Abstract
Mature oilfields usually encounter the problem of high watercut. It is practical to use chemical methods for water-shutoff in production wells, however conventional water-shutoff agents have problems of long gelation time, low gel strength, and poor stability under low temperature and high salinity conditions. In this work a novel polymer gel for low temperature and high salinity reservoirs was developed. This water-shutoff agent had controllable gelation time, adjustable gel strength and good stability performance. The crosslinking process of this polymer gel was studied by rheological experiments. The process could be divided into an induction period, a fast crosslinking period, and a stable period. Its gelation behaviors were investigated in detail. According to the Gel Strength Code (GSC) and vacuum breakthrough method, the gel strength was displayed in contour maps. The composition of the polymer gel was optimized to 0.25~0.3% YG100 + 0.6~0.9% resorcinol + 0.2~0.4% hexamethylenetetramine (HMTA) + 0.08~0.27% conditioner (oxalic acid). With the concentration increase of the polymer gel and temperature, the decrease of pH, the induction period became shorter and the crosslinking was more efficient, resulting in better stability performance. Various factors of the gelation behavior which have an impact on the crosslinking reaction process were examined. The relationships between each impact factor and the initial crosslinking time were described with mathematical equations.
Highlights
The problem of heterogeneity is very common in mature oilfields, which leads to water breakthrough along highly permeable channels in long-term oilfield waterflooding
The results indicated that the HQ-HMTA system has a longer gelation time and better thermal stability
Gelation time is the time where a gel is formed from a liquid state to high strength gel, which is an important index to evaluate the applicability of any plugging agent system
Summary
The problem of heterogeneity is very common in mature oilfields, which leads to water breakthrough along highly permeable channels in long-term oilfield waterflooding. Energies 2017, 10, 913 in high permeable channels To remediate this problem and increase the volumetric sweep efficiency [1], water shut-off treatments are widely used [2,3,4]. The HQ-HMTA crosslinking polyacrylamide gel system displays good thermal stability and salt-resistance. Dovan [24] compared the gelation characteristics and thermal stability of various organically crosslinked polymer gels. The results indicated that the gel system could withstand temperatures up to 140 ◦ C He [30] investigated a polymer gel made by crosslinking partially hydrolyzed polyacrylamide (HPAM) with resorcinol and HMTA at 57 ◦ C. A large number of experiments were conducted on the resorcinol-HMTA polymer gel at low temperature and high salinity. The mathematical expressions of gelation time and these factors were established, which could provide basic information and guidance for the plugging depth and project design for the gel system in field applications
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