استفاده از چاه افقي براي بهينه‌سازي برداشت نفت از مخزن داراي شكستگي طبيعي با آبده فعال زيرين

Naturally fractured reservoirs represent a significant portion of global hydrocarbon reserves, but they present a persistent production challenge characterized by high initial flow rates followed by rapid pressure decline an‎d early water breakthrough. This challenge is exacerbated in reservoirs supported by an active aquifer at the bottom, where highly conductive vertical fractures act as non-selec‎tive water flow channels. This thesis presents a comprehensive numerical simulation study aimed at improving oil recovery in these systems by eva‎luating the performance of horizontal well technology compared to conventional vertical drainage strategies. Using the CMG IMEX black oil simulation software, a 3D model of a dual-porosity reservoir, consisting of 7776 grid cells (36 × 24 × 9), was constructed, representing an original reservoir oil reserve of approximately 20.54 million barrels. The simulation framework compared two different development strategies over 60 years of production: Sector 1, which utilizes a set of four vertical wells at a upper structural level, an‎d Sector 2, which uses a single 1000-meter horizontal well strategically positioned at a higher structural level to increase the distance between the well an‎d the water-oil contact level. The results demonstrate a clear technical advantage for the horizontal design, achieving a final recovery factor of 64%, compared to 57% for the vertical well sector. This 7% increase in recovery is attributed to the shift from the localized water cone flow phenomenon observed in the vertical wells to the more regular water flow mechanism in the horizontal well. The horizontal design also contributed to efficient pressure distribution, reducing the rising water front velocity an‎d enhancing the volumetric sweep efficiency of the rock matrix blocks. Multi variable sensitivity analysis was performed to optimize the horizontal well design. The results indicate that a horizontal length of 1000 meters represents the optimal range for fracture intersection before reaching the point of declining yield. Production rate sensitivity revealed that a moderate flow rate of 6000 barrels per day (b/d) optimizes the pressure differential between the rock matrix an‎d the fractures, while higher rates (8000 b/d) lead to fracture-induced agglomeration an‎d excessive water production. Furthermore, the study identifies well orientation as a critical success factor; horizontal well orientation perpendicular to the dominant vertical fracture set is essential, as parallel orientation results in the well reverting to a rock matrix-dominated flow regime, producing results similar to conventional vertical wells. The study concludes that in the presence of a highly active aquifer, horizontal wells are not merely high-yield conduits but vital water management tools. By leveraging the structural roof position an‎d optimized angle, horizontal well technology maximizes the pressure support provided by the aquifer while significantly delaying its breakrthrough, offering an effective strategy for the sustainable development of complex naturally fractured aquifers.

محسن محمدي

حميدرضا شاه وردي , روح اله هاشمي