Abstract
NB35-2 oilfield is a typical offshore sandstone reservoir with viscous crude oil and high permeability. Due to the inherent severe heterogeneity, the efficiency of conventional water flooding is pretty low and usually accompanied with early water breakthrough. In order to recover the residual oil and better realize its potential, applications of enhanced oil recovery (EOR) technology are necessary. However, the selection of EOR method and related parameters may directly impact the final results and can be noticeably different for different reservoirs; therefore, to optimize the oil production rate and final oil recovery, systematical optimization of every detail based on the condition of a specific reservoir is of key importance. In this paper, physical simulations were first conducted to select the best recovery methods for the target area based on the static geophysical model under the guidance of reservoir engineering theory. Then, detailed development variants for each method were determined by numerical simulation with the support of data obtained from previous pilot tests (polymer gel flooding and thermal fluid huff and puff) conducted in this area. Three exploitation methods were developed for the target well group, including polymer gel flooding (conformance control, Pattern 1), steam huff and puff (thermal recovery method, Pattern 2), and a combination of polymer gel flooding and steam huff and puff (conformance control and thermal recovery, Pattern 3). The numerical simulation result also showed that Pattern 3 yielded the highest oil recovery. Moreover, the amount of additional oil being recovered by applying Pattern 3 was even higher than the total additional oil being extracted by Patterns 1 and 2. In addition, sensitivity analysis was conducted to rank the most important parameters based on the three Patterns. At last, it is thought that the synergistic effect between conformance control and thermal recovery made more oil recovered, which was intuitively clarified in the mechanism analysis.
Highlights
At present, the production of terrestrial oil and gas is decreasing year by year, while the oil demand of national industrial construction and people’s daily lives is steadily increasing [1, 2]
Bohai Oilfield is a famous offshore oilfield with huge crude oil reserves in China, with heavy oil occupying about two-thirds of its total reserves
NB35-2 oilfield lies in the center of the Bohai Sea with high permeability and serious heterogeneity, and its crude oil is of high viscosity (450~950 mPa·s)
Summary
The production of terrestrial oil and gas is decreasing year by year, while the oil demand of national industrial construction and people’s daily lives is steadily increasing [1, 2]. Effective exploitation technologies should be taken to recover the residual oil after conventional water flooding. Steam huff and puff or steam flooding is the normally applied technology to exploit heavy oil reservoirs [4,5,6,7]. Steam flooding effectively supplies formation pressure, the steam fluid channeling is always a serious challenge because of the reservoir anisotropy and high mobility of the steam, which decreases the sweep volume and thermal efficiency and harms the normal operation of oil well artificial lifting system [11]. More than 1000 × 104 t additional oil has been recovered in the continuous ten years [12,13,14] Another success story of conformance control is that Henan Oilfield has been carried out using polymer gel before the polymer flooding since
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