# Evaluation of Novel Preformed Particle Gel System for Conformance Control in Mature Oil Reservoirs
## 1 Introduction  
With the world's increasing energy demands, the application of Improved Oil Recovery (IOR) techniques becomes crucial for tapping into mature reservoirs that hold significant quantities of untapped oil. As conventional reservoirs deplete, their natural production rates decline, necessitating advanced methods to enhance oil extraction efficiency. IOR involves the implementation of various technologies, such as water flooding, gas injection, or chemical treatments, to optimize oil recovery from existing wells. Mature oil reservoirs that have undergone extended periods of water flooding and are characterized by declining production rates and increased water cuts present a unique challenge in the field of petroleum engineering. As these reservoirs age, the need for efficient methods to enhance oil recovery and reduce excessive water production becomes increasingly crucial. During water flooding operations, the injected water or gas tends to flow through high-permeability zones, like fractures or channels, leaving a substantial amount of oil untapped. This results in poor sweep efficiency or a conformance issue [1]. The need to treat the significant volume of produced water will add a substantial load on the facilities, consequently diminishing the feasibility of the producing well. Various methods can be employed to address conformance problems, including the use of viscosity-enhancing materials and plugging agents. Gel applications for conformance control have emerged as a promising strategy to block high-permeability zones and divert the injected fluids toward low-permeability zones [2]. A successful application of gel treatment in a heterogeneous reservoir will result in a reduction in water production and an increase in oil production, as a result of sweep efficiency modification. Two major types of gel treatments were applied: in situ gels and preformed particle gels. In the context of in situ gels, a low-viscosity gelant is injected into the reservoir. Once the gelling conditions are met, this gelant transforms into a bulk gel, serving to block the targeted zone [3]. However, in situ gels have their drawbacks, including chromatographic separation during injection and uncertainties surrounding gelation conditions. Furthermore, they exhibit limited plugging efficiency in large fractures and may cause damage to the adjacent oil-bearing matrix. Preformed particle gel (PPG) was introduced in 1996 to address the limitations of in situ gel systems. PPGs are pre-crosslinked gel particles that offer size and strength controllability. PPGs have the ability to swell up to 200 times their original size when mixed with water before injection [4]. They have proven to be effective in blocking fractures and fracture-like features without causing damage to the oil-bearing formation [5]. Preformed particle gels are applied successfully in more than 10,000 wells in China and the United States [6]. Many proposed and commercially available preformed gels are comprised of synthetic polymer-based polyacrylamide derivatives materials [7; 8; 9; 10; 11], crosslinked with organic agents such as N,N\({}^{\prime}\)-methylene bisacrylamide (MBA) [12], polyethylene glycol diacrylate (PEGd) [13], divinylbenzene (DVB) [14], 1,6-hexanediol diacrylate [15], or inorganic crosslinkers like chromium [16], potassium [17], and aluminum [18]. Additionally, various monomers like styrene sulfonate [19] and dimethyldiallylammonium chloride [20], as well as additives like clay, silica, and graphene [21; 22], are introduced into the formulation to enhance swelling, elevate resistance to high temperatures, and modulate strength. Polysaccharides, distinguished by their exceptional properties such as biodegradability, renewability, nontoxicity, and cost-effectiveness, offer a promising avenue for sustainable PPG development [23; 24; 25; 26].