Research On Imbibition Mechanism Of Low-permeability Glutenite Reservoir In Xinjiang

Low permeability glutenite reservoir in Xinjiang had a low recovery degree in anhydrous period and low water-cut period. Just 50% of the recoverable reserves would be recoveried when the water saturation is 70%. Most of the recoverable reserves would be recoveried in middle and high water-cut period. In order to evaluate the imbibition effect on low permeability glutenite reservoir in Xinjiang, this paper based on imbibition theory, used physical modeling experiment technologies such as mercury injection technology, nuclear magnetic resonance (NMR) technology, spontaneous imbibition experiment and dynamic imbibition experiment, studied microscopic pore structure characteristics of low permeability glutenite reservoir in Xinjiang and revealed the laws of spontaneous imbibition and dynamic imbibition of low permeability glutenite reservoir in Xinjiang. Combined with geologic features and production performance of low permeability glutenite reservoir in Xinjiang, the author established and solved imbibition mathematical model and analyzed the effects of various factors on imbibition, such as crack density, wettability, oil viscosity and water saturation. The main achievements are followed.1. The low permeability glutenite reservoir in Xinjiang is a low porosity and low permeability or extra-low permeability reservoir. Its microscopic heterogeneity is strong and connectivity is good, which is the basis of enhanced oil recovery by imbibition in this kind of reservoir.2. Wettability is the key factor that affects imbibition. Under laboratory conditions, imbibition oil recovery of strong hydrophilic core is about 50%, and imbibition oil recovery of neutral and weak hydrophilic core is approximately 17%. The shorter the core is, which is equivalent to saying that the more developed the reservoir fracture is, the greater the imbibition rate is.3. For the strong heterogeneity glutenite core, flooding recovery is the main recovery method before water injection rate is 0.4 PV, and imbibition recovery is the main recovery method after water injection rate is 0.4 PV. Imbibition’s contribution to the recovery is 25%～30%.4. During the cyclic flooding experiment, the well is shut in when water saturation reaches to 98%. The oil in small pore is exchanged into medium and large pore by imbibition during shut-in, which enhances water flooding recovery by 14%.5. Low permeability glutenite reservoir in Xinjiang was simplified to matrix fracture reservoir. Imbibition mathematical model that reflected characteristics of low permeability glutenite pore structures was established. Besides, the effect laws of various factors (including crack density, wettability, oil viscosity and water saturation) on the imbibition were analyzed.The above results provided theoretical basis for the follow-up imbibition recovery of low permeability glutenite reservoir in Xinjiang, can effectively guide later development of low permeability glutenite reservoir during medium and high water cut period.