the oil sweep area, enhancing recovery efficiency, and noticeably reducing residual oil compared to water flooding. During poly-surfactant flooding, a substantial amount of residual oil is extracted and transformed into droplets. The rapid emulsification of the polymeric surfactant solution with crude oil forms a stable emulsion, contributing to its significant oil recovery effect. This research provides valuable technical support for EOR in thin and low-quality reservoirs of onshore multi-layered sandstone reservoirs.

To determine the development mode of layered sandstone reservoir, a system economic model was established, which thought the layer in production and its upper (downer) layer as a system, and the overall benefits of the two modes were contrasted using the existing well (UEWM) or the method of drilling a new well (DNWM); then, the upper (downer) oil layer development mode could be determined quickly by the model. The method can avoid the chemical agent effect of the upper target layer, which also makes the calculation more accurate. In the model, the cumulative oil production limits of the producing layer are described at different oil prices of DNWM and UEWM methods. Then, an economic ultimate water cut (EUWC) model is established. According to this model, when the water cut attains to EUWC, the oilfield should be abandoned. Meantime, the arctangent prediction model for water cut is combined with the water drive curve method, to forecast the accumulative oil from the planning time of the upper target layer production to the abandonment time of the first production layer of oilfield. And then, the development mode could be decided through contrast with the cumulative oil production limit. When the oil price is 40$/bbl, the EUWC of the block is 97.55%, and time is May 2020, earlier than the planned upper layer production time January 2023, so its rest cumulative production would be , which is less than the cumulative production limit of . Hence, the UEWM should be chosen. When the oil price is $70/bbl, EUWC is 98.93%, and the corresponding time is August 2027. From the planned return time of January 2023 to August 2027, the block has cumulative oil production of , greater than the cumulative oil limitation of . The old exiting well still has larger economic productivity; hence, the DNWM method should be chosen. This work provides theoretical support for up (down) formation development mode of production layer. It is of great significance to guide the development of layered sandstone reservoirs. The system economic model established can decide development mode with drilling wells or using exiting well, and it was first created in the field of oil reservoirs. This method fills up the theoretical blank of development mode for upper or downer layer of the producing layer in layered sandstone reservoir.

To determine the development mode of different oil field in layered sandstone reservoir, a system economic model was established, including the primary production layer section and the upper layer. The cumulative oil production limits of the primary layer were described under different oil prices, using the existing well method (UEWM) and drilling new well method (DNWM). The first layer’s oil production limit for DNWM and UEWM was determined. The established economic ultimate water cut (EUWC) model, the solution prediction model of water cut arctangent, and the water drive curve were combined, to calculate the accumulative oil production from planning time of the upper layer production to the economic limited water cut of block. When the oil price is 40$/BBL, the SME block should be developed by UEWM method. While for 70$/BBL, DNWM should be adopted. This work provides theoretical support for the optimization of up (down) layer return development mode. It is of great significance to guide the development of layered sandstone reservoir.

Daqing Oilfield is in the forefront, because of polymer flooding well pattern was used to next production layer, so, first development layer was sealed after polymer well was used to next layer, and whose storage reserves is very huge. To 2021, OOIP of the first set of reserves of type II reservoirs has been sealed up to 9603 × 10⁴ t. In order to release the reserves and reduce the influence on oil yield, water drive well pattern was used to product the sealed reserves through additional perforating, but the economic boundary standard to release the sealed layer using water drive well pattern is not determined, so, based on the principle of break-even and the seepage flow theory, this paper establishes the formula for calculating the economic limits of the various unsealing indexes by water flood well, which can effectively solve the problem of communicating and understanding the economic and engineering parameters of the released well, quantificational the limit of layer selection standard of well for releasing. The result showed the cumulative and daily oil production limit is gradually decreases with oil prices increasing, and vertically, the limit is increases with the input-output ratio (ROI) increases. FWHP of oil well b1-40-527 is 0.4 Mpa, well spacing is 300 m, oil well radius is 0.1 m, viscosity is 8.8 mPa. s, production time of 300 d, density of 0.86 g/cm³, when ROI is 1:2, the lower limit of the cumulative oil raised production is 206.9 t and daily increasing oil floor is 0.69 t/d, the minimum released effective thickness is 8.4 m as oil price is 60 $/BBL, meanwhile, the lower limit of the cumulative oil raised production is 421.4 t and daily increasing oil floor is 1.4 t/d when oil price is 40 $/BBL. After increasing the thickness of released layer according the limit, it is verified by actual data, that the increasing oil production of daily and accumulated reached to the calculation minimum limit after thickness increased by re-unsealing. The fluid production daily of the well b1-40-527 was 41.41 t/d and oil production was 1.53 t/d, water cut was 96.3% before the well releasing, then, the well was released firstly in July 2021, total effective thickness released is 6.6 m, after the released, the daily oil production was 1.92 t/d, the daily water cut was 96.3%, and oil production daily increased is 0.39 t/d, which is lower than the requirement of 0.79 t with oil price is 60 $/BBL and ROI is 1:2, therefore, the lower permeability layers were added, the total released thickness is to 10.7 m, which meets the requirement of unsealing, and the daily fluid production of the well b1-40-527 was to 67.79 t/d, the daily oil production was 3.2 t/d, the daily water cut was 95.3%, daily oil production increased was by 1.25 t/d, water cut decreased is 1.0%, and the releasing measure is valid still now.